CD137 accurately identifies and enriches for naturally occurring tumor-reactive T cells in tumor.

Purpose: Upregulation of CD137 (4-1BB) on recently activated CD8(+) T cells has been used to identify rare viral or tumor antigen-specific T cells from peripheral blood. Here, we evaluated the immunobiology of CD137 in human cancer and the utility of a CD137-positive separation methodology for the identification and enrichment of fresh tumor-reactive tumor-infiltrating lymphocytes (TIL) or tumor-associated lymphocytes (TAL) from ascites for use in adoptive immunotherapy.
Experimental Design: TILs from resected ovarian cancer or melanoma were measured for surface CD137 expression directly or after overnight incubation in the presence of tumor cells and homeostatic cytokines. CD137(pos) TILs were sorted and evaluated for antitumor activity in vitro and in vivo.
Results: Fresh ovarian TILs and TALs naturally expressed higher levels of CD137 than circulating T cells. An HLA-dependent increase in CD137 expression was observed following incubation of fresh enzyme-digested tumor or ascites in IL-7 and IL-15 cytokines, but not IL-2. Enriched CD137(pos) TILs, but not PD-1(pos) or PD-1(neg) CD137(neg) cells, possessed autologous tumor reactivity in vitro and in vivo. In melanoma studies, all MART-1-specific CD8(+) TILs upregulated CD137 expression after incubation with HLA-matched, MART-expressing cancer cells and antigen-specific effector function was restricted to the CD137(pos) subset in vitro. CD137(pos) TILs also mediated superior antitumor effects in vivo, compared with CD137(neg) TILs.
Conclusions: Our findings reveal a role for the TNFR-family member CD137 in the immunobiology of human cancer where it is preferentially expressed on tumor-reactive subset of TILs, thus rationalizing its agonistic engagement in vivo and its use in TIL selection for adoptive immunotherapy trials.