Final results of a phase I trial of HERV-E TCR transduced T cells for the treatment of HLA-A*11 patients with metastatic clear cell renal cell carcinoma (mccRCC).

435 Background: Human endogenous retrovirus type E (HERV-E) is specifically expressed in ccRCC providing a safe target for T cell-based therapies. We investigated T cells transduced with a TCR targeting HERV-E (HERV-E T cells) for the treatment of mccRCC. Methods: This first-in-human study assessed the safety & efficacy of escalating doses of HERV-E T cells and manufacturing/clinical endpoints correlative analysis. HLA-A*11+ mccRCC patients (pts) were treated with a conditioning regimen, infusion of HERV-E T cells & IL-2. (NCT03354390). Results: Nineteen of185 pts tested were found to express HLA-A*11. 17 HLA-A*11 + pts enrolled on the study: 3 pts on each DL1-3 & 6 pts on DL4. 2 pts did not receive HERV-E T cells given disease progression during manufacturing period. Median age was 57 years. 86% received ≥ 3 prior systemic treatment (range 1-8). The manufacturing failure rate after first apheresis was 12% (n=2); both met target dose after second apheresis and repeat in vitro expansion. All HERV-E T cell products met release criteria for infusion including INF-γ production in response to HERV-E/HLA-A11-expressing tumor cells. Median HERV-E vector copy number (VCN) was 1.9. No dose-limiting toxicities (DLT), off-target toxicities or treatment-related deaths occurred. Pt#17 is on DLT monitoring period. 7 pts completed the planned 14 doses of IL-2 and all received at least 8 doses. Reasons for IL-2 discontinuation: hemodynamic (57%), cardiovascular (28%), pulmonary (28%), renal (14%) criteria & pts decision (14%). The best response was partial response in 7% & stable disease at least 8 weeks in 29% pts. HERV-E mRNA expression was detected in 5 primary & 9 metastatic specimens. HERV-E T cells were measurable in circulation post-dosing, with peak concentrations in the peripheral blood mononuclear compartment on day(D)+7. [DL1: 0.3 %, DL2: 1.2%, DL3: 0.5%, DL4: 12.3%]. Median HERV-E T cell VCN showed no correlation with HERV-E T cells peak concentration on D+4 & D+7. Conclusions: Proof of concept that HERV-T cells can induce tumor regression without evidence of causing off-target toxicities has been established by this trial. Infused HERV-E T cells were detectable transiently in vivo and induce effector cytokine production. Our initial results support the further development of HERV-E-directed therapies that focus on methods to improve in vivo persistence of TCR engineered T-cells and to target HERV-E antigens expressed on more commonly expressed HLA alleles.[Table: see text]