Leases

12 Months Ended

Dec. 31, 2025

In July 2017, the Company entered into a lease of office and laboratory space for its headquarters in Watertown, Massachusetts, or the Watertown Lease. The Watertown Lease had a non-cancelable term of ten years with an option to extend for one additional five-year period and is subject to rent escalation throughout the term. Additionally, the Watertown Lease required the Company to provide collateral, which was recorded as restricted cash on the consolidated balance sheets. The Watertown Lease commenced in April 2018. The Watertown Lease was classified as an operating lease and, upon the commencement in April 2018, the Company recorded a lease liability of $15.1 million and a right-of-use asset of $16.7 million, which is inclusive of $1.5 million of construction costs funded by the Company. In initially calculating the lease liability and the right-of-use asset, the Company did not include the additional five-year period option as management did not believe there was reasonable certainty that the Company would exercise the option. In addition to rent, the Company is also responsible for paying its pro rata share of costs incurred for common area maintenance, real estate taxes and property insurance related to the leased space, which are accounted for as variable lease costs.

In November 2021, the Company entered into an amendment to the Watertown Lease, or the Amended Lease. The Amended Lease serves to extend the lease term of the Company’s existing leased space, or the Existing Leased Space, and provides additional office and laboratory space, or the Newly Leased Space. The Amended Lease commenced in January 2022 and the Company’s obligation to pay rent on the Newly Leased Space commenced in March 2022, with the amount of this new rent obligation added to the Company’s continuing obligation to pay rent on the Existing Leased Space. The Amended Lease terminates in March 2032, which is 10 years from the rent commencement date for the Newly Leased Space. The Amended Lease is subject to fixed rate rent escalations, provides for up to $2.6 million in tenant improvements, and provides an option for the Company to extend the lease term of the Amended Lease for one additional five-year period. Upon executing the Amended Lease, the Company increased its collateral to $3.3 million, which is recorded as restricted cash on the accompanying consolidated balance sheets as of December 31, 2025 and 2024. In addition to rent, under the terms of the Amended Lease, the Company is also responsible for paying its pro rata share of costs incurred for common area maintenance, real estate taxes and property insurance related to the leased space, including both the Existing Leased Space and, as of January 2022, the Newly Leased Space, which amounts are accounted for as variable lease costs.

Accounting for the amended lease

As the Amended Lease extends the term of the Existing Leased Space and provides access to the Newly Leased Space, in accordance with the provisions of ASC 842, the Company accounted for the Amended Lease as two separate contracts: 1) modification of the existing lease agreement to extend the lease term of the Existing Leased Space, and 2) new lease agreement for the right-of-use of the Newly Leased Space.

As the Company maintained control of the Existing Leased Space upon execution of the Amended Lease, the Company recorded an increase in right-of-use asset and lease liability of $20.1 million related to the new rental payments during the extended term and current incremental borrowing rate of the Existing Leased Space upon execution of the Amended Lease. The calculation of the lease liability and the right-of-use asset of the Existing Leased Space does not include the additional five-year period option as the Company does not believe there is reasonable certainty that the option will be exercised.

As noted above, the lease for the Newly Leased Space commenced in January 2022. As a result, the Company recorded a right-of-use asset of $44.4 million, and a corresponding lease liability of $44.1 million for the Newly Leased Space. The calculation of the lease liability and the right-of-use asset of the Newly Leased Space does not include the additional five-year period option provided under the Amended Lease as the Company does not believe there is reasonable certainty that the option will be exercised. As stated above, the Amended Lease provides for up to $2.6 million of tenant improvement allowance which was used in full in the year ended December 31, 2023.

In May 2022, the Company entered into a sublease agreement with a third party, or the Sublease, for a portion of the office and laboratory space in Suite 200 at 490 Arsenal Way, Watertown, Massachusetts. The term of the Sublease ended in June 2025.

In September 2025, the Company entered into a sublease agreement with a third party, or the 2025 Sublease, for a portion of the office and laboratory space in Suite 200 at 490 Arsenal Way, Watertown, Massachusetts. The term of the 2025

Sublease commences in February 2026 and ends in January 2029, with an option to extend for an additional two year term. This transaction triggered an impairment analysis, which resulted in the recognition of a $10.6 million impairment charge for the Suite 200 right-of-use (ROU) asset for the year ended December 31, 2025.

The impairment charge reduces the carrying value of the associated ROU asset, leasehold improvements and certain furniture and fixture assets that remained in the facility to their estimated fair values. The fair values are estimated using a discounted cash flows approach based on forecasted future cash flows expected to be derived from the property based on current sublease market rent, which is considered a Level 3 input in the fair value hierarchy, and other key assumptions such as future sublease market conditions and the discount rate.

The elements of lease costs were as follows (in thousands):


	Years Ended December 31,
	2025		2024
Lease cost:
Operating lease cost	$	9,747	$	10,030
Variable lease cost	2,649		1,843
Sublease income	(1,637)		(2,626)
Total lease cost	$	10,759	$	9,247

The following table summarizes the lease term and incremental borrowing rate applied in arriving at the lease liability:


	As of December 31,
	2025		2024
Remaining lease term	6.1 years		7.1 years
Incremental borrowing rate	5.3	%	5.3	%

Future lease payments under non-cancelable leases as of December 31, 2025 for each of the years ending December 31 are as follows (in thousands):


Undiscounted lease payments:
2026	$	9,366
2027	9,646
2028	11,362
2029	12,413
2030	12,785
Thereafter	15,553
Total undiscounted lease payments	71,125
Less: imputed interest	(11,143)
Total operating lease liability as of December 31, 2025	$	59,982