0001564590-21-027662 | 10-Q | XBRL Viewer

Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2021	May 07, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Entity Registrant Name	89bio, Inc.
Entity Central Index Key	0001785173
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		20,060,268
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	500-4614
Document Quarterly Report	true
Document Transition Report	false

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 68,007	$ 98,183
Restricted cash	25	25
Short-term available-for-sale securities	121,618	106,446
Prepaid and other current assets	8,286	5,548
Total current assets	197,936	210,202
Property and equipment, net	161	166
Other assets	557	706
Total assets	198,654	211,074
Current liabilities:
Accounts payable	4,521	2,065
Accrued expenses	3,938	6,048
Total current liabilities	8,459	8,113
Commitments and contingencies (Note 5)
Stockholders’ equity:
Common stock	20	20
Additional paid-in capital	328,055	326,046
Accumulated other comprehensive loss	(3)	(10)
Accumulated deficit	(137,877)	(123,095)
Total stockholders’ equity	190,195	202,961
Total liabilities and stockholders’ equity	$ 198,654	$ 211,074

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating expenses:
Research and development	$ 10,131	$ 7,778
General and administrative	4,608	2,924
Total operating expenses	14,739	10,702
Loss from operations	(14,739)	(10,702)
Other (expenses) income, net	(43)	157
Net loss before tax	(14,782)	(10,545)
Income tax benefit		1
Net loss	(14,782)	(10,544)
Other comprehensive income (loss):
Unrealized loss on available-for-sale securities	(4)
Foreign currency translation adjustments	11
Total other comprehensive income	7
Comprehensive loss	$ (14,775)	$ (10,544)
Net loss per share, basic and diluted	$ 0.74	$ 0.76
Weighted-average shares used to compute net loss per share, basic and diluted	20,010,412	13,789,786

Condensed Consolidated Statements of Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance at Dec. 31, 2019	$ 89,944	$ 14	$ 163,526	$ 0	$ (73,596)
Beginning balance, shares at Dec. 31, 2019		13,788,982
Issuance of common stock upon exercise of stock options	9		9	0
Issuance of common stock upon exercise of stock options, shares		4,876
Stock-based compensation	493		493	0
Net loss	(10,544)			0	(10,544)
Ending balance at Mar. 31, 2020	79,902	$ 14	164,028	0	(84,140)
Ending balance, shares at Mar. 31, 2020		13,793,858
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 upon exercise of stock options	$ 216		216	0
Issuance of common stock upon exercise of stock options, shares	103,170	103,170
Stock-based compensation	$ 1,793		1,793	0
Net loss	(14,782)			0	(14,782)
Other comprehensive income	7			7
Ending balance at Mar. 31, 2021	$ 190,195	$ 20	$ 328,055	$ (3)	$ (137,877)
Ending balance, shares at Mar. 31, 2021		20,034,830

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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+ Details

- Definition

Amount after tax and reclassification adjustments of other comprehensive income (loss).

+ References

+ Details

- Definition

Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

+ References + Details

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net loss	$ (14,782)	$ (10,544)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	15	12
Stock-based compensation	1,793	493
Amortization of premium on available-for-sale securities	229
Amortization of debt issuance costs	77
Changes in operating assets and liabilities:
Prepaid and other current assets	(2,726)	109
Other assets	72
Accounts payable	2,450	3,066
Accrued expenses	(2,110)	(888)
Net cash used in operating activities	(14,982)	(7,752)
Cash flows from investing activities:
Purchases of available-for-sale securities	(45,302)
Proceeds from maturities of available-for-sale securities	29,896
Purchases of property and equipment	(4)	(61)
Net cash used in investing activities	(15,410)	(61)
Cash flows from financing activities:
Proceeds from issuance of common stock upon stock option exercises	216	9
Net cash provided by financing activities	216	9
Net decrease in cash and cash equivalents, and restricted cash	(30,176)	(7,804)
Cash and cash equivalents, and restricted cash at beginning of period	98,208	93,360
Cash and cash equivalents, and restricted cash at end of period	68,032	85,556
Components of cash and cash equivalents, and restricted cash:
Cash and cash equivalents	68,007	85,532
Restricted cash	25	24
Cash and cash equivalents, and restricted cash at end of period	68,032	85,556
Supplemental cash flow disclosures:
Property and equipment purchases included in accounts payable and accrued expenses	6	$ 54
Cash paid for taxes	$ 154

Organization and Basis of Presentation

3 Months Ended

Mar. 31, 2021

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, 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, for the purpose of completing an initial public offering and related transactions in order to carry on the business of 89Bio Ltd., which was incorporated in Israel in January 2018.

Public Offerings

In July 2020, the Company completed an underwritten public offering of 3,047,040 shares of its common stock, at the public offering price of $27.50 per share. The Company raised a total of $78.2 million in net proceeds after deducting underwriting discounts and commissions of $5.0 million and offering costs of approximately $0.6 million.

In September 2020, the Company completed an underwritten public offering of 3,025,000 shares of its common stock, at a public offering price of $28.00 per share. The Company raised a total of $79.5 million in net proceeds after deducting underwriting discounts and commissions of $4.6 million and offering costs of approximately $0.6 million.

Liquidity

The accompanying condensed 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, cash equivalents and short-term available-for-sale securities of $189.6 million as of March 31, 2021.

The Company expects that its cash, cash equivalents and short-term available-for-sale securities as of March 31, 2021, together with proceeds available from the Company’s term loan (see Note 6), will be sufficient to fund operating expenses and capital expenditure requirements for a period of at least one year from the date these unaudited condensed consolidated financial statements are filed with the Securities and Exchange Commission (“SEC”).

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2021

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Unaudited Condensed Consolidated Financial Statements

The accompanying interim unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“U.S. GAAP”) and applicable rules and regulations of the SEC regarding interim financial reporting.

The accompanying interim condensed consolidated financial statements are unaudited. The interim unaudited condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements as of and for the year ended December 31, 2020 and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company’s consolidated financial position, results of operations and comprehensive loss, and cash flows. The results of operations for the three months ended March 31, 2021 are not necessarily indicative of the results to be expected for the year ending December 31, 2021 or for any other future annual or interim period. The condensed consolidated balance sheet as of December 31, 2020 was derived from the audited financial statements as of that date. These condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements included in the Annual Report on Form 10-K for the year ended December 31, 2020, which was filed with the SEC on March 25, 2021.

Principles of Consolidation

The accompanying condensed 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 condensed 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 condensed consolidated financial statements and the reported amounts of expenses during the reporting period. Significant estimates and assumptions made in the accompanying condensed consolidated financial statements include but are not limited to the fair value of stock options and certain accrued expenses. 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.

Fair Value Measurements

Financial assets and liabilities are recorded at fair value on a recurring basis in the condensed 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. 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;

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.

Risks and Uncertainties

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 Company does not yet know the full extent of potential delays to clinical trials, which could prevent or delay the Company from obtaining approval for BIO89-100. The extent to which the COVID-19 pandemic may impact the Company’s future operating results and financial condition is uncertain.

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 earnings 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 other (expenses) income, net. The cost of investments sold is based on the specific-identification method. There are no material realized gains or losses on investments for the periods presented. Interest on available-for-sale securities is included in other (expenses) income, net.

Comprehensive Loss

The Company’s comprehensive loss is comprised of changes in unrealized gains or losses on available-for-sale securities and foreign currency translation adjustments.

Recent Accounting Pronouncements

In February 2016, the Financial Standards Accounting Board (the “FASB”) issued Accounting Standards Update (“ASU”) 2016-02—Leases (“ASU 2016-02”), requiring the recognition of lease assets and liabilities on the balance sheet. The standard: (a) clarifies the definition of a lease; (b) requires a dual approach to lease classification similar to current lease classifications; and (c) causes lessees to recognize leases on the balance sheet as a lease liability with a corresponding right-of-use asset for leases with a lease-term of more than twelve months. The standard is effective for public entities for fiscal years beginning after December 15, 2018 and for nonpublic entities for fiscal years beginning after December 15, 2021. As an emerging growth company, ASU 2016-02 is effective for the Company for the year ending December 31, 2022 and interim periods within the year ending December 31, 2023. The Company is currently evaluating the impact of this standard on its consolidated financial statements and related disclosures.

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. The standard is effective for public entities for fiscal years beginning after December 15, 2019 and for nonpublic entities for fiscal years beginning after December 15, 2022. 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 currently evaluating the impact of this standard on its consolidated financial statements and related disclosures.

Fair Value Measurements

3 Months Ended

Mar. 31, 2021

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 March 31, 2021 (in thousands):

		March 31, 2021
	Valuation	Amortized		Unrealized		Unrealized
	Hierarchy	Cost		Gains		Losses			Fair Value
Money market funds	Level 1	$	53,011	$	—	$	—		$	53,011
Commercial paper	Level 2		74,420		—		(6	)		74,414
Agency bonds	Level 2		21,367		14		—			21,381
Corporate debt securities	Level 2		18,794		1		(9	)		18,786
Municipal bonds	Level 2		6,241		2		—			6,243
U.S. government bonds	Level 2		5,554		2		—			5,556
Non-U.S. debt securities	Level 2		2,537		—		—			2,537
Total cash equivalents and available-for-sale securities		$	181,924	$	19	$	(15	)	$	181,928
Classified as:
Cash equivalents									$	60,310
Short-term available-for-sale securities										121,618
Total cash equivalents and available-for-sale securities									$	181,928

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

	March 31, 2021
Within one year	$	173,388
After one year through two years		8,540
Total cash equivalents and available-for-sale securities	$	181,928

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, 2020 (in thousands):

		December 31, 2020
	Valuation	Amortized		Unrealized		Unrealized
	Hierarchy	Cost		Gains		Losses			Fair Value
Money market funds	Level 1	$	46,134	$	—	$	—		$	46,134
Commercial paper	Level 2		76,605		—		(2	)		76,603
Agency bonds	Level 2		29,654		15		—			29,669
Corporate debt securities	Level 2		11,890		—		(6	)		11,884
U.S. government bonds	Level 2		7,093		—		—			7,093
Municipal bonds	Level 2		5,592		2		(1	)		5,593
U.S. treasury bills	Level 2		4,680		—		—			4,680
Agency discount securities	Level 2		200		—		—			200
Total cash equivalents and available-for-sale securities		$	181,848	$	17	$	(9	)	$	181,856
Classified as:
Cash equivalents									$	75,410
Short-term available-for-sale securities										106,446
Total cash equivalents and available-for-sale securities									$	181,856

The following table summarizes the Company’s available-for-sale securities by contractual maturity as of December 31, 2020 (in thousands):

	December 31, 2020
Within one year	$	160,304
After one year through two years		21,552
Total cash equivalents and available-for-sale securities	$	181,856

- 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

Accrued Expenses

3 Months Ended

Mar. 31, 2021

Payables And Accruals [Abstract]

Accrued Expenses

4. Accrued Expenses

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

	March 31,		December 31,
	2021		2020
Accrued research and development expense	$	2,121	$	2,884
Accrued employee and related expenses		1,067		2,552
Accrued professional and legal fees		543		453
Accrued other expenses		207		159
Total accrued expenses	$	3,938	$	6,048

Commitments and Contingencies

3 Months Ended

Mar. 31, 2021

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

5. Commitments and Contingencies

Leases

Future minimum lease payments under the Company’s non-cancellable operating lease obligations as of March 31, 2021, are as follows (in thousands):

	March 31, 2021
Remainder of 2021	$	166
2022		8
Total future minimum annual payments	$	174

Rent expense was $73,000 and $60,000 for the three months ended March 31, 2021 and 2020, respectively.

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 program, including the compound TEV-47948 (BIO89-100), 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, after the first anniversary of the effective date, upon 120 days’ written notice to Teva, (ii) by either party, if the other party materially breaches any of its obligations under the 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 three months ended March 31, 2021 and 2020, there were no license payment expenses related to the Teva Agreements.

Term Loan

3 Months Ended

Mar. 31, 2021

Debt Disclosure [Abstract]

Term Loan

6. Term Loan

Loan and Security Agreement

In April 2020, the Company and certain of its subsidiaries entered into a Loan and Security Agreement, (as amended, the “Loan Agreement”) with the lenders referred to therein (the “Lenders”), and Silicon Valley Bank, as collateral agent. The Loan Agreement provides 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 is available to be drawn through May 31, 2021 (see Note 9). The Term A Loan Facility matures on November 1, 2022, provided, that if the Term B Loan Facility is funded, the facilities instead mature on September 1, 2023. The loans will bear interest at the greater of (i) 4.50% and (ii) the sum of (a) the Prime Rate as reported in The Wall Street Journal plus (b) 1.25%. As of March 31, 2021, the Company had not drawn any amount under the Loan Agreement.

In April 2020, in connection with the execution of the Loan Agreement, the Company issued Silicon Valley Bank 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. The initial expiration date of April 7, 2030 was changed to June 30, 2025 in connection with the July 2020 offering. 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 0.75%, no dividends, expected volatility of 92.30% and expected term of 10.0 years. Upon issuance, the fair value allocated to the warrant of $0.6 million was recorded as a debt issuance cost and classified within other assets and met the requirements for equity classification within additional paid-in capital on the condensed consolidated balance sheets. An additional warrant to purchase 8,333 shares of the Company’s common stock will be issued in connection with the Term B Loan Facility, if funded, with the exercise price determined on the Company’s stock price at the time of issuance.

Additionally, the Company incurred $0.2 million in closing costs that were recorded as debt issuance costs and classified within other assets on the condensed consolidated balance sheets.

The deferred assets related to the debt issuance cost and warrant are recognized as interest expense over the duration of the Loan Agreement and are recorded within other (expenses) income, net on the condensed consolidated statements of operations and comprehensive loss. As of March 31, 2021, the remaining unamortized debt issuance costs classified within other assets on the condensed consolidated balance sheet is $0.5 million.

Stockholders' Equity

3 Months Ended

Mar. 31, 2021

Equity [Abstract]

Stockholders' Equity

7. Stockholders’ Equity

Equity Incentive Plan

The Company’s board of directors approved the 2019 Equity Incentive Plan (the “2019 Plan”), which 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, commencing on January 1, 2020, 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. As of March 31, 2021, there were 1,633,644 shares of common stock available for issuance as future option grants under the 2019 Plan.

Employee Stock Purchase Plan

In October 2019, the Company 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 will be accomplished through the participation of discrete offering periods and each offering is expected to be 6 months long. 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. The first six month offering period under the ESPP commenced on January 1, 2020.

As of March 31, 2021, there were 555,122 shares of common stock available for issuance under the ESPP.

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

	Three Months Ended
	March 31,
	2021		2020
Research and development	$	639	$	192
General and administrative		1,154		301
Total stock-based compensation	$	1,793	$	493

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

	Three Months Ended
	March 31,
	2021			2020
Stock Options
Expected term (years)		6.1		6.0-6.1
Contractual term (years)		10.0			10.0
Expected volatility	97.5-97.6		%	86.4-87.5		%
Risk-free interest rate	0.7-0.8		%	0.5-1.5		%
Expected dividend		—			—

The following table summarizes stock option activity for the three months ended March 31, 2021:

						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, 2020		1,898,395		$	12.79		8.60	$	25,918
Granted		538,613			23.04
Exercised		(103,170	)		2.09
Cancelled		(52,728	)		16.42
Balance outstanding as of March 31, 2021		2,281,110			15.61		8.65	$	22,657
Exercisable as of March 31, 2021		627,372		$	8.06		7.87	$	10,725

Restricted Stock Units (“RSUs”)

In February 2021, the Company granted 56,545 service based RSUs to its employees with a total grant date fair value of $1.3 million. The RSUs vest annually over a three-year period. The Company recognized $0.1 million of compensation expense related to the service based RSUs in the three months ended March 31, 2021.

In February 2021, the Company granted 61,500 performance based RSUs to certain executives, one-third of which vest on each one-year anniversary date subject to achievement of a development milestone and continued service to the Company. The performance based RSUs have a total grant date fair value of $1.4 million. The Company recognized $0.1 million of compensation expense, using the accelerated attribution method, related to the performance based RSUs in the three months ended March 31, 2021.

Net Loss Per Share

3 Months Ended

Mar. 31, 2021

Earnings Per Share [Abstract]

Net Loss Per Share

8. Net Loss Per Share

Basic net loss per share is computed by dividing net loss by the weighted-average number of shares of common stock outstanding for the period. Since the Company was in a loss position for all periods presented, diluted net loss per share is the same as basic net loss per share for all periods as the inclusion of all potential shares of common stock outstanding would have been anti-dilutive.

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

	Three Months Ended
	March 31,
	2021		2020
Stock options to purchase common stock		2,281,110		1,714,685
Shares available for future option grants		1,633,644		1,676,191
Unvested restricted stock units		111,728		—
Employee stock purchase plan		2,357		1,735
Total		4,028,839		3,392,611

Subsequent Event

3 Months Ended

Mar. 31, 2021

Subsequent Events [Abstract]

Subsequent Event

9. Subsequent Event

In April 2021, the Company entered into an amendment to the Loan and Security Agreement with Silicon Valley Bank to extend the draw period for both the Term Loan A Facility and Term Loan B Facility to May 31, 2021.

Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Mar. 31, 2021
Accounting Policies [Abstract]
Unaudited Condensed Consolidated Financial Statements	Unaudited Condensed Consolidated Financial Statements The accompanying interim unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“U.S. GAAP”) and applicable rules and regulations of the SEC regarding interim financial reporting. The accompanying interim condensed consolidated financial statements are unaudited. The interim unaudited condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements as of and for the year ended December 31, 2020 and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company’s consolidated financial position, results of operations and comprehensive loss, and cash flows. The results of operations for the three months ended March 31, 2021 are not necessarily indicative of the results to be expected for the year ending December 31, 2021 or for any other future annual or interim period. The condensed consolidated balance sheet as of December 31, 2020 was derived from the audited financial statements as of that date. These condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements included in the Annual Report on Form 10-K for the year ended December 31, 2020, which was filed with the SEC on March 25, 2021.
Principles of Consolidation	Principles of Consolidation The accompanying condensed 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 condensed 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 condensed consolidated financial statements and the reported amounts of expenses during the reporting period. Significant estimates and assumptions made in the accompanying condensed consolidated financial statements include but are not limited to the fair value of stock options and certain accrued expenses. 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.
Fair Value Measurements	Fair Value Measurements Financial assets and liabilities are recorded at fair value on a recurring basis in the condensed 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. 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; 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.
Risk and Uncertainties	Risks and Uncertainties 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 Company does not yet know the full extent of potential delays to clinical trials, which could prevent or delay the Company from obtaining approval for BIO89-100. The extent to which the COVID-19 pandemic may impact the Company’s future operating results and financial condition is uncertain.
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 earnings 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 other (expenses) income, net. The cost of investments sold is based on the specific-identification method. There are no material realized gains or losses on investments for the periods presented. Interest on available-for-sale securities is included in other (expenses) income, net.
Comprehensive Loss	Comprehensive Loss The Company’s comprehensive loss is comprised of changes in unrealized gains or losses on available-for-sale securities and foreign currency translation adjustments.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In February 2016, the Financial Standards Accounting Board (the “FASB”) issued Accounting Standards Update (“ASU”) 2016-02—Leases (“ASU 2016-02”), requiring the recognition of lease assets and liabilities on the balance sheet. The standard: (a) clarifies the definition of a lease; (b) requires a dual approach to lease classification similar to current lease classifications; and (c) causes lessees to recognize leases on the balance sheet as a lease liability with a corresponding right-of-use asset for leases with a lease-term of more than twelve months. The standard is effective for public entities for fiscal years beginning after December 15, 2018 and for nonpublic entities for fiscal years beginning after December 15, 2021. As an emerging growth company, ASU 2016-02 is effective for the Company for the year ending December 31, 2022 and interim periods within the year ending December 31, 2023. The Company is currently evaluating the impact of this standard on its consolidated financial statements and related disclosures. 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. The standard is effective for public entities for fiscal years beginning after December 15, 2019 and for nonpublic entities for fiscal years beginning after December 15, 2022. 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 currently evaluating the impact of this standard on its consolidated financial statements and related disclosures.

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2021

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 March 31, 2021 (in thousands):

		March 31, 2021
	Valuation	Amortized		Unrealized		Unrealized
	Hierarchy	Cost		Gains		Losses			Fair Value
Money market funds	Level 1	$	53,011	$	—	$	—		$	53,011
Commercial paper	Level 2		74,420		—		(6	)		74,414
Agency bonds	Level 2		21,367		14		—			21,381
Corporate debt securities	Level 2		18,794		1		(9	)		18,786
Municipal bonds	Level 2		6,241		2		—			6,243
U.S. government bonds	Level 2		5,554		2		—			5,556
Non-U.S. debt securities	Level 2		2,537		—		—			2,537
Total cash equivalents and available-for-sale securities		$	181,924	$	19	$	(15	)	$	181,928
Classified as:
Cash equivalents									$	60,310
Short-term available-for-sale securities										121,618
Total cash equivalents and available-for-sale securities									$	181,928

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, 2020 (in thousands):

		December 31, 2020
	Valuation	Amortized		Unrealized		Unrealized
	Hierarchy	Cost		Gains		Losses			Fair Value
Money market funds	Level 1	$	46,134	$	—	$	—		$	46,134
Commercial paper	Level 2		76,605		—		(2	)		76,603
Agency bonds	Level 2		29,654		15		—			29,669
Corporate debt securities	Level 2		11,890		—		(6	)		11,884
U.S. government bonds	Level 2		7,093		—		—			7,093
Municipal bonds	Level 2		5,592		2		(1	)		5,593
U.S. treasury bills	Level 2		4,680		—		—			4,680
Agency discount securities	Level 2		200		—		—			200
Total cash equivalents and available-for-sale securities		$	181,848	$	17	$	(9	)	$	181,856
Classified as:
Cash equivalents									$	75,410
Short-term available-for-sale securities										106,446
Total cash equivalents and available-for-sale securities									$	181,856

Schedule of Contractual Maturities of Available-for-Sale Securities

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

	March 31, 2021
Within one year	$	173,388
After one year through two years		8,540
Total cash equivalents and available-for-sale securities	$	181,928

The following table summarizes the Company’s available-for-sale securities by contractual maturity as of December 31, 2020 (in thousands):

	December 31, 2020
Within one year	$	160,304
After one year through two years		21,552
Total cash equivalents and available-for-sale securities	$	181,856

Accrued Expenses (Tables)

3 Months Ended

Mar. 31, 2021

Payables And Accruals [Abstract]

Schedule of Accrued Expenses

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

	March 31,		December 31,
	2021		2020
Accrued research and development expense	$	2,121	$	2,884
Accrued employee and related expenses		1,067		2,552
Accrued professional and legal fees		543		453
Accrued other expenses		207		159
Total accrued expenses	$	3,938	$	6,048

Commitments and Contingencies (Tables)

3 Months Ended

Mar. 31, 2021

Commitments And Contingencies Disclosure [Abstract]

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

Future minimum lease payments under the Company’s non-cancellable operating lease obligations as of March 31, 2021, are as follows (in thousands):

	March 31, 2021
Remainder of 2021	$	166
2022		8
Total future minimum annual payments	$	174

Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2021

Equity [Abstract]

Summary of Stock-Based Compensation

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

	Three Months Ended
	March 31,
	2021		2020
Research and development	$	639	$	192
General and administrative		1,154		301
Total stock-based compensation	$	1,793	$	493

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

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

	Three Months Ended
	March 31,
	2021			2020
Stock Options
Expected term (years)		6.1		6.0-6.1
Contractual term (years)		10.0			10.0
Expected volatility	97.5-97.6		%	86.4-87.5		%
Risk-free interest rate	0.7-0.8		%	0.5-1.5		%
Expected dividend		—			—

Summary of Stock Option Activity

The following table summarizes stock option activity for the three months ended March 31, 2021:

						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, 2020		1,898,395		$	12.79		8.60	$	25,918
Granted		538,613			23.04
Exercised		(103,170	)		2.09
Cancelled		(52,728	)		16.42
Balance outstanding as of March 31, 2021		2,281,110			15.61		8.65	$	22,657
Exercisable as of March 31, 2021		627,372		$	8.06		7.87	$	10,725

Net Loss Per Share (Tables)

3 Months Ended

Mar. 31, 2021

Earnings Per Share [Abstract]

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

	Three Months Ended
	March 31,
	2021		2020
Stock options to purchase common stock		2,281,110		1,714,685
Shares available for future option grants		1,633,644		1,676,191
Unvested restricted stock units		111,728		—
Employee stock purchase plan		2,357		1,735
Total		4,028,839		3,392,611

Organization and Basis of Presentation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		3 Months Ended
	Sep. 30, 2020	Jul. 31, 2020	Mar. 31, 2021
Subsidiary Sale Of Stock [Line Items]
Date of incorporation			Jun. 30, 2019
Cash equivalents and short term available-for-sale securities			$ 189.6
Underwritten public offering \| Common Stock
Subsidiary Sale Of Stock [Line Items]
Shares issued and sold	3,025,000	3,047,040
Proceeds from issuance of common stock, net of underwriters discount and commissions	$ 79.5	$ 78.2
IPO price per share	$ 28.00	$ 27.50
Payment of underwriting discounts, commissions	$ 4.6	$ 5.0
Other offering expenses	$ 0.6	$ 0.6

Summary of Significant Accounting Policies - Additional Information (Details)	3 Months Ended
	Mar. 31, 2021 USD ($)
Accounting Policies [Abstract]
Realized gains or losses on investments	$ 0

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Aggregated Fair Value	$ 181,928	$ 181,856
Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	181,924	181,848
Short-term investments, Gross Unrealized Holding Gains	19	17
Short-term investments, Gross Unrealized Holding Losses	(15)	(9)
Short-term investments, Aggregated Fair Value	181,928	181,856
Recurring \| Cash equivalents
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Aggregated Fair Value	60,310	75,410
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	121,618	106,446
Recurring \| Level 1 \| Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	53,011	46,134
Short-term investments, Aggregated Fair Value	53,011	46,134
Recurring \| Level 2 \| Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	74,420	76,605
Short-term investments, Gross Unrealized Holding Losses	(6)	(2)
Short-term investments, Aggregated Fair Value	74,414	76,603
Recurring \| Level 2 \| Agency bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	21,367	29,654
Short-term investments, Gross Unrealized Holding Gains	14	15
Short-term investments, Aggregated Fair Value	21,381	29,669
Recurring \| Level 2 \| Corporate Debt
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	18,794	11,890
Short-term investments, Gross Unrealized Holding Gains	1
Short-term investments, Gross Unrealized Holding Losses	(9)	(6)
Short-term investments, Aggregated Fair Value	18,786	11,884
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	5,554	7,093
Short-term investments, Gross Unrealized Holding Gains	2
Short-term investments, Aggregated Fair Value	5,556	7,093
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	2,537
Short-term investments, Aggregated Fair Value	2,537
Recurring \| Level 2 \| Municipal Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	6,241	5,592
Short-term investments, Gross Unrealized Holding Gains	2	2
Short-term investments, Gross Unrealized Holding Losses		(1)
Short-term investments, Aggregated Fair Value	$ 6,243	5,593
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		4,680
Short-term investments, Aggregated Fair Value		4,680
Recurring \| Level 2 \| Agency discount securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost		200
Short-term investments, Aggregated Fair Value		$ 200

Fair Value Measurements - Schedule of Contractual Maturities of Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Within one year	$ 173,388	$ 160,304
After one year through two years	8,540	21,552
Total cash equivalents and available-for-sale securities	$ 181,928	$ 181,856

Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Payables And Accruals [Abstract]
Accrued research and development expense	$ 2,121	$ 2,884
Accrued employee and related expenses	1,067	2,552
Accrued professional and legal fees	543	453
Accrued other expenses	207	159
Total accrued expenses	$ 3,938	$ 6,048

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under Non-cancellable Operating Lease Obligations (Details) $ in Thousands	Mar. 31, 2021 USD ($)
Commitments And Contingencies Disclosure [Abstract]
Remainder of 2021	$ 166
2022	8
Total future minimum annual payments	$ 174

Commitments and Contingencies - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended
	Apr. 30, 2018	Mar. 31, 2021	Mar. 31, 2020
Loss Contingencies [Line Items]
Operating leases, rent expense		$ 73,000	$ 60,000
Teva Agreements
Loss Contingencies [Line Items]
Nonrefundable upfront payment	$ 6,000,000
Payment upon achievement of certain clinical and commercial milestones	135,000,000
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
Teva Agreements \| Research and Development Expenses
Loss Contingencies [Line Items]
Up-front license payment		$ 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

Term Loan - Additional Information (Details) - Loan Agreement	1 Months Ended
	Apr. 30, 2020 USD ($) $ / shares shares	Mar. 31, 2021 USD ($)	Jul. 31, 2020
Debt Instrument [Line Items]
Credit facility maturity date	Sep. 01, 2023
Line of credit facility, description	In April 2020, the Company and certain of its subsidiaries entered into a Loan and Security Agreement, (as amended, the “Loan Agreement”) with the lenders referred to therein (the “Lenders”), and Silicon Valley Bank, as collateral agent. The Loan Agreement provides 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 is available to be drawn through May 31, 2021 (see Note 9). The Term A Loan Facility matures on November 1, 2022, provided, that if the Term B Loan Facility is funded, the facilities instead mature on September 1, 2023. The loans will bear interest at the greater of (i) 4.50% and (ii) the sum of (a) the Prime Rate as reported in The Wall Street Journal plus (b) 1.25%.
Warrant expiration date	Apr. 07, 2030		Jun. 30, 2025
Debt issuance costs, gross	$ 600,000	$ 500,000
Debt issuance costs		200,000
Dividends
Debt Instrument [Line Items]
Fair value of warrant assumptions, dividends	$ 0
Black Scholes Option Pricing Model \| Risk-Free Interest Rate
Debt Instrument [Line Items]
Fair Measurement Input	0.0075
Black Scholes Option Pricing Model \| Expected Volatility
Debt Instrument [Line Items]
Fair Measurement Input	0.9230
Black Scholes Option Pricing Model \| Expected Term
Debt Instrument [Line Items]
Fair Measurement Input	10 years
Prime Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	1.25%
Minimum
Debt Instrument [Line Items]
Debt instrument, interest rate	4.50%
Term A Loan Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 10,000,000
Credit facility maturity date	Nov. 01, 2022
Amount drawn		0
Warrants to purchase common stock \| shares	25,000
Warrant exercise price \| $ / shares	$ 22.06
Term B Loan Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 5,000,000
Amount drawn		$ 0
Warrants to purchase common stock \| shares	8,333

Stockholders' Equity - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended
	Feb. 28, 2021	Oct. 31, 2019	Mar. 31, 2021	Mar. 31, 2020
Stockholders' Equity [Line Items]
Shares granted			538,613
Share base compensation expense			$ 1,793,000	$ 493,000
Service-based RSUs \| Employee
Stockholders' Equity [Line Items]
Shares granted	56,545
Total grant date fair value	$ 1,300,000
Share base compensation expense	$ 100,000
Vesting period	3 years
Performance RSUs \| Executive Officer
Stockholders' Equity [Line Items]
Shares granted	61,500
Total grant date fair value	$ 1,400,000
Share base compensation expense	$ 100,000
Vesting period	1 year
Employee Stock Purchase Plan
Stockholders' Equity [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%
Number of shares of common stock available for issuance under ESPP			555,122
2019 Plan
Stockholders' Equity [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%
Common stock reserved and available for issuance as future option grants			1,633,644
Maximum [Member] \| Employee Stock Purchase Plan
Stockholders' Equity [Line Items]
Period for increase in number of shares of common stock reserved for issuance		10 years
Maximum [Member] \| 2019 Plan
Stockholders' Equity [Line Items]
Period for increase in number of shares of common stock reserved for issuance			10 years

Stockholders' Equity - Summary of Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 1,793	$ 493
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	639	192
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 1,154	$ 301

Stockholders' Equity - Summary of Estimated Fair Value of Option Awards Granted Using Black-Scholes Option-Pricing Model (Details)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 years 1 month 6 days
Contractual term (years)	10 years	10 years
Expected volatility, minimum	97.50%	86.40%
Expected volatility, maximum	97.60%	87.50%
Risk-free interest rate, minimum	0.70%	0.50%
Risk-free interest rate, maximum	0.80%	1.50%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)		6 years
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)		6 years 1 month 6 days

Stockholders' Equity - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Number of Options
Outstanding, Beginning Balance	1,898,395
Granted	538,613
Exercised	(103,170)
Cancelled	(52,728)
Outstanding, Ending Balance	2,281,110	1,898,395
Exercisable as of March 31, 2021	627,372
Weighted Average Exercise Price
Weighted Average Exercise Price Outstanding, Beginning Balance	$ 12.79
Weighted Average Exercise Price, Granted	23.04
Weighted Average Exercise Price, Exercised	2.09
Weighted Average Exercise Price, Cancelled	16.42
Weighted Average Exercise Price Outstanding, Ending Balance	15.61	$ 12.79
Weighted Average Exercise Price, Exercisable as of March 31, 2021	$ 8.06
Weighted Average Remaining Contractual Term (In years)
Weighted Average Remaining Contractual Term (In years), Outstanding	8 years 7 months 24 days	8 years 7 months 6 days
Weighted Average Remaining Contractual Term (In years), Exercisable as of March 31, 2021	7 years 10 months 14 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value Outstanding	$ 25,918
Aggregate Intrinsic Value Outstanding	22,657	$ 25,918
Aggregate Intrinsic Value, Exercisable as of March 31, 2021	$ 10,725

Net Loss Per Share - Schedule of Outstanding Potentially Dilutive Securities Excluded From Calculation of Diluted Net Loss (Details) - shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	4,028,839	3,392,611
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	2,281,110	1,714,685
Shares Available for Future Option Grants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	1,633,644	1,676,191
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	111,728
Employee Stock Purchase Plan
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	2,357	1,735

Subsequent Event - Additional Information (Details) - Loan Agreement	1 Months Ended
	Apr. 30, 2021	Apr. 30, 2020
Subsequent Event [Line Items]
Line of credit facility, description		In April 2020, the Company and certain of its subsidiaries entered into a Loan and Security Agreement, (as amended, the “Loan Agreement”) with the lenders referred to therein (the “Lenders”), and Silicon Valley Bank, as collateral agent. The Loan Agreement provides 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 is available to be drawn through May 31, 2021 (see Note 9). The Term A Loan Facility matures on November 1, 2022, provided, that if the Term B Loan Facility is funded, the facilities instead mature on September 1, 2023. The loans will bear interest at the greater of (i) 4.50% and (ii) the sum of (a) the Prime Rate as reported in The Wall Street Journal plus (b) 1.25%.
Subsequent Event
Subsequent Event [Line Items]
Line of credit facility, description	In April 2021, the Company entered into an amendment to the Loan and Security Agreement with Silicon Valley Bank to extend the draw period for both the Term Loan A Facility and Term Loan B Facility to May 31, 2021