0001326190-23-000047 | 10-Q | XBRL Viewer

Operating Leases

9 Months Ended

Sep. 30, 2023

4. Operating Leases

The Company’s operating leases consist of leases for office and laboratory space in the United States, which expire in April 2025. Rent expense under the Company’s operating leases was $0.1 million and $0.4 million during the three and nine months ended September 30, 2023. During the three and nine months ended September 30, 2022, rent expense under the Company’s operating leases was $0.1 million and $0.4 million, respectively. Rent expense includes short-term leases and variable lease costs that are not included in the lease obligation.

Short-term leases are leases having a term of twelve months or less. The Company recognizes short-term leases on a straight-line basis and does not record a related lease asset or liability for such leases.

The office space lease provides for increases in future minimum annual rental payments as defined in the lease agreements. The office space lease also includes an option to renew the lease as of the end of the term. The Company has determined that the lease renewal option is not reasonably certain of being exercised.

The cash paid for operating lease liabilities for each of the nine months ended September 30, 2023 and 2022 was $0.4 million.

Supplemental other information related to the operating leases balance sheet information is as follows (in thousands):



	September 30, 2023			December 31, 2022
Operating lease obligations (see Note 5 and 6)	$	788		$	1,124
Operating lease right-of-use assets (included in "Other assets" in Balance Sheet)	$	424		$	596
Weighted-average remaining lease term (years)		1.6			2.3
Weighted-average discount rate		7.2	%		7.2	%

Net Loss Per Share - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) - shares	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Common Stock Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	145,600	145,600
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	5,144,429	3,542,534
Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	618,543	470,275
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share		13,454

Other Long-Term Liabilities

9 Months Ended

Sep. 30, 2023

Other Long-Term Liabilities

Other Long-Term Liabilities

6. Other Long-Term Liabilities

The Company’s other long-term liabilities are summarized as follows (in thousands):


	September 30, 2023		December 31, 2022
Research and development incentive credit	$	3,796	$	3,599
Lease obligation, long-term portion (see Note 4)		303		672
Conditional economic incentive grants		160		250
Other		46		60
Total other long-term liabilities	$	4,305	$	4,581

Fair Value Measurements

9 Months Ended

Sep. 30, 2023

Fair Value Measurements

Fair Value Measurements

3. Fair Value Measurements

The Company’s assets measured at fair value on a recurring basis as of September 30, 2023 consisted of the following (in thousands):


	Fair Value Measurement at September 30, 2023
	Total		Level 1		Level 2		Level 3
Assets:
Cash equivalents - money market funds	$	82,102	$	82,102	$	—	$	—
Short-term investments		53,924		—		53,924		—
Total	$	136,026	$	82,102	$	53,924	$	—

The Company’s assets measured at fair value on a recurring basis as of December 31, 2022 consisted of the following (in thousands):


	Fair Value Measurement at December 31, 2022
	Total		Level 1		Level 2		Level 3
Assets:
Cash equivalents - money market funds	$	105,794	$	105,794	$	—	$	—
Short-term investments		73,783		—		73,783		—
Total	$	179,577	$	105,794	$	73,783	$	—

Short-term investments have been initially valued at the transaction price and subsequently valued at the end of each reporting period utilizing third party pricing services or other market observable data (Level 2). The pricing services utilize industry standard valuation models, including both income and market-based approaches and observable market inputs to determine value.

Short-term investments with quoted prices as of September 30, 2023 as shown below (in thousands):


	September 30, 2023
	Amortized Cost		Unrealized (Loss) Gain		Credit loss		Market Value
United States treasury securities	$	9,857	$	(7)	$	—	$	9,850
Commercial paper and corporate debt securities		33,328		(53)		—		33,275
Asset backed securities		2,937		(12)		—		2,925
Agency debt securities		7,886		(12)		—		7,874
Total	$	54,008	$	(84)	$	—	$	53,924

Short-term investments with quoted prices as of December 31, 2022 as shown below (in thousands):


	December 31, 2022
	Amortized Cost		Unrealized (Loss) Gain		Credit Loss		Market Value
United States treasury securities	$	15,868	$	(86)	$	—	$	15,782
Commercial paper and corporate debt securities		50,747		(71)		—		50,676
Asset backed securities		5,427		(35)		—		5,392
Agency debt securities		1,928		5		—		1,933
Total	$	73,970	$	(187)	$	—	$	73,783

Separate disclosure is required for assets and liabilities measured at fair value on a recurring basis from those measured at fair value on a non-recurring basis. Assets recorded at fair value on a non-recurring basis, such as property and equipment and intangible assets are recognized at fair value when they are impaired. During the nine months ended September 30, 2023 and year ended December 31, 2022, the Company had no significant assets or liabilities that were measured at fair value on a non-recurring basis.

- Definition

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

+ References + Details

Subsequent Events (Details) - $ / shares			1 Months Ended
Subsequent Events (Details) - $ / shares	Oct. 18, 2023	Jan. 24, 2022	Oct. 31, 2023	Sep. 30, 2023
Subsequent Event [Line Items]
Exercise price of warrants or rights				$ 0.66
Warrants outstanding				1,015,166
Pre-Funded Warrants
Subsequent Event [Line Items]
Shares of common stock sold		760,870
Warrants outstanding				869,566
Number of securities called by warrants or rights		760,870
Subsequent Event [Member] \| Pre-Funded Warrants
Subsequent Event [Line Items]
Shares of common stock sold	869,530
Warrants outstanding	0
Number of securities called by warrants or rights	869,566
Subsequent Event [Member] \| Other Warrants
Subsequent Event [Line Items]
Exercise price of warrants or rights			$ 5.31
Number of warrants expired unexercised			95,600
Subsequent Event [Member] \| Warrants Maturing on March 12, 2024
Subsequent Event [Line Items]
Exercise price of warrants or rights			$ 3.21
Warrants outstanding			50,000

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (56,806)	$ (63,053)
Adjustments to reconcile net loss to net cash used in operating activities:
Change in fair value of contingent consideration liability		86
Stock-based compensation expense	8,171	6,209
Depreciation and amortization	(1,413)	31
Loss on foreign currency exchange	(134)	(183)
Changes in operating assets and liabilities:
Accounts receivable	(704)	(204)
Prepaid expenses and other assets	(2,043)	3,204
Accounts payable	(1,758)	(615)
Accrued expenses and other liabilities	(3,306)	7,555
Income tax and R&D incentive receivables	(1,284)	1,690
Net cash used in operating activities	(59,277)	(45,280)
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from sales and maturities of short-term investments	76,544
Purchases of short-term investments	(54,806)	(74,292)
Purchases of property and equipment, net	(47)	(88)
Net cash provided by (used in) investing activities	21,691	(74,380)
CASH FLOWS FROM FINANCING ACTIVITIES:
Payments of deferred offering costs	(195)
Proceeds from issuance of common stock in at-the-market offerings, net	13,862	56,166
Proceeds from issuance of common stock from Employee Stock Purchase Plan	215	181
Payment of conditional economic incentive	(90)
Proceeds from exercises of stock options	61	868
Payment for tax withholding in share-based compensation	(502)	(391)
Net cash provided by financing activities	13,351	56,824
Net decrease in cash and cash equivalents and restricted cash	(24,235)	(62,836)
Cash, cash equivalents and restricted cash at beginning of period	111,131	190,335
Cash, cash equivalents and restricted cash at end of period	$ 86,896	127,499
SUPPLEMENTAL NON-CASH ACTIVITIES:
Fair value of common stock retired in exchange for issuance of common stock warrant		$ 6,176

Accrued Expenses

9 Months Ended

Sep. 30, 2023

Accrued Expenses and Other Current Liabilities.

Accrued Expenses

5. Accrued Expenses

Accrued expenses and other current liabilities consist of the following (in thousands):


	September 30, 2023		December 31, 2022
Accrued professional services	$	313	$	276
Accrued payroll and employee benefits		2,427		2,955
Accrued research and development		5,537		7,295
Lease obligation, current portion (see Note 4)		485		452
Excess tax refund payable		—		1,169
Accrued interest and other		63		103
Total accrued expenses and other current liabilities	$	8,825	$	12,250

Common Stock

9 Months Ended

Sep. 30, 2023

Common Stock

Common Stock

7. Common Stock

The Amended and Restated Certificate of Incorporation, as amended (“Charter”), authorizes the Company to issue 200,000,000 shares of common stock, par value $0.0001 per share. As of September 30, 2023, the Company had 52,858,920 shares of common stock issued and outstanding.

Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are not entitled to receive dividends, unless declared by the board of directors.

The Charter also authorizes the Company to issue 1,000,000 shares of preferred stock, par value $0.0001 per share. As of September 30, 2023, the Company had no shares of preferred stock issued and outstanding.

At-the-Market Offerings

On February 28, 2023, the Company entered into an Equity Distribution Agreement (the “2023 Agreement”) with Evercore Group L.L.C., JMP Securities LLC and B. Riley Securities, Inc., serving as sales agents (the “Sales Agents”), with respect to an at-the-market offerings program under which the Company may offer and sell, from time to time at its sole discretion, shares of its common stock, having an aggregate offering price of up to $150.0 million (the “Shares”) through the Sales Agents (the “2023 Offering”). All Shares offered and sold in the 2023 Offering will be issued pursuant to the Company’s Registration Statement on Form S-3ASR filed with the SEC on February 28, 2023, which was declared effective immediately, the prospectus supplement relating to the 2023 Offering filed with the SEC on February 28, 2023 and any applicable additional prospectus supplements related to the 2023 Offering that form a part of the Registration Statement. The Company capitalized approximately $0.2 million of other offering costs which will offset the proceeds received from the shares sold under the 2023 Agreement. During the nine months ended September 30, 2023, the Company sold 3,536,284 shares of common stock under the 2023 Agreement resulting in approximately $13.9 million in proceeds, net of $0.4 million commission and other offering costs. As of September 30, 2023, $135.7 million remained available to be sold under the 2023 Agreement. As of September 30, 2023, there was $0.2 million in deferred offering costs included in prepaid expenses and other current assets on the accompanying consolidated balance sheets.

On February 25, 2021, the Company entered into an Equity Distribution Agreement (the “2021 Agreement”) with Piper Sandler & Co., Evercore Group L.L.C. and B. Riley Securities, Inc., serving as sales agents (the “2021 Sales Agents”), with respect to an at-the-market offerings program under which the Company offered and sold shares of its common stock, having an aggregate offering price of up to $125.0 million (the “2021 Shares”) through the 2021 Sales Agents (the “2021 Offering”). All 2021 Shares offered and sold in the 2021 Offering were issued pursuant to the Company’s Registration Statement on Form S-3 filed with the SEC on December 31, 2020, which was declared effective on January 11, 2021, the prospectus supplement relating to the 2021 Offering filed with the SEC on February 25, 2021 and any applicable additional prospectus supplements related to the 2021 Offering that form a part of the Registration Statement. Under the 2021 Agreement, the Company sold 10,004,869 shares of common stock resulting in approximately $121.0 million in proceeds, net of $4.0 million commission and other offering costs. As of September 30, 2023, there were no remaining shares available under the 2021 Agreement.

Public Offering

On July 16, 2020, the Company offered and sold (i) 3,369,564 shares of common stock, at a price to the public of $23.00 per share, and (ii) pre-funded warrants of the Company to purchase 1,630,436 shares of common stock at an exercise price equal to $0.0001 per share (the “Pre-Funded Warrants”), at a price to the public of $22.9999 per share of common stock underlying the Pre-Funded Warrants (equal to the public offering price per share of common stock, minus the exercise price of each Pre-Funded Warrant). The Pre-Funded Warrants are exercisable at any time, provided that each Pre-Funded Warrant holder will be prohibited from exercising such Pre-Funded Warrants into shares of the Company’s common stock if, as a result of such exercise, the holder, together with its affiliates, would own more than 4.99% of the total number of shares of the Company’s common stock then issued and outstanding, which percentage may change at the holders’ election to any other number less than or equal to 19.99% upon 61 days’ notice to the Company.

The Company has assessed the Pre-Funded Warrants for appropriate equity or liability classification and determined that the Pre-Funded Warrants are freestanding instruments that do not meet the definition of a liability pursuant to ASC 480 and do not meet the definition of a derivative pursuant to FASB Accounting Standards Codification Topic 815, Derivatives and Hedging (“ASC 815”). The Pre-Funded Warrants are indexed to the Company’s common stock and meet all other conditions for equity classification under ASC 480 and ASC 815. Accordingly, the Pre-Funded Warrants were classified as equity and are accounted for as a component of additional paid-in capital at the time of issuance. On January 24, 2022, 760,870 of the Pre-Funded Warrants were exercised, resulting in the issuance of 760,870 shares of common stock. As of September 30, 2023, there were 869,566 remaining Pre-Funded Warrants unexercised. Subsequent to September 30, 2023, the remaining Pre-Funded Warrants were net cashless exercised, and currently no Pre-Funded Warrants remain available for exercise (see Note 11 Subsequent Events).

As of September 30, 2023, including the remaining 869,566 Pre-Funded Warrants, there were 1,015,166 outstanding warrants with a weighted-average exercise price of $0.66 and weighted-average contractual term of 0.2 years.

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2023	Dec. 31, 2022
CONSOLIDATED BALANCE SHEETS
Common stock, par or stated value per share	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	52,858,920	49,199,845
Common stock, shares outstanding	52,858,920	49,199,845

Operating Leases - Summary of Supplemental other Information Related to Operating Leases Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Leases
Operating lease obligations (see Note 5 and 6)	$ 788	$ 1,124
Operating lease right-of-use assets (included in "Other assets" in Balance Sheet)	$ 424	$ 596
Weighted-average remaining lease term (years)	1 year 7 months 6 days	2 years 3 months 18 days
Weighted-average discount rate	7.20%	7.20%

Common Stock - Additional Information (Detail) $ / shares in Units, $ in Thousands					1 Months Ended	3 Months Ended					9 Months Ended		22 Months Ended
	Oct. 18, 2023 shares	Jan. 24, 2022 shares	Feb. 25, 2021 USD ($)	Jul. 16, 2020 $ / shares shares	Feb. 28, 2023 USD ($)	Sep. 30, 2023 USD ($) item $ / shares shares	Jun. 30, 2023 shares	Sep. 30, 2022 shares	Jun. 30, 2022 shares	Mar. 31, 2022 shares	Sep. 30, 2023 USD ($) item $ / shares shares	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($) $ / shares shares
Changes In Equity And Comprehensive Income Line Items [Line Items]
Proceeds from issuance of common stock in public offering \| $											$ 13,862	$ 56,166
Common stock, shares authorized						200,000,000					200,000,000		200,000,000
Common stock, par or stated value per share \| $ / shares						$ 0.0001					$ 0.0001		$ 0.0001
Common stock, shares issued						52,858,920					52,858,920		49,199,845
Common stock, shares outstanding						52,858,920					52,858,920		49,199,845
Preferred stock, shares authorized						1,000,000					1,000,000
Preferred stock, par or stated value per share \| $ / shares						$ 0.0001					$ 0.0001
Preferred stock, shares issued						0					0
Preferred stock, shares outstanding						0					0
Warrants outstanding						1,015,166					1,015,166
Exercise price of warrants or rights \| $ / shares						$ 0.66					$ 0.66
Weighted average remaining contractual term, warrants											2 months 12 days
Pre-Funded Warrants [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Number of securities called by warrants or rights		760,870
Shares of common stock sold		760,870
Warrants outstanding						869,566					869,566
Pre-Funded Warrants [Member] \| Subsequent Event
Changes In Equity And Comprehensive Income Line Items [Line Items]
Number of securities called by warrants or rights	869,566
Shares of common stock sold	869,530
Warrants outstanding	0
Common Stock [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Voting right \| item						1					1
Shares of common stock sold						171,653	3,364,631	2,711,013	2,157,717	335,485
Public Offering [Member] \| Pre-Funded Warrants [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Purchase price of warrants issued \| $ / shares				$ 22.9999
Ownership percentage on exercise of warrants without notice, minimum				4.99%
Ownership percentage on exercise of warrants with notice, maximum				19.99%
Notice period to increase ownership percentage on exercise of warrants				61 days
Number of securities called by warrants or rights				1,630,436
Exercise price of warrants or rights \| $ / shares				$ 0.0001
Public Offering [Member] \| Common Stock [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Public offering price, per share \| $ / shares				$ 23.00
Shares of common stock sold				3,369,564
At-The-Market Offering [Member] \| Equity Distribution Agreement [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Remaining shares available for issuance						0					0
At-The-Market Offering [Member] \| Equity Distribution Agreement [Member] \| Evercore Group and JMP Securities LLC and B Riley Securities [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Common stock available to be sold \| $						$ 135,700					$ 135,700
Deferred Offering Costs \| $					$ 200	$ 200					200
Proceeds from issuance of common stock in public offering \| $											$ 13,900
Aggregate offering price \| $					$ 150,000
Shares of common stock sold											3,536,284
Issuance costs \| $											$ 400
At-The-Market Offering [Member] \| Equity Distribution Agreement [Member] \| Piper Sandler company and Evercore group limited liability company and B Riley Securities inc [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Proceeds from issuance of common stock in public offering \| $													$ 121,000
Aggregate offering price \| $			$ 125,000
Shares of common stock sold													10,004,869
Issuance costs \| $													$ 4,000

Nature of Business and Organization

9 Months Ended

Sep. 30, 2023

Nature of Business and Organization

Nature of Business and Organization

1. Nature of Business and Basis of Presentation

Nature of Business

Altimmune, Inc., headquartered in Gaithersburg, Maryland, United States, together with its subsidiaries (collectively, the “Company” or “Altimmune”) is a clinical stage biopharmaceutical company incorporated under the laws of the State of Delaware.

The Company is focused on developing treatments for obesity and liver diseases. The Company’s pipeline includes next generation peptide therapeutics for obesity and non-alcoholic steatohepatitis (“NASH”) (for both, pemvidutide, formerly known as ALT-801), and for chronic hepatitis B (“HepTcell^TM”). Since its inception, the Company has devoted substantially all of its efforts to business planning, research and development, recruiting management and technical staff and raising capital, and has financed its operations through the issuance of common and preferred stock, long-term debt and proceeds from research grants and government contracts. The Company has not generated any revenues from the sale of any products to date, and there is no assurance of any future revenues from product sales.

Basis of Presentation

The accompanying unaudited consolidated financial statements are prepared pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Accordingly, they do not include all of the information and disclosures required by accounting principles generally accepted in the United States (“U.S. GAAP”) for complete consolidated financial statements and should be read in conjunction with the audited consolidated financial statements for the year ended December 31, 2022 included in the Annual Report on Form 10-K which was filed with the SEC on February 28, 2023. In the opinion of management, the Company has prepared the accompanying unaudited consolidated financial statements on the same basis as the audited consolidated financial statements, and these consolidated financial statements include all adjustments, consisting only of normal recurring adjustments, necessary for a fair presentation of the results of the interim periods presented. The operating results for the interim periods presented are not necessarily indicative of the results expected for the full year 2023 or any future years or periods.

The accompanying unaudited consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All significant intercompany accounts and transactions have been eliminated in consolidation.

The accompanying unaudited consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets, and the satisfaction of liabilities in the ordinary course of business. The financial statements do not include any adjustments relating to the recoverability and classification of recorded assets and liabilities that might be necessary should the Company be unable to continue as a going concern.

Commitments and Contingencies

9 Months Ended

Sep. 30, 2023

Commitments And Contingencies.

Commitments and Contingencies

10. Commitments and Contingencies

Spitfire Acquisition

In July 2019, the Company entered into the Spitfire merger agreement to acquire all of the equity interests of Spitfire Pharma, Inc. (“Spitfire”). As part of the agreement, the Company is obligated to make payments of up to $80.0 million upon the achievement of specified worldwide net sales of all products developed using the technology acquired from Spitfire Pharma Inc. (the “Sales Milestone”) within ten years following the approval of a new drug application filed with the U. S. Food and Drug Administration (the “FDA”).

The contingent payments related to the Sales Milestones are predominately cash-based payments accounted for under FASB Accounting Standards Codification Topic 450, Contingencies. Accordingly, the Company will recognize the Sales Milestones when the contingency is probable and the amount can be reasonably estimated.

Litigation

The Company is a party in various contracts and subject to disputes, litigation, and potential claims arising in the ordinary course of business none of which are currently reasonably possible or probable of material loss.

Accrued Expenses - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Accrued Liabilities And Other Liabilities [Abstract]
Accrued professional services	$ 313	$ 276
Accrued payroll and employee benefits	2,427	2,955
Accrued research and development	5,537	7,295
Lease obligation, current portion (see Note 4)	485	452
Excess tax refund payable		1,169
Accrued interest and other	63	103
Total accrued expenses and other current liabilities	$ 8,825	$ 12,250

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Employees purchased, value	$ 80		$ 135	$ 68		$ 113
Stock-based compensation expense							$ 8,171	$ 6,209
Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Stock Options, Granted							1,760,026
Stock options granted, weighted-average exercise price							$ 9.71
Stock option expiration Period							10 years
Weighted-average grant date fair value of stock options granted							$ 7.86
Unrecognized compensation cost, stock options	$ 17,900						$ 17,900
Unrecognized stock-based compensation expense, period for recognition							2 years 8 months 12 days
Restricted stock vesting period							4 years
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation expense, period for recognition							2 years 8 months 12 days
Restricted stock authorized and granted							319,700
Weighted average grant date fair value of restricted stock award							$ 13.20
Unrestricted common stock							61,928
Number of shares vested							100,642
Common stock withheld to satisfy tax withholding obligations.							38,714
Unvested restricted stock, shares	618,543						618,543
Unrecognized compensation expense	$ 5,100						$ 5,100
Restricted stock vesting period							4 years
Common Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrestricted common stock	1,261	6,320	54,347	(7,744)	(5,865)	17,568
Employees purchased, shares	28,345		13,215	9,945		16,450
2019 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Employees purchased, shares							41,560
Employees purchased, value							$ 200
Stock-based compensation expense							$ 100	$ 200

Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2023	Nov. 03, 2023
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Trading Symbol	ALT
Entity Registrant Name	ALTIMMUNE, INC.
Entity Central Index Key	0001326190
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		53,728,871
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common stock, par value $0.0001 per share
Security Exchange Name	NASDAQ
Entity File Number	001-32587
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-2726770
Entity Address, Address Line One	910 Clopper Road
Entity Address, Address Line Two	Suite 201S
Entity Address, City or Town	Gaithersburg
Entity Address, State or Province	MD
Entity Address, Postal Zip Code	20878
City Area Code	240
Local Phone Number	654-1450
Document Transition Report	false

Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2023

Stock-Based Compensation

Schedule of Information Related to Stock Options Outstanding

Information related to stock options outstanding as of September 30, 2023 is as follows:


				Weighted-Average
		Weighted-		Remaining
	Number of	Average		Contractual Term	Aggregate Intrinsic
	Stock Options	Exercise Price		(Years)	Value (In thousands)
Outstanding	5,079,329	$	9.31	5.9	$	239
Exercisable	2,260,984	$	8.81	5.8	$	200
Vested and expected to vest	4,769,311	$	9.28	5.9	$	235

Schedule of Stock-based Compensation Expense

Stock-based compensation expense is classified in the unaudited consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2023 and 2022 as follows (in thousands):


	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2023		2022		2023		2022
Research and development	$	1,164	$	743	$	3,560	$	2,024
General and administrative		1,546		1,385		4,611		4,185
Total	$	2,710	$	2,128	$	8,171	$	6,209

Commitments and Contingencies - Additional Information (Details) - Spitfire Pharma, Inc. [Member] - Sales Milestones [Member] $ in Millions	Jul. 12, 2019 USD ($)
Commitments And Contingencies [Line Items]
Estimated future contingent consideration	$ 80.0
License agreement term	10 years

Subsequent Events

9 Months Ended

Sep. 30, 2023

Subsequent Events

Subsequent Events

11. Subsequent Events

On October 18, 2023, warrant holders exercised the remaining 869,566 Pre-Funded Warrants in a net cashless exercise and were issued 869,530 shares of common stock in a net cashless exercise (see Note 7 Common Stock).

In addition, in October 2023, 95,600 various other warrants with a weighted-average exercise price of $5.31 expired unexercised. The only remaining outstanding 50,000 warrants have an exercise price of $3.21 and have a maturity date of March 12, 2024.

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2023

Fair Value Measurements

Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis

The Company’s assets measured at fair value on a recurring basis as of September 30, 2023 consisted of the following (in thousands):


	Fair Value Measurement at September 30, 2023
	Total		Level 1		Level 2		Level 3
Assets:
Cash equivalents - money market funds	$	82,102	$	82,102	$	—	$	—
Short-term investments		53,924		—		53,924		—
Total	$	136,026	$	82,102	$	53,924	$	—

The Company’s assets measured at fair value on a recurring basis as of December 31, 2022 consisted of the following (in thousands):


	Fair Value Measurement at December 31, 2022
	Total		Level 1		Level 2		Level 3
Assets:
Cash equivalents - money market funds	$	105,794	$	105,794	$	—	$	—
Short-term investments		73,783		—		73,783		—
Total	$	179,577	$	105,794	$	73,783	$	—

Schedule of Short Term Investments

Short-term investments with quoted prices as of September 30, 2023 as shown below (in thousands):


	September 30, 2023
	Amortized Cost		Unrealized (Loss) Gain		Credit loss		Market Value
United States treasury securities	$	9,857	$	(7)	$	—	$	9,850
Commercial paper and corporate debt securities		33,328		(53)		—		33,275
Asset backed securities		2,937		(12)		—		2,925
Agency debt securities		7,886		(12)		—		7,874
Total	$	54,008	$	(84)	$	—	$	53,924

Short-term investments with quoted prices as of December 31, 2022 as shown below (in thousands):


	December 31, 2022
	Amortized Cost		Unrealized (Loss) Gain		Credit Loss		Market Value
United States treasury securities	$	15,868	$	(86)	$	—	$	15,782
Commercial paper and corporate debt securities		50,747		(71)		—		50,676
Asset backed securities		5,427		(35)		—		5,392
Agency debt securities		1,928		5		—		1,933
Total	$	73,970	$	(187)	$	—	$	73,783

Other Long-Term Liabilities - Summary of Other Long-Term Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Other Long-Term Liabilities
Research and development incentive credit	$ 3,796	$ 3,599
Lease obligation, long-term portion (see Note 4)	303	672
Conditional economic incentive grants	160	250
Other	46	60
Total other long-term liabilities	$ 4,305	$ 4,581

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2022
Summary of Significant Accounting Policies
Income tax expense (benefit)	$ 197	$ 197

- Definition

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

+ References + Details

Fair Value Measurements - Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 53,924	$ 73,783
Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments		73,783
Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	53,924
Total	136,026	179,577
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	82,102	105,794
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	53,924
Total	53,924	73,783
Money Market Funds [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	82,102	105,794
Money Market Funds [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	$ 82,102	$ 105,794

Net Loss Per Share

9 Months Ended

Sep. 30, 2023

Net Loss Per Share

Net Loss Per Share

9. Net Loss Per Share

Because the Company has reported a net loss attributable to common stockholders for the nine months ended September 30, 2023 and 2022, basic and diluted net loss per share attributable to common stockholders in each period are the same.

Basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted average numbers of shares of common stock outstanding for the period. Basic

shares outstanding includes the weighted average effect of the Company’s outstanding pre-funded warrants, the exercise of which requires little or no consideration for the delivery of shares of common stock.

Diluted net loss per share is calculated by adjusting weighted average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period. As such, all unvested restricted stock, RSUs, common stock warrants, and stock options have been excluded from the computation of diluted weighted average shares outstanding because such securities would have an anti-dilutive impact for all periods presented.

Potential common shares issuable upon conversion, vesting or exercise of unvested restricted stock, RSUs, common stock warrants, and stock options that are excluded from the computation of diluted weighted-average shares outstanding, as they are anti-dilutive, are as follows:


	Nine Months Ended
	September 30,
	2023	2022
Common stock warrants	145,600	145,600
Common stock options	5,144,429	3,542,534
Restricted stock units	618,543	470,275
Restricted stock	—	13,454

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2023

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

During the nine months ended September 30, 2023, there have been no significant changes to the Company’s summary of significant accounting policies contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2022 as filed with the SEC, except for the recently adopted accounting standard for ASU No. 2016-13 as disclosed below.

Use of Estimates

The preparation of these financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Significant estimates and assumptions made in the accompanying condensed consolidated financial statements include, but are not

limited to, the valuation of share-based awards, income taxes, and accruals for research and development activities. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable. However, actual results could differ from those estimates and there may be changes to the Company’s estimates in future periods.

Short-term Investments

The Company’s short-term investments are comprised of U.S. Treasuries, corporate debt securities and certificates of deposit that have original maturities less than or equal to one year and are classified as available-for-sale (“AFS”) securities. Such securities are carried at estimated fair value, net of allowance for credit loss determined based on the Current Expected Credit Loss. Any unrealized holding gains or losses are reported as accumulated other comprehensive income or loss, which is a separate component of stockholders’ equity. In the event that the AFS security's fair value is below the amortized cost and (i) the Company intends to sell the AFS security and (ii) the AFS security is required to be sold before recovery of the loss, the AFS security's amortized cost base will be written down to its fair value and the loss will be recognized in the income statement. If the Company intends not to sell the AFS security and the AFS security is not required to be sold before recovery of the loss, the Company evaluates whether a portion of the unrealized loss is a result of credit loss. The portion of unrealized loss related to credit loss will be recorded as allowance for credit loss in the balance sheet with the corresponding credit loss in the income statement and the portion of unrealized loss not related to credit loss will be recognized in other comprehensive income (“OCI”). Dividend and interest income are recognized in other income when earned. The cost of securities sold is calculated using the specific identification method. The Company places all investments with government agencies, or corporate institutions whose debt is rated as investment grade. As of September 30, 2023, none of the unrealized losses on the Company’s short-term investments are a result of credit loss, and therefore, the unrealized losses were recognized in OCI.

Income Taxes

During the three and nine months ended September 30, 2022, the Company recorded a total of $0.2 million income tax benefit related to interest received and receivable on income tax refunds. Other than the tax benefit related to interest, the Company did not record an income tax expense (benefit) for either of the three and nine months ended September 30, 2023 or 2022 due to a full valuation allowance. The Company calculates its quarterly income tax provision based on an estimated, annual effective tax rate applied to ordinary income (or loss) and other known items computed and recognized as they occur. The Company’s total provision is based on the United States statutory rate, increased by state and foreign taxes and reduced by a full valuation allowance on the Company’s deferred tax assets.

Recently adopted accounting pronouncements

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU No. 2016-13”). ASU No. 2016-13 requires financial assets measured at amortized cost to be presented at the net amount expected to be collected and any unrealized loss relating to available-for-sale debt securities to be recorded through an allowance for credit losses. The Company adopted this new accounting standard on January 1, 2023 using a modified retrospective method. Adoption of this update did not have a material impact on the Company’s financial statements and related disclosures.

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 86,855	$ 111,097
Restricted cash	41	34
Total cash, cash equivalents and restricted cash	86,896	111,131
Short-term investments	53,924	73,783
Accounts receivable	876	173
Income tax and R&D incentive receivables	3,653	2,368
Prepaid expenses and other current assets	7,615	5,358
Total current assets	152,964	192,813
Property and equipment, net	765	1,081
Indefinite-lived intangible asset	12,419	12,419
Other assets	425	615
Total assets	166,573	206,928
Current liabilities:
Accounts payable	3,046	4,804
Accrued expenses and other current liabilities	8,825	12,250
Total current liabilities	11,871	17,054
Other long-term liabilities	4,305	4,581
Total liabilities	16,176	21,635
Commitments and contingencies (Note 10)
Stockholders' equity:
Common stock, $0.0001 par value; 200,000,000 shares authorized; 52,858,920 and 49,199,845 shares issued and outstanding as of September 30, 2023 and December 31, 2022, respectively	5	5
Additional paid-in capital	590,206	568,399
Accumulated deficit	(434,690)	(377,884)
Accumulated other comprehensive loss, net	(5,124)	(5,227)
Total stockholders' equity	150,397	185,293
Total liabilities and stockholders' equity	$ 166,573	$ 206,928

Accrued Expenses (Tables)

9 Months Ended

Sep. 30, 2023

Accrued Expenses and Other Current Liabilities.

Schedule of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consist of the following (in thousands):


	September 30, 2023		December 31, 2022
Accrued professional services	$	313	$	276
Accrued payroll and employee benefits		2,427		2,955
Accrued research and development		5,537		7,295
Lease obligation, current portion (see Note 4)		485		452
Excess tax refund payable		—		1,169
Accrued interest and other		63		103
Total accrued expenses and other current liabilities	$	8,825	$	12,250

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]	Total
Beginning Balance at Dec. 31, 2021	$ 4	$ 497,342	$ (293,171)	$ (5,040)	$ 199,135
Beginning Balance (in shares) at Dec. 31, 2021	40,993,768
Stock-based compensation		2,033			2,033
Exercise of stock options		197			197
Exercise of stock options (in shares)	95,771
Vesting of restricted stock awards including withholding, net		(170)			(170)
Vesting of restricted stock awards including withholding, net (in shares)	17,568
Issuance of common stock from Employee Stock Purchase Plan		113			113
Issuance of common stock from Employee Stock Purchase Plan (in shares)	16,450
Issuance of common stock in at the market offerings, net		2,990			2,990
Issuance of common stock in at the market offerings, net (in shares)	335,485
Issuance of common stock upon exercise of warrants (in shares)	1,760,854
Net loss			(19,430)		(19,430)
Ending Balance at Mar. 31, 2022	$ 4	502,505	(312,601)	(5,040)	184,868
Ending Balance (in shares) at Mar. 31, 2022	43,219,896
Beginning Balance at Dec. 31, 2021	$ 4	497,342	(293,171)	(5,040)	199,135
Beginning Balance (in shares) at Dec. 31, 2021	40,993,768
Unrealized (loss) gain on short-term investments					(263)
Net loss					(63,053)
Ending Balance at Sep. 30, 2022	$ 5	566,551	(356,224)	(5,303)	205,029
Ending Balance (in shares) at Sep. 30, 2022	49,161,637
Beginning Balance at Mar. 31, 2022	$ 4	502,505	(312,601)	(5,040)	184,868
Beginning Balance (in shares) at Mar. 31, 2022	43,219,896
Stock-based compensation		2,048			2,048
Exercise of stock options		403			403
Exercise of stock options (in shares)	152,913
Vesting of restricted stock awards including withholding, net		(80)			(80)
Vesting of restricted stock awards including withholding, net (in shares)	(5,865)
Issuance of common stock in at the market offerings, net	$ 1	21,346			21,347
Issuance of common stock in at the market offerings, net (in shares)	2,157,717
Issuance of common stock related to contingent consideration liability		6,176			6,176
Issuance of common stock related to contingent consideration liability (in shares)	847,444
Unrealized (loss) gain on short-term investments				(120)	(120)
Net loss			(20,107)		(20,107)
Ending Balance at Jun. 30, 2022	$ 5	532,398	(332,708)	(5,160)	194,535
Ending Balance (in shares) at Jun. 30, 2022	46,372,105
Stock-based compensation		2,128			2,128
Exercise of stock options		268			268
Exercise of stock options (in shares)	76,161
Vesting of restricted stock awards including withholding, net		(140)			(140)
Vesting of restricted stock awards including withholding, net (in shares)	(7,744)
Issuance of common stock from Employee Stock Purchase Plan		68			68
Issuance of common stock from Employee Stock Purchase Plan (in shares)	9,945
Issuance of common stock in at the market offerings, net		31,829			31,829
Issuance of common stock in at the market offerings, net (in shares)	2,711,013
Other increase (in shares)	157
Unrealized (loss) gain on short-term investments				(143)	(143)
Net loss			(23,516)		(23,516)
Ending Balance at Sep. 30, 2022	$ 5	566,551	(356,224)	(5,303)	205,029
Ending Balance (in shares) at Sep. 30, 2022	49,161,637
Beginning Balance at Dec. 31, 2022	$ 5	568,399	(377,884)	(5,227)	185,293
Beginning Balance (in shares) at Dec. 31, 2022	49,199,845
Stock-based compensation		2,675			2,675
Exercise of stock options		61			61
Exercise of stock options (in shares)	19,303
Vesting of restricted stock awards including withholding, net		(484)			(484)
Vesting of restricted stock awards including withholding, net (in shares)	54,347
Issuance of common stock from Employee Stock Purchase Plan		135			135
Issuance of common stock from Employee Stock Purchase Plan (in shares)	13,215
Unrealized (loss) gain on short-term investments				126	126
Net loss			(20,074)		(20,074)
Ending Balance at Mar. 31, 2023	$ 5	570,786	(397,958)	(5,101)	167,732
Ending Balance (in shares) at Mar. 31, 2023	49,286,710
Beginning Balance at Dec. 31, 2022	$ 5	568,399	(377,884)	(5,227)	185,293
Beginning Balance (in shares) at Dec. 31, 2022	49,199,845
Unrealized (loss) gain on short-term investments					103
Net loss					(56,806)
Ending Balance at Sep. 30, 2023	$ 5	590,206	(434,690)	(5,124)	150,397
Ending Balance (in shares) at Sep. 30, 2023	52,858,920
Beginning Balance at Mar. 31, 2023	$ 5	570,786	(397,958)	(5,101)	167,732
Beginning Balance (in shares) at Mar. 31, 2023	49,286,710
Stock-based compensation		2,786			2,786
Vesting of restricted stock awards including withholding, net		(16)			(16)
Vesting of restricted stock awards including withholding, net (in shares)	6,320
Issuance of common stock in at the market offerings, net		13,352			13,352
Issuance of common stock in at the market offerings, net (in shares)	3,364,631
Unrealized (loss) gain on short-term investments				(79)	(79)
Net loss			(16,061)		(16,061)
Ending Balance at Jun. 30, 2023	$ 5	586,908	(414,019)	(5,180)	167,714
Ending Balance (in shares) at Jun. 30, 2023	52,657,661
Stock-based compensation		2,710			2,710
Vesting of restricted stock awards including withholding, net		(2)			(2)
Vesting of restricted stock awards including withholding, net (in shares)	1,261
Issuance of common stock from Employee Stock Purchase Plan		80			80
Issuance of common stock from Employee Stock Purchase Plan (in shares)	28,345
Issuance of common stock in at the market offerings, net		510			510
Issuance of common stock in at the market offerings, net (in shares)	171,653
Unrealized (loss) gain on short-term investments				56	56
Net loss			(20,671)		(20,671)
Ending Balance at Sep. 30, 2023	$ 5	$ 590,206	$ (434,690)	$ (5,124)	$ 150,397
Ending Balance (in shares) at Sep. 30, 2023	52,858,920

Operating Leases (Tables)

9 Months Ended

Sep. 30, 2023

Leases

Summary of Supplemental other Information Related to Operating Leases Balance Sheet

Supplemental other information related to the operating leases balance sheet information is as follows (in thousands):



	September 30, 2023			December 31, 2022
Operating lease obligations (see Note 5 and 6)	$	788		$	1,124
Operating lease right-of-use assets (included in "Other assets" in Balance Sheet)	$	424		$	596
Weighted-average remaining lease term (years)		1.6			2.3
Weighted-average discount rate		7.2	%		7.2	%

Other Long-Term Liabilities (Tables)

9 Months Ended

Sep. 30, 2023

Other Long-Term Liabilities

Summary of Other Long-Term Liabilities

The Company’s other long-term liabilities are summarized as follows (in thousands):


	September 30, 2023		December 31, 2022
Research and development incentive credit	$	3,796	$	3,599
Lease obligation, long-term portion (see Note 4)		303		672
Conditional economic incentive grants		160		250
Other		46		60
Total other long-term liabilities	$	4,305	$	4,581

Operating Leases - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Leases
Cash paid for operating lease liabilities			$ 0.4	$ 0.4
Operating lease rent expense	$ 0.1	$ 0.1	$ 0.4	$ 0.4

Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2023
Summary of Significant Accounting Policies
Use of Estimates	Use of Estimates The preparation of these financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Significant estimates and assumptions made in the accompanying condensed consolidated financial statements include, but are not limited to, the valuation of share-based awards, income taxes, and accruals for research and development activities. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable. However, actual results could differ from those estimates and there may be changes to the Company’s estimates in future periods.
Short-term Investments	Short-term Investments The Company’s short-term investments are comprised of U.S. Treasuries, corporate debt securities and certificates of deposit that have original maturities less than or equal to one year and are classified as available-for-sale (“AFS”) securities. Such securities are carried at estimated fair value, net of allowance for credit loss determined based on the Current Expected Credit Loss. Any unrealized holding gains or losses are reported as accumulated other comprehensive income or loss, which is a separate component of stockholders’ equity. In the event that the AFS security's fair value is below the amortized cost and (i) the Company intends to sell the AFS security and (ii) the AFS security is required to be sold before recovery of the loss, the AFS security's amortized cost base will be written down to its fair value and the loss will be recognized in the income statement. If the Company intends not to sell the AFS security and the AFS security is not required to be sold before recovery of the loss, the Company evaluates whether a portion of the unrealized loss is a result of credit loss. The portion of unrealized loss related to credit loss will be recorded as allowance for credit loss in the balance sheet with the corresponding credit loss in the income statement and the portion of unrealized loss not related to credit loss will be recognized in other comprehensive income (“OCI”). Dividend and interest income are recognized in other income when earned. The cost of securities sold is calculated using the specific identification method. The Company places all investments with government agencies, or corporate institutions whose debt is rated as investment grade. As of September 30, 2023, none of the unrealized losses on the Company’s short-term investments are a result of credit loss, and therefore, the unrealized losses were recognized in OCI.
Income Taxes	Income Taxes During the three and nine months ended September 30, 2022, the Company recorded a total of $0.2 million income tax benefit related to interest received and receivable on income tax refunds. Other than the tax benefit related to interest, the Company did not record an income tax expense (benefit) for either of the three and nine months ended September 30, 2023 or 2022 due to a full valuation allowance. The Company calculates its quarterly income tax provision based on an estimated, annual effective tax rate applied to ordinary income (or loss) and other known items computed and recognized as they occur. The Company’s total provision is based on the United States statutory rate, increased by state and foreign taxes and reduced by a full valuation allowance on the Company’s deferred tax assets.
Recently Adopted Accounting Pronouncements	Recently adopted accounting pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU No. 2016-13”). ASU No. 2016-13 requires financial assets measured at amortized cost to be presented at the net amount expected to be collected and any unrealized loss relating to available-for-sale debt securities to be recorded through an allowance for credit losses. The Company adopted this new accounting standard on January 1, 2023 using a modified retrospective method. Adoption of this update did not have a material impact on the Company’s financial statements and related disclosures.

- Definition

Disclosure of accounting policy for income taxes, which may include its accounting policies for recognizing and measuring deferred tax assets and liabilities and related valuation allowances, recognizing investment tax credits, operating loss carryforwards, tax credit carryforwards, and other carryforwards, methodologies for determining its effective income tax rate and the characterization of interest and penalties in the financial statements.

+ References + Details

- Definition

Disclosure of accounting policy for investment in financial asset.

+ References + Details

Fair Value Measurements - Schedule of Short Term Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 54,008	$ 73,970
Unrealized (Loss) Gain	(84)	(187)
Market Value	53,924	73,783
United States Treasury Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	9,857	15,868
Unrealized (Loss) Gain	(7)	(86)
Market Value	9,850	15,782
Commercial Paper and Corporate Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	33,328	50,747
Unrealized (Loss) Gain	(53)	(71)
Market Value	33,275	50,676
Asset Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	2,937	5,427
Unrealized (Loss) Gain	(12)	(35)
Market Value	2,925	5,392
Agency Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	7,886	1,928
Unrealized (Loss) Gain	(12)	5
Market Value	$ 7,874	$ 1,933

- 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aa)
-Publisher FASB
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-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

+ Details

Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Fair Value Measurements
Assets or liabilities measured at fair value on a non-recurring basis.	$ 0	$ 0

Stock-Based Compensation - Schedule of Stock-based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock based compensation expense	$ 2,710	$ 2,128	$ 8,171	$ 6,209
Research and Development [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock based compensation expense	1,164	743	3,560	2,024
General and Administrative [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock based compensation expense	$ 1,546	$ 1,385	$ 4,611	$ 4,185

Net Loss Per Share (Tables)

9 Months Ended

Sep. 30, 2023

Net Loss Per Share

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share


	Nine Months Ended
	September 30,
	2023	2022
Common stock warrants	145,600	145,600
Common stock options	5,144,429	3,542,534
Restricted stock units	618,543	470,275
Restricted stock	—	13,454

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
CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS
Revenues	$ 362	$ 2	$ 389	$ 42
Operating expenses:
Research and development	18,388	20,262	48,890	51,359
General and administrative	4,514	4,492	13,805	13,329
Total operating expenses	22,902	24,754	62,695	64,688
Loss from operations	(22,540)	(24,752)	(62,306)	(64,646)
Other income (expense):
Interest expense	(29)	(64)	(33)	(191)
Interest income	1,884	1,053	5,387	1,402
Other income (expense), net	14	50	146	185
Total other income (expense), net	1,869	1,039	5,500	1,396
Net loss before income taxes	(20,671)	(23,713)	(56,806)	(63,250)
Income tax expense (benefit)		(197)		(197)
Net loss	(20,671)	(23,516)	(56,806)	(63,053)
Other comprehensive income - unrealized gain (loss) on short-term investments	56	(143)	103	(263)
Comprehensive loss	$ (20,615)	$ (23,659)	$ (56,703)	$ (63,316)
Net loss per share, basic	$ (0.39)	$ (0.48)	$ (1.10)	$ (1.37)
Net loss per share, diluted	$ (0.39)	$ (0.48)	$ (1.10)	$ (1.37)
Weighted-average common shares outstanding, basic	53,633,354	49,286,535	51,495,957	45,881,547
Weighted-average common shares outstanding, diluted	53,633,354	49,286,535	51,495,957	45,881,547

Stock-Based Compensation

9 Months Ended

Sep. 30, 2023

Stock-Based Compensation

Stock-Based Compensation

8. Stock-Based Compensation

Stock Options

The Company’s stock option awards generally vest over four years and typically have a contractual life of ten years. As of September 30, 2023, there was $17.9 million of unrecognized compensation cost related to stock options, which is expected to be recognized over a weighted-average period of 2.7 years. During the nine months ended September 30, 2023, the Company granted 1,760,026 stock options with a weighted average exercise price of $9.71 and per share weighted average grant date fair value of $7.86.

Information related to stock options outstanding as of September 30, 2023 is as follows:


				Weighted-Average
		Weighted-		Remaining
	Number of	Average		Contractual Term	Aggregate Intrinsic
	Stock Options	Exercise Price		(Years)	Value (In thousands)
Outstanding	5,079,329	$	9.31	5.9	$	239
Exercisable	2,260,984	$	8.81	5.8	$	200
Vested and expected to vest	4,769,311	$	9.28	5.9	$	235

Restricted Stock Units (RSUs)

During the nine months ended September 30, 2023, the Company granted 319,700 shares of RSUs with a weighted average grant date fair value of $13.20 which vest over four years. As of September 30, 2023, the Company had unvested RSUs of 618,543 shares with total unrecognized compensation expense of $5.1 million, which the Company expects to recognize over a weighted average period of approximately 2.7 years. During the nine months ended September 30, 2023, the Company issued 61,928 shares of unrestricted common stock as a result of the vesting of 100,642 RSUs net of 38,714 shares of common stock withheld to satisfy tax withholding obligations.

2019 Employee Stock Purchase Plan (ESPP)

Under the ESPP, employees purchased 41,560 shares for $0.2 million during the nine months ended September 30, 2023. During the nine months ended September 30, 2023 and 2022, the Company recognized compensation expense of $0.1 million and $0.2 million, respectively.

Stock-based Compensation Expense


	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2023		2022		2023		2022
Research and development	$	1,164	$	743	$	3,560	$	2,024
General and administrative		1,546		1,385		4,611		4,185
Total	$	2,710	$	2,128	$	8,171	$	6,209

Stock-Based Compensation - Schedule of Information Related to Stock Options Outstanding (Detail) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($) $ / shares shares
Stock-Based Compensation
Number of Stock Options, Outstanding \| shares	5,079,329
Number of Stock Options, Exercisable \| shares	2,260,984
Number of Stock Options, Vested and expected to vest \| shares	4,769,311
Weighted-average Exercise Price, Outstanding \| $ / shares	$ 9.31
Weighted-average Exercise Price, Exercisable \| $ / shares	8.81
Weighted-average Exercise Price, Vested and expected to vest \| $ / shares	$ 9.28
Weighted-average Remaining Contractual Term, Outstanding	5 years 10 months 24 days
Weighted-average Remaining Contractual Term, Exercisable	5 years 9 months 18 days
Weighted-average Remaining Contractual Term, Vested and expected to vest	5 years 10 months 24 days
Aggregate Intrinsic Value, Outstanding \| $	$ 239
Aggregate Intrinsic Value, Exercisable \| $	200
Aggregate Intrinsic Value, Vested and expected to vest \| $	$ 235