LEASES	9 Months Ended
Sep. 30, 2020
Leases [Abstract]
LEASES	13. LEASES The Company has real estate operating leases in Cambridge, Andover and Burlington, Massachusetts and Dublin and Columbus, Ohio that provide for scheduled annual rent increases throughout each lease’s term. There have been no significant changes to the real estate leases in the nine months ended September 30, 2020. The Company has also identified embedded leases in its manufacturing and supply agreements with Catalent, Inc. (“Catalent”) and Thermo Fisher Scientific, Inc. (“Thermo”). For additional details relating to these two agreements, please read Note 21, Commitments and Contingencies of the Annual Report on Form 10-K for the year ended December 31, 2019. The Company determined that both the Catalent and Thermo agreements contain an embedded lease because the Company controls the use of the facilities and related equipment therein. The Company also determined that it does not control the facilities or related equipment during construction and, thus, the lease does not fall in the scope of “build-to-suit” accounting. The lease on two of the four dedicated clean room suites at Catalent and four of the eight dedicated clean room suites at Thermo commenced during the first and second quarter of fiscal 2020, respectively, which is when the dedicated clean room suites became available for use by the Company. Accordingly, the fixed and in-substance fixed contract consideration associated with the dedicated clean room suites was allocated to the lease and non-lease components. The lease component was determined based on the estimated standalone price of the leased clean rooms and the associated equipment based on available market and specific cost information. The non-lease component was determined using the residual estimation approach as the standalone price of the gene therapy manufacturing and supply services provided by both Catalent and Thermo is highly variable. Consequently, as of the nine months ended September 30, 2020, the Company had aggregate right of use (“ROU”) assets of $36.3 million and aggregate lease liabilities of $32.2 million relating to the dedicated clean room suites at both Catalent and Thermo. The initial ROU assets and lease liabilities recorded were based on the present value of estimated future payments associated with the lease component of the Catalent and Thermo clean room suites at discount rates of 8.0% and 7.5%, respectively, representing the rate at which the Company could borrow on a collateralized basis the amount of the lease payments in a similar term. The difference between the ROU assets and the lease liabilities results from certain prepayments made to Catalent and Thermo by the Company prior to the commencement of the leases. The weighted average remaining lease term on the leases for the dedicated clean room suites range between 4.3 and 7.2 years. The total lease liability payments are expected to be paid in equal installments through the five-year and eight-year terms of the Catalent and Thermo agreements, respectively. The leases on the remaining two clean room suites at Catalent and four clean room suites at Thermo have not commenced as of September 30, 2020 because these clean room suites are not yet available for use by the Company. Accordingly, cumulative payments totaling $24.0 million and $47.9 million made to Catalent and Thermo, respectively, relating to the remaining clean room suites which have not become available to the Company have been recorded as other assets in the accompanying unaudited condensed consolidated balance sheets, a portion of which will be considered in the initial measurement of the cost of the ROU asset at the lease commencement date, currently anticipated to occur in the fourth quarter of 2020 for Catalent and the first half of 2021 for Thermo. For the three and nine months ended September 30, 2020, the Company recorded aggregate operating lease costs of $2.2 million and $5.0 million related to the Catalent and Thermo embedded leases, respectively. For the three and nine months ended September 30, 2020, the Company recorded aggregate variable lease costs of $3.0 million and $7.5 million, respectively. The operating lease costs and variable lease costs of the Thermo and Catalent embedded leases were included in research and development expense in the accompanying unaudited condensed consolidated statements of operations and comprehensive loss.

LEASES

9 Months Ended

Sep. 30, 2020

13. LEASES

The Company has real estate operating leases in Cambridge, Andover and Burlington, Massachusetts and Dublin and Columbus, Ohio that provide for scheduled annual rent increases throughout each lease’s term. There have been no significant changes to the real estate leases in the nine months ended September 30, 2020. The Company has also identified embedded leases in its manufacturing and supply agreements with Catalent, Inc. (“Catalent”) and Thermo Fisher Scientific, Inc. (“Thermo”). For additional details relating to these two agreements, please read Note 21, Commitments and Contingencies of the Annual Report on Form 10-K for the year ended December 31, 2019. The Company determined that both the Catalent and Thermo agreements contain an embedded lease because the Company controls the use of the facilities and related equipment therein. The Company also determined that it does not control the facilities or related equipment during construction and, thus, the lease does not fall in the scope of “build-to-suit” accounting.

The lease on two of the four dedicated clean room suites at Catalent and four of the eight dedicated clean room suites at Thermo commenced during the first and second quarter of fiscal 2020, respectively, which is when the dedicated clean room suites became available for use by the Company. Accordingly, the fixed and in-substance fixed contract consideration associated with the dedicated clean room suites was allocated to the lease and non-lease components. The lease component was determined based on the estimated standalone price of the leased clean rooms and the associated equipment based on available market and specific cost information. The non-lease component was determined using the residual estimation approach as the standalone price of the gene therapy manufacturing and supply services provided by both Catalent and Thermo is highly variable. Consequently, as of the nine months ended September 30, 2020, the Company had aggregate right of use (“ROU”) assets of $36.3 million and aggregate lease liabilities of $32.2 million relating to the dedicated clean room suites at both Catalent and Thermo. The initial ROU assets and lease liabilities recorded were based on the present value of estimated future payments associated with the lease component of the Catalent and Thermo clean room suites at discount rates of 8.0% and 7.5%, respectively, representing the rate at which the Company could borrow on a collateralized basis the amount of the lease payments in a similar term. The difference between the ROU assets and the lease liabilities results from certain prepayments made to Catalent and Thermo by the Company prior to the commencement of the leases. The weighted average remaining lease term on the leases for the dedicated clean room suites range between 4.3 and 7.2 years. The total lease liability payments are expected to be paid in equal installments through the five-year and eight-year terms of the Catalent and Thermo agreements, respectively.

The leases on the remaining two clean room suites at Catalent and four clean room suites at Thermo have not commenced as of September 30, 2020 because these clean room suites are not yet available for use by the Company. Accordingly, cumulative payments totaling $24.0 million and $47.9 million made to Catalent and Thermo, respectively, relating to the remaining clean room suites which have not become available to the Company have been recorded as other assets in the accompanying unaudited condensed consolidated balance sheets, a portion of which will be considered in the initial measurement of the cost of the ROU asset at the lease commencement date, currently anticipated to occur in the fourth quarter of 2020 for Catalent and the first half of 2021 for Thermo.

For the three and nine months ended September 30, 2020, the Company recorded aggregate operating lease costs of $2.2 million and $5.0 million related to the Catalent and Thermo embedded leases, respectively. For the three and nine months ended September 30, 2020, the Company recorded aggregate variable lease costs of $3.0 million and $7.5 million, respectively. The operating lease costs and variable lease costs of the Thermo and Catalent embedded leases were included in research and development expense in the accompanying unaudited condensed consolidated statements of operations and comprehensive loss.