Abstract 586: Discovery of a novel TIM3 binding partner and a key role for TIM3 on macrophages: Identification of specific antibodies capable of converting immune-suppressive macrophages to immune-enhancing

Our Translational Science Platform uses an unbiased bioinformatics-based approach to interrogate particular cell types within the tumor microenvironment (TME). Given the correlation between high levels of immune-suppressive macrophages within the tumor TME and poor patient prognosis across a number of solid tumor types we focused initially on developing novel immunotherapies to modify this cell type. We identified 10 targets as candidates for converting tumor-associated macrophages from immune-suppressing to immune-enhancing. One of these targets was TIM3. To date, TIM3 has been pursued mainly as a checkpoint target for T cell-directed immunotherapies based on its expression on exhausted T cells. Anti-TIM3 mAbs, generated by multiple groups, induce responsiveness in T cells and demonstrate anti-tumor benefit in certain mouse models. However, our macrophage-centric approach has identified a previously unrecognized protein-protein interaction between TIM3 and one of our additional macrophage targets. Based on knowledge of this interaction, we were able to generate and select for panels of mAbs to TIM3 and to its binding partner capable of converting macrophages from an “M2” to an “M1” pro-inflammatory phenotype. In contrast to published anti-TIM3 mAbs, our particular anti-TIM3 mAbs lacked activity in T cell-based assays, but promoted an increase in pro-inflammatory cytokines with a reduction or no effect in anti-inflammatory cytokines in a macrophage activity assay. In this assay, monocytes were prepared from human peripheral blood and cultured in the presence of M-CSF to bias toward an M2 phenotype. Under sub-optimal stimulation with LPS or CD40L or HMGB1, treatment of these cells with the anti-TIM3 mAbs led to increases in pro-inflammatory cytokines including IL-1β and TNFα. The conversion to an “M1” macrophage by anti-TIM3 mAbs had downstream consequences on T cells as demonstrated by mixed lymphocyte reaction experiments. In these studies, the addition of anti-TIM3 led to a macrophage-dependent increase in IFNγ from the T cells. To assess the impact of our anti-TIM3 mAbs in the tumor setting, tumor histoculture experiments were performed. Tumor tissue slices from ovarian cancer patients treated with anti-TIM3 showed an increase in a range of cytokines and in this tumor setting the initial sub-optimal stimulus was not required. Specific antibodies to TIM3 and its binding partner that are able to promote a pro-inflammatory macrophage phenotype have been ge