As discussed in Note 1, because our registrational trials in bempegaldesleukin did not meet their primary endpoints, we decided to discontinue all development of bempegaldesleukin and wind down the clinical trials studying bempegaldesleukin. In April 2022, we announced the 2022 Restructuring Plan pursuant to which we completed an approximate 70% reduction of our workforce during 2022. We also sold our research facility in India in December 2022 and decided to sublease certain of our leased premises in San Francisco, CA, including all of our office leased space in the Third Street Facility and portions of our office and laboratory space in the Mission Bay Facility.

Pursuant to plans approved by our Board in March 2023, we announced the 2023 Restructuring Plan to further reduce our San Francisco-based workforce by approximately 60%, which was substantially completed by June 30, 2023. In addition, under the 2023 Restructuring Plan, we decided to sublease our remaining office and laboratory space in the Mission Bay Facility, which we had not planned to sublease pursuant to the 2022 Restructuring Plan.

In connection with our 2022 and 2023 Restructuring Plans, we report the following costs in restructuring, impairment and costs of terminated program:

Restructuring, impairment and costs of terminated program includes the following (in thousands):


	Year Ended December 31,
	2023						2022
	2022 Restructuring Plan		2023 Restructuring Plan		Total		2022 Restructuring Plan
Clinical trial expense, other third-party and employee costs for the wind down of the bempegaldesleukin program	$	5,492	$	—	$	5,492	$	31,693
Severance and benefit expense		—		7,885		7,885		30,904
Impairment of right-of-use assets and property, plant and equipment		14,728		20,600		35,328		65,761
Loss (gain) on sale or disposal of other property, plant and equipment, net		—		1,300		1,300		(3,326	)
Contract termination and other restructuring costs		1,919		34		1,953		10,898
Restructuring, impairment and costs of terminated program	$	22,139	$	29,819	$	51,958	$	135,930

In prior periods through March 31, 2022, we reported the clinical trial costs, other third-party costs and employee costs related to the bempegaldesleukin program primarily in research and development expense. Beginning in the second quarter of 2022, we began reporting clinical trial, other third-party costs and employee costs for the wind down of the bempegaldesleukin program in restructuring, impairment and costs of terminated program.

The clinical trial expense, other third-party and employee costs for the wind down of the bempegaldesleukin program for the year ended December 31, 2022 includes reductions of $20.8 million, for the net reimbursement from BMS. The net reimbursement payable to BMS for the year ended December 31, 2023 was not significant.

Employees affected by the reduction in force under the 2022 and 2023 Restructuring Plans are entitled to receive severance payments and certain Company funded benefits. The restructuring charges are recorded at fair value.

For the 2022 Restructuring Plan, we recognized severance and benefit expense in full for employees who had no requirements for future service upon approval of the 2022 Restructuring Plan by the Board in April 2022. We recognized severance and benefit expense for employees who were required to render services to receive their severance and benefits ratably over the service period. This service period began on the communication date in April 2022 and was completed for all employees during 2022. We recognized $30.9 million in total severance and benefit expense during 2022 and paid the remaining liability of $3.3 million in January 2023.

For the 2023 Restructuring Plan, we recognized $7.9 million of severance and benefit expense for the year ended December 31, 2023 and paid the final liability of $0.2 million in January 2024. We do not expect to recognize any further severance expense for the 2023 Restructuring Plan.

The following table provides details regarding the severance and benefit expense for the years ended December 31, 2023 and 2022 pursuant to the 2022 and 2023 Restructuring Plans and a reconciliation of the severance and benefits liability for the year ended December 31, 2023 pursuant to the 2022 and 2023 Restructuring Plans, which we report within accrued expenses on our Consolidated Balance Sheets (in thousands):


	2023 Restructuring Plan			2022 Restructuring Plan			Total
Liability balance as of December 31, 2021	$	—		$	—		$	—
Expense recognized during the period		—			30,904			30,904
Payments during the period		—			(27,605	)		(27,605	)
Liability balance as of December 31, 2022	$	—		$	3,299		$	3,299
Expense recognized during the period		7,885			—			7,885
Payments during the period		(7,689	)		(3,299	)		(10,988	)
Liability balance as of December 31, 2023	$	196		$	—		$	196

As a result of our 2022 and 2023 Restructuring Plans, we have decided to sublease all of our leased spaces in the Third Street Facility and the Mission Bay Facility. Accordingly, we evaluated each space for impairment when management decided to sublease the respective space and at each reporting date thereafter, as facts and circumstances change. The significant assumptions in our impairment analysis relate to sublease income, including the length of time to enter into a sublease, sublease rental payments, free rent periods, tenant improvement allowances and broker commissions. When available, we use sublease negotiations or agreements, but in the absence of such information, we develop our own subjective estimates based on current real estate trends and market conditions. Accordingly, our estimates are subject to significant risk, and the terms of sublease agreements, if any, and the resulting amount and timing of sublease income, if ever realized, may be materially different than our estimates.

As part of our evaluation of each sublease space, we separately compare the estimated undiscounted sublease income, as described above, for each sublease to the net book value of the related long-term assets, which include right-of-use assets and certain property, plant and equipment, primarily for leasehold improvements (collectively, sublease assets). If such sublease income exceeds the net book value of the sublease assets, we do not record an impairment charge. Otherwise, we record an impairment charge by reducing the net book value of the sublease assets to their estimated fair value, which we determined by discounting the estimated sublease income using the estimated borrowing rate of a market participant subtenant, which has ranged from 6.4% for the three months ended June 30, 2022 to 8.7% for the three months ended September 30, 2023.

We recorded non-cash impairment charges of lease assets pertaining to the 2022 and 2023 Restructuring Plans as follows (in thousands):


	Three-months Ended
Sublease Spaces	June 30, 2022		September 30, 2022		December 31, 2022		March 31, 2023		June 30, 2023		September 30, 2023		December 31, 2023		Total
Mission Bay Blvd. South	$	3,000	$	1,200	$	361	$	—	$	7,061	$	1,467	$	—	$	13,089
Third St		49,200		—		12,000		—		6,200		—		—		67,400
Total 2022 Restructuring Plan		52,200		1,200		12,361		—		13,261		1,467		—		80,489
Mission Bay Blvd. South - 2023 Restructuring Plan	N/A		N/A		N/A			11,500		—		9,100		—		20,600
Total impairment of lease assets	$	52,200	$	1,200	$	12,361	$	11,500	$	13,261	$	10,567	$	—	$	101,089

The following are reconciliations of the impairment charges we recorded for the years ended December 31, 2023 and 2022, including the net book values of the sublease assets before the impairment and the fair values of the sublease assets. Since we recorded multiple impairment charges for certain spaces as a resulting of worsening lease markets, we present the net book value before the first impairment in such year and the fair value after the second impairment in such year (in thousands):


	Year Ended December 31, 2022
	Operating Lease			Property, Plant and
	Right-of-Use Assets			Equipment			Total
Net book value of impaired sublease assets	$	72,481		$	16,348		$	88,829
Less: Fair value of impaired sublease assets — Level 3 of Fair Value Hierarchy		(16,174	)		(4,780	)		(20,954	)
Book value in excess of fair value		56,307			11,568			67,875
Less: Amounts recorded as amortization between June 30, 2022 and December 31, 2022 for Third St. facility		(1,717	)		(397	)		(2,114	)
Total impairment of sublease assets	$	54,590		$	11,171		$	65,761


	Year Ended December 31, 2023
	Operating Lease Right-of-Use Assets			Property, Plant and Equipment			Total
Net book value of impaired facilities before write-off	$	46,292		$	7,206		$	53,498
Less: Fair value of impaired facilities — Level 3 of Fair Value Hierarchy		(14,364	)		(2,172	)		(16,536	)
Book value in excess of fair value		31,928			5,034			36,962
Less: Amounts recorded as amortization between March 31, 2023 and September 30, 2023 for Mission Bay facility		(1,371	)		(263	)		(1,634	)
Total impairment of right-of-use assets and property, plant and equipment	$	30,557		$	4,771		$	35,328

In connection with our 2022 Restructuring Plan, we terminated all research and development activities at our owned facility in India, which we sold in December 2022. We also sold excess lab equipment and disposed of software to support the commercialization of bempegaldesleukin. In 2023, we sold additional lab equipment under the 2023 Restructuring Plan. We recorded the gains and losses as follows (in thousands):

The following is a reconciliation of the contract termination and other costs for the 2022 Restructuring Plan and the related liability of which we report $3.0 million within accrued expenses and the remaining within other long-term liabilities on our Consolidated Balance Sheet as of December 31, 2023:


	Year Ended
	December 31, 2023
Liability balance as of December 31, 2021	$	—
Expense recognized during the period		10,898
Payments during the period		(3,188	)
Liability balance as of December 31, 2022		7,710
Expense recognized during the period		1,919
Payments during the period		(4,087	)
Liability balance as of December 31, 2023	$	5,542