0000950170-24-056997 | 10-Q | XBRL Viewer

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Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Prepaid expenses and other current assets	$ 8,355	$ 7,195
Accounts payable	2,980	7,461
Accrued expenses	$ 19,143	$ 18,553
Preferred stock par value	$ 0.0001	$ 0.0001
Preferred stock shares authorized	50,000,000	50,000,000
Preferred stock shares issued	0	0
Preferred stock shares outstanding	0	0
Common stock par value	$ 0.0001	$ 0.0001
Common stock shares authorized	500,000,000	500,000,000
Common stock shares issued	49,718,443	48,497,853
Common stock shares outstanding	49,055,192	47,666,438
Related party
Accrued expenses	$ 27	$ 33

Marketable Securities

3 Months Ended

Mar. 31, 2024

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

4. Marketable Securities

The following tables present the fair value of available-for-sale marketable debt securities by type of security as follows (in thousands):


	March 31, 2024
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Marketable securities:
U.S. treasury notes	$	84,318	$	1	$	(76	)	$	84,243
U.S. government agency bonds		47,476		—		(52	)		47,424
Total	$	131,794	$	1	$	(128	)	$	131,667


	December 31, 2023
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Marketable securities:
U.S. treasury notes	$	43,036	$	16	$	(2	)	$	43,050
U.S. government agency bonds		43,775		4		(24	)		43,755
Total	$	86,811	$	20	$	(26	)	$	86,805

At March 31, 2024 and December 31, 2023, all available-for-sale marketable securities had contractual maturities of less than one year.

As of March 31, 2024, the Company reviewed its investment portfolio to assess the unrealized losses on its available-for-sale investments. In making this assessment, the Company considered the extent to which fair value is less than amortized cost, any changes to the rating of the security by a rating agency, and adverse conditions specifically related to the security, among other factors. The Company also evaluated whether it intended to sell the security and whether it was more likely than not that the Company would be required to sell the security before recovering its amortized cost basis. The Company determined no portion of the unrealized losses relate to a credit loss. There have been no impairments of the Company’s assets measured and carried at fair value during the three months ended March 31, 2024.

Subsequent Event - Additional Information (Details)	Jun. 15, 2023 USD ($)
Term Loan 1 Borrowing January 1, 2024 through July 19, 2024 \| Term Loan 1 \| Loan Agreement \| Maximum
Subsequent Event [Line Items]
Debt instrument, available credit under loan agreement	$ 15,000,000

Long-Term Debt

3 Months Ended

Mar. 31, 2024

Debt Disclosure [Abstract]

Long-Term Debt

9. Long-Term Debt

The Company’s Term Loan consists of the following (in thousands):


	March 31, 2024
Long-term debt	$	25,000
Accumulated PIK interest		810
Total principal (including PIK interest)		25,810
Unamortized debt discount		(357	)
Long-term debt, net of debt discount	$	25,453

On April 18, 2022, the Company entered into a Loan and Security Agreement (the “Existing Loan Agreement” and, as amended by the First Amendment (as defined below) the "Loan Agreement") with Hercules Capital, Inc., as administrative and collateral agent (in such capacity, "Hercules"), and the lenders from time to time party thereto (the "Lenders"), providing for term loans (“Term Loans”) of up to $75.0 million. Prior to June 16, 2023, the Company had borrowed $15.0 million in term loans under the Existing Loan Agreement and had the right thereunder to borrow (i) an additional $15.0 million of term loans until June 30, 2023 (“Term Loan Tranche 1”), (ii) an additional $20.0 million of term loans until

June 30, 2023 (“Term Loan Tranche 2”), and (iii) subject to the achievement of certain clinical development milestones by the Company, an additional $25.0 million until March 31, 2024 ("Term Loan Tranche 3”).

On June 16, 2023, the Company entered into a First Amendment to Loan and Security Agreement (the "First Amendment") with Hercules and the Lenders party thereto, which amended the Existing Loan Agreement. In connection with the First Amendment, the Company borrowed $10.0 million under Term Loan Tranche 1. Additionally, the First Amendment, among other things, amended the following: (i) with respect to the remaining $5.0 million under Term Loan Tranche 1, modified the period during which the Company may borrow thereunder to start on December 1, 2023 and end May 31, 2024 (or such earlier date if Lenders elect in their sole discretion), (ii) with respect to Term Loan Tranche 2, modified the period during which the Company may borrow thereunder to start on December 1, 2023 and end May 31, 2024 (or such earlier date if Lenders elect in their sole discretion) and (iii) with respect to Term Loan Tranche 3, (a) added as a new condition to borrow thereunder that (x) the Company’s Phase 2b clinical trial evaluating the safety, immunogenicity and efficacy of HIL-214 in infants ("NEST-IN1”) has achieved the protocol-specified primary efficacy endpoint and (y) HIL-214 has demonstrated acceptable safety results in the NEST-IN1 clinical trial, and, as a result, the Company supports the initiation of a Phase 3 registrational trial as the next immediate step in the development of HIL-214 (the “Tranche 3 Milestone”) and (b) modified the period during which the Company may borrow thereunder to start on the date the Company achieves the Tranche 3 Milestone and end on the earlier of (x) June 15, 2024 and (y) 30 days following the date the Company achieves the Tranche 3 Milestone. The First Amendment was accounted for as a debt modification; as such, the financing costs of $0.2 million were reflected as additional debt discount and is amortized as an adjustment to interest expense over the term of the First Amendment.

On November 9, 2023, the Company entered into a Second Amendment to Loan and Security Agreement (the "Second Amendment") with Hercules and the Lenders party thereto, which amended the Existing Loan Agreement. The Second Amendment amended the following: (i) with respect to the remaining $5.0 million under Term Loan Tranche 1, modified the period during which the Company may borrow thereunder to start on January 1, 2024 and end July 19, 2024 (or such earlier date if Lenders elect in their sole discretion), (ii) with respect to Term Loan Tranche 2, modified the period during which the Company may borrow thereunder to start on January 1, 2024 and end July 19, 2024 (or such earlier date if Lenders elect in their sole discretion) and (iii) with respect to Term Loan Tranche 3, modified the period during which the Company may borrow thereunder to end on the earlier of (x) September 15, 2024 and (y) 30 days following the date the Company achieves the Tranche 3 Milestone. The Company did not incur any fees in connection with the Second Amendment. All Term Loans are subject to a minimum draw amount of $5.0 million and no event of default under the Loan Agreement having occurred and is continuing. The borrowings under the Loan Agreement are collateralized by substantially all of our assets, including intellectual property and certain other assets.

The Term Loans bear (a) cash interest at a floating rate of the higher of (i) the Wall Street Journal prime rate (or 5.00% if less) plus 1.05%, or (ii) 4.55% (interest rate of 6.05% as of March 31, 2024), and (b) additional interest ("PIK Interest") at a per annum rate equal to 2.85%, with such interest being added to the outstanding principal balance of the Term Loans on a monthly basis. The monthly payments consist of interest-only through June 1, 2025 or, if prior to April 30, 2025, the Company achieves the Tranche 3 Milestone, subject to reasonable verification by Hercules, through June 1, 2026. Subsequent to the interest-only period, the Term Loans will be payable in equal monthly installments of principal, plus accrued and unpaid interest, through the maturity date of May 1, 2027. In addition, the Company is obligated to pay a final payment fee equal to the greater of (i) $2.145 million and (ii) 7.15% of the original principal amount of the Term Loans (which is $2.1 million as of March 31, 2024). The final payment fee is recorded as a debt discount amortized over the life of the debt. The Company may elect to prepay all or a portion of the Term Loans prior to maturity, subject to a prepayment fee of up to 1.00% of the then outstanding principal balance and the pro rata application of such payment to the final payment fee. After repayment, no Term Loan amounts may be borrowed again.

The Loan Agreement contains certain customary affirmative and negative covenants and events of default. The affirmative covenants include, among others, covenants requiring the Company to maintain its legal existence and governmental approvals, deliver certain financial reports, maintain insurance coverage and satisfy certain requirements regarding its operating accounts. The negative covenants include, among others, limitations on the Company’s ability to incur additional indebtedness and liens, merge with other companies or consummate certain changes of control, acquire other companies or businesses, make certain investments, pay dividends, transfer or dispose of assets, amend certain material agreements, including the Takeda License, or enter into various specified transactions. Upon the occurrence of an event of default, subject to any specified cure periods, all amounts owed by the Company would begin to bear interest at a rate that is 4.00% above the rate effective immediately before the event of default and may be declared immediately due and payable by Hercules, as collateral agent.

As of March 31, 2024, the Company had borrowed $25.0 million pursuant to the Loan Agreement. During the three months ended March 31, 2024, the Company recognized interest expense of $0.7 million related to the Term Loans using the effective interest method. Included in such expense was $0.2 million related to accretion of the final payment fee to

other long-term liabilities, $0.2 million of PIK interest, $0.3 million of coupon interest, and an immaterial amount of debt discount amortization.

Future minimum principal and interest payments, including the final payment fee, as of March 31, 2024 are as follows (in thousands):


	March 31, 2024
Years ending December 31:
2024	$	1,206
2025		8,433
2026		13,303
2027		10,645
Total principal payments, interest payments and final payment fee		33,587
Less: interest, PIK interest and final payment fee		(7,777	)
Long-term debt	$	25,810

Stockholders' Equity - Schedule of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total	$ 5,194	$ 2,642
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total	2,708	1,276
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total	$ 2,486	$ 1,366

Stockholder's Equity (Tables)

3 Months Ended

Mar. 31, 2024

Stockholders' Equity Note [Abstract]

Summary of Stock Option Activity

A summary of the Company’s stock option activity under the Plans is as follows (in thousands, except share and per share data):


	Number of Outstanding Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Balance at December 31, 2023		3,896,061		$	13.89		8.82	$	11,826
Granted		1,716,895			15.06
Exercised		(22,365	)		15.06
Cancelled		(49,800	)		13.41
Balance at March 31, 2024		5,540,791		$	14.28		8.96	$	15,493
Vested and expected to vest at March 31, 2024		5,540,791		$	14.28		8.96	$	15,493
Exercisable at March 31, 2024		1,311,890		$	12.39		8.27	$	6,158

Summary of Assumptions used in Black-Scholes Option Pricing Model to Determine Fair Value of Stock Option Grants

The assumptions used in the Black-Scholes option pricing model to determine the fair value of stock option grants were as follows:


	Three Months Ended March 31,
	2024	2023
Risk-free interest rate	3.9%–4.3%	1.9%–4.2%
Expected volatility	95.1%–96.2%	83.4%–94.3%
Expected term (in years)	6.1	5.3–6.1
Expected dividend yield	0%	0%

Schedule of Stock-based Compensation Expense

Stock-based compensation expense has been reported in the condensed consolidated statements of operations as follows (in thousands):


	Three Months Ended March 31,
	2024		2023
Research and development	$	2,708	$	1,276
General and administrative		2,486		1,366
Total	$	5,194	$	2,642

Summary of Unvested Shares

A summary of the Company’s unvested shares is as follows:


	Number of Unvested Shares			Weighted Average Grant-Date Fair Value
Balance at December 31, 2023		1,571,716		$	8.474
Shares granted		1,036,450			15.019
Shares forfeited		(13,024	)		15.336
Share vested		(349,439	)		9.426
Balance at March 31, 2024		2,245,703			11.319

Schedule of Common Stock Reserved for Future Issuance

Common stock reserved for future issuance consists of the following:


	March 31, 2024
Common stock options outstanding		5,540,791
Shares available for issuance under the Plans		3,268,133
Shares available for issuance under the ESPP		1,208,801
		10,017,725

Fair Value Measurements - Additional Information (Details) - Non-Recurring	3 Months Ended
	Mar. 31, 2024 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-financial assets at fair value	$ 0
Non-financial liabilities at fair value	$ 0

Summary of Significant Accounting Policies - Schedule of Potential Dilutive Securities Not Included in the Calculation of Diluted Net Loss Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	7,822,350	5,510,787
Common Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	5,540,791	3,373,332
Unvested common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	2,245,703	2,117,453
ESPP shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	35,856	20,002

Other Balance Sheet Details - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Balance Sheet Related Disclosures [Abstract]
Cash and cash equivalents	$ 141,076	$ 216,678
Restricted cash	1,631	1,631
Total cash, cash equivalents and restricted cash	$ 142,707	$ 218,309	$ 262,173	$ 281,032

Commitments and Contingencies

3 Months Ended

Mar. 31, 2024

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

8. Commitments and Contingencies

License Agreement with Takeda

On July 2, 2021, the Company entered into a license agreement with Takeda pursuant to which it was granted an exclusive sublicensable, royalty-bearing license (the “Takeda License”) to develop and commercialize HIL-214 pharmaceutical products for all human uses on a worldwide basis outside of Japan (the “Territory”).

The Company is obligated to pay Takeda $7.5 million upon the achievement of a specified development milestone, up to an aggregate of $150.0 million in sales milestones upon the achievement of specified annual sales levels of HIL-214 products in the Territory, and tiered high single-digit to low-teen percentage royalties on net sales of HIL-214 products in the Territory, subject to specified offsets and reductions. Takeda has agreed to pay the Company tiered mid-single digit to low-double digit percentage royalties on net sales of HIL-214 products in Japan, subject to specified offsets and reductions. Royalties will be payable, on a product-by-product and country-by-country basis from the first commercial sale of such product in such country, until the latest of expiration of the licensed patents covering the applicable product, expiration of regulatory exclusivity in such country, or 20 years following first commercial sale of such product in such country. The obligations related to contingent payments are recognized in the accompanying condensed consolidated financial statements when the contingency is resolved and the consideration is paid or becomes payable. As of March 31, 2024, none of the remaining contingent payments were due or payable.

Absent early termination, the Takeda License expires on a country-by-country and product-by-product basis upon the expiration of the applicable royalty term with respect to each product in each country, as applicable, or in its entirety upon the expiration of the royalty term with respect to the last product commercialized in the last country. The Company may terminate the Takeda License upon six months’ prior written notice. The Company and Takeda may terminate the Takeda License in the case of the other party’s insolvency, or upon prior written notice within a specified time period for the other party’s material uncured breach. Takeda may terminate the Takeda License if the Company challenges licensed patents, or assists any third-party in challenging such patents.

The Company did not make any milestone payments to Takeda during the three months ended March 31, 2024 and 2023.

Transitional Services Agreement with Takeda

As contemplated by the Takeda License, on December 17, 2021, the Company entered into a Transitional Services Agreement (“TSA”) with Takeda under which the Company will be obligated to pay Takeda for certain services, including pass-through costs, related to research and development and regulatory assistance services, oversight and management of ongoing clinical and research studies, and maintenance of third party vendor contracts. The TSA and related activities are considered related party transactions. Unless earlier terminated under its terms, the TSA will remain in effect until all transitional services are completed. The Company may terminate the provision of any or all services under the TSA upon certain written notice. The Company and Takeda may terminate the TSA in the case of the other party’s insolvency, or upon prior written notice within a specified time period for the other party’s material uncured breach. Takeda may terminate the TSA for non-payment and, in certain circumstances, upon a change of control of the Company.

License Agreement with Kangh

On January 8, 2024, the Company entered into an exclusive license agreement with Chengdu Kanghua Biological Products Co., Ltd. ("Kangh"), for rights to Kangh’s hexavalent virus-like particle vaccine candidate for norovirus (the "Kangh License"), referred to by the Company as HIL-216, outside of Greater China (the “Territory”).

In consideration of the Kangh License, the Company has an upfront payment amount of $15.0 million, of which $13.5 million has been paid as of March 31, 2024 and the remaining $1.5 million is expected to be paid by December 31, 2024. In addition, the Company has the potential to pay Kangh up to $255.5 million upon achieving certain development and sales milestones. Kangh is also eligible to receive a single-digit tiered royalty on net sales outside of Greater China.

The acquisition of the Kangh License has been accounted for as an asset acquisition as substantially all of the fair value is concentrated in a group of similar assets. In March 2024, the Company paid Kangh an upfront amount of $13.5 million for the Kangh License, which has no alternative future use, and was recorded as in-process research and development in the Company’s consolidated statement of operations for the year ended March 31, 2024.

401(k) Plan

The Company established a defined-contribution plan under Section 401(k) of the Internal Revenue Code (the 401(k) Plan). The 401(k) Plan covers all eligible employees who meet defined minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. Beginning November 2022, the Company made matching contributions equal to 100% of the employee’s contributions, subject to a maximum of 4% of eligible compensation. The Company made matching contributions of $0.3 million and $0.2 million during the three months ended March 31, 2024 and 2023, respectively.

Contingencies

In the event the Company becomes subject to claims or suits arising in the ordinary course of business, the Company would accrue a liability for such matters when it is probable that future expenditures will be made and such expenditures can be reasonably estimated.

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating expenses:
Research and development (includes related party amounts of $27 and $168, respectively)	$ 25,978	$ 23,164
In-process research and development	15,325
General and administrative (includes related party amounts of $0 and $3, respectively)	8,494	5,795
Total operating expenses	49,797	28,959
Loss from operations	(49,797)	(28,959)
Other income (expense):
Interest income	2,402	2,574
Interest expense	(727)	(449)
Other income (expense)	1,293	(55)
Total other income	2,968	2,070
Net loss	(46,829)	(26,889)
Other comprehensive income (loss):
Unrealized loss on marketable securities	(121)
Pension and other postemployment benefits	78	(1)
Total comprehensive loss	$ (46,872)	$ (26,890)
Net loss per share, basic	$ (0.97)	$ (0.71)
Net loss per share, diluted	$ (0.97)	$ (0.71)
Weighted-average shares of common stock outstanding, basic	48,460,185	37,753,522
Weighted-average shares of common stock outstanding, diluted	48,460,185	37,753,522

Leases - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended
	Mar. 31, 2022	Aug. 31, 2021	Mar. 31, 2024
Switzerland
Lessee, Lease, Description [Line Items]
Operating lease term		5 years
Operating lease option to extend			The Company has an option to extend the lease for a period of five years which the Company is not reasonably certain to exercise.
Operating lease, existence of option to extend [true false]		true
Operating lease renewal term		5 years
Boston, Massachusetts
Lessee, Lease, Description [Line Items]
Operating lease option to extend			an option for the Company to extend the lease for a period of five years
Operating lease, existence of option to extend [true false]	true
Operating lease renewal term	5 years
Increase in operating lease liability			$ 6.2
Maximum lessee operating lease tenant improvement allowances for reimbursement cost			6.2
Lease incentive			6.2
Irrevocable standby letter of credit secured by restricted cash amount			$ 1.6

Stockholders' Equity - Summary of Stock Option Activity (Details) - Plans - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of outstanding options, Beginning balance	3,896,061
Number of outstanding options, Granted	1,716,895
Number of outstanding options, Exercised	(22,365)
Number of outstanding options, Cancelled	(49,800)
Number of outstanding options, Ending Balance	5,540,791	3,896,061
Number of outstanding options, Vested and expected to vest at March 31, 2024	5,540,791
Number of outstanding options, Exercisable at March 31, 2024	1,311,890
Weighted average exercise price, Beginning balance	$ 13.89
Weighted average exercise price, Granted	15.06
Weighted average exercise price, Exercised	15.06
Weighted average exercise price, Cancelled	13.41
Weighted average exercise price, Ending balance	14.28	$ 13.89
Weighted average exercise price, Vested and expected to vest at March 31, 2024	14.28
Weighted average exercise price, Exercisable at March 31, 2024	$ 12.39
Weighted-average remaining contractual term (in years)	8 years 11 months 15 days	8 years 9 months 25 days
Weighted-average remaining contractual term (in years), Vested and expected to vest at March 31, 2024	8 years 11 months 15 days
Weighted-average remaining contractual term (in years) Exercisable at March 31, 2024	8 years 3 months 7 days
Aggregate intrinsic value	$ 15,493	$ 11,826
Aggregate intrinsic value, Vested and expected to vest at March 31, 2024	15,493
Aggregate intrinsic value, Exercisable at March 31, 2024	$ 6,158

Other Balance Sheet Details

3 Months Ended

Mar. 31, 2024

Balance Sheet Related Disclosures [Abstract]

Other Balance Sheet Details

5. Other Balance Sheet Details

Property and Equipment

Property and equipment, net consisted of the following (in thousands):


	March 31,		December 31,
	2024		2023
Computer equipment	$	103	$	103
Furniture and equipment		377		377
Leasehold improvements		11,964		11,964
Lab equipment		2,331		2,116
Construction in progress		153		338
Total property and equipment, at cost		14,928		14,898
Less accumulated depreciation		1,336		880
Property and equipment, net	$	13,592	$	14,018

Depreciation expense for the three months ended March 31, 2024 was $0.5 million. Depreciation expense for the three months ended March 31, 2023 was not material.

Accrued Expenses

Accrued expenses consisted of the following (in thousands):


	March 31,		December 31,
	2024		2023
Accrued external research and development costs	$	13,818	$	12,665
Accrued payroll and payroll-related costs		2,048		5,233
Accrued professional costs		1,017		498
Other		2,260		157
Total accrued expenses	$	19,143	$	18,553

Cash, Cash Equivalents and Restricted Cash

The following table provides a reconciliation of cash, cash equivalents and restricted cash recorded within the accompanying condensed consolidated balance sheets that sum to the amounts shown in the condensed consolidated statements of cash flows (in thousands):


	March 31,		December 31,
	2024		2023
Cash and cash equivalents	$	141,076	$	216,678
Restricted cash		1,631		1,631
Total cash, cash equivalents and restricted cash	$	142,707	$	218,309

Other Balance Sheet Details - Summary of Components of Property and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	$ 14,928	$ 14,898
Less accumulated depreciation	1,336	880
Property, Plant and Equipment, Net, Total	13,592	14,018
Computer equipment
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	103	103
Furniture and equipment
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	377	377
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	11,964	11,964
Lab equipment
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	2,331	2,116
Construction in progress
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	$ 153	$ 338

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Cash flows from operating activities
Net loss	$ (46,829)	$ (26,889)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	456	1
Stock-based compensation	5,194	2,642
Amortization of operating lease right-of-use assets	251	360
Amortization of debt discount	159	126
Issuance of PIK interest debt	174	94
Acquired in-process research and development	15,325
Net accretion/amortization of premiums and discounts on marketable securities	(1,299)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,160)	1,895
Accounts payable, accrued expenses and other long-term liabilities (includes related party amounts of $(6) and $31, respectively)	(5,180)	4,384
Accrued interest	1	24
Operating lease right-of-use assets and liabilities	(94)	1,409
Net cash used in operating activities	(33,002)	(15,954)
Cash flows from investing activities
Cash paid for purchased in-process research and development	(13,825)
Purchases of property and equipment	(153)	(2,985)
Purchases of marketable securities	(92,684)
Proceeds from sales or maturities of marketable securities	49,000
Net cash used in investing activities	(57,662)	(2,985)
Cash flows from financing activities
Proceeds from issuance of common stock under share-based compensation arrangements	175	80
Proceeds from issuance of at-the-market offering, net	14,887
Net cash provided by financing activities	15,062	80
Net decrease in cash, cash equivalents and restricted cash	(75,602)	(18,859)
Cash, cash equivalents and restricted cash-beginning of period	218,309	281,032
Cash, cash equivalents and restricted cash-end of period	142,707	262,173
Supplemental disclosure of cash flow information
Cash paid for interest	382	192
Supplemental disclosure of noncash investing and financing activities
Unpaid in-process research and development	1,500
Unpaid property and equipment purchases	13	3,453
Accreted final interest payment fees	$ 124	$ 109

Commitments and Contingencies - Additional Information (Details) - USD ($)		1 Months Ended		3 Months Ended		12 Months Ended
	Jul. 02, 2021	Mar. 31, 2024	Nov. 30, 2022	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2024
Commitments And Contingencies Disclosure [Line Items]
Company made matching contributions				$ 300,000	$ 200,000
Matching contribution				the Company made matching contributions equal to 100% of the employee’s contributions, subject to a maximum of 4% of eligible compensation. The Company made matching contributions of $0.3 million and $0.2 million during the three months ended March 31, 2024 and 2023, respectively.
Percentage Of employee's contributions			100.00%
Percentage of maximum eligible compensation			4.00%
Kangh
Commitments And Contingencies Disclosure [Line Items]
Upfront payment		$ 15,000,000		$ 15,000,000
License agreement upfront amount paid		13,500,000		13,500,000
Kangh \| Maximum
Commitments And Contingencies Disclosure [Line Items]
Development and sales milestones		$ 255,500,000		255,500,000
Kangh \| Scenario Forecast
Commitments And Contingencies Disclosure [Line Items]
Remaining upfront payment expected to be paid						$ 1,500,000
Takeda
Commitments And Contingencies Disclosure [Line Items]
Development Milestones	$ 7,500,000
Sales Milestones	$ 150,000,000
License agreement milestone payments				$ 0	$ 0

Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2024

Accounting Policies [Abstract]

Schedule of Estimated Useful Life of the Related assets

Property and equipment are stated at cost and depreciated on a straight-line basis over the estimated useful life of the related assets as follows:


		Estimated Useful Life
Computer equipment		3 years
Lab equipment		5 years
Furniture and fixtures		5 years
Leasehold improvements		3 – 10 years or term of lease

Schedule of Potentially Dilutive Securities Not Included in the Calculation of Diluted Net Loss Per Share

Potentially dilutive securities not included in the calculation of diluted net loss per share, because to do so would be anti-dilutive, are as follows (in common stock equivalent shares):


	March 31,
	2024		2023
Common stock options		5,540,791		3,373,332
Unvested common stock		2,245,703		2,117,453
ESPP shares		35,856		20,002
Total potentially dilutive shares		7,822,350		5,510,787

Summary of Significant Accounting Policies - Additional Information (Details)	3 Months Ended
	Mar. 31, 2024 Segment shares	Mar. 31, 2023 shares
Summary of Significant Accounting Policies [Line Item]
Number of operating segment \| Segment	1
Basic weighted-average common shares outstanding	48,460,185	37,753,522
Weighted-average unvested shares excluded from computation of earnings per share amount	811,413	1,492,789

Stockholders' Equity

3 Months Ended

Mar. 31, 2024

Stockholders' Equity Note [Abstract]

Stockholders' Equity

10. Stockholders’ Equity

Initial Public Offering

On May 3, 2022, the Company completed its IPO whereby it sold 13,529,750 shares of common stock at a public offering price of $17.00 per share, for net proceeds of approximately $209.5 million, after deducting underwriting discounts, commissions and offering costs of approximately $20.5 million. In connection with the Company's IPO, the Company increased the number of authorized shares of the Company's common stock and preferred stock to 500,000,000 shares and 50,000,000 shares, respectively.

At-the-Market-Offering

On May 12, 2023, the Company entered into an At-the-Market Equity Offering Sales Agreement (the "Sales Agreement") with Stifel, Nicolaus & Company, Incorporated (the “Agent”), pursuant to which the Company may offer and sell shares of the Company’s common stock having an aggregate offering price of up to $100.0 million from time to time, in “at the market” offerings through the Agent. Sales of the shares of common stock, if any, will be made at prevailing market prices at the time of sale, or as otherwise agreed with the Agent. The Agent will receive a commission from the Company of up to 3.0% of the gross proceeds of any shares of common stock sold under the Sales Agreement. The Company is not obligated to sell, and the Agent is not obligated to buy or sell, any shares of common stock under the Sales Agreement. During the three months ended March 31, 2024, the Company sold 1,016,950 shares of common stock for total net proceeds of approximately $14.9 million, after deducting commission fees and offering expenses.

Underwritten Public Offering

On September 22, 2023, the Company completed an underwritten public offering whereby it sold 9,200,000 shares of common stock, which included the exercise in full by the underwriters of their option to purchase 1,200,000 shares, at a public offering price of $12.50 per share for total net proceeds of approximately $107.8 million, after underwriting discounts and commissions and estimated offering costs.

2021 Equity Incentive Plan

On February 8, 2021, the Company’s board of directors and stockholders approved and adopted the HilleVax, Inc. 2021 Equity Incentive Plan (the “2021 Plan”). The term of the 2021 Plan is ten years from the adoption date. Under the 2021 Plan, the Company may grant stock options, restricted stock, restricted stock units, and other stock-based awards to employees, directors or consultants of the Company and its subsidiaries. The stock options granted under the plan generally vest over a four-year period from the vesting commencement date. Upon the effectiveness of the 2022 Plan defined and described below, no further grants will be made under the 2021 Plan, and any outstanding awards granted under the 2021 Plan will remain subject to the terms of the 2021 Plan and applicable award agreements.

2022 Incentive Award Plan

In April 2022, the Company’s board of directors and stockholders approved the 2022 Incentive Award Plan (the “2022 Plan,” and together with the 2021 Plan, the "Plans") under which the Company may grant stock options, restricted stock, dividend equivalents, restricted stock units, stock appreciation rights, and other stock or cash-based awards to its

employees, consultants and directors. The 2022 Plan became effective in connection with the Company’s IPO and will remain in effect until the tenth anniversary of its effective date, which will be April 28, 2032, unless earlier terminated by the Company’s board of directors. The number of shares of the Company's common stock initially available for issuance under awards granted pursuant to the 2022 Plan was the sum of (1) 4,900,000 shares of the Company’s common stock, plus (2) 216,849 shares remaining available for issuance under the 2021 Plan as of the effective date of the 2022 Plan, plus (3) any shares subject to outstanding awards under the 2021 Plan as of the effective date of the 2022 Plan that become available for issuance under the 2022 Plan thereafter in accordance with its terms. The number of shares initially available for issuance will be increased by an annual increase on January 1 of each calendar year ending in and including 2032, equal to the lesser of (1) 5% of the shares of common stock outstanding on the final day of the immediately preceding calendar year and (2) such smaller number of shares as determined by the Company’s board of directors. As of March 31, 2024, 9,580,823 shares were reserved for issuance under the 2022 Plan, of which 3,268,133 shares remained available for future issuance.

2022 Employee Stock Purchase Plan

In April 2022, the Company’s board of directors and stockholders approved the 2022 Employee Stock Purchase Plan (the “2022 ESPP”). The 2022 ESPP became effective in connection with the Company’s IPO. The 2022 ESPP permits eligible employees who elect to participate in an offering under the ESPP to have up to a specified percentage of their eligible earnings withheld, subject to certain limitations, to purchase shares of common stock pursuant to the 2022 ESPP. The price of common stock purchased under the 2022 ESPP is equal to 85% of the lower of the fair market value of the common stock on the first trading day of the offering period or the relevant purchase date. A total of 410,000 shares of the Company’s common stock was initially reserved for issuance under the 2022 ESPP. In addition, the number of shares available for issuance under the 2022 ESPP will be annually increased on January 1 of each calendar year, ending in and including 2032, by an amount equal to the lesser of (1) 1% of the shares outstanding on the final day of the immediately preceding calendar year and (2) such smaller number of shares as is determined by the Company’s board of directors, provided that no more than 10,000,000 shares of the Company’s common stock may be issued under the 2022 ESPP.

A summary of the Company’s stock option activity under the Plans is as follows (in thousands, except share and per share data):


	Number of Outstanding Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Balance at December 31, 2023		3,896,061		$	13.89		8.82	$	11,826
Granted		1,716,895			15.06
Exercised		(22,365	)		15.06
Cancelled		(49,800	)		13.41
Balance at March 31, 2024		5,540,791		$	14.28		8.96	$	15,493
Vested and expected to vest at March 31, 2024		5,540,791		$	14.28		8.96	$	15,493
Exercisable at March 31, 2024		1,311,890		$	12.39		8.27	$	6,158

Stock-Based Compensation Expense

The fair value of common stock is based on the closing price as reported on the date of grant on the primary stock exchange on which the Company's common stock is traded. The assumptions used in the Black-Scholes option pricing model to determine the fair value of stock option grants were as follows:


	Three Months Ended March 31,
	2024	2023
Risk-free interest rate	3.9%–4.3%	1.9%–4.2%
Expected volatility	95.1%–96.2%	83.4%–94.3%
Expected term (in years)	6.1	5.3–6.1
Expected dividend yield	0%	0%

Risk-free interest rate. The risk-free interest rate is based on the U.S. Treasury yield in effect at the time of grant for zero coupon U.S. Treasury notes with maturities similar to the expected term of the awards.

Expected volatility. Given the Company's limited historical stock price volatility data, the expected volatility assumption is based on volatilities of a peer group of similar companies whose share prices are publicly available. The peer group was developed based on companies in the biotechnology industry. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available.

Expected term. The expected term represents the period of time that options are expected to be outstanding. Because the Company does not have historical exercise behavior, it determines the expected life assumption using the simplified method, for employees, which is an average of the contractual term of the option and its vesting period.

Expected dividend yield. The Company bases the expected dividend yield assumption on the fact that it has never paid cash dividends and has no present intention to pay cash dividends and, therefore, used an expected dividend yield of zero.

Stock-based compensation expense has been reported in the condensed consolidated statements of operations as follows (in thousands):


	Three Months Ended March 31,
	2024		2023
Research and development	$	2,708	$	1,276
General and administrative		2,486		1,366
Total	$	5,194	$	2,642

The weighted average grant date fair value per share of option grants for the three months ended March 31, 2024 and 2023 was $11.86, and $13.80, respectively. As of March 31, 2024, total unrecognized stock-based compensation cost related to stock options was approximately $45.1 million, which is expected to be recognized over a remaining weighted-average period of approximately 3.0 years.

A summary of the Company’s unvested shares is as follows:


	Number of Unvested Shares			Weighted Average Grant-Date Fair Value
Balance at December 31, 2023		1,571,716		$	8.474
Shares granted		1,036,450			15.019
Shares forfeited		(13,024	)		15.336
Share vested		(349,439	)		9.426
Balance at March 31, 2024		2,245,703			11.319

The Company issued shares of restricted common stock during the three months ended March 31, 2024 and 2023, which consisted only of restricted stock units. The weighted average grant date fair value per share of restricted common stock grants for the three months ended March 31, 2024 and 2023 was $15.02 and $18.00, respectively. As of March 31, 2024, total unrecognized stock-based compensation cost related to restricted stock was approximately $24.2 million, which is expected to be recognized over a remaining weighted-average period of approximately 3.4 years. For accounting purposes, unvested shares of restricted common stock are not considered outstanding until they vest. As of March 31, 2024 and December 31, 2023, the Company had no material repurchase liability related to the unvested shares in the table above.

Common Stock Reserved for Future Issuance

Common stock reserved for future issuance consists of the following:


	March 31, 2024
Common stock options outstanding		5,540,791
Shares available for issuance under the Plans		3,268,133
Shares available for issuance under the ESPP		1,208,801
		10,017,725

- Definition

The entire disclosure for equity.

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+ Details

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Mar. 31, 2024	Mar. 31, 2023
Pay vs Performance Disclosure
Net Income (Loss)	$ (46,829)	$ (26,889)

- Definition

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

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Reference 29: http://www.xbrl.org/2003/role/disclosureRef
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Reference 30: http://www.xbrl.org/2003/role/disclosureRef
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Reference 31: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Leases

3 Months Ended

Mar. 31, 2024

Leases [Abstract]

Leases

6. Leases

Operating Leases

In August 2021, the Company entered into a five-year noncancelable operating lease for a facility in Switzerland, which it determined was an operating lease at the inception of the lease contract. The lease commencement date occurred in September 2021 when the Company gained access to the facility. The Company is obligated to make monthly rental payments that periodically escalate during the lease term and is subject to additional charges for common area maintenance and other costs. The Company has an option to extend the lease for a period of five years which the Company is not reasonably certain to exercise.

In March 2022, the Company entered into a lease for office and laboratory space located in Boston, Massachusetts (as amended, the “Boston Lease”), which it determined was an operating lease at the inception of the lease contract. The Boston Lease commenced in April 2022 with base rental payments beginning in January 2023. The Boston Lease includes certain tenant improvement allowances for the reimbursement of $6.2 million of costs incurred by the Company, and an option for the Company to extend the lease for a period of five years, which the Company is not reasonably certain to exercise. The Company determined that it owns the leasehold improvements related to the Boston Lease and, as such, reflected the $6.2 million lease incentive as a reduction of the rental payments used to measure the operating lease liability, and, in turn, the operating lease right-of-use asset as of the lease commencement date in April 2022. Between the lease commencement date and March 31, 2024, the Company recorded increases of $6.2 million to the operating lease liability as and when such lease incentives were received from the landlord. Under the terms of the Boston Lease, the Company provided the lessor with an irrevocable standby letter of credit secured by restricted cash in the amount of $1.6 million.

The following table summarizes operating lease expense for the three months ended March 31, 2024 and 2023 (in thousands):


	Three Months Ended March 31,
	2024		2023
Lease expense:
Operating lease expense	$	799	$	779

The Company incurred an immaterial amount of expense related to short-term leases and variable lease costs during the three months ended March 31, 2024 and March 31, 2023.

The following table summarizes the lease term and discount rate for operating leases:


	March 31,			December 31,
	2024			2023
Other information:
Weighted-average remaining lease term		8.70			9.00
Weighted-average discount rate		7.4	%		7.4	%

As there was not an implicit rate within the leases, management estimated the incremental borrowing rate based on the rate of interest the Company would have to pay to borrow a similar amount on a collateralized basis over a similar term as well as by using a set of peer companies' incremental borrowing rates.

The following table summarizes the cash paid for amounts included in the measurement of lease liabilities (in thousands):


	March 31, 2024
Cash paid for amounts included in the measurement of operating lease liabilities (operating cash flows)	$	896

At March 31, 2024, the future minimum noncancelable operating lease payments were as follows (in thousands):


	March 31, 2024
Years ending December 31:
2024		2,688
2025		3,688
2026		3,784
2027		3,860
2028		3,974
Thereafter		17,102
Total undiscounted operating lease payments		35,096
Present value adjustment		(9,241	)
Operating lease liability		25,855
Less current portion of operating lease liability		3,491
Operating lease liability, net of current portion	$	22,364

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2024

Fair Value Disclosures [Abstract]

Summary of Assets Measured at Fair Value on Recurring Basis

The following tables present the Company’s fair value hierarchy for its assets that are measured at fair value on a recurring basis and indicate the level within the fair value hierarchy of the valuation techniques the Company utilized to determine such fair value (in thousands):


			Fair Value Measurements at March 31, 2024 Using:
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents
Money market funds	$	135,411	$	135,411	$	—	$	—
Marketable securities:
U.S. treasury notes		84,243		84,243		—		—
U.S government agency bonds		47,424		—		47,424		—
Total	$	267,078	$	219,654	$	47,424	$	—


			Fair Value Measurements at December 31, 2023 Using:
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents
Money market funds	$	209,659	$	209,659	$	—	$	—
Marketable securities:
U.S. treasury notes		43,050		43,050		—		—
U.S government agency bonds		43,755		—		43,755		—
Total	$	296,464	$	252,709	$	43,755	$	—

Stockholders' Equity - Summary of Unvested Shares (Details) - $ / shares	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Stockholders' Equity Note [Abstract]
Number of unvested shares, Beginning balance	1,571,716
Number of unvested shares, Shares granted	1,036,450
Number of unvested shares, Shares forfeited	(13,024)
Number of unvested shares, Shares vested	(349,439)
Number of unvested shares, Ending balance	2,245,703
Weighted Average Grant-Date Fair Value, Beginning balance	$ 8.474
Weighted Average Grant-Date Fair Value, Shares granted	15.019	$ 18
Weighted Average Grant-Date Fair Value, Shares forfeited	15.336
Weighted Average Grant-Date Fair Value, Shares vested	9.426
Weighted Average Grant-Date Fair Value, Ending balance	$ 11.319

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2024

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

The Company's financial statements include the accounts of HilleVax Security Corporation, a wholly-owned subsidiary formed in Massachusetts, and HilleVax GmbH, a wholly-owned subsidiary formed in Zurich, Switzerland. The functional currency of the Company, HilleVax Security Corporation and HilleVax GmbH is the U.S. dollar. The Company’s assets and liabilities that are not denominated in the functional currency are remeasured into U.S. dollars at foreign currency exchange rates in effect at the balance sheet date except for nonmonetary assets, which are remeasured at historical foreign currency exchange rates in effect at the date of transaction. Net realized and unrealized gains and losses from foreign currency transactions and remeasurement are reported in other income (expense), in the condensed consolidated statements of operations and were not material for the periods presented. All intercompany transactions have been eliminated in consolidation.

Unaudited Interim Financial Information

The unaudited condensed consolidated financial statements as of March 31, 2024, and for the three months ended March 31, 2024 and 2023, have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (“SEC”), and with U.S. generally accepted accounting principles (“GAAP”) applicable to interim financial statements. These unaudited condensed consolidated financial statements have been prepared on the same basis as the Company’s audited financial statements and include all adjustments, consisting of only normal recurring

accruals, which in the opinion of management are necessary to present fairly the Company’s financial position as of the interim date and results of operations for the interim periods presented. Interim results are not necessarily indicative of results for a full year or future periods. The condensed consolidated balance sheet data as of December 31, 2023 was derived from the Company’s audited financial statements but does not include all disclosures required by GAAP. These unaudited condensed financial statements should be read in conjunction with the Company’s audited financial statements for the year ended December 31, 2023, included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023 filed with the SEC on March 20, 2024.

Use of Estimates

The preparation of the Company’s unaudited condensed consolidated financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure of contingent assets and liabilities in the Company’s condensed consolidated financial statements and accompanying notes. The most significant estimates in the Company’s unaudited condensed consolidated financial statements relate to accruals for research and development expenses. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results could differ materially from those estimates and assumptions.

Fair Value Measurements

The accounting guidance defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or non-recurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows:

Level 1: Observable inputs such as quoted prices in active markets.

Level 2: Inputs, other than the quoted prices in active markets that are observable either directly or indirectly.

Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions.

Cash and Cash Equivalents

The Company considers all highly liquid investments with original maturities of three months or less when purchased to be cash equivalents. Cash and cash equivalents include cash in readily available checking accounts and money market funds.

Restricted Cash

Restricted cash consists of a money market account securing a standby letter of credit issued in connection with the Company’s Boston Lease (as defined and described in Note 6).

Marketable Securities

Marketable securities represent holdings of available-for-sale marketable debt securities in accordance with the Company’s investment policy. The Company has classified its investments with maturities beyond one year as current, based on their highly liquid nature and because such marketable securities represent the investment of cash that is available for current operations.

Investments in marketable securities are recorded at fair value, with any unrealized gains and losses reported within accumulated other comprehensive income (loss) as a separate component of stockholders’ equity (deficit) until realized, a determination is made that an other-than-temporary decline in market value has occurred or until the security has experienced a credit loss. The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion, together with interest on securities sold, is determined based on the specific identification method and any realized gains or losses on the sale of investments are reflected as a component of other income (expense).

Concentrations of Credit Risk

Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents, marketable securities, and restricted cash. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held.

Property and Equipment, Net

Property and equipment are stated at cost and depreciated on a straight-line basis over the estimated useful life of the related assets as follows:


		Estimated Useful Life
Computer equipment		3 years
Lab equipment		5 years
Furniture and fixtures		5 years
Leasehold improvements		3 – 10 years or term of lease

Repairs and maintenance costs are charged to expense as incurred.

Leases

At the inception of a contractual arrangement, the Company determines whether the contract contains a lease by assessing whether there is an identified asset and whether the contract conveys the right to control the use of the identified asset in exchange for consideration over a period of time. Lease terms are determined at the commencement date by considering whether renewal options and termination options are reasonably assured of exercise. For its long-term operating leases, the Company recognizes a lease liability and a right-of-use (“ROU”) asset on its balance sheet and recognizes lease expense on a straight-line basis over the lease term. The lease liability is determined as the present value of future lease payments, reduced by any reimbursements for tenant improvements, using the discount rate implicit in the lease or, if the implicit rate is not readily determinable, an estimate of the Company’s incremental borrowing rate. The ROU asset is based on the lease liability, adjusted for any prepaid or deferred rent, and reduced by any reimbursements for tenant improvements. The Company aggregates all lease and non-lease components for each class of underlying assets into a single lease component and variable charges for common area maintenance and other variable costs are recognized as expense as incurred. The Company has elected to not recognize a lease liability or ROU asset in connection with short-term operating leases and recognizes lease expense for short-term operating leases on a straight-line basis over the lease term. The Company does not have any financing leases.

Impairment of Long-Lived Assets

The Company reviews long-lived assets, such as property and equipment, for impairment whenever events or changes in circumstances indicate the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to the future undiscounted net cash flows expected to be generated by the asset. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds the fair value of the assets. Fair value would be assessed using discounted cash flows or other appropriate measures of fair value. The Company has not recognized any impairment losses through March 31, 2024.

Research and Development Expenses and Accruals

All research and development costs are expensed in the period incurred and consist primarily of salaries, payroll taxes, employee benefits, stock-based compensation charges for those individuals involved in research and development efforts, external research and development costs incurred under agreements with contract research organizations and consultants to conduct and support the Company’s clinical trials of HIL-214.

The Company has entered into various research and development contracts with clinical research organizations, clinical manufacturing organizations and other companies. Payments for these activities are based on the terms of the individual agreements, which may differ from the pattern of costs incurred, and payments made in advance of performance are reflected in the accompanying balance sheets as prepaid expenses. The Company records accruals for estimated costs incurred for ongoing research and development activities. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the services, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the prepaid or accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates.

In-Process Research and Development

The Company evaluates whether acquired intangible assets are a business under applicable accounting standards. Additionally, the Company evaluates whether the acquired assets have a future alternative use. Intangible assets that do not have future alternative use are considered acquired in-process research and development. When the acquired in-process research and development assets are not part of a business combination, the value of the consideration paid is expensed on the acquisition date.

Patent Costs

Costs related to filing and pursuing patent applications are recorded as general and administrative expenses and expensed as incurred since recoverability of such expenditures is uncertain.

Stock-Based Compensation

Stock-based compensation expense represents the cost of the grant date fair value of equity awards, primarily consisting of stock options, restricted common stock, and employee stock purchase rights, recognized on a straight-line basis over the requisite service period for stock options and restricted common stock, and over the respective offering period for employee stock purchase plan rights. The Company recognizes forfeitures as they occur.

Benefit plans

The Company has established a defined contribution savings plan for its employees in the United States under Section 401(k) of the Internal Revenue Code, and a defined benefits plan for its employees outside of the United States.

The defined benefits plan is valued by an independent actuary using the projected unit credit method. The liabilities correspond to the projected benefit obligations of which the discounted net present value is calculated based on years of employment, expected salary increase, and pension adjustments. The Company reviews its actuarial assumptions on an annual basis and makes modifications to the assumptions based on current rates and trends. This plan is recognized under Accounting Standards Codification ("ASC") 715, Compensation - Retirement Benefits.

Income Taxes

The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in the condensed consolidated statements of operations in the period that includes the enactment date.

The Company recognizes net deferred tax assets to the extent that the Company believes these assets are more likely than not to be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies, and results of recent operations. If management determines that the Company would be able to realize its deferred tax assets in the future in excess of their net recorded amount, management would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes.

The Company records uncertain tax positions on the basis of a two-step process whereby (i) management determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (ii) for those tax positions that meet the more-likely-than-not recognition threshold, management recognizes the largest amount of tax benefit that is more than 50 percent likely to be realized upon ultimate settlement with the related tax authority. The Company recognizes interest and penalties related to unrecognized tax benefits within income tax expense in the condensed consolidated statements of operations. Any accrued interest and penalties are included within the related tax liability in the condensed consolidated balance sheets. The Company did not recognize any interest or penalties during the periods presented.

Comprehensive Loss

Comprehensive loss is defined as a change in equity during a period from transactions and other events and circumstances from non-owner sources. For the three months ended March 31, 2024, comprehensive loss included gains on the Company's pension benefit obligation and unrealized losses on marketable securities. For the three months ended March 31, 2023, comprehensive loss included losses on the Company's pension benefit obligation.

Segment Reporting

Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker in making decisions on how to allocate resources and assess performance. The Company views its operations and manages its business as one operating segment.

Net Loss Per Share

Basic net loss per share is computed by dividing the consolidated net loss by the weighted-average number of common shares outstanding for the period, without consideration for potentially dilutive securities. The Company has excluded weighted-average unvested shares of 811,413 shares and 1,492,789 shares from the basic weighted-average number of common shares outstanding for the three months ended March 31, 2024 and 2023, respectively. Diluted net loss per share is computed by dividing the consolidated net loss by the weighted-average number of common shares and dilutive common stock equivalents outstanding for the period determined using the treasury-stock and if-converted methods. Potentially dilutive common stock equivalents are comprised of unvested common stock, common stock options, and contingently issuable shares under the Company's employee stock purchase plan. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding as inclusion of the potentially dilutive common stock equivalents would be antidilutive.

Potentially dilutive securities not included in the calculation of diluted net loss per share, because to do so would be anti-dilutive, are as follows (in common stock equivalent shares):


	March 31,
	2024		2023
Common stock options		5,540,791		3,373,332
Unvested common stock		2,245,703		2,117,453
ESPP shares		35,856		20,002
Total potentially dilutive shares		7,822,350		5,510,787

Emerging Growth Company Status

The Company is an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012 (“JOBS Act”). Under the JOBS Act, emerging growth companies can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act until such time as those standards apply to private companies. The Company has irrevocably elected to avail itself of this exemption from new or revised accounting standards and, therefore, will not be subject to the same new or revised accounting standards as other public companies that are not emerging growth companies.

Recently Adopted Accounting Standards

There were no recently adopted accounting standards which would have a material impact on the Company's financial statements.

Recently Issued Accounting Pronouncements

In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280). The amendments in this update expand segment disclosure requirements, including new segment disclosure requirements for entities with a single reportable segment among other disclosure requirements. This update is effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. The adoption of this standard is not expected to have a material impact on the Company’s condensed consolidated financial statements.

In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740). The amendments in this update expand income tax disclosure requirements, including additional information pertaining to the rate reconciliation, income taxes paid, and other disclosures. This update is effective for annual periods beginning after December 15, 2024. The adoption of this standard is not expected to have a material impact on the Company’s condensed consolidated financial statements.

Leases - Schedule of Cash Paid for Amounts Included in the Measurement of Lease Liabilities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($)
Leases [Abstract]
Cash paid for amounts included in the measurement of operating lease liabilities (operating cash flows)	$ 896

Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance (Details)	Mar. 31, 2024 shares
Class Of Stock [Line Items]
Common stock reserved for future issuance	10,017,725
Common Stock Options
Class Of Stock [Line Items]
Common stock reserved for future issuance	5,540,791
Shares Available for Issuance Under the 2021 Plan
Class Of Stock [Line Items]
Common stock reserved for future issuance	3,268,133
Shares available for issuance under the ESPP
Class Of Stock [Line Items]
Common stock reserved for future issuance	1,208,801

- 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/exampleRef
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Reference 2: http://www.xbrl.org/2003/role/recommendedDisclosureRef
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-URI https://asc.fasb.org//1943274/2147479886/946-10-S99-3

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.6-03(i)(1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479886/946-10-S99-3

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
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Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.6-03(i)(2)(ii))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479886/946-10-S99-3

+ Details

Other Balance Sheet Details - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Other Balance Sheet Details [Abstract]
Depreciation expense	$ 456	$ 1

Related Party Transactions - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Related Party Transaction [Line Items]
Accounts payable and accrued expenses	$ 19,143,000		$ 18,553,000
Frazier
Related Party Transaction [Line Items]
Shared operating expenses	0	$ 3,000,000
Takeda \| TSA
Related Party Transaction [Line Items]
Research and development expenses	27,000,000,000	$ 200,000
Accounts payable and accrued expenses	$ 27,000		$ 33,000

Organization - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions		41 Months Ended	63 Months Ended
	May 03, 2022	May 31, 2022	Mar. 31, 2024	Dec. 31, 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Common stock shares authorized			500,000,000	500,000,000
Sale of common stock		13,529,750
Initial Public Offering
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Common stock shares authorized	500,000,000
Sale of common stock	13,529,750
Public offering price per share	$ 17
Net proceeds from initial public offering	$ 209.5	$ 209.5
Underwriting discounts, commissions and offering costs	$ 20.5
Underwritten public offering
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Sale of common stock			9,200,000
Net proceeds from common stock			$ 107.8

Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2024

Investments, Debt and Equity Securities [Abstract]

Schedule of Fair Value of Available-For-Sale Marketable Debt Securities

the fair value of available-for-sale marketable debt securities by type of security as follows (in thousands):


	March 31, 2024
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Marketable securities:
U.S. treasury notes	$	84,318	$	1	$	(76	)	$	84,243
U.S. government agency bonds		47,476		—		(52	)		47,424
Total	$	131,794	$	1	$	(128	)	$	131,667


	December 31, 2023
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Marketable securities:
U.S. treasury notes	$	43,036	$	16	$	(2	)	$	43,050
U.S. government agency bonds		43,775		4		(24	)		43,755
Total	$	86,811	$	20	$	(26	)	$	86,805

Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2024

Accounting Policies [Abstract]

Liquidity and Capital Resources

From inception to March 31, 2024, the Company has devoted substantially all of its efforts to organizing and staffing the Company, business planning, raising capital, in-licensing its initial vaccine candidate, HIL-214, preparing for and managing its clinical trials of HIL-214, and providing other general and administrative support for these operations. The Company has a limited operating history, has never generated any revenue, and the sales and income potential of its business is unproven. The Company has incurred net losses and negative cash flows from operating activities since its inception and expects to continue to incur net losses into the foreseeable future as it continues the development and potential commercialization of HIL-214. From inception to March 31, 2024, the Company has funded its operations through the issuance of convertible promissory notes, commercial bank debt, the sale of 13,529,750 shares of common stock for net proceeds of approximately $209.5 million in its initial public offering ("IPO") which closed in May 2022, and the sale of 9,200,000 shares of common stock for net proceeds of approximately $107.8 million in its underwritten public offering which closed in September 2023 (see Note 10).

The accompanying condensed consolidated financial statements have been prepared assuming the Company will continue as a going concern. Management is required to perform a two-step analysis over the Company’s ability to continue as a going concern. Management must first evaluate whether there are conditions and events that raise substantial doubt about the Company’s ability to continue as a going concern (Step 1). If management concludes that substantial doubt is raised, management is also required to consider whether its plans alleviate that doubt (Step 2). Management believes that it has sufficient working capital on hand to fund operations through at least the next twelve months from the date these financial statements were issued. There can be no assurance that the Company will be successful in acquiring additional funding, if needed, that the Company’s projections of its future working capital needs will prove accurate, or that any additional funding would be sufficient to continue operations in future years.

Basis of Presentation

Unaudited Interim Financial Information

Use of Estimates

Fair Value Measurements

Level 1: Observable inputs such as quoted prices in active markets.

Level 2: Inputs, other than the quoted prices in active markets that are observable either directly or indirectly.

Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions.

Cash and Cash Equivalents

Restricted Cash

Restricted cash consists of a money market account securing a standby letter of credit issued in connection with the Company’s Boston Lease (as defined and described in Note 6).

Marketable Securities

Concentrations of Credit Risk

Property and Equipment, Net

Property and equipment are stated at cost and depreciated on a straight-line basis over the estimated useful life of the related assets as follows:


		Estimated Useful Life
Computer equipment		3 years
Lab equipment		5 years
Furniture and fixtures		5 years
Leasehold improvements		3 – 10 years or term of lease

Repairs and maintenance costs are charged to expense as incurred.

Leases

Impairment of Long-Lived Assets

Research and Development Expenses and Accruals

In-Process Research and Development

Patent Costs

Costs related to filing and pursuing patent applications are recorded as general and administrative expenses and expensed as incurred since recoverability of such expenditures is uncertain.

Stock-Based Compensation

Potentially dilutive securities not included in the calculation of diluted net loss per share, because to do so would be anti-dilutive, are as follows (in common stock equivalent shares):


	March 31,
	2024		2023
Common stock options		5,540,791		3,373,332
Unvested common stock		2,245,703		2,117,453
ESPP shares		35,856		20,002
Total potentially dilutive shares		7,822,350		5,510,787

Emerging Growth Company Status

Recently Adopted/Issued Accounting Standards/Pronouncements

Recently Adopted Accounting Standards

There were no recently adopted accounting standards which would have a material impact on the Company's financial statements.

Recently Issued Accounting Pronouncements

Fair Value Measurements

3 Months Ended

Mar. 31, 2024

Fair Value Disclosures [Abstract]

Fair Value Measurements

3. Fair Value Measurements

The Company’s cash, cash equivalents, marketable securities, and restricted cash are carried at fair value, determined according to the fair value hierarchy discussed in Note 2. The carrying values of the Company's prepaid expenses and

other current assets, accounts payable, and accrued liabilities, approximate fair value due to their short maturities. The estimated fair value of the Company’s long-term debt approximated the carrying amount given its floating interest rate basis.


			Fair Value Measurements at March 31, 2024 Using:
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents
Money market funds	$	135,411	$	135,411	$	—	$	—
Marketable securities:
U.S. treasury notes		84,243		84,243		—		—
U.S government agency bonds		47,424		—		47,424		—
Total	$	267,078	$	219,654	$	47,424	$	—


			Fair Value Measurements at December 31, 2023 Using:
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents
Money market funds	$	209,659	$	209,659	$	—	$	—
Marketable securities:
U.S. treasury notes		43,050		43,050		—		—
U.S government agency bonds		43,755		—		43,755		—
Total	$	296,464	$	252,709	$	43,755	$	—

U.S. government money market funds were valued by the Company based on quoted market prices, which represent a Level 1 measurement within the fair value hierarchy.

As of March 31, 2024, the Company’s marketable securities consisted of U.S. Treasury notes which were valued based on Level 1 inputs and agency bonds which were valued based on Level 2 inputs. In determining the fair value of its agency bonds, the Company relied on quoted prices for similar securities in active markets or other inputs that are observable or can be corroborated by observable market data.

None of the Company’s non-financial assets or liabilities are recorded at fair value on a non-recurring basis. No transfers between levels have occurred during the periods presented.

- 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

Leases - Schedule of Operating Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Lease expense:
Operating lease expense	$ 799	$ 779

Fair Value Measurements - Summary of Assets Measured at Fair Value on Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	$ 267,078	$ 296,464
Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	135,411	209,659
U.S. Treasury Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	84,243	43,050
U.S Government Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	47,424	43,755
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	219,654	252,709
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	135,411	209,659
Quoted Prices in Active Markets for Identical Assets (Level 1) \| U.S. Treasury Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	84,243	43,050
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	47,424
Significant Other Observable Inputs (Level 2) \| U.S Government Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	$ 47,424	$ 43,755

Condensed Consolidated Statements of Cash Flows (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Statement of Cash Flows [Abstract]
Related parties accounts payable, accrued expenses and other long-term liabilities	$ (6)	$ 31

Organization

3 Months Ended

Mar. 31, 2024

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Organization

1. Organization

Organization

HilleVax, Inc. (the “Company” or “HilleVax”) was incorporated in the state of Delaware in March 2020 under the name MokshaCo, Inc. (“MokshaCo”). On February 8, 2021, MokshaCo changed its name to HilleVax and merged with North Bridge V, Inc. (“North Bridge V”) and YamadaCo III, Inc. (“YamadaCo III”), each a Delaware corporation formed in 2019, with HilleVax being the surviving entity (the “Merger”). The Company is a biopharmaceutical company focused on developing and commercializing novel vaccines.

Liquidity and Capital Resources

Condensed Consolidated Statements of Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Sales Agreement	Common Stock	Common Stock Sales Agreement	Additional Paid-in Capital	Additional Paid-in Capital Sales Agreement	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning Balance at Dec. 31, 2022	$ 267,229		$ 4		$ 532,499		$ (281)	$ (264,993)
Beginning Balance, Shares at Dec. 31, 2022			37,656,037
Vesting of restricted shares, Shares			174,568
Stock - based compensation	2,642				2,642
Issuance of common stock under share-based compensation arrangements Shares			11,382
Issuance of common stock under share-based compensation arrangements	80				80
Pension and other postemployment benefits	(1)						(1)
Net loss	(26,889)							(26,889)
Ending Balance at Mar. 31, 2023	243,061		$ 4		535,221		(282)	(291,882)
Ending Balance, Shares at Mar. 31, 2023			37,841,987
Beginning Balance at Dec. 31, 2023	265,525		$ 5		654,986		(907)	(388,559)
Beginning Balance, Shares at Dec. 31, 2023			47,666,438
Issuance of common stock		$ 14,887				$ 14,887
Sale of common stock		1,016,950		1,016,950
Vesting of restricted shares, Shares			349,439
Stock - based compensation	5,194				5,194
Issuance of common stock under share-based compensation arrangements Shares			22,365
Issuance of common stock under share-based compensation arrangements	175				175
Unrealized loss on marketable securities	(121)						(121)
Pension and other postemployment benefits	78						78
Net loss	(46,829)							(46,829)
Ending Balance at Mar. 31, 2024	$ 238,909		$ 5		$ 675,242		$ (950)	$ (435,388)
Ending Balance, Shares at Mar. 31, 2024			49,055,192

Leases (Tables)

3 Months Ended

Mar. 31, 2024

Leases [Abstract]

Schedule of Operating Lease Expense

The following table summarizes operating lease expense for the three months ended March 31, 2024 and 2023 (in thousands):


	Three Months Ended March 31,
	2024		2023
Lease expense:
Operating lease expense	$	799	$	779

Schedule of Weighted Average Lease Term and Discount Rate for Operating Lease

The following table summarizes the lease term and discount rate for operating leases:


	March 31,			December 31,
	2024			2023
Other information:
Weighted-average remaining lease term		8.70			9.00
Weighted-average discount rate		7.4	%		7.4	%

Summary of Cash Paid for Amounts Included in Measurement of Lease Liabilities

The following table summarizes the cash paid for amounts included in the measurement of lease liabilities (in thousands):


	March 31, 2024
Cash paid for amounts included in the measurement of operating lease liabilities (operating cash flows)	$	896

Schedule of Future Minimum Noncancelable Operating Lease Payments

At March 31, 2024, the future minimum noncancelable operating lease payments were as follows (in thousands):


	March 31, 2024
Years ending December 31:
2024		2,688
2025		3,688
2026		3,784
2027		3,860
2028		3,974
Thereafter		17,102
Total undiscounted operating lease payments		35,096
Present value adjustment		(9,241	)
Operating lease liability		25,855
Less current portion of operating lease liability		3,491
Operating lease liability, net of current portion	$	22,364

Long-Term Debt (Tables)

3 Months Ended

Mar. 31, 2024

Debt Disclosure [Abstract]

Schedule of Term Loan

The Company’s Term Loan consists of the following (in thousands):


	March 31, 2024
Long-term debt	$	25,000
Accumulated PIK interest		810
Total principal (including PIK interest)		25,810
Unamortized debt discount		(357	)
Long-term debt, net of debt discount	$	25,453

Schedule of Future Minimum Principal and Interest Payments

Future minimum principal and interest payments, including the final payment fee, as of March 31, 2024 are as follows (in thousands):


	March 31, 2024
Years ending December 31:
2024	$	1,206
2025		8,433
2026		13,303
2027		10,645
Total principal payments, interest payments and final payment fee		33,587
Less: interest, PIK interest and final payment fee		(7,777	)
Long-term debt	$	25,810

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
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-Section 55
-Paragraph 69B
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+ Details

Marketable Securities - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Investments, Debt and Equity Securities [Abstract]
Marketable debt securities	$ 131,667,000	$ 86,805,000
Impairment of assets measured and carried at fair value	$ 0

Other Balance Sheet Details - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Balance Sheet Related Disclosures [Abstract]
Accrued external research and development costs	$ 13,818	$ 12,665
Accrued payroll and payroll-related costs	2,048	5,233
Accrued professional costs	1,017	498
Other	2,260	157
Total accrued expenses	$ 19,143	$ 18,553

Condensed Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Interest expense, related party	$ 727	$ 449
Related party
Research and development expenses	27	168
General and administrative, related party	$ 0	$ 3

- Definition

Amount of the cost of borrowed funds accounted for as interest expense.

+ References + Details

Summary of Accounting Policies - Schedule of Estimated Useful Life of the Related Assets (Details)	Mar. 31, 2024
Computer equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Lab equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Life	5 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Estimated Useful Life	5 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, Plant, and Equipment, Useful Life, Term, Description [Extensible Enumeration]	us-gaap:UsefulLifeTermOfLeaseMember
Leasehold improvements \| Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Leasehold improvements \| Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	10 years

Related Party Transactions

3 Months Ended

Mar. 31, 2024

Related Party Transactions

7. Related Party Transactions

Frazier Life Sciences X, L.P. or its affiliates (“Frazier”) is a principal stockholder of the Company and is represented on the Company’s board of directors. From January 8, 2019 (inception) to March 31, 2024, the Company and Frazier reimbursed each other for various goods and services, including personnel related expenses, travel, insurance, facilities and other various overhead and administrative expenses. For the three months ended March 31, 2023, the Company incurred $3,000 of shared operating expenses. The Company did not incur any shared operating expenses for the three months ended March 31, 2024.

In connection with the Takeda License (as defined and described in Note 8), Takeda became a related party stockholder with representation on the Company’s board of directors. The Company and Takeda are party to a TSA (as defined and described in Note 8) under which the Company is obligated to pay Takeda for certain services, including pass-through costs, related to research and development and regulatory assistance services, oversight and management of ongoing clinical and research studies, and maintenance of third-party vendor contracts. For the three months ended March 31, 2024 and 2023, the Company incurred $27,000 and $0.2 million, respectively, of research and development expenses for Takeda’s services. As of March 31, 2024 and December 31, 2023, the Company had $27,000 and $33,000, respectively, of accounts payable and accrued expenses due to Takeda. See Note 8 for further information regarding the Company’s related party transactions with Takeda.

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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-Paragraph 1
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+ Details

Leases - Schedule of Weighted Average Lease Term and Discount Rate for Operating Lease (Details)	Mar. 31, 2024	Dec. 31, 2023
Leases [Abstract]
Weighted-average remaining lease term	8 years 8 months 12 days	9 years
Weighted-average discount rate	7.40%	7.40%

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Mar. 31, 2024
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Other Balance Sheet Details (Tables)

3 Months Ended

Mar. 31, 2024

Balance Sheet Related Disclosures [Abstract]

Property and Equipment

Property and equipment, net consisted of the following (in thousands):


	March 31,		December 31,
	2024		2023
Computer equipment	$	103	$	103
Furniture and equipment		377		377
Leasehold improvements		11,964		11,964
Lab equipment		2,331		2,116
Construction in progress		153		338
Total property and equipment, at cost		14,928		14,898
Less accumulated depreciation		1,336		880
Property and equipment, net	$	13,592	$	14,018

Accrued Expenses

Accrued expenses consisted of the following (in thousands):


	March 31,		December 31,
	2024		2023
Accrued external research and development costs	$	13,818	$	12,665
Accrued payroll and payroll-related costs		2,048		5,233
Accrued professional costs		1,017		498
Other		2,260		157
Total accrued expenses	$	19,143	$	18,553

Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash


	March 31,		December 31,
	2024		2023
Cash and cash equivalents	$	141,076	$	216,678
Restricted cash		1,631		1,631
Total cash, cash equivalents and restricted cash	$	142,707	$	218,309

Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2024	May 06, 2024
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2024
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q3
Entity Registrant Name	HILLEVAX, INC.
Entity Central Index Key	0001888012
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Small Business	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		49,720,943
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Entity File Number	001-41365
Entity Tax Identification Number	85-0545060
Entity Address Address Line1	321 Harrison Avenue
Entity Address City Or Town	Boston
Entity Address State Or Province	MA
Entity Address Postal Zip Code	02118
Entity Incorporation State Country Code	DE
City Area Code	617
Local Phone Number	213-5054
Title of each class	Common Stock, $0.0001 par value per share
Trading Symbol	HLVX
Name of each exchange on which registered	NASDAQ
Document Quarterly Report	true
Document Transition Report	false

Long-Term Debt - Schedule of Term Loan (Details) $ in Thousands	Mar. 31, 2024 USD ($)
Debt Disclosure [Abstract]
Long-term debt	$ 25,000
Accumulated PIK interest	810
Total principal (including PIK interest)	25,810
Unamortized debt discount	(357)
Long-term debt, net of debt discount	$ 25,453

- Definition

Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

+ References + Details

Long-Term Debt - Schedule of Future Minimum Principal and Interest Payments (Details) $ in Thousands	Mar. 31, 2024 USD ($)
Debt Disclosure [Abstract]
2024	$ 1,206
2025	8,433
2026	13,303
2027	10,645
Total principal payments, interest payments and final payment fee	33,587
Less: interest, PIK interest and final payment fee	(7,777)
Long-term debt	$ 25,810

Stockholders' Equity - Summary of Assumptions used in Black-Scholes Option Pricing Model to Determine Fair Value of Stock Option Grants (Details)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	3.90%	1.90%
Risk-free interest rate, maximum	4.30%	4.20%
Expected volatility, minimum	95.10%	83.40%
Expected volatility, maximum	96.20%	94.30%
Expected term (in years)	6 years 1 month 6 days
Expected dividend yield	0.00%	0.00%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)		5 years 3 months 18 days
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)		6 years 1 month 6 days

- 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 718
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-Section 35
-Paragraph 1D
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Long-Term Debt - Additional Information (Details) - USD ($)			3 Months Ended		14 Months Ended
	Jun. 16, 2023	Apr. 18, 2022	Mar. 31, 2024	Mar. 31, 2023	Jun. 15, 2023	Nov. 09, 2023
Long Term Debt [Line Items]
Debt instrument, carrying amount			$ 25,000,000
Long-Term Debt			25,453,000
PIK interest			174,000	$ 94,000
Amortization of debt discount			159,000	$ 126,000
Loan Agreement
Long Term Debt [Line Items]
Debt instrument, amount borrowed			25,000,000
Term Loan
Long Term Debt [Line Items]
Interest expense			700,000
Debt instrument, accretion of final payment fee			200,000
PIK interest			200,000
Debt instrument, coupon interest			$ 300,000
Term Loan \| Loan Agreement
Long Term Debt [Line Items]
Debt instrument, interest rate		4.55%	6.05%
Debt instrument, maximum borrowing capacity		$ 75,000,000
Debt instrument, amount borrowed					$ 15,000,000
Debt instrument, minimum draw amount						$ 5,000,000
Debt instrument, basis spread on variable rate		5.00%
Debt instrument, interest rate per annum		2.85%
Debt instrument, payment terms		The monthly payments consist of interest-only through June 1, 2025 or, if prior to April 30, 2025, the Company achieves the Tranche 3 Milestone, subject to reasonable verification by Hercules, through June 1, 2026. Subsequent to the interest-only period, the Term Loans will be payable in equal monthly installments of principal, plus accrued and unpaid interest, through the maturity date of May 1, 2027.
Debt instrument, maturity date		May 01, 2027
Debt instrument, final payment fee		$ 2,145,000	$ 2,100,000
Percentage of original principal amount payable		7.15%
Financing costs			$ 200,000
Percentage of interest upon event of default		4.00%
Term Loan \| Loan Agreement \| Maximum
Long Term Debt [Line Items]
Percentage of prepayment fee on outstanding principal balance		1.00%
Term Loan \| Prime Rate \| Loan Agreement
Long Term Debt [Line Items]
Debt instrument, basis spread on variable rate		1.05%
Term Loan 1 Borrowing through June 30, 2023 \| Term Loan 1 \| Loan Agreement
Long Term Debt [Line Items]
Debt instrument, amount borrowed	$ 10,000,000
Term Loan 1 Borrowing through June 30, 2023 \| Term Loan 1 \| Loan Agreement \| Maximum
Long Term Debt [Line Items]
Debt instrument, available credit under loan agreement					15,000,000
Term Loan 2 Borrowing through June 30, 2023 \| Term Loan 2 \| Loan Agreement \| Maximum
Long Term Debt [Line Items]
Debt instrument, available credit under loan agreement					20,000,000
Term Loan 3 Borrowing through March 31, 2024 \| Term Loan 3 \| Loan Agreement \| Maximum
Long Term Debt [Line Items]
Debt instrument, available credit under loan agreement					$ 25,000,000
Term Loan 1 Borrowing December 1, 2023 through May 31, 2024 \| Term Loan 1 \| Loan Agreement \| Maximum
Long Term Debt [Line Items]
Debt instrument, available credit under loan agreement	$ 5,000,000
Term Loan 1 Borrowing January 1, 2024 through July 19, 2024 \| Term Loan 1 \| Loan Agreement \| Maximum
Long Term Debt [Line Items]
Debt instrument, available credit under loan agreement						$ 5,000,000

Leases - Schedule of Future Minimum Noncancelable Operating Lease Payments (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Leases [Abstract]
2024	$ 2,688
2025	3,688
2026	3,784
2027	3,860
2028	3,974
Thereafter	17,102
Total undiscounted operating lease payments	35,096
Present value adjustment	(9,241)
Operating lease liability	25,855
Less current portion of operating lease liability	3,491	$ 3,118
Operating lease liability, net of current portion	$ 22,364	$ 22,831

Marketable Securities - Schedule of Fair Value of Available-For-Sale Marketable Debt Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	$ 131,794	$ 86,811
Gross Unrealized Gains	1	20
Gross Unrealized Losses	(128)	(26)
Fair Value	131,667	86,805
U.S. Treasury Notes
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	84,318	43,036
Gross Unrealized Gains	1	16
Gross Unrealized Losses	(76)	(2)
Fair Value	84,243	43,050
U.S. Government Agency Bonds
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	47,476	43,775
Gross Unrealized Gains		4
Gross Unrealized Losses	(52)	(24)
Fair Value	$ 47,424	$ 43,755

- 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

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+ Details

Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands				1 Months Ended	3 Months Ended		41 Months Ended
	Sep. 22, 2023	May 12, 2023	May 03, 2022	Apr. 30, 2022	Mar. 31, 2024	Mar. 31, 2023	May 31, 2022	Dec. 31, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected dividend yield					0.00%	0.00%
Number of issued shares of restricted common stock grants					1,036,450
Weighted Average Grant-Date Fair Value, Shares granted					$ 15.019	$ 18
Weighted average grant date fair value per share of option grants					$ 11.86	$ 13.8
Total unrecognized stock-based compensation cost related to stock options					$ 45,100
Sale of common stock							13,529,750
Increase in number of authorized shares of common stock					500,000,000			500,000,000
Increase in number of authorized shares of preferred stock					50,000,000			50,000,000
Shares reserved for issuance					10,017,725
Total unrecognized stock-based compensation cost related to restricted stock					$ 24,200
Sales Agreement
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Sale of common stock					1,016,950
Net proceeds from initial public offering			$ 14,900
Agreegate offering price					$ 14,887
Sales agreement date		May 12, 2023
Maximum commission percentage on gross proceeds of shares of common stock sold		3.00%
Maximum \| Sales Agreement
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Agreegate offering price		$ 100,000
Common Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unrecognized stock-based compensation cost expected to be recognized over remaining weighted-average period					3 years
Shares reserved for issuance					5,540,791
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unrecognized stock-based compensation cost expected to be recognized over remaining weighted-average period					3 years 4 months 24 days
Initial Public Offering
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Public offering price per share			$ 17
Sale of common stock			13,529,750
Net proceeds from initial public offering			$ 209,500				$ 209,500
Underwriting discounts, commissions and offering costs			$ 20,500
Increase in number of authorized shares of common stock			500,000,000
Increase in number of authorized shares of preferred stock			50,000,000
Underwritten Public Offering
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Public offering price per share	$ 12.5
Sale of common stock	9,200,000
Net proceeds after deducting underwriters commission	$ 107,800
Common Stock \| Sales Agreement
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Sale of common stock					1,016,950
Common Stock \| Underwritten Public Offering
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Sale of common stock	1,200,000
2021 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Plan term					ten years
Vesting period					4 years
Shares reserved for issuance					3,268,133
Number of shares remained available for issuance under awards granted				216,849
2022 Incentive Award Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Plan term						The 2022 Plan became effective in connection with the Company’s IPO and will remain in effect until the tenth anniversary of its effective date, which will be April 28, 2032, unless earlier terminated by the Company’s board of directors. The number of shares of the Company's common stock initially available for issuance under awards granted pursuant to the 2022 Plan was the sum of (1) 4,900,000 shares of the Company’s common stock, plus (2) 216,849 shares remaining available for issuance under the 2021 Plan as of the effective date of the 2022 Plan, plus (3) any shares subject to outstanding awards under the 2021 Plan as of the effective date of the 2022 Plan that become available for issuance under the 2022 Plan thereafter in accordance with its terms.
Shares reserved for issuance					9,580,823
Number of shares remained available for issuance under awards granted				4,900,000	3,268,133
Shares issuance, ending year				2032
Percentage of shares issued from outstanding number of shares				5.00%
2022 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved for issuance				410,000
Shares reserved for issuance					1,208,801
Maximum number of shares that may be authorized in accordance with plan				10,000,000
Shares issuance, ending year				2032
Percentage of shares issued from outstanding number of shares				1.00%
Purchase price of common stock, percent				85.00%

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 141,076	$ 216,678
Marketable securities	131,667	86,805
Prepaid expenses and other current assets (includes related party amounts of $77 and $0, respectively)	8,355	7,195
Total current assets	281,098	310,678
Property and equipment, net	13,592	14,018
Operating lease right-of-use assets	17,831	18,082
Restricted cash	1,631	1,631
Other assets	23	25
Total assets	314,175	344,434
Current liabilities:
Accounts payable	2,980	7,461
Accrued expenses (includes related party amounts of $27 and $33, respectively)	19,143	18,553
Accrued interest	135	134
Current portion of operating lease liability	3,491	3,118
Total current liabilities	25,749	29,266
Operating lease liability, net of current portion	22,364	22,831
Long-term debt, net of debt discount	25,453	25,244
Other long-term liabilities	1,700	1,568
Total liabilities	75,266	78,909
Commitments and contingencies (Note 8)
Stockholders' equity:
Preferred stock, $0.0001 par value; authorized shares- 50,000,000 at March 31, 2024 and December 31, 2023; no shares issued and outstanding at March 31, 2024 and December 31, 2023
Common stock, $0.0001 par value; authorized shares-500,000,000 at March 31, 2024 and December 31, 2023; issued shares- 49,718,443 and 48,497,853 at March 31, 2024 and December 31, 2023, respectively; outstanding shares-49,055,192 and 47,666,438 at March 31, 2024 and December 31, 2023, respectively	5	5
Additional paid-in capital	675,242	654,986
Accumulated other comprehensive loss	(950)	(907)
Accumulated deficit	(435,388)	(388,559)
Total stockholders' equity	238,909	265,525
Total liabilities and stockholders' equity	$ 314,175	$ 344,434