IMPAIRMENT OF GOODWILL AND LONG-LIVED ASSETS	3 Months Ended
IMPAIRMENT OF GOODWILL AND LONG-LIVED ASSETS	Mar. 31, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
IMPAIRMENT OF GOODWILL AND LONG-LIVED ASSETS	IMPAIRMENT OF GOODWILL AND LONG-LIVED ASSETS During the year ended December 31, 2023, the Company experienced a sustained decline in stock price and related market capitalization, the collaboration agreements with Biogen and Novartis were terminated, and actions were initiated including deferral and reprioritization of certain research and development programs, announcement and execution of restructuring of operations and reductions in force. As a result, throughout the year the Company tested various long-lived and indefinite-life intangible assets for impairment and recognized a pre-tax goodwill impairment charge of $38.1 million, a pre-tax indefinite-lived intangible asset impairment charge of $51.4 million along with the income tax benefit from the reduction of the associated deferred tax liability of $6.3 million, and a pre-tax long-lived assets impairment charge of $65.5 million during the year ended December 31, 2023. Three months ended March 31, 2024 During the three months ended March 31, 2024, the Company’s Board of Directors approved the wind-down of operations in France and corresponding reduction in workforce, including closure of the Company’s cell therapy manufacturing facility and research labs in Valbonne, France (the “France Restructuring”), and also initiated several actions aimed at reducing costs, including actions to commence the closure of its facility in Brisbane, California. As such, the Company reassessed its long-lived assets for impairment as of March 31, 2024. In connection with the France Restructuring, the Company concluded its equipment, furniture and fixtures located in France met the held for sale criteria as of March 31, 2024. The Company wrote down the carrying value of these assets to their estimated fair value of $1.0 million, net of the estimated costs to sell, recognizing a loss of $1.8 million. Assets held for sale are included within prepaid expenses and other current assets on the Company’s Condensed Consolidated Balance Sheet as of March 31, 2024. The fair value measurement represents a level 3 nonrecurring fair value measurement. The loss is included in impairment of long-lived assets in the accompanying Condensed Consolidated Statements of Operations. The sale of these assets is expected to occur within one year, either collectively or separately through vendor(s) or at auction. The Company also reassessed whether its remaining long-lived assets continued to represent a single asset group for purposes of impairment assessment. After considering changes in the manner in which the right-of-use assets and leasehold improvements related to the Company’s Brisbane and Valbonne, France, facilities are used, costs incurred to cease use of these assets, the France Restructuring, and the Company’s activities to market these facilities for sublease, the Company concluded the identifiable operations and cash flows of these assets are now largely independent of the operations and the cash flows of each other, as well as of the remainder of the Company. Accordingly, the Company assessed impairment of the resulting asset groups separately. Based on the changes in the use of assets related to the Brisbane and Valbonne facility leases, the Company concluded there were indicators of impairment for these asset groups, and further established that the carrying values of these asset groups were not recoverable. The Company proceeded to determine their fair values using a discounted cash flow method, which represents a level 3 nonrecurring fair value measurement. As a result, the Company recognized pre-tax long-lived asset impairment charges of $2.0 million on the right-of-use assets and $0.5 million on the related leasehold improvements during the three months ended March 31, 2024. No impairment was recognized on the remaining long-lived assets, as their carrying values were not in excess of their fair values. The Company will continue to assess whether its long-lived assets are impaired in future periods. As the Company finalizes the wind-down of its France operations and corresponding reduction in force of all France employees, as well as the closure of its Brisbane facility, it is reasonably possible that additional impairment charges will be recognized, for example, if sublease rates of leased facilities or selling prices of the assets held for sale are less than those estimated. Three months ended March 31, 2023 During the three months ended March 31, 2023, as a result of the sustained decline in the Company’s stock price and related market capitalization, termination of the collaboration agreements with Biogen and Novartis, the Company performed an impairment assessment of goodwill, indefinite-lived intangible assets, and other long-lived assets. The Company operated as a single reporting unit based on its business and reporting structure. For goodwill, a quantitative impairment assessment was performed using a market approach, whereby the Company’s fair value of equity was compared to its carrying value. The fair value of equity was derived using both the market capitalization of the Company and an estimate of a reasonable range of values of a control premium applied to the Company’s implied business enterprise value. The control premium was estimated based upon control premiums observed in comparable market transactions. This represented a level 2 nonrecurring fair value measurement. Based on this analysis, the Company recognized a pre-tax goodwill impairment charge of $38.1 million during the three months ended March 31, 2023. As a result, the goodwill was fully impaired as of March 31, 2023. Before completing the goodwill impairment assessment, the Company also tested its indefinite-lived intangible assets and then its long-lived assets for impairment. Based on the qualitative assessment, the Company determined it was more likely than not that its indefinite-lived intangible assets were not impaired. The Company determined all of its long-lived assets represented one asset group for purposes of long-lived asset impairment assessment. The Company concluded that the carrying value of the asset group was not recoverable as it exceeded the future undiscounted cash flows the assets were expected to generate from the use and eventual disposition. To allocate and recognize the impairment loss, the Company determined individual fair values of its long-lived assets. The Company applied a discounted cash flow method to estimate fair values of its leasehold improvements and right-of-use assets, including leasehold improvements in the process of construction and a cost replacement method to estimate the fair value of its furniture, fixtures and laboratory and manufacturing equipment. These represented level 3 nonrecurring fair value measurements. Based on this analysis, the Company recognized pre-tax long-lived asset impairment charges of $11.2 million on the right-of-use assets, $5.0 million on the related leasehold improvements, and $4.2 million on construction-in-progress, during the three months ended March 31, 2023. No impairment was recognized on the remaining long-lived assets as their carrying values were not in excess of their fair values.