In June 2015, the Company entered into a lease agreement for the lease of research facility space in Cambridge, Massachusetts, with a commencement date of November 15, 2015, or the 2015 Lease. The lease was subsequently amended in both 2017 and 2020 and now expires in 2022 with no further option to extend. The 2015 Lease contains escalating rent clauses, which require higher rent payments in future years.

In May 2016, the Company entered into a sublease agreement for its primary office and research facility in Cambridge, Massachusetts, with a commencement date of December 23, 2016, or the 2016 Sublease. The sublease was subsequently amended in 2021 and now expires in 2022. The right-of-use assets and right-of-use liabilities were adjusted in the second quarter of 2021, accordingly. The 2016 Sublease contains escalating rent clauses, which require higher rent payments in future years.

In May 2019, the Company entered into a lease agreement for office facility space in Cambridge, Massachusetts, with a commencement date of June 1, 2019, or the 2019 Lease. The lease expires in November 2026, and the Company has an option to extend the term of the lease for an additional five-year period based on certain conditions within the Company’s control. The 2019 Lease contains escalating rent clauses which require higher rent payments in future years. The right-of-use asset and corresponding lease liability does not include the additional five-year period under the renewal option as the Company is not reasonably certain to exercise that option.

In December 2019, Casebia became a wholly-owned subsidiary of the Company. In connection therewith, Casebia assigned its sublease for an office and research facility in Cambridge, Massachusetts, or the 2019 Sublease, to the Company. The sublease was subsequently amended in 2021 and now expires in 2022 with no further option to extend. The right-of-use assets and right-of-use liabilities were adjusted in the second quarter of 2021, accordingly. The 2019 Sublease contains escalating rent clauses which require higher rent payments in future years.

In May 2020, the Company entered into a lease agreement for a cell therapy manufacturing facility in Framingham, Massachusetts, or the Framingham Lease, for clinical and commercial production of the Company’s investigational cell therapy product candidates. The Framingham Lease expires in March 2036 and the Company has an option to extend the term of the lease for two additional seven-year periods. The right-of-use asset and corresponding lease liability does not include the additional seven-year periods under the renewal option as the Company is not reasonably certain to exercise that option.

In July 2020, the Company entered into a lease agreement for an office and laboratory facility in Boston, Massachusetts, or the 2020 Lease. The 2020 Lease commenced in the second quarter of 2021, and at lease commencement, the Company recorded a right-of-use asset of $149.8 million and a corresponding operating lease liability of $147.9 million. Tenant incentives of $49.2 million were recorded as a reduction to the operating lease asset and liability at lease commencement. The right-of-use asset and corresponding lease liability does not include the additional five-year periods under the renewal option as the Company is not reasonably certain to exercise that option. The lease expires in March 2034 and the Company has an option to extend the term of the lease for two additional five-year periods.

In addition, the Company rents certain office space in Zug, Switzerland, on a short-term basis for which a right-of-use asset and liability are not recorded, in accordance with the practical expedient elected.

The Company has embedded leases in certain research and license agreements for which the Company has recorded a right of use asset and liability. These arrangements are not significant in comparison to the Company’s total operating lease assets and liabilities. In addition, the Company has identified certain short-term leases embedded within its manufacturing contracts which are not recorded on the Company’s balance sheet in accordance with the practical expedient elected.

The Company identified and assessed the following estimates in recognizing the right-of-use asset and corresponding liability:

The following table summarizes the lease assets and liabilities as of December 31, 2021 and 2020 (in thousands):


	As of December 31,
	2021		2020
Assets
Operating lease assets	$	174,460	$	50,865
Total lease assets		174,460		50,865
Liabilities
Current
Operating lease liabilities		12,158		11,362
Non-current
Operating lease liabilities, net of current portion		212,872		50,067
Total lease liabilities	$	225,030	$	61,429

The following table summarizes operating lease costs included in research and development and general and administrative expense, as well as sublease income for the twelve months ended December 31, 2021, 2020 and 2019 (in thousands):


	Years Ended December 31,
	2021			2020			2019
Operating lease costs	$	22,520		$	14,342		$	8,067
Short-term lease costs		11,087			7,339			4,554
Variable lease costs		8,402			6,368			4,282
Sublease income		(5,253	)		(587	)		(525	)
Net lease cost	$	36,756		$	27,462		$	16,378

The following table summarizes the maturity of undiscounted payments due under lease liabilities and the present value of those liabilities as of December 31, 2021 (in thousands):


	Total
2022		18,256
2023		26,633
2024		26,137
2025		26,347
2026		26,844
Thereafter		227,528
Total	$	351,745
Present value adjustment		(126,715	)
Present value of lease liabilities	$	225,030

The following table summarizes the lease term (in years) and discount rate for operating leases as of December 31, 2021 and 2020:


	As of December 31,
	2021			2020
Weighted-average remaining lease term		12.4			9.1
Weighted-average discount rate		5.9	%		9.3	%

The following table summarizes the cash paid for amounts included in the measurement of lease liabilities for the year ended December 31, 2021 and 2020 (in thousands):


	Years Ended December 31,
	2021			2020			2019
Cash paid for amounts included in measurement of lease liabilities:
Operating cash flows used in operating leases	$	(19,753	)	$	(13,161	)	$	(8,420	)
Operating lease non-cash items:
Right-of-use assets (decreased) increased through lease modifications and reassessments		(14,230	)		3,169			826
Right-of-use assets obtained in exchange for operating lease liabilities		152,486			13,956			18,088
Leasehold improvements paid directly by landlord		30,500			—			—