0000950170-23-061134 | 10-Q | XBRL Viewer

Other Accrued Expenses

9 Months Ended

Sep. 30, 2023

Note 4 – Other Accrued Expenses

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


	September 30, 2023		December 31, 2022
Accrued expenses:
Accrued compensation	$	3,738	$	6,228
Accrued restructuring charges		—		599
Accrued professional fees and other		148		490
Total accrued expenses	$	3,886	$	7,317

Stock-Based Compensation - Summary of Assumptions Used to Estimate Fair Values of Stock Options Grants (Details) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award
Exercise price	$ 0.98
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award
Exercise price		$ 1.66	$ 0.89	$ 1.53
Expected volatility	77.50%	78.60%	77.50%	78.60%
Risk-free rate	4.23%	2.62%	3.59%	1.41%
Expected term (years)	5 years 6 months	5 years 6 months	5 years 6 months	5 years 6 months
Maximum
Share-based Compensation Arrangement by Share-based Payment Award
Exercise price		$ 2.19	$ 1.53	$ 2.45
Expected volatility	83.10%	81.70%	83.10%	81.70%
Risk-free rate	4.24%	4.15%	4.24%	4.15%
Expected term (years)	7 years	7 years	7 years 6 months	7 years 6 months

- 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.

+ References

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+ Details

Sale of Common Stock	9 Months Ended
Sep. 30, 2023
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 September 30, 2023. During the nine months ended September 30, 2023, the Company sold 3,134,045 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. The Company did not sell any shares of common stock under the 2020 ATM during the three and nine months ended September 30, 2022.

Sale of Common Stock

9 Months Ended

Sep. 30, 2023

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 September 30, 2023. During the nine months ended September 30, 2023, the Company sold 3,134,045 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. The Company did not sell any shares of common stock under the 2020 ATM during the three and nine months ended September 30, 2022.

- Definition

The entire disclosure for equity.

+ References

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+ Details

Fair Value Measurements and Investments in Marketable Securities

9 Months Ended

Sep. 30, 2023

Investments, Debt and Equity Securities [Abstract]

Fair Value Measurements and Investments in Marketable Securities

Note 3 – 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):


	September 30, 2023
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Cash equivalents
Money market fund	$	23,058	$	—	$	—		$	23,058
U.S. treasury securities		2,696		—		—			2,696
Total cash equivalents		25,754		—		—			25,754
Short-term marketable securities
U.S. treasury securities		17,565		1		(3	)		17,563
U.S. and foreign commercial paper		1,991		—		—			1,991
Total short-term marketable securities		19,556		1		(3	)		19,554
Total cash equivalents and marketable securities	$	45,310	$	1	$	(3	)	$	45,308


	December 31, 2022
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Cash equivalents
Money market fund	$	49,676	$	—	$	—		$	49,676
Total cash equivalents		49,676		—		—			49,676
Short-term marketable securities
U.S. and foreign corporate debt securities		18,903		—		(306	)		18,597
U.S. treasury securities		11,968		—		(224	)		11,744
U.S. and foreign commercial paper		8,851		—		—			8,851
Total short-term marketable securities		39,722		—		(530	)		39,192
Total cash equivalents and marketable securities	$	89,398	$	—	$	(530	)	$	88,868

As of September 30, 2023 and 2022, 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 and nine months ended September 30, 2023 and 2022.

Accrued interest receivable was $0.1 million and $0.3 million as of September 30, 2023 and December 31, 2022, respectively, 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 and nine months ended September 30, 2023 and 2022.

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


	September 30, 2023
	Level 1		Level 2		Level 3		Fair Value
Cash equivalents
Money market fund	$	23,058	$	—	$	—	$	23,058
U.S. treasury securities		2,696		—		—		2,696
Total cash equivalents		25,754		—		—		25,754
Short-term marketable securities
U.S. treasury securities		—		17,563		—		17,563
U.S. and foreign commercial paper		—		1,991		—		1,991
Total short-term marketable securities		—		19,554		—		19,554
Total assets measured at fair value	$	25,754	$	19,554	$	—	$	45,308


	December 31, 2022
	Level 1		Level 2		Level 3		Fair Value
Cash equivalents
Money market fund	$	49,676	$	—	$	—	$	49,676
Total cash equivalents		49,676		—		—		49,676
Short-term marketable securities
U.S. and foreign corporate debt securities		—		18,597		—		18,597
U.S. treasury securities		—		11,744		—		11,744
U.S. and foreign commercial paper		—		8,851		—		8,851
Total short-term marketable securities		—		39,192		—		39,192
Total assets measured at fair value	$	49,676	$	39,192	$	—	$	88,868

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 during the periods presented.

Milestones and Research Agreements - Additional Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Milestones And Research Agreements [Abstract]
Potential milestone payment	$ 0.8
Milestone payment, diligence maintenance fees	$ 0.1	$ 0.1

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Cash flows from operating activities
Net loss	$ (50,266)	$ (70,697)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	366	374
Stock-based compensation	4,160	4,580
Net (accretion) amortization of investments in marketable debt securities	(534)	234
Non-cash rent expense	2,525	2,644
Changes in operating assets and liabilities:
Accounts receivable from collaboration	944	(910)
Prepaid expenses and other current assets	951	2,060
Other assets	337	90
Accounts payable	(1,735)	(717)
Accrued research and development expenses	(1,503)	1,062
Other accrued expenses	(3,429)	(1,182)
Operating lease liabilities	(2,720)	(2,747)
Net cash used in operating activities	(50,904)	(65,209)
Cash flows from investing activities
Proceeds from maturities of marketable securities	46,315	66,000
Purchases of property and equipment	(184)	(102)
Purchases of marketable securities	(25,615)	(18,820)
Proceeds from sale of marketable securities	0	27,000
Net cash provided by investing activities	20,516	74,078
Cash flows from financing activities
Proceeds from the issuance of common stock under ATM equity offering program, net of issuance costs	4,546	0
Proceeds from the issuance of common stock under ESPP	80	177
Net cash provided by financing activities	4,626	177
Net (decrease) increase in cash and cash equivalents	(25,762)	9,046
Cash and cash equivalents at the beginning of the period	52,418	45,627
Cash and cash equivalents at the end of the period	26,656	54,673
Supplemental non-cash investing and financing activities
Operating lease liabilities arising from obtaining ROU assets	$ 0	$ 171

Restructuring

9 Months Ended

Sep. 30, 2023

Restructuring and Related Activities [Abstract]

Restructuring

Note 5 – Restructuring

In July 2022, the Company and its board of directors approved a strategic plan to align with its refocused pipeline on its next generation capsid assembly modulators (CAMs) and research programs and reduced its workforce by approximately 30%. The Company incurred cumulative restructuring charges of $1.1 million representing all costs to be incurred. These restructuring charges consisted solely of employee severance and related benefits, including $1.0 million in severance payments to executive officers impacted by the restructuring, $0.8 million in one-time termination severance payments and other employee-related costs associated with the restructuring and a reversal of $0.7 million

for previously recognized stock-based compensation expense related to forfeited awards based on the Company's policy of recognizing stock-based awards with graded vesting schedules using an accelerated attribution method on a straight-line basis over the requisite service period for each separately vesting portion of the award and to recognize forfeitures when they occur.

There were no restructuring charges incurred during the three and nine months ended September 30, 2023. The Company incurred $0.8 million in restructuring charges for the three months ended September 30, 2022, $0.7 million of which were included in research and development expenses and $0.1 million in general and administrative expenses. The Company incurred $1.8 million in restructuring charges for the nine months ended September 30, 2022, $1.3 million of which were included in research and development expenses and $0.5 million in general and administrative expenses.

A summary of accrued restructuring charges, included as a component of other accrued expenses on the Company's condensed consolidated balance sheet as of September 30, 2023, is as follows (in thousands):


Accrued balance as of December 31, 2022	$	599
Reductions for cash payments		(599	)
Accrued balance as of September 30, 2023	$	—

Stock-Based Compensation

9 Months Ended

Sep. 30, 2023

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 September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Research and development	$	512	$	613	$	1,747	$	2,044
General and administrative		623		943		2,413		2,536
Total stock-based compensation expense	$	1,135	$	1,556	$	4,160	$	4,580

As of September 30, 2023, there was $3.7 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 1.5 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 September 30,		Nine Months Ended September 30,
	2023	2022	2023	2022
Exercise price	$0.98	$1.66 - $2.19	$0.89 - $1.53	$1.53 - $2.45
Expected volatility	77.5% - 83.1%	78.6% - 81.7%	77.5% - 83.1%	78.6% - 81.7%
Risk-free rate	4.23% - 4.24%	2.62% - 4.15%	3.59% - 4.24%	1.41% - 4.15%
Expected term (years)	5.5 - 7.0	5.5 - 7.0	5.5 - 7.5	5.5 - 7.5
Expected dividend yield	0%	0%	0%	0%

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2023	Dec. 31, 2022
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	52,614,194	48,894,973
Common stock, shares outstanding	52,614,194	48,894,973

Fair Value Measurements and Investments in Marketable Securities - Schedule of Fair Value of Financial Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Short-term marketable securities
Short-term marketable securities	$ 19,554	$ 39,192
U.S. treasury securities
Short-term marketable securities
Short-term marketable securities	17,563	11,744
U.S and foreign corporate debt securities
Short-term marketable securities
Short-term marketable securities		18,597
Recurring
Cash equivalents
Cash equivalents	25,754	49,676
Short-term marketable securities
Short-term marketable securities	19,554	39,192
Long-term marketable securities
Total assets measured at fair value	45,308	88,868
Recurring \| U.S and foreign corporate debt securities
Short-term marketable securities
Short-term marketable securities		18,597
Recurring \| U.S. treasury securities
Cash equivalents
Cash equivalents	2,696
Short-term marketable securities
Short-term marketable securities	17,563	11,744
Recurring \| U.S. and foreign commercial paper
Short-term marketable securities
Short-term marketable securities	1,991	8,851
Recurring \| Money market fund
Cash equivalents
Cash equivalents	23,058	49,676
Recurring \| Level 1
Cash equivalents
Cash equivalents	25,754	49,676
Short-term marketable securities
Short-term marketable securities	0	0
Long-term marketable securities
Total assets measured at fair value	25,754	49,676
Recurring \| Level 1 \| U.S and foreign corporate debt securities
Short-term marketable securities
Short-term marketable securities		0
Recurring \| Level 1 \| U.S. treasury securities
Cash equivalents
Cash equivalents	2,696
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	23,058	49,676
Recurring \| Level 2
Cash equivalents
Cash equivalents	0	0
Short-term marketable securities
Short-term marketable securities	19,554	39,192
Long-term marketable securities
Total assets measured at fair value	19,554	39,192
Recurring \| Level 2 \| U.S and foreign corporate debt securities
Short-term marketable securities
Short-term marketable securities		18,597
Recurring \| Level 2 \| U.S. treasury securities
Cash equivalents
Cash equivalents	0
Short-term marketable securities
Short-term marketable securities	17,563	11,744
Recurring \| Level 2 \| U.S. and foreign commercial paper
Short-term marketable securities
Short-term marketable securities	1,991	8,851
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
Recurring \| Level 3 \| U.S. treasury securities
Cash equivalents
Cash equivalents	0
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

Restructuring - Schedule of Accrued Restructuring Charges (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($)
Restructuring and Related Activities [Abstract]
Accrued balance as of December 31, 2022	$ 599
Reductions for cash payments	(599)
Accrued balance as of September 30, 2023	$ 0

Nature of Business

9 Months Ended

Sep. 30, 2023

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 antiviral therapeutics with the potential to improve the lives of patients worldwide by targeting serious viral diseases, including high-recurrence genital herpes, transplant-related herpesviruses, chronic hepatitis delta virus (HDV) infection and chronic hepatitis B virus (HBV) infection. 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. In October 2023, the Company received $100.0 million upon entering into the Option, License and Collaboration Agreement (the Gilead Collaboration Agreement) and the Common Stock Purchase Agreement and an Investor Rights Agreement (collectively, the Gilead Equity Agreements) with Gilead Sciences, Inc. (Gilead). 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.

Leases

9 Months Ended

Sep. 30, 2023

Leases [Abstract]

Leases

Note 10 - Leases

Lease Commitments

In August 2023, the Company entered into a sublease agreement for office and laboratory space in South San Francisco, California to serve as the Company's new corporate headquarters for a term of 24 months with monthly base rent of $0.1 million, resulting in aggregate future lease payments of $2.6 million. The Company has the option to extend the sublease through September 30, 2029. The sublease is expected to commence in the fourth quarter of 2023 when the Company takes possession of the premises. As the sublease has not commenced as of September 30, 2023, the Company has not recorded an operating lease right-of-use asset or lease liability for this sublease in the condensed consolidated balance sheets.

Other Accrued Expenses - Schedule of Other Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Accrued expenses:
Accrued compensation	$ 3,738	$ 6,228
Accrued restructuring charges	0	599
Accrued professional fees and other	148	490
Total accrued expenses	$ 3,886	$ 7,317

Sale of Common Stock - Additional Information (Details) - 2020 At the Market Offerings - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Aug. 31, 2020
Subsidiary Sale Of Stock [Line Items]
Initial public offering value of shares authorized					$ 100.0
Number of shares sold	0	0	3,134,045	0
Net proceeds from the issuance of common stock through equity plans			$ 4.5

Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2023	Oct. 27, 2023
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2023
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	331 Oyster Point Blvd.
Entity Address, Address Line Two	Fourth 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	2023
Document Fiscal Period Focus	Q3
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		65,709,112
Entity Shell Company	false
Entity Emerging Growth Company	false
Entity Small Business	true

Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2023

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 September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Research and development	$	512	$	613	$	1,747	$	2,044
General and administrative		623		943		2,413		2,536
Total stock-based compensation expense	$	1,135	$	1,556	$	4,160	$	4,580

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 September 30,		Nine Months Ended September 30,
	2023	2022	2023	2022
Exercise price	$0.98	$1.66 - $2.19	$0.89 - $1.53	$1.53 - $2.45
Expected volatility	77.5% - 83.1%	78.6% - 81.7%	77.5% - 83.1%	78.6% - 81.7%
Risk-free rate	4.23% - 4.24%	2.62% - 4.15%	3.59% - 4.24%	1.41% - 4.15%
Expected term (years)	5.5 - 7.0	5.5 - 7.0	5.5 - 7.5	5.5 - 7.5
Expected dividend yield	0%	0%	0%	0%

Collaboration Agreements - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Research And Development Arrangement Contract To Perform For Others [Line Items]
Deferred revenue	$ 2,733,000		$ 2,733,000		$ 2,733,000
Research and development expense	10,824,000	$ 18,130,000	37,894,000	$ 53,127,000
BeiGene Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Deferred revenue	2,700,000		2,700,000		2,700,000
Research and development expense	0	0	0	0
Incremental costs			3,500,000
BeiGene Agreement \| Other Assets
Research And Development Arrangement Contract To Perform For Others [Line Items]
Incremental costs			200,000		$ 200,000
Arbutus Biopharma Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research and development expense	$ 100,000	$ 700,000	$ 1,200,000	$ 1,900,000

Subsequent Event

9 Months Ended

Sep. 30, 2023

Subsequent Events [Abstract]

Subsequent Event

Note 11 - Subsequent Event

On October 15, 2023, the Company entered into the Gilead Collaboration Agreement pursuant to which Gilead will exclusively license to the Company its helicase primase inhibitor program and non-nucleoside polymerase inhibitor 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 for a 12-year collaboration term. In addition to the Gilead Collaboration Agreement, the Company and Gilead entered into the Gilead Equity Agreements, pursuant to which Gilead purchased 13,073,668 shares of the Company’s common stock at a purchase price of $1.16 per share. The Company received total proceeds of $100.0 million, consisting of $84.8 million as an upfront payment under the Gilead Collaboration Agreement and $15.2 million under the Gilead Equity Agreements.

Pursuant to the terms of the Gilead Collaboration Agreement, during the term 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 – and 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, depending on the clinical stage of the program at the time of the opt-in. Following Gilead’s exercise of its option for each Company program, 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 both the Company’s 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.

Pursuant to the terms of the Gilead Equity Agreements, if the Company completes equity financing by July 15, 2024 which results in at least $30.0 million of proceeds to the Company, then, subject to approval by the Company’s stockholders, the Company may require Gilead to purchase additional shares of common stock from the Company in an amount that results in Gilead owning 29.9% of the Company’s then-outstanding voting capital stock. If the Company does not complete the equity financing or does not require Gilead to purchase the additional shares, Gilead may elect to purchase additional shares of common stock from the Company in an amount that results in Gilead owning 29.9% of the Company’s then-outstanding voting capital stock, subject to stockholder approval. The purchase price per share for additional shares purchased by Gilead will be equal to the lesser of a 35% premium to the 30-day volume weighted average price immediately prior to the date of purchase or a 35% premium to the 30-day volume weighted average price immediately prior to delivery by Gilead of notice of the anticipated closing date. The Gilead Equity Agreements also include a three-year standstill and lockup provisions, with customary exceptions, and provide Gilead with certain other stock purchase rights and registration rights, as well as the right to designate two directors to the Company’s board of directors.

Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2023

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 September 30,						Nine Months Ended September 30,
	2023			2022			2023			2022
Numerator:
Net loss	$	(14,420	)	$	(23,145	)	$	(50,266	)	$	(70,697	)
Denominator:
Weighted average common shares outstanding - basic and diluted		52,565,333			48,448,399			51,951,123			48,289,501
Net loss per share - basic and diluted	$	(0.27	)	$	(0.48	)	$	(0.97	)	$	(1.46	)

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:


	September 30,
	2023		2022
Options to purchase common stock		9,945,471		9,441,215
Common stock subject to purchase under ESPP		80,543		102,772
Unvested RSUs		1,088,889		1,837,049
Total		11,114,903		11,381,036

Restructuring - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Jul. 31, 2022	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Restructuring Cost and Reserve [Line Items]
Percentage of workforce reduced	30.00%
Restructuring charges		$ 0.0	$ 0.8	$ 0.0	$ 1.8
Cumulative restructuring charges		$ 1.1		$ 1.1
Employee severance and related benefits	$ 1.0
Restructuring one-time termination Cost	0.8
Restructuring costs reversal	$ 0.7
Research and Development Expenses
Restructuring Cost and Reserve [Line Items]
Restructuring charges			0.7		1.3
General and Administrative Expenses
Restructuring Cost and Reserve [Line Items]
Restructuring charges			$ 0.1		$ 0.5

Summary of Significant Accounting Policies - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Numerator:
Net loss	$ (14,420)	$ (23,145)	$ (50,266)	$ (70,697)
Denominator:
Weighted average common shares outstanding - basic	52,565,333	48,448,399	51,951,123	48,289,501
Weighted average common shares outstanding - diluted	52,565,333	48,448,399	51,951,123	48,289,501
Net loss per share - basic	$ (0.27)	$ (0.48)	$ (0.97)	$ (1.46)
Net loss per share - diluted	$ (0.27)	$ (0.48)	$ (0.97)	$ (1.46)

- 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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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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+ Details

- Definition

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

+ References

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+ Details

Summary of Significant Accounting Policies - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Details) - shares	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of loss per share	11,114,903	11,381,036
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of loss per share	9,945,471	9,441,215
Common stock subject to purchase under ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of loss per share	80,543	102,772
Unvested RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of loss per share	1,088,889	1,837,049

Milestones and Research Agreements

9 Months Ended

Sep. 30, 2023

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 has been party to an exclusive License Agreement dated September 3, 2013 with Indiana University Research and Technology Corporation (IURTC) from whom it has licensed aspects of the Company’s HBV program held by IURTC. The license agreement requires 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, should all milestones through development be met, is $0.8 million, with a portion having been paid. The Company is obligated to pay IURTC royalty payments based on net sales of the licensed technology as well as a portion of any sublicensing revenue Assembly receives. The Company is also required to pay diligence maintenance fees each year to the extent that the royalty, sublicensing, and milestone payments to IURTC are less than such fees for that year. The Company paid IURTC $0.1 million in diligence maintenance fees during both the nine months ended September 30, 2023 and 2022.

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2023

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Note 2 - Summary of Significant Accounting Policies

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, 2022, which are contained in the 2022 Annual Report. The results for the three and nine months ended September 30, 2023 are not necessarily indicative of results to be expected for the entire year ending December 31, 2023 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 of 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

The Company relies on contract research organizations (CROs), including one located in Ukraine that temporarily shut down operations due to Russia’s invasion. Though this CRO has resumed operations and the Company continues to utilize this CRO, the Company has reallocated certain work to other global CROs in case the CRO shuts down operations again.

U.S. and global financial markets have experienced volatility and disruption due to other 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, the Israel-Hamas war, as well as the ongoing impact of the COVID-19 pandemic. 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.

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.

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 September 30,						Nine Months Ended September 30,
	2023			2022			2023			2022
Numerator:
Net loss	$	(14,420	)	$	(23,145	)	$	(50,266	)	$	(70,697	)
Denominator:
Weighted average common shares outstanding - basic and diluted		52,565,333			48,448,399			51,951,123			48,289,501
Net loss per share - basic and diluted	$	(0.27	)	$	(0.48	)	$	(0.97	)	$	(1.46	)

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


	September 30,
	2023		2022
Options to purchase common stock		9,945,471		9,441,215
Common stock subject to purchase under ESPP		80,543		102,772
Unvested RSUs		1,088,889		1,837,049
Total		11,114,903		11,381,036

Recently Adopted Accounting Standards

In June 2016, the Financial Accounting Standards Board (the FASB) issued Accounting Standards Update (ASU) No. 2016-13, Instruments – Credit Losses: Measurement of Credit Losses on Financial Instruments (ASU 2016-13), which requires expected credit losses relating to financial assets measured on an amortized cost basis and available-for-sale debt securities be recorded through an allowance for credit losses. ASU 2016-13 limits the amount of credit losses to be recognized for available-for-sale debt securities to the amount by which carrying value exceeds fair value and requires the reversal of previously recognized credit losses if fair value increases. The FASB issued additional amendments to the new guidance related to transition and clarification and deferred the effective date of this standard for all entities except SEC filers that are not smaller reporting companies to fiscal years beginning after December 15, 2022, including interim periods within those fiscal years. The Company adopted ASU 2016-13 effective January 1, 2023 on a modified retrospective basis. The Company elected to exclude accrued interest receivable from the amortized cost basis of its available-for-sale debt securities and to not measure an allowance for credit losses for accrued interest receivable. The adoption of ASU 2016-13 did not have a material impact on the Company’s consolidated financial statements.

Leases - Additional Information (Details) - USD ($)	1 Months Ended
Leases - Additional Information (Details) - USD ($)	Aug. 31, 2023	Sep. 30, 2023
Leases [Abstract]
Lease not yet commence, term of contract	24 months
Monthly sublease base rent	$ 100,000
Lessee, operating lease, lease not yet commenced, future lease payments	$ 2,600,000
Lessee, Operating Lease, Lease Not yet Commenced, Existence of Option to Extend [true false]	true
Lessee, operating lease, lease not yet commenced, option to extend	The Company has the option to extend the sublease through September 30, 2029.
Lessee, operating lease, lease not yet commenced, operating lease right-of-use asset		$ 0
Lessee, operating lease, lease not yet commenced, operating lease liability		$ 0

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Current assets
Cash and cash equivalents	$ 26,656	$ 52,418
Marketable securities - short-term	19,554	39,192
Accounts receivable from collaboration	0	944
Prepaid expenses and other current assets	3,462	4,413
Total current assets	49,672	96,967
Property and equipment, net	561	743
Operating lease right-of-use (ROU) assets	844	3,195
Other assets	552	889
Total assets	51,629	101,794
Current liabilities
Accounts payable	758	2,493
Accrued research and development expenses	1,619	3,122
Other accrued expenses	3,886	7,317
Operating lease liabilities - short-term	869	3,364
Total current liabilities	7,132	16,296
Deferred revenue	2,733	2,733
Operating lease liabilities - long-term	50	101
Total liabilities	9,915	19,130
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 September 30, 2023 and December 31, 2022; 52,614,194 and 48,894,973 shares issued and outstanding as of September 30, 2023 and December 31, 2022, respectively	53	49
Additional paid-in capital	816,722	807,938
Accumulated other comprehensive loss	(275)	(803)
Accumulated deficit	(774,786)	(724,520)
Total stockholders' equity	41,714	82,664
Total liabilities and stockholders' equity	$ 51,629	$ 101,794

Other Accrued Expenses (Tables)

9 Months Ended

Sep. 30, 2023

Payables and Accruals [Abstract]

Schedule of Other Accrued Expenses

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


	September 30, 2023		December 31, 2022
Accrued expenses:
Accrued compensation	$	3,738	$	6,228
Accrued restructuring charges		—		599
Accrued professional fees and other		148		490
Total accrued expenses	$	3,886	$	7,317

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, 2021	$ 168,929	$ 48	$ 800,728	$ (419)	$ (631,428)
Balance (in shares) at Dec. 31, 2021		48,120,437
Issuance of common stock under Employee Stock Purchase Plan (ESPP)	177		177
Issuance of common stock under Employee Stock Purchase Plan (ESPP) (in shares)		134,888
Issuance of common stock for settlement of restricted stock units (RSUs) (in shares)		225,869
Unrealized gain (loss) on marketable debt securities	(580)			(580)
Stock-based compensation	4,575		4,575
Net loss	(70,697)				(70,697)
Balance at Sep. 30, 2022	102,404	$ 48	805,480	(999)	(702,125)
Balance (in shares) at Sep. 30, 2022		48,481,194
Balance at Jun. 30, 2022	123,980	$ 48	803,910	(998)	(678,980)
Balance (in shares) at Jun. 30, 2022		48,362,736
Issuance of common stock for settlement of restricted stock units (RSUs) (in shares)		118,458
Unrealized gain (loss) on marketable debt securities	(1)			(1)
Stock-based compensation	1,570		1,570
Net loss	(23,145)				(23,145)
Balance at Sep. 30, 2022	102,404	$ 48	805,480	(999)	(702,125)
Balance (in shares) at Sep. 30, 2022		48,481,194
Balance at Dec. 31, 2022	82,664	$ 49	807,938	(803)	(724,520)
Balance (in shares) at Dec. 31, 2022		48,894,973
Issuance of common stock under at-the-market (ATM) equity offering program, net of issuance costs	4,546	$ 3	4,543
Issuance of common stock under at-the-market (ATM) equity offering program, net of issuance costs (in shares)		3,134,045
Issuance of common stock under Employee Stock Purchase Plan (ESPP)	80		80
Issuance of common stock under Employee Stock Purchase Plan (ESPP) (in shares)		90,407
Issuance of common stock for settlement of restricted stock units (RSUs)		$ 1	(1)
Issuance of common stock for settlement of restricted stock units (RSUs) (in shares)		494,769
Unrealized gain (loss) on marketable debt securities	528			528
Stock-based compensation	4,162		4,162
Net loss	(50,266)				(50,266)
Balance at Sep. 30, 2023	41,714	$ 53	816,722	(275)	(774,786)
Balance (in shares) at Sep. 30, 2023		52,614,194
Balance at Jun. 30, 2023	54,949	$ 52	815,588	(325)	(760,366)
Balance (in shares) at Jun. 30, 2023		52,450,731
Issuance of common stock for settlement of restricted stock units (RSUs)		$ 1	(1)
Issuance of common stock for settlement of restricted stock units (RSUs) (in shares)		163,463
Unrealized gain (loss) on marketable debt securities	50			50
Stock-based compensation	1,135		1,135
Net loss	(14,420)				(14,420)
Balance at Sep. 30, 2023	$ 41,714	$ 53	$ 816,722	$ (275)	$ (774,786)
Balance (in shares) at Sep. 30, 2023		52,614,194

Fair Value Measurements and Investments in Marketable Securities (Tables)

9 Months Ended

Sep. 30, 2023

Investments, Debt and Equity Securities [Abstract]

Schedule of Investments in Marketable Securities

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


	September 30, 2023
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Cash equivalents
Money market fund	$	23,058	$	—	$	—		$	23,058
U.S. treasury securities		2,696		—		—			2,696
Total cash equivalents		25,754		—		—			25,754
Short-term marketable securities
U.S. treasury securities		17,565		1		(3	)		17,563
U.S. and foreign commercial paper		1,991		—		—			1,991
Total short-term marketable securities		19,556		1		(3	)		19,554
Total cash equivalents and marketable securities	$	45,310	$	1	$	(3	)	$	45,308


	December 31, 2022
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Cash equivalents
Money market fund	$	49,676	$	—	$	—		$	49,676
Total cash equivalents		49,676		—		—			49,676
Short-term marketable securities
U.S. and foreign corporate debt securities		18,903		—		(306	)		18,597
U.S. treasury securities		11,968		—		(224	)		11,744
U.S. and foreign commercial paper		8,851		—		—			8,851
Total short-term marketable securities		39,722		—		(530	)		39,192
Total cash equivalents and marketable securities	$	89,398	$	—	$	(530	)	$	88,868

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):


	September 30, 2023
	Level 1		Level 2		Level 3		Fair Value
Cash equivalents
Money market fund	$	23,058	$	—	$	—	$	23,058
U.S. treasury securities		2,696		—		—		2,696
Total cash equivalents		25,754		—		—		25,754
Short-term marketable securities
U.S. treasury securities		—		17,563		—		17,563
U.S. and foreign commercial paper		—		1,991		—		1,991
Total short-term marketable securities		—		19,554		—		19,554
Total assets measured at fair value	$	25,754	$	19,554	$	—	$	45,308


	December 31, 2022
	Level 1		Level 2		Level 3		Fair Value
Cash equivalents
Money market fund	$	49,676	$	—	$	—	$	49,676
Total cash equivalents		49,676		—		—		49,676
Short-term marketable securities
U.S. and foreign corporate debt securities		—		18,597		—		18,597
U.S. treasury securities		—		11,744		—		11,744
U.S. and foreign commercial paper		—		8,851		—		8,851
Total short-term marketable securities		—		39,192		—		39,192
Total assets measured at fair value	$	49,676	$	39,192	$	—	$	88,868

Restructuring (Tables)

9 Months Ended

Sep. 30, 2023

Restructuring and Related Activities [Abstract]

Schedule of Accrued Restructuring Charges


Accrued balance as of December 31, 2022	$	599
Reductions for cash payments		(599	)
Accrued balance as of September 30, 2023	$	—

Fair Value Measurements and Investments in Marketable Securities - Additional Information (Details) - USD ($)	Sep. 30, 2023	Dec. 31, 2022
Investments in marketable securities:
Accrued interest receivable	$ 100,000	$ 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.

+ References

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+ Details

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2023

Accounting Policies [Abstract]

Basis of Presentation

Use of Estimates

Other Risks and Uncertainties

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 September 30,						Nine Months Ended September 30,
	2023			2022			2023			2022
Numerator:
Net loss	$	(14,420	)	$	(23,145	)	$	(50,266	)	$	(70,697	)
Denominator:
Weighted average common shares outstanding - basic and diluted		52,565,333			48,448,399			51,951,123			48,289,501
Net loss per share - basic and diluted	$	(0.27	)	$	(0.48	)	$	(0.97	)	$	(1.46	)

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


	September 30,
	2023		2022
Options to purchase common stock		9,945,471		9,441,215
Common stock subject to purchase under ESPP		80,543		102,772
Unvested RSUs		1,088,889		1,837,049
Total		11,114,903		11,381,036

Recently Adopted Accounting Standards

Summary of Significant Accounting Policies - Additional Information (Details) - ASU 2016-13	Sep. 30, 2023
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 01, 2023
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true

- Definition

Indicates (true false) whether accounting standards update was adopted.

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+ Details

Fair Value Measurements and Investments in Marketable Securities - Schedule of Investments in Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Investments in marketable securities:
Amortized Cost	$ 26,656	$ 52,418
Amortized Cost, Short-term marketable securities	19,556	39,722
Gross Unrealized Gain, Short-term marketable securities	1	0
Gross Unrealized Loss, Short-term marketable securities	(3)	(530)
Fair Value, Short-term marketable securities	19,554	39,192
Amortized Cost	45,310	89,398
Gross Unrealized Gain	1	0
Gross Unrealized Loss	(3)	(530)
Fair Value	45,308	88,868
Cash equivalents
Investments in marketable securities:
Amortized Cost	25,754	49,676
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Fair Value	25,754	49,676
Money market fund \| Cash equivalents
Investments in marketable securities:
Amortized Cost	23,058	49,676
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Fair Value	23,058	49,676
U.S and foreign corporate debt securities
Investments in marketable securities:
Amortized Cost, Short-term marketable securities		18,903
Gross Unrealized Gain, Short-term marketable securities		0
Gross Unrealized Loss, Short-term marketable securities		(306)
Fair Value, Short-term marketable securities		18,597
U.S. treasury securities
Investments in marketable securities:
Amortized Cost, Short-term marketable securities	17,565	11,968
Gross Unrealized Gain, Short-term marketable securities	1	0
Gross Unrealized Loss, Short-term marketable securities	(3)	(224)
Fair Value, Short-term marketable securities	17,563	11,744
U.S. treasury securities \| Cash equivalents
Investments in marketable securities:
Amortized Cost	2,696
Gross Unrealized Gain	0
Gross Unrealized Loss	0
Fair Value	2,696
U.S. and foreign commercial paper
Investments in marketable securities:
Amortized Cost, Short-term marketable securities	1,991	8,851
Gross Unrealized Gain, Short-term marketable securities	0	0
Gross Unrealized Loss, Short-term marketable securities	0	0
Fair Value, Short-term marketable securities	$ 1,991	$ 8,851

Stock-Based Compensation - Additional Information (Details) $ in Millions	9 Months Ended
	Sep. 30, 2023 USD ($)
Share-Based Payment Arrangement [Abstract]
Unrecognized stock-based compensation expense	$ 3.7
Unrecognized stock-based compensation expense expected to be recognized, term	1 year 6 months

Nature of Business - Additional Information (Details) $ in Millions		9 Months Ended
	Oct. 15, 2023 USD ($)	Sep. 30, 2023 Segment Product
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Operating segments (in segments) \| Segment		1
FDA approved products (in products) \| Product		0
Subsequent Event \| Gilead Sciences, Inc. \| Option, License and Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Proceeds received in collaboration agreement \| $	$ 100.0

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Operating expenses
Research and development	$ 10,824	$ 18,130	$ 37,894	$ 53,127
General and administrative	4,224	5,271	14,201	18,009
Total operating expenses	15,048	23,401	52,095	71,136
Loss from operations	(15,048)	(23,401)	(52,095)	(71,136)
Other income
Interest and other income, net	628	256	1,829	439
Total other income	628	256	1,829	439
Net loss	(14,420)	(23,145)	(50,266)	(70,697)
Other comprehensive loss
Unrealized gain (loss) on marketable securities	50	(1)	528	(580)
Comprehensive loss	$ (14,370)	$ (23,146)	$ (49,738)	$ (71,277)
Net loss per share, basic	$ (0.27)	$ (0.48)	$ (0.97)	$ (1.46)
Net loss per share, diluted	$ (0.27)	$ (0.48)	$ (0.97)	$ (1.46)
Weighted average common shares outstanding, basic	52,565,333	48,448,399	51,951,123	48,289,501
Weighted average common shares outstanding, diluted	52,565,333	48,448,399	51,951,123	48,289,501

Subsequent Event - Additional Information (Details) - Subsequent Event - Gilead Sciences, Inc.	Oct. 15, 2023 USD ($) Timepoint Program Director $ / shares shares
Option, License and Collaboration Agreement
Subsequent Event [Line Items]
Collaboration term	12 years
Proceeds received in collaboration agreement	$ 100,000,000
Upfront cash payment received	$ 84,800,000
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	$ 45,000,000
Option, License and Collaboration Agreement \| Maximum
Subsequent Event [Line Items]
Threshold payment of opt-in fee	125,000,000
Option, License and Collaboration Agreement \| Regulatory and Commercial Milestones \| Maximum
Subsequent Event [Line Items]
Potential milestone payments	330,000,000
Gilead Equity Agreements \| Common Stock
Subsequent Event [Line Items]
Upfront equity investment	$ 15,200,000
Number of shares sold \| shares	13,073,668
Sale of stock, price per share \| $ / shares	$ 1.16
Expected equity financing completion date	Jul. 15, 2024
Percentage of then-outstanding voting capital stock subject to stockholder approval	29.90%
Purchase price per share of additional shares description	The purchase price per share for additional shares purchased by Gilead will be equal to the lesser of a 35% premium to the 30-day volume weighted average price immediately prior to the date of purchase or a 35% premium to the 30-day volume weighted average price immediately prior to delivery by Gilead of notice of the anticipated closing date.
Number of days volume considered for weighted average price to calculate premium	30 days
Number of years of standstill and lockup provisions	3 years
Number of directors, right to designate in company board \| Director	2
Gilead Equity Agreements \| Common Stock \| Minimum
Subsequent Event [Line Items]
Potential proceeds from equity financing	$ 30,000,000
Gilead Equity Agreements \| Common Stock \| Maximum
Subsequent Event [Line Items]
Percentage of premium to weighted average price immediately prior to date of purchase	35.00%
Percentage of premium to weighted average price immediately prior to delivery of notice of closing date	35.00%
Third Year of Collaboration Agreement
Subsequent Event [Line Items]
Potential proceeds from collaboration extension fees	$ 75,000,000
Fifth Year of Collaboration Agreement
Subsequent Event [Line Items]
Potential proceeds from collaboration extension fees	75,000,000
Seventh Year of Collaboration Agreement
Subsequent Event [Line Items]
Potential proceeds from collaboration extension fees	$ 75,000,000

Collaboration Agreements

9 Months Ended

Sep. 30, 2023

Collaboration Agreement [Abstract]

Collaboration Agreements

Note 8 - Collaboration Agreements

BeiGene Agreement

In July 2020, the Company and BeiGene, Ltd. (BeiGene) entered into a Collaboration Agreement (the BeiGene Agreement) to develop and commercialize the Company’s novel CAM product candidates vebicorvir (VBR), ABI-H2158 and ABI-H3733 (the Licensed Product Candidates) for chronic HBV infection in the People’s Republic of China, Hong Kong, Taiwan and Macau.

As of September 30, 2023, the only remaining performance obligation under the BeiGene Agreement not considered to be complete is the transfer of the ABI-H3733 License. The transaction price allocated to ABI-H3733 of $2.7 million was recognized as a long-term deferred revenue contract liability as of September 30, 2023 and December 31, 2022, and will be recognized as revenue when the Company provides pre-Phase 3 clinical study know-how and development results for ABI-H3733 to BeiGene or a termination of the BeiGene Agreement for ABI-H3733. During the three and nine months ended September 30, 2023 and 2022, the Company did not recognize any revenue or increase or reduction of research and development expense under the BeiGene Agreement. In conjunction with the Company entering into the Gilead Collaboration Agreement with Gilead in October 2023, the Company will no longer seek partnering or further development of ABI-H3733 (see Note 11).

The Company incurred $3.5 million in incremental costs of obtaining the BeiGene Agreement in 2020. These contract costs have been capitalized and are being recognized consistent with the pattern of recognition of revenue associated with the Licensed Product Candidates. As of September 30, 2023 and December 31, 2022, the remaining unamortized contract costs are $0.2 million and are included in other assets on the condensed consolidated balance sheet.

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 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 closing the study.

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. During the three and nine months ended September 30, 2023, the Company recognized a reduction of research and development expenses of $0.1 million and $1.2 million, respectively, under the Arbutus Biopharma Agreement. During the three and nine months ended September 30, 2022, the Company recognized a reduction of research and development expenses of $0.7 million and $1.9 million, respectively, under the Arbutus Biopharma Agreement.

Stock-Based Compensation - Schedule of Recognized Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Compensation expense:
Stock-based compensation expense	$ 1,135	$ 1,556	$ 4,160	$ 4,580
Research and Development
Compensation expense:
Stock-based compensation expense	512	613	1,747	2,044
General and Administrative
Compensation expense:
Stock-based compensation expense	$ 623	$ 943	$ 2,413	$ 2,536