Overall response rate of 40% consistent across sarcoma indications; median duration of response ~11 months with patients still in response at time of analysis

Interim analysis data reinforces the potential of lete-cel to bolster Adaptimmune's sarcoma franchise by expanding addressable sarcoma patient population

Full results from the pivotal IGNYTE-ESO trial are expected in late 2024

Philadelphia, Pennsylvania and Oxford, United Kingdom--(Newsfile Corp. - June 3, 2024) - Adaptimmune Therapeutics plc (NASDAQ: ADAP), a company working to redefine the treatment of solid tumor cancers with cell therapy, is presenting data from its pivotal IGNYTE-ESO trial of lete-cel (letetresgene autoleucel), an engineered cell therapy targeting NY-ESO-1, in synovial sarcoma (SyS) and myxoid/round cell liposarcoma (MRCLS) at the American Society of Clinical Oncology's (ASCO) annual meeting. Dr. Sandra D'Angelo of the Memorial Sloan Kettering Cancer Center will present "Lete-cel in patients with synovial sarcoma or myxoid/round cell liposarcoma: Planned interim analysis of the pivotal IGNYTE-ESO trial" in an oral session at 11:30 a.m. CDT, Monday, June 3rd, in Hall D2 as part of the Developmental Therapeutics-Immunotherapy track.

Dennis Williams, PharmD., Senior Vice President, Late-Stage Development, Adaptimmune: "We're encouraged by the findings from the IGNYTE-ESO trial and the potential of our sarcoma franchise. Our lead cell therapy product, afami-cel, targets MAGE-A4 in synovial sarcoma and the ability to now also target the NY-ESO-1 cancer antigen with lete-cel will enable us to reach a greater number of people impacted by advanced sarcomas. We are eager to continue advancing lete-cel to further realise the promise of engineered TCR T-cell therapies for patients and healthcare providers. We look forward to sharing the full results of the IGNYTE-ESO trial in late 2024. We continue to work toward commercializing afami-cel later this year and lete-cel in 2026."

Dr. Sandra D'Angelo M.D., Sarcoma Medical Oncology, Memorial Sloan Kettering Cancer Center, lead author and presenter: "Data from this planned interim analysis support the potential of lete-cel to serve as a novel therapy for people with advanced or metastatic MRCLS or synovial sarcoma. As the current treatment options in these two indications are significantly limited, both represent a greatly unmet medical need for novel, innovative therapies."

Lete-cel data at ASCO

At the planned interim analysis, 18/45 patients who received a single dose of lete-cel had clinical responses (previously reported). The overall response rate (ORR) of 40% was consistent across both SyS and MRCLS, and markedly greater than historical standard of care outcomes in these indications. The primary endpoint success criterion for efficacy was met by the interim analysis 40% ORR. Responses to lete-cel are durable, with the median duration of response (mDOR) at ~11 months, with 9/18 patients censored from mDOR calculation as their responses were ongoing at the time of the interim analysis. The complete primary analyses from IGNYTE-ESO, including more mature duration of response, are currently in progress with a full dataset anticipated in late 2024.

Given the success of the pivotal IGNYTE-ESO trial, Adaptimmune plans to initiate a rolling Biologics License Application (BLA) submission for lete-cel for the treatment of advanced or metastatic MRCLS and synovial sarcoma during 2025. Lete-cel will allow Adaptimmune to bolster its sarcoma franchise by expanding the addressable patient population to NY-ESO-1 positive MRCLS and synovial sarcoma solid tumors.

About lete-cel

Lete-cel is an engineered TCR T-cell therapy targeting the solid tumor antigen NY-ESO-1. Lete-cel is being investigated for the treatment of synovial sarcoma and myxoid/round cell liposarcoma (MRCLS) in the pivotal IGNYTE-ESO (NCT03967223) trial in patients who received prior anthracycline treatment.

About Synovial Sarcoma

There are more than 50 different types of soft tissue sarcomas which are categorised by tumors that appear in fat, muscle, nerves, fibrous tissues, blood vessels, or deep skin tissues.¹ Synovial sarcoma accounts for approximately 5% to 10% of all soft tissue sarcomas (there are approximately 13,400 new soft tissue cases in the U.S. each year).² One third of patients with synovial sarcoma will be diagnosed under the age of 30.² The five-year survival rate for people with metastatic disease is just 20% and most people undergoing standard of care treatment for advanced disease experience recurrence and go through multiple lines of therapy, often exhausting all options.³

About Myxoid/round cell liposarcoma (MRCLS)
Myxoid/round cell liposarcoma (MRCLS) is a type of soft tissue sarcoma that is predominantly found in the limbs. MRCLS accounts for approximately 5% to 10% of all soft tissue sarcomas.⁴ One-third of MRCLS cases will become metastatic with tumors spreading to unusual bone and soft tissue locations. MRCLS commonly presents at an age ranging from 35-55 years and has a poor prognosis because it recurs locally and tends to metastasize quickly and widely. The 5-year survival rate for metastatic MRCLS is only 5%.⁵

About Adaptimmune
Adaptimmune is a fully integrated cell therapy company working to redefine how cancer is treated. With its unique engineered T cell receptor (TCR) platform, the Company is developing personalized medicines designed to target and destroy difficult-to-treat solid tumor cancers and to radically improve the patient's cancer treatment experience.

Forward-Looking Statements
This release contains "forward-looking statements" within the meaning of the Private Securities Litigation Reform Act of 1995 (PSLRA). These forward-looking statements involve certain risks and uncertainties. Such risks and uncertainties could cause our actual results to differ materially from those indicated by such forward-looking statements, and include, without limitation: the success, cost and timing of our product development activities and clinical trials and our ability to successfully advance our TCR therapeutic candidates through the regulatory and commercialization processes. For a further description of the risks and uncertainties that could cause our actual results to differ materially from those expressed in these forward-looking statements, as well as risks relating to our business in general, we refer you to our Annual Report on Form 10-K filed with the Securities and Exchange Commission for the year ended 31 December, 2023, our Quarterly Reports on Form 10-Q, Current Reports on Form 8-K, and other filings with the Securities and Exchange Commission. The forward-looking statements contained in this press release speak only as of the date the statements were made and we do not undertake any obligation to update such forward-looking statements to reflect subsequent events or circumstances.

Dr. Sandra D'Angelo has financial interests related to Adaptimmune.

Adaptimmune Contact

Investor Relations
Juli P. Miller, Ph.D. - VP, Corporate Affairs and Investor Relations
T : +1 215 825 9310
M : +1 215 460 8920
Juli.Miller@adaptimmune.com

Media Relations
Dana Lynch, Senior Director of Corporate Communications
M: +1 267 990 1217
Dana.Lynch@adaptimmune.com

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2. Synovial Sarcoma - NCI (cancer.gov).
3. Aytekin MN, et al. J Orthop Surg (Hong Kong). 2020;28(2).
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