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. Clin Cancer Res; 20(1); 44–55. ©2013 AACR.