In November 2018, the Company entered into an operating lease, as amended from time to time, for approximately 186,000 square feet of office, laboratory and manufacturing facilities at a new building to be constructed at 9804 Medical Center Drive in Rockville, Maryland (the 9804 Medical Center Drive Lease), which will serve as the Company’s corporate, research and manufacturing headquarters. The initial construction of the building was performed by the landlord and the lease commenced in September 2020 upon delivery of the leased premises to the Company to make additional improvements to the building. Monthly payments under the lease began in September 2021 and escalate annually in accordance with the lease agreement. The lease expires in September 2036, subject to extension and termination options held by the Company. The Company has the option to extend the term of the lease for up to 10 additional years and the option to terminate the lease, with payment of an early termination fee, after 12 years from the delivery of the leased premises to the Company. As of December 31, 2021, the Company’s extension and termination options under the 9804 Medical Center Drive Lease have been excluded from the measurement of the right-of-use assets and lease liabilities as they were not reasonably certain of exercise. As required by the lease agreement, the Company has provided the landlord with an irrevocable letter of credit of $1.1 million which the landlord may draw upon in the event of any uncured default by the Company under the terms of the lease.

Pursuant to the 9804 Medical Center Drive Lease, the Company received a $19.5 million tenant improvement allowance from the landlord to perform improvements to the leased premises. The tenant improvement allowance has been recorded as a reduction of the right-of-use assets for the lease and is amortized on a straight-line basis as a reduction of lease expense over the term of the lease. As of December 31, 2021, the Company had unreimbursed amounts remaining under the tenant improvement allowance of $1.5 million, which were deemed in-substance lease payments and recorded as a reduction of the lease liability. The Company began occupation of a portion of the facility in 2021, while the buildout of the remaining portion of the building, including the manufacturing facility, is expected to be completed in the first half of 2022. As of December 31, 2021, the Company had recorded property and equipment at cost of $113.2 million related to the buildout at 9804 Medical Center Drive, of which $41.2 million was placed in service upon the initial occupation of the building in 2021 and $72.0 million, primarily related to the manufacturing facility, has not yet been placed in service.

The Company recorded the right-of-use assets and lease liabilities related to the 9804 Medical Center Drive Lease upon its commencement in September 2020. As of December 31, 2021, the Company had recorded right-of-use assets of $48.3 million and lease liabilities of $72.5 million related to the 9804 Medical Center Drive Lease.

In March 2015, the Company entered into an operating lease for office space at 9712 Medical Center Drive in Rockville, Maryland (the 9712 Medical Center Drive Lease). The lease term commenced in April 2015, and monthly payments under the lease began in October 2015 and escalate annually in accordance with the lease agreement.

The 9712 Medical Center Drive Lease has been amended from time to time to include additional office and laboratory space at an adjacent building located at 9714 Medical Center Drive and extend the term of the lease. In October 2020, the 9712 Medical Center Drive Lease was amended to extend the lease term from September 2021 to February 2027, subject to extension options held by the Company. The October 2020 amendment resulted in a $7.2 million increase in the right-of-use assets and lease liabilities under the 9712 Medical Center Drive Lease. The Company has an option to extend the term of the lease for three additional years, as well as an option to extend the lease term to be coterminous with the 9804 Medical Center Drive Lease, which expires in September 2036. As of December 31, 2021, the Company’s extension options under the 9712 Medical Center Drive Lease have been excluded from the measurement of the right-of-use assets and lease liabilities as they were not reasonably certain of exercise. The Company received a $0.4 million tenant improvement allowance from the landlord which has been recorded as a reduction of the right-of-use assets for the lease and is amortized on a straight-line basis as a reduction of lease expense over the term of the lease.

In May 2016, the Company entered into an operating lease for office space at 400 Madison Avenue in New York, New York (the 400 Madison Lease). The lease term commenced in July 2016, and monthly payments under the lease began in October 2016 and escalate annually in accordance with the lease agreement. In May 2019, the 400 Madison Lease was amended to include additional office space and extend the lease term from October 2020 to April 2027. The May 2019 amendment resulted in a $5.2 million increase in the right-of-use assets and lease liabilities under the 400 Madison Lease. The Company received a $0.7 million tenant improvement allowance from the landlord which has been recorded as a reduction of the right-of-use assets for the lease and is amortized on a straight-line basis as a reduction of lease expense over the term of the lease. As required by the lease agreement, the Company has provided the landlord with an irrevocable letter of credit of $0.2 million which the landlord may draw upon in the event of any uncured default by the Company under the terms of the lease.

In November 2020, the Company exercised its termination option under the operating lease for its former corporate headquarters at 9600 Blackwell Road in Rockville, Maryland (the 9600 Blackwell Road Lease). Upon exercise of the termination option, the Company was obligated to pay an early termination fee of $0.4 million and the lease term was reduced from September 2023 to September 2021. The exercise of the termination option in November 2020 resulted in a $0.7 million decrease in the right-of-use assets and lease liabilities under the 9600 Blackwell Road Lease, and the lease was terminated upon its expiration in September 2021.

The Company leases additional laboratory and other equipment under operating leases with various expiration dates through 2028, including leases which have been executed but have not yet commenced.

All of the Company’s leases are classified as operating leases. The following table summarizes the Company’s lease costs and supplemental cash flow information related to its operating leases (in thousands):

	Years Ended December 31,
	2021			2020			2019
Operating lease cost	$	9,729		$	5,246		$	3,040
Variable lease cost		2,348			1,104			666
Total lease cost	$	12,077		$	6,350		$	3,706

Cash paid (received) for amounts included in operating lease liabilities	$	(6,765	)	$	(678	)	$	2,724
Right-of-use assets acquired through operating lease liabilities	$	1,955		$	56,956		$	5,114

Cash received for amounts included in operating lease liabilities for the years ended December 31, 2021 and 2020 includes $11.4 million and $5.0 million, respectively, received by the Company during the period under its tenant improvement allowances, which were deemed in-substance lease payments and included in the calculation of the lease liability. Right-of-use assets acquired through operating lease liabilities for the years ended December 31, 2020 and 2019 include additions and reductions to right-of-use assets resulting from lease modifications and changes in lease term. Short-term lease expense for the years ended December 31, 2021, 2020 and 2019 was not material and is included in operating lease cost in the table above. Variable lease cost under the Company’s operating leases includes items such as common area maintenance, utilities, taxes and other charges.

The weighted-average remaining lease term and weighted-average discount rate of the Company’s operating leases were as follows:

	As of December 31,
	2021			2020
Weighted-average remaining lease term (years)		13.2			13.7
Weighted-average discount rate		5.6	%		5.6	%

The following table presents a reconciliation of the undiscounted future minimum lease payments remaining under the Company’s operating leases to the amounts reported as operating lease liabilities on the consolidated balance sheet as of December 31, 2021 (in thousands):

	As of
	December 31, 2021
Undiscounted future minimum lease payments:
2022	$	6,556
2023		9,163
2024		10,224
2025		10,383
2026		10,388
Thereafter		83,050
Total undiscounted future minimum lease payments	$	129,764
Amount representing imputed interest		(41,619	)
Tenant improvement allowance not yet received		(1,464	)
Total operating lease liabilities		86,681
Current portion of operating lease liabilities		(1,752	)
Operating lease liabilities, non-current	$	84,929

The table above excludes future minimum lease payments for leases which were executed but had not yet commenced as of December 31, 2021, the total of which were not material.