Abstract CT285: Trial in progress: A phase 1/2 study to investigate the safety and efficacy of OBX-115 engineered tumor-infiltrating lymphocyte (TIL) cell therapy in patients (pts) with immune checkpoint inhibitor (ICI)-resistant advanced or metastatic melanoma

Abstract Introduction ICI have improved outcomes for pts with melanoma; however, most pts (~60%) do not achieve long-term survival. Unengineered bulk TIL cell therapy has an objective response rate (ORR) of 31-49% in pts with unresectable or metastatic melanoma (Rohaan NEJM 2022, Chesney JITC 2022), but requires co-administration of systemic high-dose IL2, which is associated with safety risks and limits pt eligibility. OBX-115 TIL are engineered to express regulatable membrane-bound IL15 (mbIL15) under dose-dependent regulation using acetazolamide (ACZ), an FDA-approved small-molecule diuretic, avoiding the need for high-dose IL2. A first-in-human single-institution study (NCT05470283) evaluating the safety of OBX-115 in metastatic melanoma is currently enrolling. The current study (NCT06060613) is enrolling at multiple US sites using centralized manufacturing. Methods This phase 1/2, single-arm, open-label, nonrandomized, multicenter study will assess the safety, tolerability, and efficacy of the OBX-115 engineered autologous TIL cell therapy regimen in pts with unresectable or metastatic melanoma resistant to ICI (Table). Primary objectives of Phase 1 are to characterize safety and tolerability and identify a recommended Phase 2 dose of the OBX-115 regimen; Phase 2 will evaluate efficacy (ORR using RECIST v1. 1). Cryopreserved OBX-115 is generated from the pt’s own tumor tissue procured by surgical excision or core biopsy, and is infused after standard- or low-dose (based on clinical eligibility) lymphodepletion (cyclophosphamide and fludarabine). ACZ is administered at cohort-defined doses once daily for up to 10 days, with ACZ redosing at Week 6-8 for 10 days if the initial observed tumor response is less than partial response. No systemic high-dose IL2 is administered. Two sites are open and recruiting pts. TABLE 1. NAND Key Eligibility Criteria Key Inclusion Criteria Key Exclusion Criteria Age ≥18 years Uveal melanoma Histologically confirmed diagnosis of unresectable Stage IIIC, IIID, or Stage IV metastatic melanoma Brain metastasis or leptomeningeal disease Documented radiographic disease progression after systemic therapy containing a PD-1- or PD-L1-blocking antibody (if adjuvant setting, progression during or within 12 weeks after the last dose) Active autoimmune disease, including active uveitis or any other medical illness that would pose increased risks for study participation Received a BRAF inhibitor ± MEK inhibitor if BRAF V600 mutation-positive Prior allogeneic organ transplant, allogeneic cell therapy, or genetically engineered cell therapy (not including autologous stem cell or unengineered TIL cell therapy) ≥1 lesion suitable for OBX-115 generation with expected minimum of 1. 5-cm diameter; minimally invasive tumor tissue procurement (core biopsy) may be considered on a case-by-case basis after discussion with the Medical Monitor Systemic steroid therapy 10 mg/day of prednisone or equivalent ≥1 RECIST 1. 1-measurable lesion remaining after tumor tissue procurement ECOG performance status 0 or 1 Estimated life expectancy 6 months Citation Format: Sajeve S. Thomas, Jason A. Chesney, Omid Hamid, Gino K. In, Alexander N. Shoushtari, Yazan Samhouri, Parameswaran Hari, Giridharan Ramsingh, Prakash Prabhakar, Lauren Mclaughlin, Allison Betof Warner. Trial in progress: A phase 1/2 study to investigate the safety and efficacy of OBX-115 engineered tumor-infiltrating lymphocyte (TIL) cell therapy in patients (pts) with immune checkpoint inhibitor (ICI) -resistant advanced or metastatic melanoma abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (7Suppl): Abstract nr CT285.