PD-1 Polyfunctional T Cells Dominate the Periphery After Tumor-Infiltrating Lymphocyte Therapy for Cancer

Infusion of highly heterogeneous populations of autologous tumor-infiltrating lymphocytes (TIL) can result in tumor regression of exceptional duration. Initial tumor regression has been associated with persistence of tumor-specific TILs 1 month after infusion, but mechanisms leading to long-lived memory responses are currently unknown. Here, we studied the dynamics of bulk tumor-reactive CD8 T-cell populations in patients with metastatic melanoma following treatment with TILs. We analyzed the function and phenotype of tumor-reactive CD8 T cells contained in serial blood samples of 16 patients treated with TILs. Polyfunctional tumor-reactive CD8 T cells accumulated over time in the peripheral lymphocyte pool. Combinatorial analysis of multiple surface markers (CD57, CD27, CD45RO, PD-1, and LAG-3) showed a unique differentiation pattern of polyfunctional tumor-reactive CD8 T cells, with highly specific PD-1 upregulation early after infusion. The differentiation and functional status appeared largely stable for up to 1 year after infusion. Despite some degree of clonal diversification occurring within the bulk tumor-reactive CD8 T cells, further analyses showed that CD8 T cells specific for defined tumor antigens had similar differentiation status. We demonstrated that tumor-reactive CD8 T-cell subsets that persist after TIL therapy are mostly polyfunctional, display a stable partially differentiated phenotype, and express high levels of PD-1. These partially differentiated PD-1 polyfunctional TILs have a high capacity for persistence and may be susceptible to PD-L1/PD-L2-mediated inhibition. .