Commitments and Contingencies	6 Months Ended
Jun. 30, 2025
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 Vaccines, Inc. (“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 June 30, 2025, 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 and six months ended June 30, 2025 and 2024. 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 paid an upfront amount of $15.0 million. 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 three and six months ended June 30, 2024. The Company did not make any milestone payments to Kangh during the three and six months ended June 30, 2025. 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. During the year ended December 31, 2022, the Company began matching contributions equal to 100% of the employee’s contributions, subject to a maximum of 4% of eligible compensation. The Company made an immaterial amount of matching contributions during the three and six months ended June 30, 2025 and 2024. 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. The Company did not have any material contingent liabilities as of June 30, 2025 and December 31, 2024.

Commitments and Contingencies

6 Months Ended

Jun. 30, 2025

Commitments and Contingencies Disclosure [Abstract]

8. Commitments and Contingencies

License Agreement with Takeda

On July 2, 2021, the Company entered into a license agreement with Takeda Vaccines, Inc. (“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 June 30, 2025, 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 and six months ended June 30, 2025 and 2024.

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 paid an upfront amount of $15.0 million. 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 three and six months ended June 30, 2024. The Company did not make any milestone payments to Kangh during the three and six months ended June 30, 2025.

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. During the year ended December 31, 2022, the Company began matching contributions equal to 100% of the employee’s contributions, subject to a maximum of 4% of eligible compensation. The Company made an immaterial amount of matching contributions during the three and six months ended June 30, 2025 and 2024.

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. The Company did not have any material contingent liabilities as of June 30, 2025 and December 31, 2024.