Abstract A062: TIM-3 plays distinct roles in different immune cells to regulate antitumor immune responses

T-cell immunoglobulin and mucin-domain containing-3 (TIM-3) was originally identified as an inhibitory receptor that is expressed on Th1 T-cells to dampen T-cell immunity upon interaction with several putative ligands. The inhibitory role of TIM-3 is supported by multiple preclinical disease models, such as viral and bacterial infections, experimental autoimmune encephalitis, and allograft rejection. Recent evidence suggests that induction of TIM-3 expression on T-cells may promote resistance to cancer immunotherapy, including in response to treatment with PD-1/PD-L1 inhibitors. Thus, TIM-3 represents a putative novel immuno-oncology target. Here we report that in naive mice TIM-3 is absent on T-cells, but is constitutively expressed on myeloid cells, including dendritic cells and macrophages. In tumor-bearing mice, TIM-3 expression is highly enriched on PD-1 positive CD4 and CD8 T-cells in the tumor microenvironment, but not on T-cells in draining lymph nodes or peripheral blood. Prophylactic or therapeutic treatment with anti-PD-1 blocking antibody delays tumor growth in wild-type mice. However, unexpectedly, TIM-3 genetic deficiency reduced overall survival of tumor-bearing mice treated with anti-PD-1 compared to wild-type control mice. Using a series of in vitro functional cell-based assays, we found that blocking TIM-3 function by either genetic knock-out or an inhibitory Ab increased proliferation of, and IFN-γ production by, effector CD8 T-cells following direct antigen stimulation. By contrast, TIM-3 gene knockout in bone marrow-derived macrophages did not impact responses to stimulation with Toll-like receptor ligands, and TIM-3 blockade reduced phagocytosis of apoptotic tumor cells by a macrophage cell line. Taken together, our results suggest TIM-3 may play opposite roles in T-cells and macrophages (inhibitory vs activating, respectively), and highlight the pleiotropic roles of TIM-3 in different immune cells in tumor immunology. Citation Format: Jie Dai, Jerry Pei, Markus Mohrs, Gavin Thurston, Ella Ioffe. TIM-3 plays distinct roles in different immune cells to regulate antitumor immune responses [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A062.