0000950170-23-007929 | 10-K | XBRL Viewer

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Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2022	Mar. 03, 2023	Jun. 30, 2022
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2022
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY
Entity Registrant Name	89bio, Inc.
Entity Central Index Key	0001785173
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Well-known Seasoned Issuer	No
Entity Public Float			$ 30.4
Entity Common Stock, Shares Outstanding		52,230,621
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Title of 12(b) Security	Common stock, par value $0.001 per share
Trading Symbol	ETNB
Security Exchange Name	NASDAQ
Entity File Number	001-39122
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	36-4946844
Entity Address, Address Line One	142 Sansome Street
Entity Address Address Line Two	Second Floor
Entity Address, City or Town	San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94104
City Area Code	415
Local Phone Number	432-9270
Document Annual Report	true
Document Transition Report	false
Documents Incorporated by Reference	Portions of the Registrant’s definitive proxy statement relating to its 2023 Annual Meeting of Stockholders, to be held on or about May 31, 2023, are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated. Such proxy statement will be filed with the U.S. Securities and Exchange Commission within 120 days after the end of the fiscal year to which this report relates.
Auditor Firm ID	185
Auditor Name	KPMG LLP
Auditor Location	San Francisco, California, USA

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 55,255	$ 52,432
Restricted cash	0	25
Short-term available-for-sale securities	132,905	98,288
Prepaid and other current assets	7,920	11,237
Total current assets	196,080	161,982
Operating lease right-of-use asset	363
Property and equipment, net	92	150
Other assets	289	290
Total assets	196,824	162,422
Current liabilities:
Accounts payable	12,502	6,843
Accrued expenses	11,944	10,194
Operating lease liability, current	168
Term loan, current		2,500
Total current liabilities	24,614	19,537
Operating lease liability, non-current	186
Term loan, non-current, net	19,691	16,898
Other non-current liability	501	30
Total liabilities	44,992	36,465
Commitments and contingencies (Note 5)
Stockholders’ equity:
Preferred stock, $0.001 par value, 10,000,000 shares authorized as of December 31, 2022 and 2021; no shares issued and outstanding as of December 31, 2022 and 2021
Common stock, $0.001 par value, 100,000,000 shares authorized as of December 31, 2022 and 2021; 50,560,590 and 20,317,204 shares issued and outstanding as of December 31, 2022 and 2021, respectively	51	20
Additional paid-in capital	467,374	339,218
Accumulated other comprehensive loss	(350)	(64)
Accumulated deficit	(315,243)	(213,217)
Total stockholders’ equity	151,832	125,957
Total liabilities and stockholders’ equity	$ 196,824	$ 162,422

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	50,560,590	20,317,204
Common stock, shares outstanding	50,560,590	20,317,204

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Operating expenses:
Research and development	$ 80,796	$ 70,330
General and administrative	21,453	19,413
Total operating expenses	102,249	89,743
Loss from operations	(102,249)	(89,743)
Interest expense	(1,922)	(674)
Interest income and other, net	2,164	148
Net loss before income tax	(102,007)	(90,269)
Income tax (expense) benefit	(19)	147
Net loss	(102,026)	(90,122)
Other comprehensive (loss) income:
Unrealized loss on available-for-sale securities	(299)	(71)
Foreign currency translation adjustments	13	17
Total other comprehensive loss	(286)	(54)
Comprehensive loss	$ (102,312)	$ (90,176)
Net loss per share, basic	$ (2.93)	$ (4.48)
Net loss per share, diluted	$ (2.93)	$ (4.48)
Weighted-average shares used to compute net loss per share, basic	34,806,349	20,098,340
Weighted-average shares used to compute net loss per share, diluted	34,806,349	20,098,340

Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	A T M Facility	Public Offerings	Common Stock	Common Stock A T M Facility	Common Stock Public Offerings	Additional Paid-in Capital	Additional Paid-in Capital A T M Facility	Additional Paid-in Capital Public Offerings	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance at Dec. 31, 2020	$ 202,961			$ 20			$ 326,046			$ (10)	$ (123,095)
Beginning balance, shares at Dec. 31, 2020				19,931,660
Issuance of common stock		$ 3,289						$ 3,289
Issuance of common stock, shares					186,546
Issuance of common stock upon exercise of stock options	487						487
Issuance of common stock upon exercise of stock options, shares				188,286
Issuance of common stock upon ESPP purchase	144						144
Issuance of common stock upon ESPP purchase, Shares				10,712
Issuance of common stock warrant in connection with term loan facility	574						574
Stock-based compensation	8,678						8,678
Net loss	(90,122)										(90,122)
Other comprehensive loss	(54)									(54)
Ending balance at Dec. 31, 2021	125,957			$ 20			339,218			(64)	(213,217)
Ending balance, shares at Dec. 31, 2021				20,317,204
Issuance of common stock		$ 28,453	$ 88,239		$ 4	$ 20		$ 28,449	$ 88,219
Issuance of common stock, shares					3,948,611	18,675,466
Issuance of common stock upon cashless exercise of warrants				$ 3			(3)
Issuance of common stock upon cashless exercise of warrants, shares				3,143,682
Issuance of common stock upon exercise of warrants	1,082			$ 4			1,078
Issuance of common stock upon exercise of warrants				4,202,499
Issuance of common stock upon vesting of restricted stock units, net of withholding taxes	(298)						(298)
Issuance of common stock upon vesting of restricted stock units, net of withholding taxes, shares				103,703
Issuance of common stock upon exercise of stock options	305						305
Issuance of common stock upon exercise of stock options, shares				151,061
Issuance of common stock upon ESPP purchase	50						50
Issuance of common stock upon ESPP purchase, Shares				18,364
Stock-based compensation	10,356						10,356
Net loss	(102,026)										(102,026)
Other comprehensive loss	(286)									(286)
Ending balance at Dec. 31, 2022	$ 151,832			$ 51			$ 467,374			$ (350)	$ (315,243)
Ending balance, shares at Dec. 31, 2022				50,560,590

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities:
Net loss	$ (102,026)	$ (90,122)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	10,356	8,678
Net (accretion) amortization on available-for-sale securities	(980)	865
Amortization of debt issuance costs and accretion of final payment fee	764	617
Non-cash operating lease expense	175
Depreciation	65	79
Deferred tax assets	0	(150)
Changes in operating assets and liabilities:
Prepaid and other current assets	3,331	(5,672)
Accounts payable	5,659	4,778
Accrued expenses	1,750	4,146
Operating lease liability	(184)
Net cash used in operating activities	(81,090)	(76,781)
Cash flows from investing activities:
Proceeds from sales and maturities of available-for-sale securities	118,760	148,422
Purchases of available-for-sale securities	(152,696)	(141,200)
Purchases of property and equipment	(7)	(63)
Net cash (used in) provided by investing activities	(33,943)	7,159
Cash flows from financing activities:
Proceeds from issuance of common stock and warrants in public offering, net of issuance costs	88,239
Proceeds from issuance of common stock in at-the-market public offering, net of issuance costs	28,453	3,289
Proceeds from issuance of common stock upon exercise of warrants	1,082
Proceeds from issuance of common stock upon exercise of stock options	305	487
Proceeds from issuance of common stock upon ESPP purchases	50	144
Payment of withholding taxes related to restricted stock units	(298)
Proceeds from term loan facility, net of issuance costs		19,951
Net cash provided by financing activities	117,831	23,871
Net change in cash and cash equivalents, and restricted cash	2,798	(45,751)
Cash and cash equivalents, and restricted cash at beginning of period	52,457	98,208
Cash and cash equivalents, and restricted cash at end of period	55,255	52,457
Components of cash and cash equivalents, and restricted cash:
Cash and cash equivalents	55,255	52,432
Restricted cash	0	25
Total cash and cash equivalents, and restricted cash	55,255	52,457
Supplemental disclosures of cash information:
Cash paid for interest	1,076	16
Cash paid for operating leases	234
Supplemental disclosures of noncash information:
Remeasurement of lease liability and right of use asset in connection with lease modification	$ 338
Issuance of common stock warrant in connection with term loan facility		$ 574

Organization and Basis of Presentation

12 Months Ended

Dec. 31, 2022

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Organization and Basis of Presentation

1. Organization and Basis of Presentation

Description of Business

89bio, Inc. (“89bio” or the “Company”) is a clinical-stage biopharmaceutical company focused on the development and commercialization of innovative therapies for the treatment of liver and cardio-metabolic diseases. The Company’s lead product candidate, pegozafermin (previously BIO89-100), a specifically engineered glycoPEGylated analog of fibroblast growth factor 21, is currently being developed for the treatment of nonalcoholic steatohepatitis and for the treatment of severe hypertriglyceridemia.

89bio, Inc. was formed as a Delaware corporation in June 2019 to carry on the business of 89Bio Ltd., which was incorporated in Israel in January 2018.

Liquidity

The accompanying consolidated financial statements have been prepared assuming the Company will continue as a going concern, which contemplates the realization of assets and liquidation of liabilities in the normal course of business. To date, the Company has not generated revenues from its activities and has incurred substantial operating losses. Management expects the Company to continue to generate substantial operating losses for the foreseeable future until it completes development of its products and seeks regulatory approvals to market such products. The Company had cash and cash equivalents and short-term available-for-sale securities of $188.2 million as of December 31, 2022.

The Company expects that its cash and cash equivalents and short-term available-for-sale securities as of December 31, 2022, together with proceeds received in January and February 2023 from its ATM Facility (see Note 7 and Note 11), and proceeds available from the 2023 Loan Agreement (see Note 6 and Note 11), will be sufficient to fund operating expenses and capital expenditure requirements for a period of at least one year from the date these audited consolidated financial statements are filed with the Securities and Exchange Commission.

Summary of Significant Accounting Policies	12 Months Ended
Summary of Significant Accounting Policies	Dec. 31, 2022
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“U.S. GAAP”). Reclassification Certain prior year amounts in the Company’s consolidated statements of operations and comprehensive loss have been reclassified to conform to the current year presentation. Specifically, interest expense is disclosed separately on the Company’s consolidated statements of operations and comprehensive loss, which had no impact on reported net loss, comprehensive loss, or loss per share. Principles of Consolidation The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of expenses during the reporting period. Significant estimates and assumptions made in the accompanying consolidated financial statements include but are not limited to accrued research and development expenses and to the fair value of stock options. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates. Foreign Currencies Certain transactions during the year ended December 31, 2022 and 2021 were denominated in currencies other than the U.S. dollar. Gains and losses from foreign currency transactions were not material for all periods presented and are reflected in the consolidated statements of operations and comprehensive loss as a component of interest income and other, net. The Company’s subsidiary in Lithuania uses the Euro as its functional currency for financial reporting. The re-measurement from Euros to U.S. dollars results in translation gain and loss adjustments, which are reflected as a component of comprehensive loss as foreign currency translation adjustments. Fair Value Measurements Financial assets and liabilities are recorded at fair value on a recurring basis in the consolidated balance sheets. The carrying values of Company’s financial assets and liabilities, including cash and cash equivalents, restricted cash, prepaid and other current assets, accounts payable, and accrued expenses approximate to their fair value due to the short-term nature of these instruments. The fair value of the Company’s term loan approximates its carrying value, or amortized cost, due to the prevailing market rates of interest rates it bears. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the reporting date. Assets and liabilities recorded at fair value are categorized based upon the level of judgment associated with the inputs used to measure their fair value. Hierarchical levels are directly related to the amount of subjectivity with the inputs to the valuation of these assets or liabilities as follows: Level 1—Observable inputs such as unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date; Level 2—Inputs (other than quoted prices included in Level 1) are either directly or indirectly observable inputs for similar assets or liabilities. These include quoted prices for identical or similar assets or liabilities in active markets and quoted prices for identical or similar assets or liabilities in markets that are not active; and Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Concentrations of Credit Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist primarily of cash and cash equivalents and short-term available-for-sale securities. Bank deposits are held by accredited financial institutions and these deposits may at times be in excess of insured limits. The Company limits its credit risk associated with cash and cash equivalents by placing them with financial institutions that it believes are of high quality. The Company has not experienced any losses on its deposits of cash or cash equivalents. The Company limits amounts invested in available-for-sale securities by credit rating, maturity, industry group, investment type and issuer, except for securities issued by the U.S. government. The Company is not exposed to any significant concentrations of credit risk from these financial instruments. Other Risks and Uncertainties The Company’s future results of operations involve a number of other risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, the Company’s early stages of clinical drug development; the Company’s ability to advance product candidates into, and successfully complete, clinical trials on the timelines it projects; the Company’s ability to adequately demonstrate sufficient safety and efficacy of its product candidates; the Company’s ability to enroll patients in its ongoing and future clinical trials; the Company’s ability to successfully manufacture and supply its product candidates for clinical trials; the Company’s ability to obtain additional capital to finance its operations; uncertainties related to the projections of the size of patient populations suffering from the diseases the Company is targeting; the Company’s ability to obtain, maintain, and protect its intellectual property rights; developments relating to the Company’s competitors and its industry, including competing product candidates and therapies; general economic and market conditions; and other risks and uncertainties. The Company’s product candidates will require approvals from the U.S. Food and Drug Administration and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any product candidates will receive the necessary approvals. If the Company is denied approval, approval is delayed or the Company is unable to maintain approval for any product candidate, it could have a materially adverse impact on the Company. The ongoing COVID-19 pandemic has disrupted and may continue to disrupt the Company’s business and delay its preclinical and clinical programs and timelines. The extent to which the COVID-19 pandemic may impact the Company’s future operating results and financial condition is uncertain. Segment Reporting The Company has one operating segment. The Company’s chief operating decision maker, its Chief Executive Officer, manages the Company’s operations on a consolidated basis for the purposes of allocating resources and evaluating financial performance. Cash and Cash Equivalents The Company considers all highly liquid investments purchased with original maturities of three months or less from the purchase date to be cash equivalents. Cash equivalents consist primarily of amounts invested in money market funds and commercial paper that are stated at fair value. Investments Investments have been classified as available-for-sale and are carried at estimated fair value as determined based upon quoted market prices or pricing models for similar securities. Management determines the appropriate classification of its available-for-sale investments in debt securities at the time of purchase. Generally, investments with original maturities beyond three months at the date of purchase are classified as short-term because it is management’s intent to use the investments to fund current operations or to make them available for current operations. Unrealized gains and losses are excluded from net loss and are reported as a component of comprehensive loss. The Company periodically evaluates whether declines in fair values of its available-for-sale securities below their book value are other-than-temporary. This evaluation consists of several qualitative and quantitative factors regarding the severity and duration of the unrealized loss as well as the Company’s ability and intent to hold the available-for-sale security until a forecasted recovery occurs. Additionally, the Company assesses whether it has plans to sell the security or it is more likely than not it will be required to sell any available-for-sale securities before recovery of its amortized cost basis. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on available-for-sale securities are included in interest income and other, net. The cost of investments sold is based on the specific-identification method. The Company has not experienced any material realized gains or losses or other-than-temporary losses in the periods presented. Leases The Company is a lessee in noncancellable operating leases for office space. Beginning in 2022, the Company accounts for leases in accordance with Accounting Standards Update (“ASU”) 2016-02, Leases (Topic 842). The Company determines if an arrangement is a lease or contains an embedded lease at inception. The Company accounts for a contract as a lease when it has the right to control the asset for a period of time while obtaining substantially all of the asset’s economic benefits. For arrangements that meet the definition of a lease, the Company determines the initial classification and measurement of its right-of-use (“ROU”) asset and lease liability at the lease commencement date and thereafter if modified. Operating lease ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make the contractual lease payments over the lease term. The ROU asset is initially measured at cost, which comprises the initial amount of the lease liability adjusted for lease payments made at or before the lease commencement date, plus any initial direct costs incurred less any lease incentives received. The operating lease liability is initially measured at the present value of the unpaid lease payments at the lease commencement date. The lease liability is subsequently measured at amortized cost using the effective-interest method. The lease term includes any renewal options that the Company is reasonably assured to exercise. The present value of lease payments is determined by using the interest rate implicit in the lease, if that rate is readily determinable, otherwise, the Company uses its estimated collateralized incremental borrowing rate for the lease term. The Company has elected not to record leases with an original term of twelve months or less on its consolidated balance sheets and recognizes those lease payments in operating expenses in the consolidated statements of operations and comprehensive loss. The Company’s short-term lease is not material. In addition, the Company’s leases may require it to pay additional costs, such as utilities, maintenance, and other operating costs, which are generally referred to as non-lease components and vary based on future outcomes. The Company has elected to not separate lease and non-lease components. Only the fixed costs for lease components and their associated non-lease components are accounted for as a single lease component and recognized as part of a ROU asset and lease liability. Any variable expenses are recognized in operating expenses as incurred. Rent expense for an operating lease liability is recognized on a straight-line basis over the lease term and is included in operating expenses in the consolidated statements of operations and comprehensive loss. Property and Equipment, Net Property and equipment are stated at cost, less accumulated depreciation. Depreciation is calculated on a straight-line basis over the estimated useful lives of the related assets, generally ranging from three to seven years. Leasehold improvements are amortized on a straight-line basis over the shorter of the assets’ estimated useful life or the remaining term of the lease. Upon retirement or sale of the assets, the cost and related accumulated depreciation and amortization are removed from the consolidated balance sheets and the resulting gains or losses are recorded in the consolidated statements of operations and comprehensive loss. Maintenance and repair costs are expensed as incurred. Impairment of Long-Lived Assets The Company periodically evaluates its long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets or group of assets may not be fully recoverable. If indicators of impairment exist and the undiscounted future cash flows that the assets are expected to generate are less than the carrying value of the assets, then the Company will reduce the carrying amount of the assets through an impairment charge, to their estimated fair values based on a discounted cash flow approach or, when available and appropriate, to comparable market values. There were no such indicators for the periods presented. Accrued Research and Development Expenses The Company estimates preclinical and clinical study and research expenses based on the services performed, pursuant to contracts with research institutions that conduct and manage preclinical and clinical studies and research services on its behalf. The Company records the costs of research and development activities based upon the estimated services provided but not yet invoiced and includes these costs in accrued expenses in the consolidated balance sheets. These costs are a component of the Company’s research and development expenses. The Company accrues for these costs based on factors such as estimates of the work completed in accordance with agreements established with its third-party service providers. The Company makes judgments and estimates in determining the accrued expenses balance. As actual costs become known, the Company adjusts its accrued expenses. The Company has not experienced any material differences between accrued costs and actual costs incurred. However, the status and timing of actual services performed may vary from the Company’s estimates, resulting in adjustments to expense in future periods. Changes in these estimates that result in material changes to the Company’s accrued expenses could materially affect the Company’s results of operations. Contingent milestone payments, if any, are expensed when the milestone results are probable and estimable, which is generally upon achievement of the milestone. Warrants to Purchase Common Stock The Company classifies warrants indexed to its common stock and meeting the requirements for equity classification within stockholders’ equity. This assessment is conducted at the time of warrant issuance and as of each reporting period that the warrants remain outstanding. Research and Development Expenses Research and development expenses consist primarily of costs incurred for the development of the Company’s lead product candidate, pegozafermin. Research and development expenses consist primarily of external costs related to preclinical and clinical development and related supplies and personnel costs. Personnel costs consist of salaries, employee benefits and stock-based compensation for individuals involved in research and development efforts. Payments associated with agreements to acquire licenses to develop, use, manufacture and commercialize products and purchases of pegozafermin from contract manufacturing organizations that have not reached technological feasibility and do not have alternate future commercial use are expensed as incurred. Stock-Based Compensation The Company provides equity awards in the form of stock options and restricted stock units. The Company measures its equity awards made to employees, directors, and non-employee service providers based on estimated fair values and recognizes stock-based compensation over the requisite service period. The Company accounts for forfeitures as they occur. The Company estimates the fair value of stock option awards on the date of grant using a Black-Scholes option pricing model. The Company recognizes compensation for the value of stock options awards, which have graded vesting, using the straight-line method over the requisite service period of each award. The Black-Scholes option pricing model requires a number of assumptions, of which the most significant are expected volatility, expected option term (the time from the grant date until the options are exercised or expire), risk-free rate, and expected dividend rate. These assumptions include: • Expected volatility—Since the Company has limited trading history for its common stock, expected volatility is estimated based on weighting the Company’s volatility and the volatility of comparable publicly traded biotechnology companies during the equivalent period of the calculated expected term of the options granted. The comparable companies were chosen based on their similar size, stage in the life cycle, or area of specialty. There is a degree of uncertainty in determining a comparable peer group as each of the peers are engaged in varied research and development activities, the timing and progress of which differ within the peer group. • Expected term—The expected term of options granted to employees and directors is determined using the “simplified” method. Under this approach, the expected term is presumed to be the midpoint between the weighted-average vesting term and the contractual term of the option. The simplified method makes the assumption that the employee will exercise stock options evenly over the period when the stock options are vested and ending on the date when the stock options would expire. The expected option term for options granted to non-employees is estimated on a grant-by-grant basis. • Risk-free interest rate—The risk-free interest rate is based on the U.S. Treasury zero coupon bonds in effect on the grant date for periods with an equivalent expected term as the option. • Expected dividend—The Company has never paid dividends and has no foreseeable plans to pay dividends on its shares of common stock. Therefore, an expected dividend of zero is used. The fair value of restricted stock units is based on the fair value of the Company’s common stock on the date of grant. The grant date fair value of restricted stock units with service vesting conditions is recognized over the requisite service period on a straight-line basis. For restricted stock units with performance vesting conditions, the Company evaluates the probability of achieving the performance condition at each reporting date and recognizes expense for such performance awards over the requisite service period using the accelerated attribution method. Income Taxes Income taxes are accounted for under the asset and liability method. Under this method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the consolidated financial statements carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates applied to taxable income in the years in which those temporary differences are expected to be realized. The effect on deferred tax assets and liabilities of a change in tax rates is recognized as income or loss in the period that includes the enactment date. A valuation allowance is established when necessary to reduce deferred tax assets to the amount expected to be realized. Interest and penalties related to unrecognized tax benefits are included within the provision of income tax. Basic and Diluted Net Loss per Share Basic loss per share is computed by dividing net loss by the weighted-average number of shares of common stock outstanding during the period. Diluted loss per share is computed by dividing net loss by the weighted-average number of shares of common stock outstanding together with the number of additional shares of common stock that would have been outstanding if all potentially dilutive shares of common stock had been issued. Since the Company is in a loss position for the periods presented, basic net loss per share is the same as diluted net loss per share since the effects of potentially dilutive securities are antidilutive. Shares of the Company’s common stock underlying pre-funded warrants exercisable for nominal consideration are included in the computation of basic and diluted net loss per share, even if antidilutive. Comprehensive Loss The Company’s comprehensive loss is comprised of net loss and changes in unrealized gains or losses on available-for-sale securities and foreign currency translation adjustments. Recently Adopted Accounting Standards In February 2016, the Financial Accounting Standards Board (“FASB”) issued ASU 2016-02, Leases (Topic 842), or Accounting Standards Codification (“ASC”) 842, which requires lessees to recognize leases on the balance sheet and disclose key information about leasing arrangements. ASC 842 establishes a ROU model that requires a lessee to recognize a ROU asset and lease liability on the balance sheet for all leases with a term longer than 12 months. Leases are classified as finance or operating, with classification affecting the pattern and classification of expense recognition in the income statement. On January 1, 2022, the Company adopted ASC 842 using the modified retrospective transition method and elected the practical expedients to not reassess whether any expired or existing contracts are or contain leases, carry forward its historical lease classification and not reassess initial direct costs for existing leases. Upon adoption of ASC 842, the Company recorded an operating ROU asset of $0.2 million and an operating lease liability of $0.2 million on its consolidated balance sheet. There was no adjustment to the opening balance of accumulated deficit as a result of adoption. Results for the year ended December 31, 2022 are presented under ASC 842. Prior period amounts preceding January 1, 2022 continue to be reported in accordance with the Company’s historical accounting under the previous lease guidance, ASC 840. Recent Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”), which replaces the existing incurred loss impairment model with an expected credit loss model and requires a financial asset measured at amortized cost to be presented at the net amount expected to be collected. As an emerging growth company, ASU 2016-13 is effective for the Company for the year ending December 31, 2023 and interim periods within that fiscal year and must be adopted using a modified retrospective approach, with certain exceptions. The Company is evaluating the impact of this standard and does not expect the adoption of ASU 2016-13 to have a material impact on the Company’s consolidated financial statements and related disclosures.

Fair Value Measurements

12 Months Ended

Dec. 31, 2022

Fair Value Disclosures [Abstract]

Fair Value Measurements

3. Fair Value Measurements

The following table presents the Company’s financial assets measured at fair value on a recurring basis by level within the fair value hierarchy as of December 31, 2022 (in thousands):


	Valuation	Amortized		Unrealized		Unrealized			Fair
	Hierarchy	Cost		Gains		Losses			Value
Money market funds	Level 1	$	18,224	$	—	$	—		$	18,224
Commercial paper	Level 2		104,279		1		(84	)		104,196
U.S. government bonds	Level 2		18,225		1		(109	)		18,117
Agency bonds	Level 2		13,986		—		(78	)		13,908
Corporate debt securities	Level 2		10,488		—		(62	)		10,426
U.S. treasury bills	Level 2		7,414		1		(21	)		7,394
Agency discount securities	Level 2		5,216		9		—			5,225
Non-U.S. debt securities	Level 2		3,975		—		(20	)		3,955
Total cash equivalents and available-for- sale securities		$	181,807	$	12	$	(374	)	$	181,445
Classified as:
Cash equivalents									$	48,540
Short-term available-for-sale securities										132,905
Total cash equivalents and available-for- sale securities									$	181,445

The following table summarizes the Company’s cash equivalents and available-for-sale securities by contractual maturity as of December 31, 2022 (in thousands):


Within one year	$	175,243
After one year through two years		6,202
Total cash equivalents and available-for-sale securities	$	181,445

The following table presents the Company’s financial assets measured at fair value on a recurring basis by level within the fair value hierarchy as of December 31, 2021 (in thousands):


	Valuation	Amortized		Unrealized		Unrealized			Fair
	Hierarchy	Cost		Gains		Losses			Value
Money market funds	Level 1	$	21,477	$	—	$	—		$	21,477
Commercial paper	Level 2		59,647		—		(10	)		59,637
U.S. government bonds	Level 2		21,662		—		(42	)		21,620
Corporate debt securities	Level 2		8,776		1		(1	)		8,776
Agency bonds	Level 2		7,747		1		(7	)		7,741
Municipal bonds	Level 2		4,251		—		(4	)		4,247
Non-U.S. debt securities	Level 2		2,506		—		(1	)		2,505
Total cash equivalents and available-for- sale securities		$	126,066	$	2	$	(65	)	$	126,003
Classified as:
Cash equivalents									$	27,715
Short-term available-for-sale securities										98,288
Total cash equivalents and available-for- sale securities									$	126,003

The following table summarizes the Company’s cash equivalents and available-for-sale securities by contractual maturity as of December 31, 2021 (in thousands):


Within one year	$	120,726
After one year through two years		5,277
Total cash equivalents and available-for-sale securities	$	126,003

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Consolidated Balance Sheet Components

12 Months Ended

Dec. 31, 2022

Balance Sheet Related Disclosures [Abstract]

Consolidated Balance Sheet Components

4. Consolidated Balance Sheet Components

Prepaid and other current assets consist of the following as of the periods presented (in thousands):


	As of December 31,
	2022		2021
Prepaid research and development	$	5,727	$	7,895
Prepaid taxes		646		836
Prepaid other		1,547		2,506
Total prepaid and other current assets	$	7,920	$	11,237

Accrued expenses consist of the following as of the periods presented (in thousands):


	As of December 31,
	2022		2021
Accrued research and development expenses	$	6,499	$	6,195
Accrued employee and related expenses		4,165		3,168
Accrued professional and legal fees		1,052		495
Accrued other expenses		228		336
Total accrued expenses	$	11,944	$	10,194

Commitments and Contingencies

12 Months Ended

Dec. 31, 2022

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

5. Commitments and Contingencies

Leases

On January 1, 2022, the Company adopted ASC 842 (see Note 2), and the following disclosures as of and for the year ended December 31, 2022 are presented under ASC 842, while prior period amounts have not been adjusted and continue to be reported in accordance with the historical accounting under ASC 840. Upon adoption, the Company recorded an operating lease ROU asset and lease liability for its lease in San Francisco, which was due to expire in January 2023. Effective August 31, 2022, the Company amended the lease to extend the expiration date of the lease to January 2025, with one option to renew for an additional year that is not reasonably certain to be exercised. The amendment resulted in the remeasurement of the lease liability and ROU asset as of the modification date to reflect the extended term and the Company recorded an incremental ROU asset and lease liability of $0.3 million.

For the year ended December 31, 2022, the Company incurred $0.2 million in rent expense. For the year ended December 31, 2022, variable lease payments and short-term lease costs were immaterial. As of December 31, 2022, the remaining lease term was 2.0 years and the Company’s incremental borrowing rate used to determine the operating lease liability was 6.5%.

As of December 31, 2022, the undiscounted future minimum lease payments due under the Company’s non-cancellable operating lease are as follows (in thousands):


2023	$	185
2024		185
2025		7
Total undiscounted future minimum lease payments	$	377
Less: imputed interest		(23	)
Present value of operating lease liability	$	354

In accordance with ASC 840, rent expense for the year ended December 31, 2021 was $0.3 million. The total future minimum annual payments for operating leases in effect as of December 31, 2021 were as follows (in thousands):


2022	$	212
2023	7
Total future minimum annual payments	$	219

Asset Transfer and License Agreement with Teva Pharmaceutical Industries Ltd

In April 2018, the Company concurrently entered into two Asset Transfer and License Agreements (the “Teva Agreements”) with Teva Pharmaceutical Industries Ltd (“Teva”) under which it acquired certain patents and intellectual property relating to two programs: (1) Teva’s glycoPEGylated FGF21 fibroblast growth factor 21 (“FGF21”) program, including the compound TEV-47948 (pegozafermin), a glycoPEGylated long-acting FGF21 and (2) Teva’s development program of small molecule inhibitors of fatty acid synthase. Pursuant to the Teva Agreements, the Company paid Teva an initial nonrefundable upfront payment of $6.0 million and the Company

could be obligated to pay Teva up to $67.5 million under each program, for a total of $135.0 million, upon the achievement of certain clinical development and commercial milestones. In addition, the Company is obligated to pay Teva tiered royalties at percentages in the low-to-mid single-digits on worldwide net sales on all products containing the Teva compounds.

The Teva Agreements can be terminated (i) by the Company without cause upon 120 days’ written notice to Teva, (ii) by either party, if the other party materially breaches any of its obligations under the Teva Agreements and fails to cure such breach within 60 days after receiving notice thereof, or (iii) by either party, if a bankruptcy petition is filed against the other party and is not dismissed within 60 days. In addition, Teva can also terminate the agreement related to the Company’s glycoPEGylated FGF21 program in the event the Company, or any of its affiliates or sublicensees, challenges any of the Teva patents licensed to the Company, and the challenge is not withdrawn within 30 days of written notice from Teva.

During the year ended December 31, 2022 and 2021, none of the development and commercial milestones were met and accordingly, there were no milestone payments related to the Teva Agreements.

Term Loan

12 Months Ended

Dec. 31, 2022

Debt Disclosure [Abstract]

Term Loan

6. Term Loan

Loan and Security Agreement

In April 2020, the Company entered into a Loan and Security Agreement, (the “Loan Agreement”) with the lenders referred to therein, and Silicon Valley Bank (“SVB”), as collateral agent. The Loan Agreement provided for (i) a secured term A loan facility (the “Term A Loan Facility”) of up to $10.0 million and (ii) a secured term B loan facility (the “Term B Loan Facility”) of up to $5.0 million that became available upon the satisfaction of certain milestones, each of which was available to be drawn through May 31, 2021. The term loan is secured by certain assets of the Borrowers (as defined in the Loan Agreement), including substantially all of the assets of the Company, excluding the Company’s intellectual property. The term loan contains customary representations, warranties, affirmative covenants and also certain restrictive covenants.

In April 2020, in connection with the execution of the Loan Agreement, the Company issued SVB a warrant to purchase 25,000 shares of the Company’s common stock with a warrant exercise price of $22.06 per share that is immediately exercisable and expires on June 30, 2025, as amended. The fair value of the warrant at the issuance date was determined by using the Black-Scholes option-pricing model and the fair value allocated to the warrant of $0.6 million met the requirements for equity classification within additional paid-in capital. Additionally, the Company incurred $0.2 million in closing costs, which together with the value of the warrants, were recorded as debt issuance costs.

In May 2021, the parties further amended the Loan Agreement (as amended, the “2021 Loan Agreement”). The 2021 Loan Agreement increased the Term A Loan Facility to up to $20.0 million, which was fully drawn as of December 2021. The Term B Loan Facility of up to $5.0 million was available to be drawn upon on achievement of certain additional milestones, on or before September 30, 2022, which expired unused. The 2021 Loan Agreement provided for interest-only payments until October 1, 2022, which could be extended to April 1, 2023, if on or before September 30, 2022, the Company received net cash proceeds of at least $75.0 million from the sale of its equity securities. In July 2022, the Company met the net cash proceeds requirement (see Note 7) and on September 1, 2022, the interest-only period was extended to April 1, 2023. Consecutive monthly payments of principal and interest commence on April 1, 2023 and continue through September 1, 2024, the maturity date of the term loan. The term loan bears interest at the greater of (i) 4.25% and (ii) the sum of (a) the Prime Rate as reported in The Wall Street Journal plus (b) 1.00%. The interest rate on the term loan was 4.25% at inception and 8.50% as of December 31, 2022. In addition, a final payment fee of 5.0% of the principal amount of the loan is due when the term loan becomes due or upon prepayment of the term loan. If the Company elects to prepay the loan, there is also a prepayment fee of between 1.0% and 3.0% of the principal amount of the term loan depending on the timing of prepayment.

In May 2021, in connection with the execution of the 2021 Loan Agreement, the Company issued SVB a warrant to purchase 33,923 shares of the Company’s common stock with a warrant exercise price of $19.12 per share that is immediately exercisable and expires on May 28, 2031. The Company determined the fair value of the

warrant at the issuance date by using the Black-Scholes option-pricing model with the following assumptions: risk-free interest rate of 1.6%, no dividends, expected volatility of 98.6% and expected term of 10.0 years. Upon issuance, the fair value of the warrant of $0.6 million was recorded as a debt issuance cost and met the requirements for equity classification within additional paid-in capital in the consolidated balance sheets. In addition, closing costs incurred were not material. In connection with Term B Loan Facility, if funded, the Company was to issue an additional warrant to purchase 11,305 shares of the Company’s common stock with the exercise price at the Company’s stock price at the time of issuance. However, the Term Loan B Facility expired unused and therefore no additional warrant was issued.

The 2021 Loan Agreement was accounted for as a modification to a credit facility. The related debt issuance costs incurred in May 2021, including the fair value of the warrant, together with the remaining unamortized debt issuance costs related to the Loan Agreement of $0.4 million were recorded as deferred assets and recognized on a straight-line basis as interest expense over the availability of the draw period. As of December 31, 2021, all amounts were drawn under the Term Loan A Facility such that all debt issuance costs were recorded as a debt discount. The carrying value of the debt discount, together with the final payment fee, are recognized using the effective interest method.

In September 2022, the parties agreed the extension of the interest-only period was met as a result of the July 2022 public offering (see Note 7), which was accounted for as a debt modification. A new effective interest rate equating to the revised cash flows of the carrying amount of the original debt was applied prospectively. The Company did not incur any costs in relation to the extension.

In January 2023, the Company executed a loan and security agreement with new lenders (the “2023 Loan Agreement”) and repaid its outstanding obligations under the 2021 Loan Agreement (see Note 11). As the Company had the intent and ability to refinance amounts due under the 2021 Loan Agreement pursuant to the terms of the 2023 Loan Agreement, as of December 31, 2022, the current portion of the outstanding principal obligation under the 2021 Loan Agreement was classified as long-term. As of December 31, 2022, the Company’s total obligations under the 2021 Loan Agreement were $19.7 million classified as term loan, non-current, net and $0.5 million classified as other non-current liability related to the final payment fee. The term loan, non-current, net is comprised of the outstanding principal amount of $20.0 million net of $0.3 million of unamortized debt discount.

Stockholders' Equity

12 Months Ended

Dec. 31, 2022

Equity [Abstract]

Stockholders' Equity

7. Stockholders’ Equity

As of December 31, 2022, the Company’s shares of common stock available for future issuance were as follows:


Shares available for future grant under the equity incentive plan			241,635
Shares available for future issuance under the employee stock purchase plan			729,218
Shares available for future issuance upon the exercise of warrants and pre-funded warrants			13,966,283
Total available for future issuance			14,937,136

Public Offerings

At-the-Market Offerings

In March 2021, the Company entered into a sales agreement (as amended, the “Sales Agreement”) with SVB Securities LLC and Cantor Fitzgerald & Co. (the “Sales Agents”) pursuant to which the Company may offer and sell up to $75.0 million of shares of its common stock, from time to time, in “at-the-market” offerings (the “ATM Facility”). The Sales Agents are entitled to compensation at a commission equal to 3.0% of the aggregate gross sales price per share sold under the Sales Agreement. Pursuant to the ATM Facility, in 2021, the Company received aggregate proceeds of $3.3 million, net of commissions and offering expenses from sales of 186,546 shares of its common stock and, in 2022, received aggregate proceeds of $28.5 million, net of commissions from the sales of 3,948,611 shares of its common stock.

July 2022 Public Offering

In July 2022, the Company completed an underwritten public offering of its common stock, warrants to purchase shares of its common stock and pre-funded warrants to purchase shares of its common stock. The Company sold 18,675,466 shares of its common stock with accompanying warrants to purchase up to 9,337,733 shares of its common stock at a combined public offering price of $3.55 per share. The Company also sold 7,944,252 pre-funded warrants to purchase shares of its common stock with accompanying warrants to purchase up to 3,972,126 shares of its common stock at a combined public offering price of $3.549 per pre-funded warrant, which represents the per share public offering price for the common stock less $0.001 per share, the exercise price for each pre-funded warrant. The Company raised net proceeds of $88.2 million, after deducting underwriting discounts and commissions of $5.7 million and other offering costs of $0.6 million.

The exercise of the outstanding warrants is subject to a beneficial ownership limitation of 9.99%, or at the election of the holder prior to the issuance of the warrant, 4.99%. The exercise of the outstanding pre-funded warrants is subject to a beneficial ownership limitation of 9.99%, or at the election of the holder prior to the issuance of the pre-funded warrant, 4.99%, which a holder may increase or decrease from time to time but shall not exceed 19.99%. The exercise price and number of shares of common stock issuable upon the exercise of the warrants and pre-funded warrants are subject to adjustment in the event of any stock dividends, stock splits, reverse stock split, recapitalization, or reorganization or similar transaction, as described in the agreements. Under certain circumstances, the warrants and pre-funded warrants may be exercisable on a “cashless” basis. The warrants and pre-funded warrants were classified as a component of stockholders’ equity and additional paid-in capital because such warrants and pre-funded warrants (i) are freestanding financial instruments that are legally detachable and separately exercisable from the equity instruments, (ii) are immediately exercisable, (iii) do not embody an obligation for the Company to repurchase its shares, (iv) permit the holders to receive a fixed number of common shares upon exercise, (v) are indexed to the Company’s common stock and (vi) meet the equity classification criteria. In addition, the warrants and pre-funded warrants do not provide any guarantee of value or return.

Common Stock Warrants

As of December 31, 2022, the Company’s outstanding warrants to purchase shares of its common stock were as follows:


	Shares of Common Stock Underlying Warrants		Exercise Price Per Share		Expiration Date
Warrant issued with term loan		25,000	$	22.06	June 30, 2025
Warrant issued with term loan		33,923	$	19.12	May 28, 2031
Warrants issued in public offering		13,107,360	$	5.325	July 1, 2024
Pre-funded warrants issued in public offering		800,000	$	0.001	Do not expire
Total outstanding		13,966,283

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-URI https://asc.fasb.org/topic&trid=2208762

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496158-112644

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Topic 505
-SubTopic 10
-Section 50
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-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496171-112644

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 14
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496171-112644

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
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-Subparagraph (SX 210.3-04)
-URI https://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
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-Paragraph 18
-Subparagraph (d)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496189-112644

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
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-Section 50
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-Publisher FASB
-Name Accounting Standards Codification
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-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496189-112644

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 505
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Reference 15: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Stock-Based Compensation

12 Months Ended

Dec. 31, 2022

Share-Based Payment Arrangement [Abstract]

Stock-Based Compensation

8. Stock-Based Compensation

Equity Incentive Plan

In September 2019, the Company’s board of directors adopted the 2019 Equity Incentive Plan (the “2019 Plan”), which also became effective in September 2019. The Company initially reserved 2,844,193 shares of common stock for issuance under the 2019 Plan. In addition, the number of shares of common stock reserved for issuance under the 2019 Plan will automatically increase on the first day of January for a period of up to ten years in an amount equal to 4% of the total number of shares of the Company’s capital stock outstanding on the immediately preceding December 31, or a lesser number of shares determined by the Company’s board of directors.

The board of directors determines the period over which options become exercisable and options generally vest over a four-year period, with 25% of options vesting on the first anniversary of employment, and thereafter, the remaining options vesting quarterly, over the following 36-month period. The options expire within ten years from

the date of grant. The exercise price of awards granted will not be less than the estimated fair value of the shares on the date of grant. The 2019 Plan also permits the board of directors to grant restricted stock units, which are subject to continued service conditions.

Employee Stock Purchase Plan

In October 2019, the Company’s board of directors adopted the 2019 Employee Stock Purchase Plan (“ESPP”), which became effective in November 2019. The Company initially reserved 225,188 shares of common stock for purchase under the ESPP. The number of shares of common stock reserved for issuance under the ESPP will automatically increase on the first day of January for a period of up to ten years in an amount equal to 1% of the total number of shares of the Company’s common stock outstanding on the immediately preceding December 31, or a lesser number of shares determined by the Company’s board of directors. Purchases are accomplished through the participation of discrete offering periods and each offering is expected to be six months in duration. For each offering period, ESPP participants will purchase shares of common stock at a price per share equal to 85% of the lesser of the fair market value of the Company’s common stock on (1) the first trading day of the applicable offering period or (2) the last trading day of the applicable offering period.

Stock Options

The following table summarizes stock option activity for the year ended December 31, 2022:


						Weighted
				Weighted		Average
				Average		Remaining		Aggregate
	Number of			Exercise		Contractual		Intrinsic
	Options			Price		Term		Value
						(In years)		(In thousands)
Balance outstanding as of December 31, 2021		2,406,668		$	16.46		8.1	$	9,970
Granted		1,149,816			4.48
Exercised		(151,061	)		2.09
Cancelled and forfeited		(243,506	)		16.34
Balance outstanding as of December 31, 2022		3,161,917		$	12.80		7.9	$	16,612
Exercisable as of December 31, 2022		1,460,685		$	14.60		7.0	$	7,320

The fair value of stock options granted for the periods presented was estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions:


	Year Ended December 31,
	2022	2021
Expected term (years)	5.5-6.3	5.5-6.1
Expected volatility	89.9-91.0%	86.9-91.9%
Risk-free interest rate	1.6-3.9%	0.7-1.3%
Expected dividend	—	—

The weighted-average grant date fair value of stock options that were granted during the year ended December 31, 2022 and 2021 was $3.38 and $16.18 per share, respectively. As of December 31, 2022, there was $12.2 million of unrecognized stock-based compensation related to stock options granted under the 2019 Plan, which is expected to be recognized over a weighted-average period of 2.2 years.

Restricted Stock Units (“RSUs”)

The Company has granted certain employees service-based RSUs that generally vest annually over a two or three-year period. The restrictions lapse over time for these service-based RSUs. In the event of termination of the holder’s continuous service to the Company, any unvested portion of the service-based RSUs are cancelled. For the year ended December 31, 2022 and 2021, the Company recognized expense of $1.2 million and $0.3 million, respectively, related to the service-based RSUs.

In February 2021, the Company granted performance-based RSUs that vest as to one-third on each one-year anniversary date, subject to achievement of a development milestone and continued service to the Company. In February 2022, a portion of the performance-based RSUs vested upon achievement of the development milestone and satisfaction of the continued service condition.

In February and September 2022, the Company granted performance-based RSUs that vest during the applicable performance period, subject to the achievement of certain corporate or department targets and continued service to the Company. In September 2022, a portion of the performance-based RSUs that were granted in February 2022 vested upon achievement of specific targets and satisfaction of the continued service condition.

As of December 31, 2022, it was probable that the remaining performance conditions would be met for the Company’s performance-based RSUs and expense was recognized using the accelerated attribution method. For the year ended December 31, 2022 and 2021, the Company recognized expense of $1.5 million and $0.8 million, respectively, related to performance-based RSUs.

The following table summarizes RSU activity for the year ended December 31, 2022:


	Number of RSUs			Weighted Average Fair Value at Date of Grant per Unit
Balance outstanding as of December 31, 2021		106,394		$	23.10
Granted		1,224,391			4.61
Vested / released		(103,703	)		8.61
Cancelled / forfeited		(131,344	)		5.53
Balance outstanding as of December 31, 2022		1,095,738			5.77

As of December 31, 2022, there was $3.9 million of total unrecognized expense related to RSUs, which is expected to be recognized over a weighted-average period of 1.4 years.

The Company recorded stock-based compensation for the periods indicated as follows (in thousands):


	Year Ended December 31,
	2022		2021
Research and development	$	4,094	$	2,966
General and administrative		6,262		5,712
Total stock-based compensation	$	10,356	$	8,678

Income Taxes

12 Months Ended

Dec. 31, 2022

Income Tax Disclosure [Abstract]

Income Taxes

9. Income Taxes

Tax Rates Applicable to the Income of the Company and its Subsidiaries

The Company is taxed according to U.S. federal and state tax laws and Israeli tax laws. The statutory tax rates applicable to the income of the Company and its subsidiaries for the periods presented are as follows:


	Year Ended December 31,
	2022			2021
89bio, Inc.		21	%		21	%
89Bio Ltd.		23	%		23	%
89bio Management, Inc.		21	%		21	%
UAB 89bio Lithuania		15	%		15	%

The income tax (expense) benefit for the periods presented is comprised of (in thousands):


	Year Ended December 31,
	2022			2021
Current:
Federal	—			—
State		(3	)		(2	)
Foreign		(16	)		(1	)
Total		(19	)		(3	)
Deferred:
Federal	—				150
State	—			—
Foreign	—			—
Total	—				150
Income tax (expense) benefit		(19	)		147

Deferred Income Taxes

Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of the Company’s deferred tax assets for the periods presented are as follows (in thousands):


	As of December 31,
	2022			2021
U.S. net operating loss carryforwards	$	45,002		$	29,094
Research and development expenses		18,927			6,529
Israel net operating loss carryforwards		7,385			4,262
Stock-based compensation		4,328			1,969
Accrued expenses		317			220
Operating Lease Liability		98			—
Other		244			191
Gross deferred tax assets		76,301			42,265
Less: valuation allowance		(75,982	)		(42,046	)
Total deferred tax assets	$	319		$	219

Operating lease right-of-use asset		(100	)		—
Total deferred tax liabilities		(100	)		—
Net deferred tax assets		219			219

As of December 31, 2022 and 2021, the Company recorded a valuation allowance of $76.0 million and $42.0 million, respectively, in respect of deferred tax assets resulting from tax loss carryforwards and other temporary differences. Realization of deferred tax assets is dependent upon future earnings, if any, the time and amount of

which are uncertain. The Company regularly assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes based upon the weight of available evidence that it is more likely than not that all or a portion of deferred tax assets will not be realized, a valuation allowance is established through an adjustment to income tax expense. The valuation allowance increased by $34.0 million in 2022, which primarily relates to significant taxable losses. The Company continues to record a partial valuation allowance against the deferred tax assets in Israel due to achievement of recent profitability and the expectation of future profitability in the jurisdiction.

Available Carryforward Tax Losses and Credits

As of December 31, 2022, the Company had an accumulated tax loss carryforward of approximately $160.9 million, $169.8 million, and $32.1 million for Federal, State and Israeli tax purposes, respectively. As of December 31, 2021, the Company had an accumulated tax loss carryforward of approximately $138.5 million and $18.5 million for U.S. and Israeli tax purposes, respectively. Federal net operating losses generated after 2017 can be carried forward indefinitely but utilization will be limited to 80% of taxable income in the period that net operating losses are being utilized. Carryforward tax losses in California will begin to expire in 2041. Carryforward tax losses in Israel have no expiration date.

As of December 31, 2022 and 2021, the Company had federal research and development credit carryforwards of approximately $4.3 million and $2.1 million, respectively, which expire beginning in 2040. As of December 31, 2022 and December 31, 2021, the Company had state research and development credit carryforwards of approximately $1.8 million and $1.1 million, respectively, which will carry forward indefinitely.

Loss from Operations, Before Income Tax

The Company recorded a loss from operations, before income tax for the periods presented as follows (in thousands):


	Year Ended December 31,
	2022			2021
United States	$	(101,938	)	$	(91,141	)
Lithuania		(7	)		10
Israel		(62	)		862
Net loss before income tax	$	(102,007	)	$	(90,269	)

Reconciliation of Income Tax (Expense) Benefit

The reconciliation of income tax (expense) benefit based on the statutory tax rate to the effective tax rate for the periods presented is as follows (in thousands):


	Year Ended December 31,
	2022			2021
Income tax benefit computed at statutory rates	$	21,429		$	18,757
Change in valuation allowance		(33,936	)		(20,111	)
Foreign rate differential		1			(19	)
State income taxes, net of federal benefit		5,824			—
State deferred tax true-up due to change in apportionment		6,517			—
Change in Israel effective tax rate due to the 2019 reorganization		—			(2	)
Research and development credits, net of uncertain tax position		2,130			1,331
Other		(1,984	)		191
Income tax (expense) benefit	$	(19	)	$	147

Utilization of U.S. federal and state net operating losses and credit carryforwards may be subject to an annual limitation provided for in Section 382 of the Internal Revenue Code and similar state codes. Any annual limitation could result in a deferral of the utilization of the net operating loss and credit carryforwards.

Unrecognized Tax Benefits

A reconciliation of the unrecognized tax benefits for the year ended December 31, 2022 and 2021 is as follows (in thousands):


	As of December 31,
	2022			2021
Balance beginning of year		851			329
Decrease related to prior year positions		(19	)		(35	)
Increase related to current year positions		752			557
Balance end of year		1,584			851

During the year ended December 31, 2022 and 2021, the amount of gross unrecognized tax benefits increased by $0.7 million and $0.5 million, respectively. If the total amount of unrecognized tax benefits was recognized, it would not have an impact to the effective tax rate as it would be offset by the reversal of related deferred tax assets which are subject to a full valuation allowance.

The Company recognizes interest and penalties related to uncertain tax positions as part of the income tax provision. As of December 31, 2022 and 2021, such interest and penalties were not material.

The Company is subject to taxation in the United States, California, Colorado, North Carolina and several foreign jurisdictions. To date, the Company has not been subject to any federal or state income tax audits. The Company is currently under examination by the Israeli tax authorities for 2018 and 2019. As of December 31, 2022, all tax years remain open to examination.

On August 9, 2022 and August 16, 2022, the Creating Helpful Incentives to Produce Semiconductors (“CHIPS”) Act and the Inflation Reduction Act (“IRA”), respectively, were signed into law. The CHIPS Act and IRA contain among other things, some income tax provisions that establish a corporate alternative minimum tax and provide tax incentives for semiconductor manufacturing and research. The Company has evaluated the current legislation and at this time, does not anticipate either to have a material impact on its financial statements.

The Tax Cuts and Jobs Act (“TCJA”) included a change in the treatment of research and development (“R&D”) expenditures for tax purposes under Section 174. Effective for tax years beginning after December 31, 2021, specified R&D expenditures must undergo a 5-year amortization period for domestic spend and a 15-year amortization period for foreign spend. Prior to the effective date (2021 tax year and prior), taxpayers were able to immediately expense R&D costs under Section 174(a) or had the option to capitalize and amortize R&D expenditures over a 5-year recovery period under Section 174(b). The Company has evaluated the current legislation at this time and prepared the provision by following the treatment of R&D expenditures for tax purposes under Section 174.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 21
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 2
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 14
-URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32705-109319

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
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-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6424409&loc=d3e44925-109338

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-URI https://asc.fasb.org/topic&trid=2144680

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=6424122&loc=d3e41874-109331

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-URI https://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

Net Loss Per Share

12 Months Ended

Dec. 31, 2022

Earnings Per Share [Abstract]

Net Loss Per Share

10. Net Loss Per Share

The following outstanding potentially dilutive common stock equivalents have been excluded from the calculation of diluted net loss per share for the periods indicated due to their anti-dilutive effect:


	Year Ended December 31,
	2022		2021
Stock options to purchase common stock		3,161,917		2,406,668
Unvested restricted stock units		1,095,738		106,394
Warrants to purchase common stock1		13,166,283		58,923
Total		17,423,938		2,571,985

1 The table above excludes pre-funded warrants issued in connection with the July 2022 public offering (see Note 7).

Subsequent Events

12 Months Ended

Dec. 31, 2022

Subsequent Events [Abstract]

Subsequent Events

11. Subsequent Events

2023 Loan Agreement

In January 2023, the Company executed the 2023 Loan Agreement with the new lenders named therein. The 2023 Loan Agreement provides up to $100.0 million in aggregate principal in term loans, consisting of a first tranche of $25.0 million that was funded at closing, two subsequent tranches totaling $25.0 million that may be funded upon the achievement of certain time-based, clinical and regulatory milestones, and a fourth tranche of up to $50.0 million that may be funded upon discretionary approval by the lenders.

The term loans under the 2023 Loan Agreement mature on January 1, 2027. The maturity date may be extended to July 1, 2027, provided that the second and third tranches are funded and the Company achieves certain other financing milestones. The term loans bear interest equal to the greater of (i) 8.45% and (ii) the sum of (a) the Prime Rate as reported in The Wall Street Journal plus (b) 2.25%. Consecutive monthly payments of interest commence in February 2023 and consecutive monthly payments of principal commence in February 2025, or February 2026 provided that certain extension milestones are achieved.

2021 Loan Agreement

In January 2023, the first tranche of $25.0 million that was funded pursuant to the 2023 Loan Agreement was primarily used to repay the Company’s outstanding obligations under the 2021 Loan Agreement, including the total principal amount outstanding as of December 31, 2022 of $20.0 million, the final payment fee of $1.0 million and an early prepayment fee of $0.4 million (see Note 6).

ATM Facility

In January and February 2023, the Company received aggregate proceeds of $13.4 million, net of commissions from sales of 968,000 shares of its common stock pursuant to the ATM Facility (see Note 7).

On February 15, 2023, the Company entered into Amendment No. 1 to the Sales Agreement with the Sales Agent, pursuant to which the Company may offer and sell up to $150.0 million shares of its common stock, from time to time, through the ATM Facility (see Note 7).

Banking Relationship with SVB

The Company has a banking relationship with SVB. On March 10, 2023, SVB was closed by the California Department of Financial Protection and Innovation, which appointed the Federal Deposit Insurance Corporation ("FDIC") as receiver. On March 12, 2023, the Federal Reserve Board approved actions enabling the FDIC to complete its resolution of SVB in a manner that fully protects all depositors. Based on the foregoing and the Company’s analysis of the components of its relationship with SVB, the Company does not expect these events to have a material impact on the Company’s consolidated financial statements.

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2022
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“U.S. GAAP”).
Reclassification	Reclassification Certain prior year amounts in the Company’s consolidated statements of operations and comprehensive loss have been reclassified to conform to the current year presentation. Specifically, interest expense is disclosed separately on the Company’s consolidated statements of operations and comprehensive loss, which had no impact on reported net loss, comprehensive loss, or loss per share.
Principles of Consolidation	Principles of Consolidation The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of expenses during the reporting period. Significant estimates and assumptions made in the accompanying consolidated financial statements include but are not limited to accrued research and development expenses and to the fair value of stock options. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates.
Foreign Currencies	Foreign Currencies Certain transactions during the year ended December 31, 2022 and 2021 were denominated in currencies other than the U.S. dollar. Gains and losses from foreign currency transactions were not material for all periods presented and are reflected in the consolidated statements of operations and comprehensive loss as a component of interest income and other, net. The Company’s subsidiary in Lithuania uses the Euro as its functional currency for financial reporting. The re-measurement from Euros to U.S. dollars results in translation gain and loss adjustments, which are reflected as a component of comprehensive loss as foreign currency translation adjustments.
Fair Value Measurements	Fair Value Measurements Financial assets and liabilities are recorded at fair value on a recurring basis in the consolidated balance sheets. The carrying values of Company’s financial assets and liabilities, including cash and cash equivalents, restricted cash, prepaid and other current assets, accounts payable, and accrued expenses approximate to their fair value due to the short-term nature of these instruments. The fair value of the Company’s term loan approximates its carrying value, or amortized cost, due to the prevailing market rates of interest rates it bears. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the reporting date. Assets and liabilities recorded at fair value are categorized based upon the level of judgment associated with the inputs used to measure their fair value. Hierarchical levels are directly related to the amount of subjectivity with the inputs to the valuation of these assets or liabilities as follows: Level 1—Observable inputs such as unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date; Level 2—Inputs (other than quoted prices included in Level 1) are either directly or indirectly observable inputs for similar assets or liabilities. These include quoted prices for identical or similar assets or liabilities in active markets and quoted prices for identical or similar assets or liabilities in markets that are not active; and Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist primarily of cash and cash equivalents and short-term available-for-sale securities. Bank deposits are held by accredited financial institutions and these deposits may at times be in excess of insured limits. The Company limits its credit risk associated with cash and cash equivalents by placing them with financial institutions that it believes are of high quality. The Company has not experienced any losses on its deposits of cash or cash equivalents. The Company limits amounts invested in available-for-sale securities by credit rating, maturity, industry group, investment type and issuer, except for securities issued by the U.S. government. The Company is not exposed to any significant concentrations of credit risk from these financial instruments.
Other Risks and Uncertainties	Other Risks and Uncertainties The Company’s future results of operations involve a number of other risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, the Company’s early stages of clinical drug development; the Company’s ability to advance product candidates into, and successfully complete, clinical trials on the timelines it projects; the Company’s ability to adequately demonstrate sufficient safety and efficacy of its product candidates; the Company’s ability to enroll patients in its ongoing and future clinical trials; the Company’s ability to successfully manufacture and supply its product candidates for clinical trials; the Company’s ability to obtain additional capital to finance its operations; uncertainties related to the projections of the size of patient populations suffering from the diseases the Company is targeting; the Company’s ability to obtain, maintain, and protect its intellectual property rights; developments relating to the Company’s competitors and its industry, including competing product candidates and therapies; general economic and market conditions; and other risks and uncertainties. The Company’s product candidates will require approvals from the U.S. Food and Drug Administration and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any product candidates will receive the necessary approvals. If the Company is denied approval, approval is delayed or the Company is unable to maintain approval for any product candidate, it could have a materially adverse impact on the Company. The ongoing COVID-19 pandemic has disrupted and may continue to disrupt the Company’s business and delay its preclinical and clinical programs and timelines. The extent to which the COVID-19 pandemic may impact the Company’s future operating results and financial condition is uncertain.
Segment Reporting	Segment Reporting The Company has one operating segment. The Company’s chief operating decision maker, its Chief Executive Officer, manages the Company’s operations on a consolidated basis for the purposes of allocating resources and evaluating financial performance.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments purchased with original maturities of three months or less from the purchase date to be cash equivalents. Cash equivalents consist primarily of amounts invested in money market funds and commercial paper that are stated at fair value.
Investments	Investments Investments have been classified as available-for-sale and are carried at estimated fair value as determined based upon quoted market prices or pricing models for similar securities. Management determines the appropriate classification of its available-for-sale investments in debt securities at the time of purchase. Generally, investments with original maturities beyond three months at the date of purchase are classified as short-term because it is management’s intent to use the investments to fund current operations or to make them available for current operations. Unrealized gains and losses are excluded from net loss and are reported as a component of comprehensive loss. The Company periodically evaluates whether declines in fair values of its available-for-sale securities below their book value are other-than-temporary. This evaluation consists of several qualitative and quantitative factors regarding the severity and duration of the unrealized loss as well as the Company’s ability and intent to hold the available-for-sale security until a forecasted recovery occurs. Additionally, the Company assesses whether it has plans to sell the security or it is more likely than not it will be required to sell any available-for-sale securities before recovery of its amortized cost basis. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on available-for-sale securities are included in interest income and other, net. The cost of investments sold is based on the specific-identification method. The Company has not experienced any material realized gains or losses or other-than-temporary losses in the periods presented.
Leases	Leases The Company is a lessee in noncancellable operating leases for office space. Beginning in 2022, the Company accounts for leases in accordance with Accounting Standards Update (“ASU”) 2016-02, Leases (Topic 842). The Company determines if an arrangement is a lease or contains an embedded lease at inception. The Company accounts for a contract as a lease when it has the right to control the asset for a period of time while obtaining substantially all of the asset’s economic benefits. For arrangements that meet the definition of a lease, the Company determines the initial classification and measurement of its right-of-use (“ROU”) asset and lease liability at the lease commencement date and thereafter if modified. Operating lease ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make the contractual lease payments over the lease term. The ROU asset is initially measured at cost, which comprises the initial amount of the lease liability adjusted for lease payments made at or before the lease commencement date, plus any initial direct costs incurred less any lease incentives received. The operating lease liability is initially measured at the present value of the unpaid lease payments at the lease commencement date. The lease liability is subsequently measured at amortized cost using the effective-interest method. The lease term includes any renewal options that the Company is reasonably assured to exercise. The present value of lease payments is determined by using the interest rate implicit in the lease, if that rate is readily determinable, otherwise, the Company uses its estimated collateralized incremental borrowing rate for the lease term. The Company has elected not to record leases with an original term of twelve months or less on its consolidated balance sheets and recognizes those lease payments in operating expenses in the consolidated statements of operations and comprehensive loss. The Company’s short-term lease is not material. In addition, the Company’s leases may require it to pay additional costs, such as utilities, maintenance, and other operating costs, which are generally referred to as non-lease components and vary based on future outcomes. The Company has elected to not separate lease and non-lease components. Only the fixed costs for lease components and their associated non-lease components are accounted for as a single lease component and recognized as part of a ROU asset and lease liability. Any variable expenses are recognized in operating expenses as incurred. Rent expense for an operating lease liability is recognized on a straight-line basis over the lease term and is included in operating expenses in the consolidated statements of operations and comprehensive loss.
Property and Equipment, Net	Property and Equipment, Net Property and equipment are stated at cost, less accumulated depreciation. Depreciation is calculated on a straight-line basis over the estimated useful lives of the related assets, generally ranging from three to seven years. Leasehold improvements are amortized on a straight-line basis over the shorter of the assets’ estimated useful life or the remaining term of the lease. Upon retirement or sale of the assets, the cost and related accumulated depreciation and amortization are removed from the consolidated balance sheets and the resulting gains or losses are recorded in the consolidated statements of operations and comprehensive loss. Maintenance and repair costs are expensed as incurred.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company periodically evaluates its long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets or group of assets may not be fully recoverable. If indicators of impairment exist and the undiscounted future cash flows that the assets are expected to generate are less than the carrying value of the assets, then the Company will reduce the carrying amount of the assets through an impairment charge, to their estimated fair values based on a discounted cash flow approach or, when available and appropriate, to comparable market values. There were no such indicators for the periods presented.
Accrued Research and Development Expenses	Accrued Research and Development Expenses The Company estimates preclinical and clinical study and research expenses based on the services performed, pursuant to contracts with research institutions that conduct and manage preclinical and clinical studies and research services on its behalf. The Company records the costs of research and development activities based upon the estimated services provided but not yet invoiced and includes these costs in accrued expenses in the consolidated balance sheets. These costs are a component of the Company’s research and development expenses. The Company accrues for these costs based on factors such as estimates of the work completed in accordance with agreements established with its third-party service providers. The Company makes judgments and estimates in determining the accrued expenses balance. As actual costs become known, the Company adjusts its accrued expenses. The Company has not experienced any material differences between accrued costs and actual costs incurred. However, the status and timing of actual services performed may vary from the Company’s estimates, resulting in adjustments to expense in future periods. Changes in these estimates that result in material changes to the Company’s accrued expenses could materially affect the Company’s results of operations. Contingent milestone payments, if any, are expensed when the milestone results are probable and estimable, which is generally upon achievement of the milestone.
Warrants To Purchase Common Stock	Warrants to Purchase Common Stock The Company classifies warrants indexed to its common stock and meeting the requirements for equity classification within stockholders’ equity. This assessment is conducted at the time of warrant issuance and as of each reporting period that the warrants remain outstanding.
Research and Development Expenses	Research and Development Expenses Research and development expenses consist primarily of costs incurred for the development of the Company’s lead product candidate, pegozafermin. Research and development expenses consist primarily of external costs related to preclinical and clinical development and related supplies and personnel costs. Personnel costs consist of salaries, employee benefits and stock-based compensation for individuals involved in research and development efforts. Payments associated with agreements to acquire licenses to develop, use, manufacture and commercialize products and purchases of pegozafermin from contract manufacturing organizations that have not reached technological feasibility and do not have alternate future commercial use are expensed as incurred.
Stock-Based Compensation	Stock-Based Compensation The Company provides equity awards in the form of stock options and restricted stock units. The Company measures its equity awards made to employees, directors, and non-employee service providers based on estimated fair values and recognizes stock-based compensation over the requisite service period. The Company accounts for forfeitures as they occur. The Company estimates the fair value of stock option awards on the date of grant using a Black-Scholes option pricing model. The Company recognizes compensation for the value of stock options awards, which have graded vesting, using the straight-line method over the requisite service period of each award. The Black-Scholes option pricing model requires a number of assumptions, of which the most significant are expected volatility, expected option term (the time from the grant date until the options are exercised or expire), risk-free rate, and expected dividend rate. These assumptions include: • Expected volatility—Since the Company has limited trading history for its common stock, expected volatility is estimated based on weighting the Company’s volatility and the volatility of comparable publicly traded biotechnology companies during the equivalent period of the calculated expected term of the options granted. The comparable companies were chosen based on their similar size, stage in the life cycle, or area of specialty. There is a degree of uncertainty in determining a comparable peer group as each of the peers are engaged in varied research and development activities, the timing and progress of which differ within the peer group. • Expected term—The expected term of options granted to employees and directors is determined using the “simplified” method. Under this approach, the expected term is presumed to be the midpoint between the weighted-average vesting term and the contractual term of the option. The simplified method makes the assumption that the employee will exercise stock options evenly over the period when the stock options are vested and ending on the date when the stock options would expire. The expected option term for options granted to non-employees is estimated on a grant-by-grant basis. • Risk-free interest rate—The risk-free interest rate is based on the U.S. Treasury zero coupon bonds in effect on the grant date for periods with an equivalent expected term as the option. • Expected dividend—The Company has never paid dividends and has no foreseeable plans to pay dividends on its shares of common stock. Therefore, an expected dividend of zero is used. The fair value of restricted stock units is based on the fair value of the Company’s common stock on the date of grant. The grant date fair value of restricted stock units with service vesting conditions is recognized over the requisite service period on a straight-line basis. For restricted stock units with performance vesting conditions, the Company evaluates the probability of achieving the performance condition at each reporting date and recognizes expense for such performance awards over the requisite service period using the accelerated attribution method.
Income Taxes	Income Taxes Income taxes are accounted for under the asset and liability method. Under this method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the consolidated financial statements carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates applied to taxable income in the years in which those temporary differences are expected to be realized. The effect on deferred tax assets and liabilities of a change in tax rates is recognized as income or loss in the period that includes the enactment date. A valuation allowance is established when necessary to reduce deferred tax assets to the amount expected to be realized. Interest and penalties related to unrecognized tax benefits are included within the provision of income tax.
Basic and Diluted Net Loss per Share	Basic and Diluted Net Loss per Share Basic loss per share is computed by dividing net loss by the weighted-average number of shares of common stock outstanding during the period. Diluted loss per share is computed by dividing net loss by the weighted-average number of shares of common stock outstanding together with the number of additional shares of common stock that would have been outstanding if all potentially dilutive shares of common stock had been issued. Since the Company is in a loss position for the periods presented, basic net loss per share is the same as diluted net loss per share since the effects of potentially dilutive securities are antidilutive. Shares of the Company’s common stock underlying pre-funded warrants exercisable for nominal consideration are included in the computation of basic and diluted net loss per share, even if antidilutive.
Comprehensive Loss	Comprehensive Loss The Company’s comprehensive loss is comprised of net loss and changes in unrealized gains or losses on available-for-sale securities and foreign currency translation adjustments.
Recent Accounting Pronouncements	Recently Adopted Accounting Standards In February 2016, the Financial Accounting Standards Board (“FASB”) issued ASU 2016-02, Leases (Topic 842), or Accounting Standards Codification (“ASC”) 842, which requires lessees to recognize leases on the balance sheet and disclose key information about leasing arrangements. ASC 842 establishes a ROU model that requires a lessee to recognize a ROU asset and lease liability on the balance sheet for all leases with a term longer than 12 months. Leases are classified as finance or operating, with classification affecting the pattern and classification of expense recognition in the income statement. On January 1, 2022, the Company adopted ASC 842 using the modified retrospective transition method and elected the practical expedients to not reassess whether any expired or existing contracts are or contain leases, carry forward its historical lease classification and not reassess initial direct costs for existing leases. Upon adoption of ASC 842, the Company recorded an operating ROU asset of $0.2 million and an operating lease liability of $0.2 million on its consolidated balance sheet. There was no adjustment to the opening balance of accumulated deficit as a result of adoption. Results for the year ended December 31, 2022 are presented under ASC 842. Prior period amounts preceding January 1, 2022 continue to be reported in accordance with the Company’s historical accounting under the previous lease guidance, ASC 840. Recent Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”), which replaces the existing incurred loss impairment model with an expected credit loss model and requires a financial asset measured at amortized cost to be presented at the net amount expected to be collected. As an emerging growth company, ASU 2016-13 is effective for the Company for the year ending December 31, 2023 and interim periods within that fiscal year and must be adopted using a modified retrospective approach, with certain exceptions. The Company is evaluating the impact of this standard and does not expect the adoption of ASU 2016-13 to have a material impact on the Company’s consolidated financial statements and related disclosures.

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2022

Fair Value Disclosures [Abstract]

Summary of Financial Assets Measured at Fair Value on Recurring Basis

The following table presents the Company’s financial assets measured at fair value on a recurring basis by level within the fair value hierarchy as of December 31, 2022 (in thousands):


	Valuation	Amortized		Unrealized		Unrealized			Fair
	Hierarchy	Cost		Gains		Losses			Value
Money market funds	Level 1	$	18,224	$	—	$	—		$	18,224
Commercial paper	Level 2		104,279		1		(84	)		104,196
U.S. government bonds	Level 2		18,225		1		(109	)		18,117
Agency bonds	Level 2		13,986		—		(78	)		13,908
Corporate debt securities	Level 2		10,488		—		(62	)		10,426
U.S. treasury bills	Level 2		7,414		1		(21	)		7,394
Agency discount securities	Level 2		5,216		9		—			5,225
Non-U.S. debt securities	Level 2		3,975		—		(20	)		3,955
Total cash equivalents and available-for- sale securities		$	181,807	$	12	$	(374	)	$	181,445
Classified as:
Cash equivalents									$	48,540
Short-term available-for-sale securities										132,905
Total cash equivalents and available-for- sale securities									$	181,445

The following table presents the Company’s financial assets measured at fair value on a recurring basis by level within the fair value hierarchy as of December 31, 2021 (in thousands):


	Valuation	Amortized		Unrealized		Unrealized			Fair
	Hierarchy	Cost		Gains		Losses			Value
Money market funds	Level 1	$	21,477	$	—	$	—		$	21,477
Commercial paper	Level 2		59,647		—		(10	)		59,637
U.S. government bonds	Level 2		21,662		—		(42	)		21,620
Corporate debt securities	Level 2		8,776		1		(1	)		8,776
Agency bonds	Level 2		7,747		1		(7	)		7,741
Municipal bonds	Level 2		4,251		—		(4	)		4,247
Non-U.S. debt securities	Level 2		2,506		—		(1	)		2,505
Total cash equivalents and available-for- sale securities		$	126,066	$	2	$	(65	)	$	126,003
Classified as:
Cash equivalents									$	27,715
Short-term available-for-sale securities										98,288
Total cash equivalents and available-for- sale securities									$	126,003

Schedule of Contractual Maturities of Cash Equivalents and Available-for-Sale Securities

The following table summarizes the Company’s cash equivalents and available-for-sale securities by contractual maturity as of December 31, 2022 (in thousands):


Within one year	$	175,243
After one year through two years		6,202
Total cash equivalents and available-for-sale securities	$	181,445

The following table summarizes the Company’s cash equivalents and available-for-sale securities by contractual maturity as of December 31, 2021 (in thousands):


Within one year	$	120,726
After one year through two years		5,277
Total cash equivalents and available-for-sale securities	$	126,003

Consolidated Balance Sheet Components (Tables)

12 Months Ended

Dec. 31, 2022

Balance Sheet Related Disclosures [Abstract]

Schedule of Prepaid and Other Current Assets

Prepaid and other current assets consist of the following as of the periods presented (in thousands):


	As of December 31,
	2022		2021
Prepaid research and development	$	5,727	$	7,895
Prepaid taxes		646		836
Prepaid other		1,547		2,506
Total prepaid and other current assets	$	7,920	$	11,237

Schedule of Accrued Expenses

Accrued expenses consist of the following as of the periods presented (in thousands):


	As of December 31,
	2022		2021
Accrued research and development expenses	$	6,499	$	6,195
Accrued employee and related expenses		4,165		3,168
Accrued professional and legal fees		1,052		495
Accrued other expenses		228		336
Total accrued expenses	$	11,944	$	10,194

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2022

Commitments and Contingencies Disclosure [Abstract]

Schedule of Future Minimum Lease Payments Under Non-cancellable Operating Lease Obligations

As of December 31, 2022, the undiscounted future minimum lease payments due under the Company’s non-cancellable operating lease are as follows (in thousands):


2023	$	185
2024		185
2025		7
Total undiscounted future minimum lease payments	$	377
Less: imputed interest		(23	)
Present value of operating lease liability	$	354

The total future minimum annual payments for operating leases in effect as of December 31, 2021 were as follows (in thousands):


2022	$	212
2023	7
Total future minimum annual payments	$	219

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2022

Share-Based Payment Arrangement [Abstract]

Summary of Stock Option Activity

The following table summarizes stock option activity for the year ended December 31, 2022:


						Weighted
				Weighted		Average
				Average		Remaining		Aggregate
	Number of			Exercise		Contractual		Intrinsic
	Options			Price		Term		Value
						(In years)		(In thousands)
Balance outstanding as of December 31, 2021		2,406,668		$	16.46		8.1	$	9,970
Granted		1,149,816			4.48
Exercised		(151,061	)		2.09
Cancelled and forfeited		(243,506	)		16.34
Balance outstanding as of December 31, 2022		3,161,917		$	12.80		7.9	$	16,612
Exercisable as of December 31, 2022		1,460,685		$	14.60		7.0	$	7,320

Summary of Estimated Fair Value of Stock Options Granted Using Black-Scholes Option-Pricing Model

The fair value of stock options granted for the periods presented was estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions:


	Year Ended December 31,
	2022	2021
Expected term (years)	5.5-6.3	5.5-6.1
Expected volatility	89.9-91.0%	86.9-91.9%
Risk-free interest rate	1.6-3.9%	0.7-1.3%
Expected dividend	—	—

Summary of Restricted Stock Unit Activity

The following table summarizes RSU activity for the year ended December 31, 2022:


	Number of RSUs			Weighted Average Fair Value at Date of Grant per Unit
Balance outstanding as of December 31, 2021		106,394		$	23.10
Granted		1,224,391			4.61
Vested / released		(103,703	)		8.61
Cancelled / forfeited		(131,344	)		5.53
Balance outstanding as of December 31, 2022		1,095,738			5.77

Summary of Stock-Based Compensation

The Company recorded stock-based compensation for the periods indicated as follows (in thousands):


	Year Ended December 31,
	2022		2021
Research and development	$	4,094	$	2,966
General and administrative		6,262		5,712
Total stock-based compensation	$	10,356	$	8,678

Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2022

Equity [Abstract]

Schedule of Shares of Common Stock Available for Future Issuance

As of December 31, 2022, the Company’s shares of common stock available for future issuance were as follows:


Shares available for future grant under the equity incentive plan			241,635
Shares available for future issuance under the employee stock purchase plan			729,218
Shares available for future issuance upon the exercise of warrants and pre-funded warrants			13,966,283
Total available for future issuance			14,937,136

Schedule of Outstanding Warrants to Purchase Shares of Common Stock

As of December 31, 2022, the Company’s outstanding warrants to purchase shares of its common stock were as follows:


	Shares of Common Stock Underlying Warrants		Exercise Price Per Share		Expiration Date
Warrant issued with term loan		25,000	$	22.06	June 30, 2025
Warrant issued with term loan		33,923	$	19.12	May 28, 2031
Warrants issued in public offering		13,107,360	$	5.325	July 1, 2024
Pre-funded warrants issued in public offering		800,000	$	0.001	Do not expire
Total outstanding		13,966,283

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2022

Income Tax Disclosure [Abstract]

Summary of Statutory Tax Rates Applicable to Income of Company and Subsidiaries


	Year Ended December 31,
	2022			2021
89bio, Inc.		21	%		21	%
89Bio Ltd.		23	%		23	%
89bio Management, Inc.		21	%		21	%
UAB 89bio Lithuania		15	%		15	%

Summary of Income Tax (Expense) Benefit

The income tax (expense) benefit for the periods presented is comprised of (in thousands):


	Year Ended December 31,
	2022			2021
Current:
Federal	—			—
State		(3	)		(2	)
Foreign		(16	)		(1	)
Total		(19	)		(3	)
Deferred:
Federal	—				150
State	—			—
Foreign	—			—
Total	—				150
Income tax (expense) benefit		(19	)		147

Summary of Components of Deferred Tax Assets

Significant components of the Company’s deferred tax assets for the periods presented are as follows (in thousands):


	As of December 31,
	2022			2021
U.S. net operating loss carryforwards	$	45,002		$	29,094
Research and development expenses		18,927			6,529
Israel net operating loss carryforwards		7,385			4,262
Stock-based compensation		4,328			1,969
Accrued expenses		317			220
Operating Lease Liability		98			—
Other		244			191
Gross deferred tax assets		76,301			42,265
Less: valuation allowance		(75,982	)		(42,046	)
Total deferred tax assets	$	319		$	219

Operating lease right-of-use asset		(100	)		—
Total deferred tax liabilities		(100	)		—
Net deferred tax assets		219			219

Summary of Loss from Operations Before Taxes on Income

The Company recorded a loss from operations, before income tax for the periods presented as follows (in thousands):


	Year Ended December 31,
	2022			2021
United States	$	(101,938	)	$	(91,141	)
Lithuania		(7	)		10
Israel		(62	)		862
Net loss before income tax	$	(102,007	)	$	(90,269	)

Summary of Reconciliation of Income Tax (Expense) Benefit Statutory Tax Rate to Effective Tax Rate

The reconciliation of income tax (expense) benefit based on the statutory tax rate to the effective tax rate for the periods presented is as follows (in thousands):


	Year Ended December 31,
	2022			2021
Income tax benefit computed at statutory rates	$	21,429		$	18,757
Change in valuation allowance		(33,936	)		(20,111	)
Foreign rate differential		1			(19	)
State income taxes, net of federal benefit		5,824			—
State deferred tax true-up due to change in apportionment		6,517			—
Change in Israel effective tax rate due to the 2019 reorganization		—			(2	)
Research and development credits, net of uncertain tax position		2,130			1,331
Other		(1,984	)		191
Income tax (expense) benefit	$	(19	)	$	147

Summary of a Reconciliation of The Unrecognized Tax Benefits

A reconciliation of the unrecognized tax benefits for the year ended December 31, 2022 and 2021 is as follows (in thousands):


	As of December 31,
	2022			2021
Balance beginning of year		851			329
Decrease related to prior year positions		(19	)		(35	)
Increase related to current year positions		752			557
Balance end of year		1,584			851

Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2022

Earnings Per Share [Abstract]

Schedule of Outstanding Potentially Dilutive Securities Excluded From Calculation of Diluted Net Loss


	Year Ended December 31,
	2022		2021
Stock options to purchase common stock		3,161,917		2,406,668
Unvested restricted stock units		1,095,738		106,394
Warrants to purchase common stock1		13,166,283		58,923
Total		17,423,938		2,571,985

1 The table above excludes pre-funded warrants issued in connection with the July 2022 public offering (see Note 7).

Organization and Basis of Presentation - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($)
Subsidiary Sale Of Stock [Line Items]
Date of incorporation	Jun. 30, 2019
Cash and cash equivalents and short term available-for-sale securities	$ 188.2

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2022 USD ($) Segment	Aug. 31, 2022 USD ($)	Jan. 01, 2022 USD ($)	Dec. 31, 2021 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments \| Segment	1
Operating lease right-of-use asset	$ 363,000	$ 300,000
Operating lease liability, current	168,000	$ 300,000
Accumulated deficit	(315,243,000)			$ (213,217,000)
Other-than-temporary losses	0
Realized gains or losses on investments	$ 0
ASC 842
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]	true
Change in accounting principle, accounting standards update, adoption date	Jan. 01, 2022
Operating lease right-of-use asset			$ 200,000
Operating lease liability, current			200,000
Accumulated deficit			$ 0
Leasehold Improvements
Summary Of Significant Accounting Policies [Line Items]
Leasehold improvements amortization, description	Leasehold improvements are amortized on a straight-line basis over the shorter of the assets’ estimated useful life or the remaining term of the lease.
Minimum
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives	3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives	7 years

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Aggregated Fair Value	$ 181,445	$ 126,003
Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	181,807	126,066
Short-term investments, Gross Unrealized Holding Gains	12	2
Short-term investments, Gross Unrealized Holding Losses	(374)	(65)
Short-term investments, Aggregated Fair Value	181,445	126,003
Recurring \| Cash equivalents
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Aggregated Fair Value	48,540	27,715
Recurring \| Short-term available for sale securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Aggregated Fair Value	132,905	98,288
Recurring \| Level 1 \| Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	18,224	21,477
Short-term investments, Aggregated Fair Value	18,224	21,477
Recurring \| Level 2 \| Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	104,279	59,647
Short-term investments, Gross Unrealized Holding Gains	1
Short-term investments, Gross Unrealized Holding Losses	(84)	(10)
Short-term investments, Aggregated Fair Value	104,196	59,637
Recurring \| Level 2 \| U.S. government bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	18,225	21,662
Short-term investments, Gross Unrealized Holding Gains	1
Short-term investments, Gross Unrealized Holding Losses	(109)	(42)
Short-term investments, Aggregated Fair Value	18,117	21,620
Recurring \| Level 2 \| Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	10,488	8,776
Short-term investments, Gross Unrealized Holding Gains		1
Short-term investments, Gross Unrealized Holding Losses	(62)	(1)
Short-term investments, Aggregated Fair Value	10,426	8,776
Recurring \| Level 2 \| Agency bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	13,986	7,747
Short-term investments, Gross Unrealized Holding Gains		1
Short-term investments, Gross Unrealized Holding Losses	(78)	(7)
Short-term investments, Aggregated Fair Value	13,908	7,741
Recurring \| Level 2 \| U.S. treasury bills
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	7,414
Short-term investments, Gross Unrealized Holding Gains	1
Short-term investments, Gross Unrealized Holding Losses	(21)
Short-term investments, Aggregated Fair Value	7,394
Recurring \| Level 2 \| Non-US debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	3,975	2,506
Short-term investments, Gross Unrealized Holding Losses	(20)	(1)
Short-term investments, Aggregated Fair Value	3,955	2,505
Recurring \| Level 2 \| Agency discount securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	5,216
Short-term investments, Gross Unrealized Holding Gains	9
Short-term investments, Aggregated Fair Value	$ 5,225
Recurring \| Level 2 \| Municipal Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost		4,251
Short-term investments, Gross Unrealized Holding Losses		(4)
Short-term investments, Aggregated Fair Value		$ 4,247

Fair Value Measurements - Schedule of Contractual Maturities of Cash Equivalents and Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Within one year	$ 175,243	$ 120,726
After one year through two years	6,202	5,277
Total cash equivalents and available-for-sale securities	$ 181,445	$ 126,003

Consolidated Balance Sheet Components - Schedule of Prepaid and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Prepaid Expense and Other Assets, Current [Abstract]
Prepaid research and development	$ 5,727	$ 7,895
Prepaid taxes	646	836
Prepaid other	1,547	2,506
Total prepaid and other current assets	$ 7,920	$ 11,237

Consolidated Balance Sheet Components - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Payables and Accruals [Abstract]
Accrued research and development expenses	$ 6,499	$ 6,195
Accrued employee and related expenses	4,165	3,168
Accrued professional and legal fees	1,052	495
Accrued other expenses	228	336
Total accrued expenses	$ 11,944	$ 10,194

Commitments and Contingencies - Additional Information (Details) - USD ($)			1 Months Ended	12 Months Ended
	Aug. 31, 2022	Jan. 01, 2022	Apr. 30, 2018	Dec. 31, 2022	Dec. 31, 2021
Loss Contingencies [Line Items]
Operating lease right-of-use asset	$ 300,000			$ 363,000
Operating lease liability, current	$ 300,000			168,000
Operating leases, rent expense				200,000	$ 300,000
Variable lease payments				0
Short-term lease costs				$ 0
Remaining lease term				2 years
Incremental borrowing rate used to determine operating lease liability				6.50%
Teva Agreements
Loss Contingencies [Line Items]
Nonrefundable upfront payment			$ 6,000,000.0
Payment upon achievement of certain clinical and commercial milestones			135,000,000.0
Asset transfer and license agreement, termination period after written notice				120 days
Asset transfer and license agreement, termination period notice of breach				60 days
Asset transfer and license agreement termination notice period if bankruptcy petition filed				60 days
Milestone payments				$ 0	0
Teva Agreements \| Research and Development Expenses
Loss Contingencies [Line Items]
Milestone payments				$ 0	$ 0
Teva Agreements \| Teva's GlycoPEGylated FGF21 Program
Loss Contingencies [Line Items]
Payment upon achievement of certain clinical and commercial milestones			67,500,000
Teva Agreements \| Teva's Development Program
Loss Contingencies [Line Items]
Payment upon achievement of certain clinical and commercial milestones			$ 67,500,000
San Francisco Office
Loss Contingencies [Line Items]
Operating lease expiration month and year	2025-01	2023-01

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under Non-cancellable Operating Lease Obligations (Details) $ in Thousands	Dec. 31, 2022 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2023	$ 185
2024	185
2025	7
Total undiscounted future minimum lease payments	377
Less: imputed interest	(23)
Present value of operating lease liability	$ 354

Commitments and Contingencies - Schedule of Future Minimum Annual Payments for Operating Leases (Details) $ in Thousands	Dec. 31, 2021 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2022	$ 212
2023	7
Total future minimum annual payments	$ 219

Term Loan - Additional Information (Details) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended
	May 31, 2021 USD ($) $ / shares shares	Apr. 30, 2020 USD ($) $ / shares shares	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Debt Instrument [Line Items]
Percentage of fee on loan			5.00%
Deferred tax assets			$ 76,301	$ 42,265
Term loan, non-current, net			19,691	16,898
Other non-current liability			$ 501	$ 30
Term A Loan Facility
Debt Instrument [Line Items]
Line of credit facility, description			As of December 31, 2021, all amounts were drawn under the Term Loan A Facility such that all debt issuance costs were recorded as a debt discount.
Loan Agreement
Debt Instrument [Line Items]
Line of credit facility, description	In May 2021, the parties further amended the Loan Agreement (as amended, the “2021 Loan Agreement”). The 2021 Loan Agreement increased the Term A Loan Facility to up to $20.0 million, which was fully drawn as of December 2021. The Term B Loan Facility of up to $5.0 million was available to be drawn upon on achievement of certain additional milestones, on or before September 30, 2022, which expired unused.	In April 2020, the Company entered into a Loan and Security Agreement, (the “Loan Agreement”) with the lenders referred to therein, and Silicon Valley Bank (“SVB”), as collateral agent. The Loan Agreement provided for (i) a secured term A loan facility (the “Term A Loan Facility”) of up to $10.0 million and (ii) a secured term B loan facility (the “Term B Loan Facility”) of up to $5.0 million that became available upon the satisfaction of certain milestones, each of which was available to be drawn through May 31, 2021. The term loan is secured by certain assets of the Borrowers (as defined in the Loan Agreement), including substantially all of the assets of the Company, excluding the Company’s intellectual property. The term loan contains customary representations, warranties, affirmative covenants and also certain restrictive covenants.
Warrants to purchase common stock \| shares	33,923
Warrant exercise price \| $ / shares	$ 19.12
Warrant expiration date	May 28, 2031	Jun. 30, 2025
Debt issuance costs, gross	$ 600	$ 600
Proceeds from sale of available-for-sale securities, equity			$ 75,000
Debt instrument, interest rate		4.25%	8.50%
Deferred tax assets	400
Term loan, non-current, net			$ 19,700
Outstanding principal amount			20,000
Unamortized debt discount			300
Other non-current liability			$ 500
Loan Agreement \| Measurement Input, Expected Dividend Payment
Debt Instrument [Line Items]
Fair value of warrant assumptions, dividends	$ 0
Loan Agreement \| Valuation Technique, Option Pricing Model \| Measurement Input, Risk Free Interest Rate
Debt Instrument [Line Items]
Fair measurement input	0.016
Loan Agreement \| Valuation Technique, Option Pricing Model \| Measurement Input, Price Volatility
Debt Instrument [Line Items]
Fair measurement input	0.986
Loan Agreement \| Valuation Technique, Option Pricing Model \| Measurement Input, Expected Term
Debt Instrument [Line Items]
Fair measurement input	10 years
Loan Agreement \| Prime Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			1.00%
Loan Agreement \| Maximum
Debt Instrument [Line Items]
Prepayment fee percentage			3.00%
Loan Agreement \| Minimum
Debt Instrument [Line Items]
Debt instrument, interest rate			4.25%
Prepayment fee percentage			1.00%
Loan Agreement \| Other Assets
Debt Instrument [Line Items]
Debt issuance costs, gross		$ 200
Loan Agreement \| Term A Loan Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 10,000
Line of credit facility fully drawn amount			$ 20,000
Warrants to purchase common stock \| shares		25,000
Warrant exercise price \| $ / shares		$ 22.06
Credit facility maturity date			Sep. 01, 2024
Loan Agreement \| Term B Loan Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 5,000
Warrants to purchase common stock \| shares	11,305
Line of credit facility maximum borrowing capacity	$ 5,000
2023 Loan Agreement
Debt Instrument [Line Items]
Line of credit facility, description			In January 2023, the Company executed a loan and security agreement with new lenders (the “2023 Loan Agreement”) and repaid its outstanding obligations under the 2021 Loan Agreement (see Note 11). As the Company had the intent and ability to refinance amounts due under the 2021 Loan Agreement pursuant to the terms of the 2023 Loan Agreement, as of December 31, 2022, the current portion of the outstanding principal obligation under the 2021 Loan Agreement was classified as long-term. As of December 31, 2022, the Company’s total obligations under the 2021 Loan Agreement were $19.7 million classified as term loan, non-current, net and $0.5 million classified as other non-current liability related to the final payment fee. The term loan, non-current, net is comprised of the outstanding principal amount of $20.0 million net of $0.3 million of unamortized debt discount.

Stockholders' Equity - Schedule of Shares of Common Stock Available for Future Issuance (Details)	Dec. 31, 2022 shares
Class Of Stock [Line Items]
Total available for future issuance	14,937,136
Equity Incentive Plan
Class Of Stock [Line Items]
Total available for future issuance	241,635
Employee Stock Purchase Plan
Class Of Stock [Line Items]
Total available for future issuance	729,218
Exercise of Warrants and Pre-funded Warrants
Class Of Stock [Line Items]
Total available for future issuance	13,966,283

Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended		2 Months Ended	12 Months Ended
	Feb. 15, 2023	Jul. 31, 2022	Mar. 31, 2021	Feb. 28, 2023	Dec. 31, 2022	Dec. 31, 2021
Subsidiary Sale Of Stock [Line Items]
Proceeds from issuance of common stock, net of commissions and offering expenses					$ 50	$ 144
Common stock, par value					$ 0.001	$ 0.001
Pre-funded Warrants
Subsidiary Sale Of Stock [Line Items]
Percentage of ownership limitation		9.99%
Percentage of ownership prior to issuance		4.99%
Warrants
Subsidiary Sale Of Stock [Line Items]
Percentage of ownership limitation		9.99%
Percentage of ownership prior to issuance		4.99%
Maximum \| Pre-funded Warrants
Subsidiary Sale Of Stock [Line Items]
Percentage of ownership limitation		19.99%
Maximum \| Warrants
Subsidiary Sale Of Stock [Line Items]
Percentage of ownership limitation		19.99%
A T M Facility
Subsidiary Sale Of Stock [Line Items]
Public offering description					In January and February 2023, the Company received aggregate proceeds of $13.4 million, net of commissions from sales of 968,000 shares of its common stock pursuant to the ATM Facility (see Note 7).
A T M Facility \| Subsequent Event
Subsidiary Sale Of Stock [Line Items]
Proceeds from issuance of common stock, net of commissions and offering expenses				$ 13,400
Shares issued and sold				968,000
Public Offerings
Subsidiary Sale Of Stock [Line Items]
Proceeds from issuance of common stock, net of commissions and offering expenses		$ 88,200
Public offering description		In July 2022, the Company completed an underwritten public offering of its common stock, warrants to purchase shares of its common stock and pre-funded warrants to purchase shares of its common stock. The Company sold 18,675,466 shares of its common stock with accompanying warrants to purchase up to 9,337,733 shares of its common stock at a combined public offering price of $3.55 per share. The Company also sold 7,944,252 pre-funded warrants to purchase shares of its common stock with accompanying warrants to purchase up to 3,972,126 shares of its common stock at a combined public offering price of $3.549 per pre-funded warrant, which represents the per share public offering price for the common stock less $0.001 per share, the exercise price for each pre-funded warrant. The Company raised net proceeds of $88.2 million, after deducting underwriting discounts and commissions of $5.7 million and other offering costs of $0.6 million.
Shares issued and sold		18,675,466
Offering price per share		$ 3.55
Underwriting discounts and commissions		$ 5,700
Other offering costs		$ 600
Common stock, par value		$ 0.001
Public Offerings \| Pre-funded Warrants
Subsidiary Sale Of Stock [Line Items]
Number of prefunded warrants issued during period		7,944,252
Combined price of prefunded and common stock warrant		$ 3.549
Public Offerings \| Maximum
Subsidiary Sale Of Stock [Line Items]
Warrants to purchase shares of common stock		9,337,733
Public Offerings \| Maximum \| Pre-funded Warrants
Subsidiary Sale Of Stock [Line Items]
Warrants to purchase shares of common stock		3,972,126
Public Offerings \| A T M Facility \| Maximum
Subsidiary Sale Of Stock [Line Items]
Maximum amount of equity shares issuable			$ 75,000
Public Offerings \| A T M Facility \| Maximum \| Subsequent Event
Subsidiary Sale Of Stock [Line Items]
Maximum amount of equity shares issuable	$ 150,000
Public Offerings \| SVB Leerink LLC
Subsidiary Sale Of Stock [Line Items]
Selling commission per shares sold percentage			3.00%
Proceeds from issuance of common stock, net of commissions and offering expenses					$ 28,500	$ 3,300
Shares issued and sold					3,948,611	186,546

Stockholders' Equity - Schedule of Outstanding Warrants to Purchase Shares of Common Stock (Details)	12 Months Ended
	Dec. 31, 2022 $ / shares shares
Class Of Warrant Or Right [Line Items]
Shares of Common Stock Underlying Warrants	13,966,283
Warrants Term Loan
Class Of Warrant Or Right [Line Items]
Shares of Common Stock Underlying Warrants	25,000
Warrant exercise price \| $ / shares	$ 22.06
Warrant expiration date	Jun. 30, 2025
Warrants Term Loan
Class Of Warrant Or Right [Line Items]
Shares of Common Stock Underlying Warrants	33,923
Warrant exercise price \| $ / shares	$ 19.12
Warrant expiration date	May 28, 2031
Warrants Public Offerings
Class Of Warrant Or Right [Line Items]
Shares of Common Stock Underlying Warrants	13,107,360
Warrant exercise price \| $ / shares	$ 5.325
Warrant expiration date	Jul. 01, 2024
Pre-funded Warrants
Class Of Warrant Or Right [Line Items]
Shares of Common Stock Underlying Warrants	800,000
Warrant exercise price \| $ / shares	$ 0.001
Expiration Date	Do not expire

Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended			8 Months Ended	12 Months Ended
	Feb. 28, 2021	Oct. 31, 2019	Sep. 30, 2019	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share base compensation expense					$ 10,356	$ 8,678
Service-based RSUs \| Employee
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share base compensation expense					$ 1,200	300
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized weighted average period					1 year 4 months 24 days
Total Unrecognised expense					$ 3,900
Performance RSUs
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of option vesting	33.30%
RSUs description	In February 2021, the Company granted performance-based RSUs that vest as to one-third on each one-year anniversary date, subject to achievement of a development milestone and continued service to the Company. In February 2022, a portion of the performance-based RSUs vested upon achievement of the development milestone and satisfaction of the continued service condition.			In February and September 2022, the Company granted performance-based RSUs that vest during the applicable performance period, subject to the achievement of certain corporate or department targets and continued service to the Company. In September 2022, a portion of the performance-based RSUs that were granted in February 2022 vested upon achievement of specific targets and satisfaction of the continued service condition.
Performance RSUs \| Employee
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share base compensation expense					$ 1,500	$ 800
Performance RSUs \| Executive Officer
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	1 year
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common shares issuable under the plan (in shares)		225,188
Percentage of increase in number of shares of capital stock issued and outstanding		1.00%
Percent of purchase shares of common stock		85.00%
2019 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common shares issuable under the plan (in shares)			2,844,193
Percentage of increase in number of shares of capital stock issued and outstanding			4.00%
Vesting period					4 years
Percentage of option vesting					25.00%
Terms of award					The board of directors determines the period over which options become exercisable and options generally vest over a four-year period, with 25% of options vesting on the first anniversary of employment, and thereafter, the remaining options vesting quarterly, over the following 36-month period. The options expire within ten years from the date of grant. The exercise price of awards granted will not be less than the estimated fair value of the shares on the date of grant. The 2019 Plan also permits the board of directors to grant restricted stock units, which are subject to continued service conditions.
Remaining option vesting period					36 months
Expiration period					10 years
Unrecognized stock option granted under plan					$ 12,200
Unrecognized weighted average period					2 years 2 months 12 days
Cancelled shares					243,506
Outstanding					3,161,917	2,406,668
2020 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average fair value options granted					$ 3.38	$ 16.18
Maximum \| Service-based RSUs \| Employee
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period					3 years
Maximum \| Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Period for increase in number of shares of common stock reserved for issuance		10 years
Maximum \| 2019 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Period for increase in number of shares of common stock reserved for issuance			10 years
Minimum \| Service-based RSUs \| Employee
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period					2 years

Stock-Based Compensation - Summary of Stock Option Activity (Details) - 2019 Plan - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Number of Options
Outstanding, Beginning Balance	2,406,668
Granted	1,149,816
Exercised	(151,061)
Cancelled and forfeited	(243,506)
Outstanding, Ending Balance	3,161,917	2,406,668
Exercisable as of December 31, 2022	1,460,685
Weighted Average Exercise Price
Weighted Average Exercise Price Outstanding, Beginning Balance	$ 16.46
Weighted Average Exercise Price, Granted	4.48
Weighted Average Exercise Price, Exercised	2.09
Weighted Average Exercise Price, Cancelled and forfeited	16.34
Weighted Average Exercise Price Outstanding, Ending Balance	12.80	$ 16.46
Weighted Average Exercise Price, Exercisable as of December 31, 2022	$ 14.60
Weighted Average Remaining Contractual Term (In years)
Weighted Average Remaining Contractual Term (In years), Outstanding	7 years 10 months 24 days	8 years 1 month 6 days
Weighted Average Remaining Contractual Term (In years), Exercisable as of December 31, 2022	7 years
Aggregate Intrinsic Value
Aggregate Intrinsic Value	$ 16,612	$ 9,970
Aggregate Intrinsic Value, Exercisable as of December 31, 2022	$ 7,320

Stock-Based Compensation - Summary of Estimated Fair Value of Stock Options Granted Using Black-Scholes Option-Pricing Model (Details)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, minimum	89.90%	86.90%
Expected volatility, maximum	91.00%	91.90%
Risk-free interest rate, minimum	1.60%	0.70%
Risk-free interest rate, maximum	3.90%	1.30%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	5 years 6 months	5 years 6 months
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 years 3 months 18 days	6 years 1 month 6 days

Stock-Based Compensation - Summary of Restricted Stock Unit Activity (Details) - Restricted Stock Units (RSUs) - $ / shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding, Beginning Balance	106,394
Granted	1,224,391
Vested / released	(103,703)
Cancelled / forfeited	(131,344)
Outstanding, Ending Balance	1,095,738
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value Outstanding, Beginning Balance	$ 5.77	$ 23.10
Weighted Average Grant Date Fair Value Outstanding, Granted	4.61
Weighted Average Grant Date Fair Value Outstanding, Vested/Released	8.61
Weighted Average Grant Date Fair Value Outstanding, Cancelled/Forfeited	5.53
Weighted Average Grant Date Fair Value Outstanding, Ending Balance	$ 5.77

Stock-Based Compensation - Summary of Stock-Based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 10,356	$ 8,678
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	4,094	2,966
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 6,262	$ 5,712

Income Taxes - Summary of Statutory Tax Rates Applicable to Income of Company and Subsidiaries (Details)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Line Items]
Effective income tax rate	21.00%	21.00%
89Bio Ltd
Income Tax Disclosure [Line Items]
Effective income tax rate	23.00%	23.00%
89bio Management, Inc.
Income Tax Disclosure [Line Items]
Effective income tax rate	21.00%	21.00%
UAB 89bio Lithuania
Income Tax Disclosure [Line Items]
Effective income tax rate	15.00%	15.00%

Income Taxes - Summary of Income Tax (Expense) Benefit (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Current:
State	$ 3	$ (2)
Foreign	16	(1)
Total	19	(3)
Deferred:
Federal		150
Total		150
Income tax (expense) benefit	$ (19)	$ 147

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Income Taxes - Summary of Components of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Line Items]
Research and development expenses	$ 18,927	$ 6,529
Stock-based compensation	4,328	1,969
Accrued expenses	317	220
Operating Lease Liability	98
Other	244	191
Gross deferred tax assets	76,301	42,265
Less: valuation allowance	(75,982)	(42,046)
Total deferred tax assets	319	219
Operating lease right-of-use asset	(100)
Total deferred tax liabilities	(100)
Net deferred tax assets	219	219
United States
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	45,002	29,094
Israel
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 7,385	$ 4,262

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Line Items]
Deferred tax assets, valuation allowance	$ 75,982,000	$ 42,046,000
Deferred tax assets, change in valuation allowance	$ 34,000,000.0
Operating loss carryforwards limitations on use	Federal net operating losses generated after 2017 can be carried forward indefinitely but utilization will be limited to 80% of taxable income in the period that net operating losses are being utilized.
Taxable income utilization percentage	80.00%
Federal research and development credit carryforwards	$ 4,300,000	2,100,000
State research and development credit carryforwards	1,800,000	1,100,000
Increase in unrecognized tax benefits	700,000	500,000
Unrecognized tax benefits impact effective tax rate	$ 0
Research and Development Expenses
Income Tax Disclosure [Line Items]
Amortization period	5 years
Federal
Income Tax Disclosure [Line Items]
Accumulated tax loss carryforward	$ 160,900,000
Federal \| Research and Development Credit Carryforwards
Income Tax Disclosure [Line Items]
Carryforward tax losses expiration year	2040
Federal \| Research and Development Expenses
Income Tax Disclosure [Line Items]
Amortization period	5 years
State
Income Tax Disclosure [Line Items]
Accumulated tax loss carryforward	$ 169,800,000
Foreign \| Research and Development Expenses
Income Tax Disclosure [Line Items]
Amortization period	15 years
Israel
Income Tax Disclosure [Line Items]
Accumulated tax loss carryforward	$ 32,100,000	18,500,000
United States
Income Tax Disclosure [Line Items]
Accumulated tax loss carryforward		$ 138,500,000
California \| State
Income Tax Disclosure [Line Items]
Carryforward tax losses expiration year	2041

Income Taxes - Summary of Loss from Operations Before Taxes on Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Line Items]
Net loss before income tax	$ (102,007)	$ (90,269)
United States
Income Tax Disclosure [Line Items]
Net loss before income tax	(101,938)	(91,141)
LITHUANIA
Income Tax Disclosure [Line Items]
Net loss before income tax	(7)	10
Israel
Income Tax Disclosure [Line Items]
Net loss before income tax	$ (62)	$ 862

- Definition

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 280
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Income Taxes - Summary of Reconciliation of Income Tax (Expense) Benefit Statutory Tax Rate to Effective Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income tax benefit computed at statutory rates	$ 21,429	$ 18,757
Change in valuation allowance	(33,936)	(20,111)
Foreign rate differential	1	(19)
State income taxes, net of federal benefit	5,824
State deferred tax true-up due to change in apportionment	6,517
Change in Israel effective tax rate due to the 2019 reorganization		(2)
Research and development credits, net of uncertain tax position	2,130	1,331
Other	(1,984)	191
Income tax (expense) benefit	$ (19)	$ 147

Income Taxes - Summary of a Reconciliation of The Beginning And Ending Amount of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Balance, beginning of year	$ 851	$ 329
Decrease related to prior year positions	(19)	(35)
Increase related to current year positions	752	557
Balance, end of year	$ 1,584	$ 851

Net Loss Per Share - Schedule of Outstanding Potentially Dilutive Securities Excluded From Calculation of Diluted Net Loss (Details) - shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	17,423,938	2,571,985
Stock Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	3,161,917	2,406,668
Unvested Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	1,095,738	106,394
Warrants to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	13,166,283	58,923

Subsequent Events - Additional Information (Details) - USD ($) $ in Thousands		1 Months Ended			2 Months Ended	12 Months Ended
	Feb. 15, 2023	Jan. 31, 2023	Jul. 31, 2022	Mar. 31, 2021	Feb. 28, 2023	Dec. 31, 2022	Dec. 31, 2021
Subsequent Event [Line Items]
Proceeds from issuance of common stock, net of commissions and offering expenses						$ 50	$ 144
Public Offerings
Subsequent Event [Line Items]
ATM Facility description			In July 2022, the Company completed an underwritten public offering of its common stock, warrants to purchase shares of its common stock and pre-funded warrants to purchase shares of its common stock. The Company sold 18,675,466 shares of its common stock with accompanying warrants to purchase up to 9,337,733 shares of its common stock at a combined public offering price of $3.55 per share. The Company also sold 7,944,252 pre-funded warrants to purchase shares of its common stock with accompanying warrants to purchase up to 3,972,126 shares of its common stock at a combined public offering price of $3.549 per pre-funded warrant, which represents the per share public offering price for the common stock less $0.001 per share, the exercise price for each pre-funded warrant. The Company raised net proceeds of $88.2 million, after deducting underwriting discounts and commissions of $5.7 million and other offering costs of $0.6 million.
Proceeds from issuance of common stock, net of commissions and offering expenses			$ 88,200
Shares issued and sold			18,675,466
A T M Facility
Subsequent Event [Line Items]
ATM Facility description						In January and February 2023, the Company received aggregate proceeds of $13.4 million, net of commissions from sales of 968,000 shares of its common stock pursuant to the ATM Facility (see Note 7).
A T M Facility \| Public Offerings \| Maximum
Subsequent Event [Line Items]
Maximum amount of equity shares issuable				$ 75,000
SVB Leerink LLC \| Public Offerings
Subsequent Event [Line Items]
Proceeds from issuance of common stock, net of commissions and offering expenses						$ 28,500	$ 3,300
Shares issued and sold						3,948,611	186,546
Subsequent Event \| 2023 Loan Agreement
Subsequent Event [Line Items]
Line of credit facility, maximum borrowing capacity		$ 100,000
Debt instrument, maturity date, description		The term loans under the 2023 Loan Agreement mature on January 1, 2027. The maturity date may be extended to July 1, 2027, provided that the second and third tranches are funded and the Company achieves certain other financing milestones.
Debt instrument, maturity date		Jan. 01, 2027
Debt instrument, interest rate		8.45%
Debt instrument, basis spread on variable rate		2.25%
Subsequent Event \| 2021 Loan Agreement
Subsequent Event [Line Items]
Total principal amount outstanding		$ 20,000
Debt instrument, final payment fee		1,000
Debt instrument, early prepayment fee		400
Subsequent Event \| A T M Facility
Subsequent Event [Line Items]
Proceeds from issuance of common stock, net of commissions and offering expenses					$ 13,400
Shares issued and sold					968,000
Subsequent Event \| A T M Facility \| Public Offerings
Subsequent Event [Line Items]
Sales Agreement transaction date	Feb. 15, 2023
Subsequent Event \| A T M Facility \| Public Offerings \| Maximum
Subsequent Event [Line Items]
Maximum amount of equity shares issuable	$ 150,000
Tranche one \| Subsequent Event \| 2023 Loan Agreement
Subsequent Event [Line Items]
Line of credit facility, maximum borrowing capacity		25,000
Tranche one \| Subsequent Event \| 2021 Loan Agreement
Subsequent Event [Line Items]
Loan Agreement funded outstanding amount		25,000
Tranche two and three \| Subsequent Event \| 2023 Loan Agreement
Subsequent Event [Line Items]
Line of credit facility, maximum borrowing capacity		$ 25,000
Debt instrument, maturity date		Jul. 01, 2027
Tranche Four \| Subsequent Event \| 2023 Loan Agreement
Subsequent Event [Line Items]
Line of credit facility, maximum borrowing capacity		$ 50,000