Infusion product characteristics to predict response to tumor-infiltrating lymphocyte (TIL) therapy in metastatic melanoma (MM).

9516 Background: Identification of the TIL therapy product (TILp) characteristics associated with objective response to therapy is critical to improve future adoptive TIL-based therapy. In this study we performed comprehensive phenotypic analysis of TILp in association with TIL therapeutic outcomes in consecutive patients with MM. Methods: Data were extracted from early-phase clinical trials of MM patients treated with TIL only, TIL plus ipilimumab, TIL plus nivolumab, and TIL plus vemurafenib at Moffitt Cancer Center. The immunophenotypic features of TILp were evaluated by flow cytometry using antibodies against checkpoints, costimulatory molecules, T cell subsets and TCRβ sequencing. Tumor reactivity was measured using HLA-matched cell lines. The relationship between TILp characteristics and both objective response and progression-free survival (PFS) was assessed in treated patients. Results: A total of 50 patients, 21 female (42%) and 29 male (58%), median age 49 [IQR 40–55] received lymphodepleting chemotherapy followed by TIL and interleukin-2 (IL-2). Median numbers [IQR] of infused TIL and IL-2 dose were 59e 9 [42-84e 9 ] and 5 [4–6], respectively. Patients with objective response had a significantly higher total number of infused TIL, total number of infused CD8 + TIL, and proportion of CD8 + cells in the infusion product (p < 0.05), with high CD8 + TIL being associated with improved PFS (p = 0.0001). The total number and proportion of infused stem cell-like memory CD8 + T cells (T SCM, CD8 + CD45RA + CCR7 + CD62L + CD95 + ) were significantly higher in responders and associated with improved PFS (p < 0.01). TILs from responders had distinct patterns of co-inhibitory and co-stimulatory receptors’ expression and were characterized by significantly higher proportion of LAG3 + and LAG3 + TIGIT + co-expressed TIL of total CD3 + TIL (p < 0.05). Proportions of LAG3 + CD8 + and TIGIT + CD8 + cells were also increased in responders (p < 0.05) with no significant differences observed in PD1 + CD8 + , BTLA + CD8 + , and TIM3 + CD8 + cells. There was an increased proportion of OX40 + CD8 + and OX40 + 4-1BB neg CD8 + cells among responders (p < 0.01). T cell clonal analysis using top 20 clones revealed high persistence in responders (p < 0.01) measured by TCRβ overlap between ACTP and post-treatment peripheral blood. There were no significant differences in clonality, diversity and evenness in responders vs. non-responders. Using HLA-matched cell lines there was a trend towards HLA-matched reactive TIL and improved PFS (p = 0.058). Conclusions: Response to TIL therapy is associated with TIL persistence and distinct TILp immunophenotypic features characterized by enhanced proportion of CD8 + TIL, T SCM CD8 + cells, and high surface expression of LAG3 + TIGIT + and OX40 + . Novel strategies to modulate ex vivo TIL expansion toward this optimal TIL phenotype may result in increased response for future trial design.