Blockade of Tim-3 binding to phosphatidylserine and CEACAM1 is a shared feature of anti-Tim-3 antibodies that have functional efficacy

Both in vivo data in preclinical Cancer models and in vitro data with T cells from patients with advanced Cancer support a role for TIM-3 blockade in promoting effective anti-tumor immunity. Consequently, there is considerable interest in the clinical development of antibody-based therapeutics that target TIM-3 for Cancer Immunotherapy. A challenge to this clinical development is the fact that several ligands for TIM-3 have been identified: Galectin-9, phosphatidylserine, HMGB1, and most recently, CEACAM1. These observations raise the important question of which of these multiple receptor:ligand relationships must be blocked by an anti-Tim-3 antibody in order to achieve therapeutic efficacy. Here, we have examined the properties of anti-murine and anti-human TIM-3 antibodies that have shown functional efficacy and find that all antibodies bind to TIM-3 in a manner that interferes with TIM-3 binding to both phosphatidylserine and CEACAM1. Our data have implications for the understanding of TIM-3 biology and for the screening of anti-Tim-3 antibody candidates that will have functional properties in vivo.