0000950170-24-055680 | 10-Q | XBRL Viewer

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CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	5,482,752	5,482,752
Common stock, shares outstanding	5,482,752	5,482,752

Collaboration Agreements

3 Months Ended

Mar. 31, 2024

Collaboration Agreement [Abstract]

Collaboration Agreements

Note 8 - Collaboration Agreements

Gilead Agreement

In October 2023, the Company entered into the Gilead Collaboration Agreement and the Gilead Equity Agreements under which it received total proceeds of $100.0 million. Under the Gilead Collaboration Agreement, Gilead exclusively licensed to the Company its HPI program and NNPI program, while retaining opt-in rights to these programs and have an option to take an exclusive license, on a program-by-program basis, to all of the Company’s other current and future pipeline programs. During the 12-year collaboration term (subject to payment of certain extension fees) and for a specified period thereafter, Gilead may exercise its opt-in rights, on a program-by-program basis, at one of two timepoints—completion of a certain Phase 1 study or completion of a certain Phase 2 study for the first product within the program—upon payment of an opt-in fee ranging from $45.0 million to $125.0 million per program depending on the type of program and when the option is exercised.

If Gilead exercises its opt-in right to any current or future program under the collaboration, the Company is eligible to receive up to $330.0 million in potential regulatory and commercial milestones on that program, in addition to royalties ranging from the high single-digits to high teens, depending on the clinical stage of the program at the time of the opt-in. Following Gilead’s exercise of its option for each of the Company’s programs, the Company may opt in to cover 40% of the research and development costs in the United States and share 40% of the profits and operating loss in the United States for products within the program in lieu of receiving milestones and royalties for that program in the United States, unless the Company later opts out of the cost/profit share for the program. Prior to Gilead’s potential exercise of its opt-in, the Company will be primarily responsible for all discovery, research and development on its programs and the two Gilead-contributed programs. Following Gilead’s opt-in, Gilead will control the further discovery, research, development, and commercialization on any optioned programs. During the term, Gilead will continue to support the collaboration through extension fees of $75.0 million in each of the third, fifth and seventh years of the collaboration.

The Gilead Collaboration Agreement is subject to termination by either party for the other party’s uncured, material breach or insolvency. Subject to certain limitations, the Company and Gilead both have certain termination for convenience rights, upon sufficient prior written notice, with respect to programs that one party in-licenses from the other (subject to Gilead’s option rights), and with respect to Gilead, for programs it has option rights to (subject to certain time limitations with respect to existing Company programs). Gilead also has a right to terminate the collaborative activities under the Gilead Collaboration Agreement at certain specified points during the collaboration term. Other customary termination rights are further provided in the Gilead Collaboration Agreement.

The Company concluded Gilead is a customer and accordingly, the Gilead Collaboration Agreement is within the scope of the revenue from contracts with customers guidance. The Company identified a single combined performance obligation for the discovery, research and development services during the collaboration term (the R&D Services). As of March 31, 2024, the total transaction price of the Gilead Collaboration Agreement was determined to be $90.7 million. The Company will reevaluate the transaction price in each reporting period as uncertain events are resolved or other changes in circumstances occur.

The transaction price is reflected as collaboration revenue when realized in the Company’s condensed consolidated statements of operations. The Company will recognize revenue over time using a cost-based input method over the initial non-cancellable term of three years since this method best reflects the transfer of services to Gilead. In applying a cost-based input method of revenue recognition, the Company uses actual costs incurred relative to estimated total costs to fulfill each performance obligation.

The Company recognized collaboration revenue of $5.8 million during the three months ended March 31, 2024. The transaction price for future collaborative activities was recorded as deferred revenue on the condensed consolidated balance sheet as of March 31, 2024, of which $32.8 million was short-term and $47.7 million was long-term. During the three months ended March 31, 2024, the Company incurred $0.2 million in reimbursable expenses due to Gilead.

The following table presents changes in the Company’s contract liabilities (in thousands):


	Balance at Beginning of Period		Additions		Deductions			Balance at End of Period
Three Months Ended March 31, 2024
Contract liabilities:
Deferred revenue	$	86,294	$	—	$	(5,785	)	$	80,509


	Three Months Ended March 31,
	2024		2023
Collaboration revenue recognized in the period from
Amounts included in deferred revenue at the beginning of the period	$	5,785	$	—
Performance obligations satisfied in previous period	$	—	$	—

Arbutus Biopharma Agreement

In August 2020, the Company and Arbutus Biopharma Corporation (Arbutus Biopharma) entered into a Clinical Trial Collaboration Agreement (the Arbutus Biopharma Agreement) to conduct a randomized, multi-center, open-label Phase 2 clinical trial to explore the safety, pharmacokinetics and antiviral activity of the triple combination of vebicorvir (VBR), AB-729 and a nucleos(t)ide analog reverse transcriptase inhibitor (NrtI) compared to the double combinations of VBR with a NrtI and AB-729 with a NrtI. Under the Arbutus Biopharma Agreement, Assembly and Arbutus Biopharma share responsibility for the costs of the trial equally, excluding manufacturing supply which are the burden of each company to supply their respective drugs, VBR and AB-729. Assembly is responsible for conducting this clinical trial with Arbutus Biopharma reimbursing Assembly its share of expenses. In February 2023, Assembly and Arbutus Biopharma decided to terminate the Phase 2 clinical trial early, at the end of the 48-week on-treatment period, and are in the process of completing the final reconciliation of costs.

Reimbursements and cost-sharing portions from Arbutus Biopharma are reflected as a reduction of research and development expense when realized in the Company’s condensed consolidated statements of operations. There were no costs incurred under the Arbutus Biopharma Agreement during the three months ended March 31, 2024. During the three months ended March 31, 2023, the Company recognized a reduction of research and development expenses of $0.6 million under the Arbutus Biopharma Agreement.

Other Accrued Expenses (Tables)

3 Months Ended

Mar. 31, 2024

Payables and Accruals [Abstract]

Schedule of Other Accrued Expenses

Other accrued expenses consist of the following (in thousands):


	March 31, 2024		December 31, 2023
Accrued expenses:
Accrued compensation	$	1,727	$	5,484
Accrued professional fees and other		324		260
Total accrued expenses	$	2,051	$	5,744

Fair Value Measurements and Investments in Marketable Securities - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Investments in marketable securities:
Realized gains and losses	$ 0	$ 0
Accrued interest receivable	300,000		$ 300,000
Fair value assets transfers between level 1, level 2 or level 3	$ 0		$ 0

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details

Stock-Based Compensation - Summary of Assumptions Used to Estimate Fair Values of Stock Options Grants (Details) - $ / shares	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award
Exercise price	$ 13.3
Risk-free rate	4.16%
Expected dividend yield	0.00%	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award
Exercise price		$ 10.68
Expected volatility	80.40%	77.50%
Risk-free rate		3.59%
Expected term (years)	5 years 6 months	5 years 6 months
Maximum
Share-based Compensation Arrangement by Share-based Payment Award
Exercise price		$ 18.36
Expected volatility	86.90%	82.80%
Risk-free rate		4.00%
Expected term (years)	7 years	7 years

- Definition

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+ Details

Stock-Based Compensation - Schedule of Recognized Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Compensation expense:
Stock-based compensation expense	$ 739	$ 1,835
Research and Development
Compensation expense:
Stock-based compensation expense	354	910
General and Administrative
Compensation expense:
Stock-based compensation expense	$ 385	$ 925

Fair Value Measurements and Investments in Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2024

Investments, Debt and Equity Securities [Abstract]

Schedule of Investments in Marketable Securities

Investments in marketable securities consisted of the following (in thousands):


	March 31, 2024
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Cash equivalents
Money market fund	$	18,110	$	—	$	—		$	18,110
Total cash equivalents		18,110		—		—			18,110
Short-term marketable securities
U.S. and foreign corporate debt securities		17,764		12		—			17,776
U.S. treasury securities		60,471		20		(6	)		60,485
U.S. and foreign commercial paper		15,958		11		(3	)		15,966
Total short-term marketable securities		94,193		43		(9	)		94,227
Total cash equivalents and marketable securities	$	112,303	$	43	$	(9	)	$	112,337


	December 31, 2023
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Cash equivalents
Money market fund	$	18,982	$	—	$	—		$	18,982
Total cash equivalents		18,982		—		—			18,982
Short-term marketable securities
U.S. and foreign corporate debt securities		17,595		41		(3	)		17,633
U.S. treasury securities		76,891		127		—			77,018
U.S. and foreign commercial paper		15,728		27		—			15,755
Total short-term marketable securities		110,214		195		(3	)		110,406
Total cash equivalents and marketable securities	$	129,196	$	195	$	(3	)	$	129,388

There were no realized gains and losses for the three months ended March 31, 2024 and 2023.

Schedule of Fair Value of Financial Assets

The following tables present the fair value of the Company’s financial assets measured at fair value on a recurring basis (in thousands):


	March 31, 2024
	Level 1		Level 2		Level 3		Fair Value
Cash equivalents
Money market fund	$	18,110	$	—	$	—	$	18,110
Total cash equivalents		18,110		—		—		18,110
Short-term marketable securities
U.S. and foreign corporate debt securities		—		17,776		—		17,776
U.S. treasury securities		—		60,485		—		60,485
U.S. and foreign commercial paper		—		15,966		—		15,966
Total short-term marketable securities		—		94,227		—		94,227
Total assets measured at fair value	$	18,110	$	94,227	$	—	$	112,337


	December 31, 2023
	Level 1		Level 2		Level 3		Fair Value
Cash equivalents
Money market fund	$	18,982	$	—	$	—	$	18,982
Total cash equivalents		18,982		—		—		18,982
Short-term marketable securities
U.S. and foreign corporate debt securities		—		17,633		—		17,633
U.S. treasury securities		—		77,018		—		77,018
U.S. and foreign commercial paper		—		15,755		—		15,755
Total short-term marketable securities		—		110,406		—		110,406
Total assets measured at fair value	$	18,982	$	110,406	$	—	$	129,388

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Income Statement [Abstract]
Collaboration revenue from a related party	$ 5,785	$ 0
Operating expenses
Research and development	11,879	14,547
General and administrative	4,635	5,012
Total operating expenses	16,514	19,559
Loss from operations	(10,729)	(19,559)
Other income
Interest and other income, net	1,652	609
Total other income	1,652	609
Net loss	(9,077)	(18,950)
Other comprehensive loss
Unrealized (loss) gain on marketable securities	(158)	290
Comprehensive loss	$ (9,235)	$ (18,660)
Net loss per share, basic	$ (1.66)	$ (4.46)
Net loss per share, diluted	$ (1.66)	$ (4.46)
Weighted average common shares outstanding, basic	5,483,313	4,251,037
Weighted average common shares outstanding, diluted	5,483,313	4,251,037

Milestones and Research Agreements

3 Months Ended

Mar. 31, 2024

Milestones And Research Agreements [Abstract]

Milestones and Research Agreements

Note 9 - Milestones and Research Agreements

HBV Research Agreement with Indiana University

Since September 2013, the Company was party to an exclusive License Agreement dated September 3, 2013 with Indiana University Research and Technology Corporation (IURTC) from whom it licensed aspects of the Company’s HBV program held by IURTC. The license agreement required the Company to make milestone payments based upon the successful accomplishment of clinical and regulatory milestones. The aggregate amount of all performance milestone payments under the IURTC license agreement, if all milestones through development were met, was $0.8 million, with a portion having been paid. The Company was obligated to pay IURTC royalty payments based on net sales of the licensed technology as well as a portion of any sublicensing revenue Assembly received. The Company was also required to pay diligence maintenance fees each year to the extent that the royalty, sublicensing, and milestone payments to IURTC were less than such fees for that year. In February 2024, following its decision to discontinue further development or partnering for ABI-H3733, the Company terminated the IURTC license agreement, which became effective April 2024. The Company paid IURTC $0.1 million in diligence maintenance fees during both the three months ended March 31, 2024 and 2023.

Collaboration Agreements - Schedule of Collaboration Revenue Recognized with the Period (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Collaboration revenue recognized in the period from
Amounts included in deferred revenue at the beginning of the period	$ 5,785	$ 0
Performance obligations satisfied in previous period	$ 0	$ 0

Nature of Business

3 Months Ended

Mar. 31, 2024

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Nature of Business

Note 1 - Nature of Business

Overview

Assembly Biosciences, Inc. (together with its subsidiaries, Assembly or the Company), incorporated in Delaware in October 2005, is a biotechnology company developing innovative therapeutics. The Company's pipeline includes two helicase-primase inhibitors (HPI) targeting recurrent genital herpes, an orally bioavailable hepatitis delta virus (HDV) entry inhibitor, a clinical stage capsid assembly modulator candidate designed to disrupt the replication cycle of hepatitis B virus (HBV) and research programs focused on a non-nucleoside polymerase inhibitor (NNPI) targeting transplant-related herpesviruses and a small molecule interferon-α (IFN-α) receptor (IFNAR) agonist targeting HBV and HDV. The Company operates in one segment and is headquartered in South San Francisco, California.

Liquidity

The Company has not derived any revenue from product sales to date and currently has no approved products. Once a product has been developed, it will need to be approved for sale by the U.S. Food and Drug Administration (FDA) or an applicable foreign regulatory agency. Since inception, the Company’s operations have been financed through the sale of equity securities, the proceeds from the exercise of warrants and stock options, the issuance of debt, and upfront payments related to collaboration agreements. The Company has incurred losses from operations since inception and expects to continue to incur substantial losses for the next several years as it continues its product development efforts. Management believes the Company currently has sufficient funds to meet its operating requirements for at least the next twelve months following the date these unaudited condensed consolidated financial statements are issued.

Nature of Business - Additional Information (Details)	3 Months Ended
Nature of Business - Additional Information (Details)	Mar. 31, 2024 Segment Product
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
FDA approved products (in products) \| Product	0
Operating segments (in segments) \| Segment	1

Other Accrued Expenses - Schedule of Other Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Accrued expenses:
Accrued compensation	$ 1,727	$ 5,484
Accrued professional fees and other	324	260
Total accrued expenses	$ 2,051	$ 5,744

Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2024

Share-Based Payment Arrangement [Abstract]

Schedule of Recognized Stock-Based Compensation Expense

The following table summarizes the components of total stock-based compensation expense included in the condensed consolidated statements of operations and comprehensive loss (in thousands):


	Three Months Ended March 31,
	2024		2023
Research and development	$	354	$	910
General and administrative		385		925
Total stock-based compensation expense	$	739	$	1,835

Summary of Assumptions Used to Estimate Fair Values of Stock Options Grants

The fair value of stock options granted during the periods indicated was estimated using the Black-Scholes option pricing model, based on the following assumptions:


	Three Months Ended March 31,
	2024	2023
Exercise price	$13.30	$10.68 - $18.36
Expected volatility	80.4% - 86.9%	77.5% - 82.8%
Risk-free rate	4.16%	3.59% - 4.00%
Expected term (years)	5.5 - 7.0	5.5 - 7.0
Expected dividend yield	0%	0%

Related Party

3 Months Ended

Mar. 31, 2024

Related Party

Note 3 – Related Party

In October 2023, the Company entered into an Option, License and Collaboration agreement (the Gilead Collaboration Agreement), and a Common Stock Purchase Agreement and an Investor Rights Agreement (collectively, the Gilead Equity Agreements) under which it received total proceeds of $100.0 million from Gilead Sciences, Inc. (Gilead). During the three months ended March 31, 2024, the Company recognized $5.8 million of collaboration revenue under the Gilead Collaboration Agreement (see Note 8). As of March 31, 2024, Gilead held 19.9% of the Company's outstanding voting common stock. Additionally, Gilead may, at the Company’s or Gilead's option, subject to certain conditions, purchase additional shares to increase its holdings up to a maximum of 29.9% of the Company's then-outstanding voting common stock. Under the Investor Rights Agreement, Gilead has the right to designate two directors to the Company's board of directors. The Company appointed each of Gilead's designees to its board of directors in December 2023 and February 2024.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

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+ Details

Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2024

Accounting Policies [Abstract]

Basis of Presentation

The accompanying unaudited condensed consolidated financial statements include the accounts of the Company and its subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.

The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with the accounting principles generally accepted in the United States of America (U.S. GAAP) for interim financial information and pursuant to the instructions to Form 10-Q and Rule 10-01 of Regulation S-X of the SEC. In management’s opinion, the unaudited condensed consolidated financial statements have been prepared on the same basis as the annual audited consolidated financial statements and include normal recurring adjustments necessary for the fair presentation of the Company’s financial position and its results of operations and comprehensive loss and its cash flows for the periods presented. These statements do not include all disclosures required by U.S. GAAP and should be read in conjunction with the Company’s audited consolidated financial statements and accompanying notes for the fiscal year ended December 31, 2023, which are contained in the 2023 Annual Report. The results for the three months ended March 31, 2024 are not necessarily indicative of results to be expected for the entire year ending December 31, 2024 or future operating periods.

Use of Estimates

The preparation of the unaudited condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that may affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of expenses during the reporting period. Actual results could differ from those estimates.

Significant estimates inherent in the preparation of the accompanying unaudited condensed consolidated financial statements include estimates for revenue recognition and costs incurred but not yet invoiced for research and development accruals.

The Company’s estimates could be affected by external conditions, including those unique to the Company and general economic conditions. It is reasonably possible these external factors could have an effect on the Company’s estimates and could cause actual results to differ materially from those estimates and assumptions.

Other Risks and Uncertainties

U.S. and global financial markets have experienced volatility and disruption due to macroeconomic and geopolitical events such as rising inflation, rising interest rates to combat inflation, the risk of a recession, the war between Russia and Ukraine and the Israel-Hamas war. The Company cannot predict at this time to what extent, if at all, it and its employees, CROs, vendors and/or collaborators could potentially be negatively impacted by these events.

Reverse Stock Split

In September 2023, the Company received a letter from the Listing Qualifications Department of the Nasdaq Stock Market notifying the Company, as the bid price for its common stock had closed below $1.00 per share for the last 30 consecutive business days, it was not in compliance with Nasdaq Listing Rule 5450(a)(1), which is the minimum bid price requirement for continued listing on the Nasdaq Global Select Market. In accordance with Nasdaq Listing Rule 5810(c)(3)(A), the Company was provided a 180-calendar day period, or until March 25, 2024, to regain compliance with the minimum bid price requirement. The continued listing standard would be met once the closing bid price of the Company’s common stock was at least $1.00 per share for a minimum of ten consecutive business days during the 180-calendar day period. In January 2024, the Company's stockholders approved a reverse stock split of its common stock at a range of ratios between 1-for-7 to 1-for-17, and the Company's board of directors approved the implementation of the reverse stock split at a ratio of 1-for-12 (the Reverse Stock Split). The Reverse Stock Split was effective as of February 9, 2024 and the Company regained compliance with the minimum bid price requirement in February 2024.

As of the effective time of the Reverse Stock Split, every 12 issued and outstanding shares of the Company’s common stock was automatically reclassified into one issued and outstanding share of the Company’s common stock. This reduced the number of shares outstanding from 65.8 million shares to 5.5 million shares. The Reverse Stock Split did not affect the number of authorized shares of common stock or the par value of the common stock. No fractional shares of common stock were issued in connection with the Reverse Stock Split and all fractional shares were rounded down to the nearest whole share with respect to outstanding shares of common stock. Any holders of common stock who would have otherwise received a fractional share of common stock pursuant to the Reverse Stock Split, received cash in lieu of the fractional share. All prior period share and per share amounts of the Company's common stock presented have been retroactively adjusted to reflect the 1-for-12 Reverse Stock Split, including reclassifying an amount equal to the reduction in par value of common stock to additional paid-in capital.

Net Loss per Share

Basic net loss per share of common stock excludes dilution and is computed by dividing net loss by the weighted average number of shares of common stock outstanding during the period. Diluted net loss per share of common stock reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock or resulted in the issuance of common stock that then shared in the earnings of the entity unless inclusion of such shares would be anti-dilutive. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss for each period presented.

A reconciliation of the numerators and the denominators of the basic and diluted net loss per common share computations is as follows (in thousands, except for share and per share amounts):


	Three Months Ended March 31,
	2024			2023
Numerator:
Net loss	$	(9,077	)	$	(18,950	)
Denominator:
Weighted average common shares outstanding - basic and diluted		5,483,313			4,251,037
Net loss per share - basic and diluted	$	(1.66	)	$	(4.46	)

Securities excluded from the computation of diluted net loss per share because including them would have been antidilutive are as follows:


	March 31,
	2024		2023
Options to purchase common stock		1,026,696		876,272
Common stock subject to purchase under Employee Stock Purchase Plan		7,545		7,740
Unvested RSUs		103,752		143,110
Total		1,137,993		1,027,122

Summary of Significant Accounting Policies - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Numerator:
Net loss	$ (9,077)	$ (18,950)
Denominator:
Weighted average common shares outstanding - basic	5,483,313	4,251,037
Weighted average common shares outstanding - diluted	5,483,313	4,251,037
Net loss per share - basic	$ (1.66)	$ (4.46)
Net loss per share - diluted	$ (1.66)	$ (4.46)

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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

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-URI https://asc.fasb.org//1943274/2147483589/942-220-S99-1

+ Details

Sale of Common Stock

3 Months Ended

Mar. 31, 2024

Equity [Abstract]

Sale of Common Stock

Note 6 – Sale of Common Stock

In August 2020, the Company entered into a sales agreement under which the Company may offer and sell shares of its common stock having an aggregate offering price of up to $100.0 million through “at-the-market” offerings (2020 ATM), pursuant to its shelf registration statement on Form S-3 on file with the SEC. The Company did not sell any shares of common stock under the 2020 ATM during the three months ended March 31, 2024. During the three months ended March 31, 2023, the Company sold 254,203 shares of common stock under the 2020 ATM, for which the Company received net proceeds of $4.5 million, after deducting commissions, fees and expenses.

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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-Name Accounting Standards Codification
-Section 50
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-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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-Name Accounting Standards Codification
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-URI https://asc.fasb.org//1943274/2147481004/946-505-50-6

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
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-URI https://asc.fasb.org//1943274/2147480237/815-40-50-6

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
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-URI https://asc.fasb.org//1943274/2147480008/505-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
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-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(e)(1))
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Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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-URI https://asc.fasb.org//505/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Section 50
-Paragraph 13
-Subparagraph (i)
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-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
-Section 50
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-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
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Reference 16: http://www.xbrl.org/2003/role/disclosureRef
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Reference 17: http://www.xbrl.org/2003/role/disclosureRef
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Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

+ Details

Milestones and Research Agreements - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Milestones And Research Agreements [Abstract]
Potential milestone payment	$ 0.8
Milestone payment, diligence maintenance fees	$ 0.1	$ 0.1

Fair Value Measurements and Investments in Marketable Securities - Schedule of Fair Value of Financial Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Cash equivalents
Cash equivalents	$ 18,110	$ 18,982
Short-term marketable securities
Short-term marketable securities	94,227	110,406
U.S. treasury securities
Short-term marketable securities
Short-term marketable securities	60,485	77,018
U.S and foreign corporate debt securities
Short-term marketable securities
Short-term marketable securities	17,776	17,633
Money market fund
Cash equivalents
Cash equivalents	18,110	18,982
Recurring
Cash equivalents
Cash equivalents	18,110	18,982
Short-term marketable securities
Short-term marketable securities	94,227	110,406
Long-term marketable securities
Total assets measured at fair value	112,337	129,388
Recurring \| U.S and foreign corporate debt securities
Short-term marketable securities
Short-term marketable securities	17,776	17,633
Recurring \| U.S. treasury securities
Short-term marketable securities
Short-term marketable securities	60,485	77,018
Recurring \| U.S. and foreign commercial paper
Short-term marketable securities
Short-term marketable securities	15,966	15,755
Recurring \| Money market fund
Cash equivalents
Cash equivalents	18,110	18,982
Recurring \| Level 1
Cash equivalents
Cash equivalents	18,110	18,982
Short-term marketable securities
Short-term marketable securities	0	0
Long-term marketable securities
Total assets measured at fair value	18,110	18,982
Recurring \| Level 1 \| U.S and foreign corporate debt securities
Short-term marketable securities
Short-term marketable securities	0	0
Recurring \| Level 1 \| U.S. treasury securities
Short-term marketable securities
Short-term marketable securities	0	0
Recurring \| Level 1 \| U.S. and foreign commercial paper
Short-term marketable securities
Short-term marketable securities	0	0
Recurring \| Level 1 \| Money market fund
Cash equivalents
Cash equivalents	18,110	18,982
Recurring \| Level 2
Cash equivalents
Cash equivalents	0	0
Short-term marketable securities
Short-term marketable securities	94,227	110,406
Long-term marketable securities
Total assets measured at fair value	94,227	110,406
Recurring \| Level 2 \| U.S and foreign corporate debt securities
Short-term marketable securities
Short-term marketable securities	17,776	17,633
Recurring \| Level 2 \| U.S. treasury securities
Short-term marketable securities
Short-term marketable securities	60,485	77,018
Recurring \| Level 2 \| U.S. and foreign commercial paper
Short-term marketable securities
Short-term marketable securities	15,966	15,755
Recurring \| Level 2 \| Money market fund
Cash equivalents
Cash equivalents	0	0
Recurring \| Level 3
Cash equivalents
Cash equivalents	0	0
Short-term marketable securities
Short-term marketable securities	0	0
Long-term marketable securities
Total assets measured at fair value	0	0
Recurring \| Level 3 \| U.S and foreign corporate debt securities
Short-term marketable securities
Short-term marketable securities	0	0
Recurring \| Level 3 \| U.S. treasury securities
Short-term marketable securities
Short-term marketable securities	0	0
Recurring \| Level 3 \| U.S. and foreign commercial paper
Short-term marketable securities
Short-term marketable securities	0	0
Recurring \| Level 3 \| Money market fund
Cash equivalents
Cash equivalents	$ 0	$ 0

Summary of Significant Accounting Policies - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of loss per share	1,137,993	1,027,122
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of loss per share	1,026,696	876,272
Common stock subject to purchase under Employee Stock Purchase Plan
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of loss per share	7,545	7,740
Unvested RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of loss per share	103,752	143,110

Collaboration Agreements (Tables)

3 Months Ended

Mar. 31, 2024

Collaboration Agreement [Abstract]

Schedule of Changes in Contract Liabilities

The following table presents changes in the Company’s contract liabilities (in thousands):


	Balance at Beginning of Period		Additions		Deductions			Balance at End of Period
Three Months Ended March 31, 2024
Contract liabilities:
Deferred revenue	$	86,294	$	—	$	(5,785	)	$	80,509

Schedule of Collaboration Revenue Recognized with the Period


	Three Months Ended March 31,
	2024		2023
Collaboration revenue recognized in the period from
Amounts included in deferred revenue at the beginning of the period	$	5,785	$	—
Performance obligations satisfied in previous period	$	—	$	—

Stock-Based Compensation

3 Months Ended

Mar. 31, 2024

Share-Based Payment Arrangement [Abstract]

Stock-Based Compensation

Note 7 – Stock-Based Compensation

The following table summarizes the components of total stock-based compensation expense included in the condensed consolidated statements of operations and comprehensive loss (in thousands):


	Three Months Ended March 31,
	2024		2023
Research and development	$	354	$	910
General and administrative		385		925
Total stock-based compensation expense	$	739	$	1,835

As of March 31, 2024, there was $4.2 million of total unrecognized stock-based compensation related to outstanding equity awards, which is expected to be recognized over a weighted average remaining amortization period of 1.9 years.

The fair value of stock options granted during the periods indicated was estimated using the Black-Scholes option pricing model, based on the following assumptions:


	Three Months Ended March 31,
	2024	2023
Exercise price	$13.30	$10.68 - $18.36
Expected volatility	80.4% - 86.9%	77.5% - 82.8%
Risk-free rate	4.16%	3.59% - 4.00%
Expected term (years)	5.5 - 7.0	5.5 - 7.0
Expected dividend yield	0%	0%

Stock-Based Compensation - Additional Information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($)
Share-Based Payment Arrangement [Abstract]
Unrecognized stock-based compensation expense	$ 4.2
Unrecognized stock-based compensation expense expected to be recognized, term	1 year 10 months 24 days

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2024

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Note 2 - Summary of Significant Accounting Policies

Basis of Presentation

Use of Estimates

Other Risks and Uncertainties

Reverse Stock Split

Net Loss per Share

A reconciliation of the numerators and the denominators of the basic and diluted net loss per common share computations is as follows (in thousands, except for share and per share amounts):


	Three Months Ended March 31,
	2024			2023
Numerator:
Net loss	$	(9,077	)	$	(18,950	)
Denominator:
Weighted average common shares outstanding - basic and diluted		5,483,313			4,251,037
Net loss per share - basic and diluted	$	(1.66	)	$	(4.46	)

Securities excluded from the computation of diluted net loss per share because including them would have been antidilutive are as follows:


	March 31,
	2024		2023
Options to purchase common stock		1,026,696		876,272
Common stock subject to purchase under Employee Stock Purchase Plan		7,545		7,740
Unvested RSUs		103,752		143,110
Total		1,137,993		1,027,122

Other Accrued Expenses

3 Months Ended

Mar. 31, 2024

Payables and Accruals [Abstract]

Other Accrued Expenses

Note 5 – Other Accrued Expenses

Other accrued expenses consist of the following (in thousands):


	March 31, 2024		December 31, 2023
Accrued expenses:
Accrued compensation	$	1,727	$	5,484
Accrued professional fees and other		324		260
Total accrued expenses	$	2,051	$	5,744

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Cash flows from operating activities
Net loss	$ (9,077)	$ (18,950)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	32	124
Stock-based compensation	739	1,835
Net accretion of investments in marketable debt securities	(1,264)	(52)
Non-cash rent expense	359	855
Changes in operating assets and liabilities:
Accounts receivable from collaboration	0	227
Prepaid expenses and other current assets	(652)	(1,598)
Other assets	0	555
Accounts payable	266	(1,269)
Accrued research and development expenses	1,174	(76)
Other accrued expenses	(3,693)	(4,161)
Deferred revenue from a related party	(5,785)	0
Operating lease liabilities	(463)	(918)
Net cash used in operating activities	(18,364)	(23,428)
Cash flows from investing activities
Proceeds from maturities of marketable securities	21,000	10,000
Purchases of property and equipment	(14)	0
Purchases of marketable securities	(3,714)	0
Net cash provided by investing activities	17,272	10,000
Cash flows from financing activities
Proceeds from the issuance of common stock under ATM equity offering program, net of issuance costs	0	4,492
Net cash provided by financing activities	0	4,492
Net decrease in cash and cash equivalents	(1,092)	(8,936)
Cash and cash equivalents at the beginning of the period	19,841	52,418
Cash and cash equivalents at the end of the period	$ 18,749	$ 43,482

Related Party - Additional Information (Details) $ in Thousands	1 Months Ended	3 Months Ended
	Oct. 31, 2023 USD ($) Director	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)
Related Party Transaction [Line Items]
Revenue recognized		$ 5,785	$ 0
Gilead Sciences, Inc. \| Gilead Equity Agreements
Related Party Transaction [Line Items]
Number of directors, right to designate in company board \| Director	2
Gilead Sciences, Inc. \| Gilead Equity Agreements \| Common Stock
Related Party Transaction [Line Items]
Percentage of outstanding voting of common stock held		0.199
Maximum percentage of then-outstanding voting capital stock	29.90%
Gilead Sciences, Inc. \| Gillead Collaboration Agreement
Related Party Transaction [Line Items]
Proceeds received in collaboration agreement	$ 100,000
Revenue recognized		$ 5,800

Fair Value Measurements and Investments in Marketable Securities - Schedule of Investments in Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Investments in marketable securities:
Amortized Cost	$ 18,110	$ 18,982
Investment, Type [Extensible Enumeration]	Cash Equivalents [Member]	Cash Equivalents [Member]
Gross Unrealized Gain	$ 0	$ 0
Gross Unrealized Loss	0	0
Fair Value	18,110	18,982
Amortized Cost, Short-term marketable securities	94,193	110,214
Gross Unrealized Gain, Short-term marketable securities	43	195
Gross Unrealized Loss, Short-term marketable securities	(9)	(3)
Fair Value, Short-term marketable securities	94,227	110,406
Amortized Cost	112,303	129,196
Gross Unrealized Gain	43	195
Gross Unrealized Loss	(9)	(3)
Fair Value	112,337	129,388
Money market fund
Investments in marketable securities:
Amortized Cost	18,110	18,982
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Fair Value	18,110	18,982
U.S and foreign corporate debt securities
Investments in marketable securities:
Amortized Cost, Short-term marketable securities	17,764	17,595
Gross Unrealized Gain, Short-term marketable securities	12	41
Gross Unrealized Loss, Short-term marketable securities	0	(3)
Fair Value, Short-term marketable securities	17,776	17,633
U.S. treasury securities
Investments in marketable securities:
Amortized Cost, Short-term marketable securities	60,471	76,891
Gross Unrealized Gain, Short-term marketable securities	20	127
Gross Unrealized Loss, Short-term marketable securities	(6)	0
Fair Value, Short-term marketable securities	60,485	77,018
U.S. and foreign commercial paper
Investments in marketable securities:
Amortized Cost, Short-term marketable securities	15,958	15,728
Gross Unrealized Gain, Short-term marketable securities	11	27
Gross Unrealized Loss, Short-term marketable securities	(3)	0
Fair Value, Short-term marketable securities	$ 15,966	$ 15,755

Collaboration Agreements - Schedule of Changes in Contract Liabilities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($)
Collaboration Agreement [Abstract]
Balance at Beginning of Period	$ 86,294
Additions	0
Deductions	(5,785)
Balance at End of Period	$ 80,509

Subsequent Event - Additional Information (Details) - Gilead Sciences, Inc. $ in Millions	1 Months Ended
	Oct. 31, 2023 USD ($) Timepoint Program
Option, License and Collaboration Agreement
Subsequent Event [Line Items]
Collaboration term	12 years
Proceeds received in collaboration agreement	$ 100.0
Number of timepoints of program \| Timepoint	2
Percentage cover of research and development costs	40.00%
Percentage share of profits and operating loss for products	40.00%
Number of fellow-contributed programs \| Program	2
Option, License and Collaboration Agreement \| Minimum
Subsequent Event [Line Items]
Threshold payment of opt-in fee	$ 45.0
Option, License and Collaboration Agreement \| Maximum
Subsequent Event [Line Items]
Threshold payment of opt-in fee	125.0
Option, License and Collaboration Agreement \| Regulatory and Commercial Milestones \| Maximum
Subsequent Event [Line Items]
Potential milestone payments	330.0
Seventh Year of Collaboration Agreement
Subsequent Event [Line Items]
Potential proceeds from collaboration extension fees	$ 75.0

CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Balance at Dec. 31, 2022	$ 82,664	$ 4	$ 807,983	$ (803)	$ (724,520)
Balance (in shares) at Dec. 31, 2022		4,074,552
Issuance of common stock under at-the-market (ATM) equity offering program, net of issuance costs	4,492		4,492
Issuance of common stock under at-the-market (ATM) equity offering program, net of issuance costs (in shares)		254,203
Issuance of common stock for settlement of restricted stock units (RSUs) (in shares)		5,820
Unrealized gain (loss) on marketable debt securities	290			290
Stock-based compensation	1,837		1,837
Net loss	(18,950)				(18,950)
Balance at Mar. 31, 2023	70,333	$ 4	814,312	(513)	(743,470)
Balance (in shares) at Mar. 31, 2023		4,334,575
Balance at Dec. 31, 2023	41,097	$ 5	826,921	(81)	(785,748)
Balance (in shares) at Dec. 31, 2023		5,482,752
Unrealized gain (loss) on marketable debt securities	(158)			(158)
Stock-based compensation	739		739
Net loss	(9,077)				(9,077)
Balance at Mar. 31, 2024	$ 32,601	$ 5	$ 827,660	$ (239)	$ (794,825)
Balance (in shares) at Mar. 31, 2024		5,482,752

- Definition

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

+ References

+ Details

- Definition

Equity impact of the value of new stock issued during the period. Includes shares issued in an initial public offering or a secondary public offering.

+ References + Details

- Definition

Amount of equity (deficit) attributable to parent. Excludes temporary equity and equity attributable to noncontrolling interest.

+ References

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+ Details

Sale of Common Stock - Additional Information (Details) - 2020 At the Market Offerings - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Aug. 31, 2020
Subsidiary Sale Of Stock [Line Items]
Initial public offering value of shares authorized			$ 100.0
Number of shares sold	0	254,203
Net proceeds from the issuance of common stock through equity plans		$ 4.5

Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2024

Accounting Policies [Abstract]

Schedule of Earnings Per Share, Basic and Diluted

A reconciliation of the numerators and the denominators of the basic and diluted net loss per common share computations is as follows (in thousands, except for share and per share amounts):


	Three Months Ended March 31,
	2024			2023
Numerator:
Net loss	$	(9,077	)	$	(18,950	)
Denominator:
Weighted average common shares outstanding - basic and diluted		5,483,313			4,251,037
Net loss per share - basic and diluted	$	(1.66	)	$	(4.46	)

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share

Securities excluded from the computation of diluted net loss per share because including them would have been antidilutive are as follows:


	March 31,
	2024		2023
Options to purchase common stock		1,026,696		876,272
Common stock subject to purchase under Employee Stock Purchase Plan		7,545		7,740
Unvested RSUs		103,752		143,110
Total		1,137,993		1,027,122

Fair Value Measurements and Investments in Marketable Securities

3 Months Ended

Mar. 31, 2024

Investments, Debt and Equity Securities [Abstract]

Fair Value Measurements and Investments in Marketable Securities

Note 4 – Fair Value Measurements and Investments in Marketable Securities

The carrying amounts of cash equivalents and marketable securities approximate their fair value based upon quoted market prices. Certain of the Company’s financial instruments are not measured at fair value on a recurring basis, but are recorded at amounts that approximate their fair value due to their liquid or short-term nature, such as cash, accounts receivable, accounts payable and accrued expenses.

The Company uses the following three-level hierarchy that maximizes the use of observable inputs and minimizes the use of unobservable inputs to value its financial instruments:

Level 1: Observable inputs such as unadjusted quoted prices in active markets for identical instruments.

Level 2: Quoted prices for similar instruments that are directly or indirectly observable in the marketplace.

Level 3: Significant unobservable inputs that are supported by little or no market activity and that are financial instruments whose values are determined using pricing models, discounted cash flow methodologies, or similar techniques, as well as instruments for which the determination of fair value requires significant judgment or estimation.

Investments in marketable securities consisted of the following (in thousands):


	March 31, 2024
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Cash equivalents
Money market fund	$	18,110	$	—	$	—		$	18,110
Total cash equivalents		18,110		—		—			18,110
Short-term marketable securities
U.S. and foreign corporate debt securities		17,764		12		—			17,776
U.S. treasury securities		60,471		20		(6	)		60,485
U.S. and foreign commercial paper		15,958		11		(3	)		15,966
Total short-term marketable securities		94,193		43		(9	)		94,227
Total cash equivalents and marketable securities	$	112,303	$	43	$	(9	)	$	112,337


	December 31, 2023
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Cash equivalents
Money market fund	$	18,982	$	—	$	—		$	18,982
Total cash equivalents		18,982		—		—			18,982
Short-term marketable securities
U.S. and foreign corporate debt securities		17,595		41		(3	)		17,633
U.S. treasury securities		76,891		127		—			77,018
U.S. and foreign commercial paper		15,728		27		—			15,755
Total short-term marketable securities		110,214		195		(3	)		110,406
Total cash equivalents and marketable securities	$	129,196	$	195	$	(3	)	$	129,388

There were no realized gains and losses for the three months ended March 31, 2024 and 2023. As of March 31, 2024 and 2023, investments which were in an unrealized loss position were not material and generally due to interest rate fluctuations, as opposed to declines in credit quality. The Company determined it has the intent and ability to hold all marketable securities that have been in a continuous loss position until recovery of their amortized cost basis, which may be until maturity. As a result, the Company did not recognize any credit losses related to its investments and all unrealized gains and losses on available-for-sale securities are recorded in accumulated other comprehensive loss on the condensed consolidated balance sheets during the three months ended March 31, 2024 and 2023.

Accrued interest receivable was $0.3 million as of March 31, 2024 and December 31, 2023 and was recorded in prepaid expenses and other current assets on the condensed consolidated balance sheets. The Company did not write off any accrued interest receivable during the three months ended March 31, 2024 and 2023.

The following tables present the fair value of the Company’s financial assets measured at fair value on a recurring basis (in thousands):


	March 31, 2024
	Level 1		Level 2		Level 3		Fair Value
Cash equivalents
Money market fund	$	18,110	$	—	$	—	$	18,110
Total cash equivalents		18,110		—		—		18,110
Short-term marketable securities
U.S. and foreign corporate debt securities		—		17,776		—		17,776
U.S. treasury securities		—		60,485		—		60,485
U.S. and foreign commercial paper		—		15,966		—		15,966
Total short-term marketable securities		—		94,227		—		94,227
Total assets measured at fair value	$	18,110	$	94,227	$	—	$	112,337


	December 31, 2023
	Level 1		Level 2		Level 3		Fair Value
Cash equivalents
Money market fund	$	18,982	$	—	$	—	$	18,982
Total cash equivalents		18,982		—		—		18,982
Short-term marketable securities
U.S. and foreign corporate debt securities		—		17,633		—		17,633
U.S. treasury securities		—		77,018		—		77,018
U.S. and foreign commercial paper		—		15,755		—		15,755
Total short-term marketable securities		—		110,406		—		110,406
Total assets measured at fair value	$	18,982	$	110,406	$	—	$	129,388

The Company estimates the fair value of its investments in marketable securities by taking into consideration valuations obtained from third-party pricing services. The pricing services utilize industry standard valuation models, including both income and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar securities, issuer credit spreads, benchmark securities, prepayment/default projections based on historical data, and other observable inputs.

There were no transfers between Level 1, Level 2 or Level 3 investments during the periods presented.

Summary of Significant Accounting Policies - Additional Information (Details)			1 Months Ended	3 Months Ended
	Feb. 09, 2024 shares	Feb. 08, 2024 shares	Jan. 31, 2024	Mar. 31, 2024 shares	Dec. 31, 2023 shares	Sep. 30, 2023 $ / shares
Significant Accounting Policies [Line Items]
Reverse stock split description				In January 2024, the Company's stockholders approved a reverse stock split of its common stock at a range of ratios between 1-for-7 to 1-for-17, and the Company's board of directors approved the implementation of the reverse stock split at a ratio of 1-for-12 (the Reverse Stock Split). The Reverse Stock Split was effective as of February 9, 2024 and the Company regained compliance with the minimum bid price requirement in February 2024.
Reverse stock split ratio	0.0833		0.0833
Common stock, shares outstanding				5,482,752	5,482,752
Common stock shares outstanding due to reverse stock split	5,500,000	65,800,000
Number of shares issued in connection with reverse stock split	0
Maximum
Significant Accounting Policies [Line Items]
Reverse stock split ratio			0.0588
Closing bid price of stock \| $ / shares						$ 1
Minimum
Significant Accounting Policies [Line Items]
Reverse stock split ratio			0.1429
Closing bid price of stock \| $ / shares						$ 1

Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2024	May 03, 2024
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Mar. 31, 2024
Entity File Number	001-35005
Entity Registrant Name	ASSEMBLY BIOSCIENCES, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-8729264
Entity Address, Address Line One	Two Tower Place
Entity Address, Address Line Two	7th Floor
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	833
Local Phone Number	509-4583
Amendment Flag	false
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Entity Central Index Key	0001426800
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Trading Symbol	ASMB
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common Stock, par value $0.001
Entity Common Stock, Shares Outstanding		5,513,308
Entity Shell Company	false
Entity Emerging Growth Company	false
Entity Small Business	true

Collaboration Agreements - Additional Information (Details)	1 Months Ended	3 Months Ended
	Oct. 31, 2023 USD ($) Timepoint Program	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research and development expense		$ 11,879,000	$ 14,547,000
Collaboration revenue		5,785,000	0
Contract liability/deferred revenue		80,509,000		$ 86,294,000
Deferred revenue - short-term		32,771,000		30,915,000
Deferred revenue - long-term		47,738,000		$ 55,379,000
Arbutus Biopharma Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research and development expense		0	$ 600,000
Option, License and Collaboration Agreement \| Gilead Sciences, Inc.
Research And Development Arrangement Contract To Perform For Others [Line Items]
Collaboration revenue		5,800,000
Proceeds received in collaboration agreement	$ 100,000,000
Collaboration term	12 years
Number of timepoints of program \| Timepoint	2
Percentage cover of research and development costs	40.00%
Percentage share of profits and operating loss for products	40.00%
Number of fellow-contributed programs \| Program	2
Contract liability/deferred revenue	$ 90,700,000
Initial non-cancellable term	3 years
Deferred revenue - short-term		32,800,000
Deferred revenue - long-term		47,700,000
Reimbursable expenses		$ 200,000
Option, License and Collaboration Agreement \| Minimum \| Gilead Sciences, Inc.
Research And Development Arrangement Contract To Perform For Others [Line Items]
Threshold payment of opt-in fee	$ 45,000,000
Option, License and Collaboration Agreement \| Maximum \| Gilead Sciences, Inc.
Research And Development Arrangement Contract To Perform For Others [Line Items]
Threshold payment of opt-in fee	125,000,000
Option, License and Collaboration Agreement \| Regulatory and Commercial Milestones \| Maximum \| Gilead Sciences, Inc.
Research And Development Arrangement Contract To Perform For Others [Line Items]
Potential milestone payments	330,000,000
Seventh Year of Collaboration Agreement \| Gilead Sciences, Inc.
Research And Development Arrangement Contract To Perform For Others [Line Items]
Potential proceeds from collaboration extension fees	$ 75,000,000

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Current assets
Cash and cash equivalents	$ 18,749	$ 19,841
Marketable securities	94,227	110,406
Accounts receivable from collaboration	43	43
Prepaid expenses and other current assets	4,149	3,497
Total current assets	117,168	133,787
Property and equipment, net	367	385
Operating lease right-of-use (ROU) assets	2,036	2,339
Other assets	312	312
Total assets	119,883	136,823
Current liabilities
Accounts payable	727	461
Accrued research and development expenses	2,059	885
Other accrued expenses	2,051	5,744
Deferred revenue from a related party - short-term	32,771	30,915
Operating lease liabilities - short-term	1,145	1,220
Total current liabilities	38,753	39,225
Deferred revenue from a related party - long-term	47,738	55,379
Operating lease liabilities - long-term	791	1,122
Total liabilities	87,282	95,726
Commitments and contingencies
Stockholders' equity
Preferred stock, $0.001 par value; 5,000,000 shares authorized; no shares issued or outstanding
Common stock, $0.001 par value; 150,000,000 shares authorized as of March 31, 2024 and December 31, 2023; 5,482,752 shares issued and outstanding as of March 31, 2024 and December 31, 2023	5	5
Additional paid-in capital	827,660	826,921
Accumulated other comprehensive loss	(239)	(81)
Accumulated deficit	(794,825)	(785,748)
Total stockholders' equity	32,601	41,097
Total liabilities and stockholders' equity	$ 119,883	$ 136,823