VISTA deficiency synergizes with a non-redundant immune checkpoint pathway and leads to enhanced immune activation (IRM10P.744)

V-domain Ig suppressor of T cell activation (VISTA) is a novel negative checkpoint ligand that suppresses T-cell mediated immune responses. Previous studies using VISTA-neutralizing monoclonal antibody show that VISTA-blockade enhances T cell-activation in an inflammatory disease model EAE, as well as in murine tumor models. Current study describes a comprehensive characterization of VISTA knockout (KO) mice. We show that despite the apparent normal hematopoietic development in young ko mice, VISTA genetic deficiency leads to a pro-inflammatory phenotype in aged animals, as well as enhanced T-cell activation in response to acute antigen immunization. In addition, we show that VISTA deficiency significantly enhanced disease development in a spontaneous model of autoimmune disease, which is correlated with the spontaneous activation of auto-antigen specific CD4+ T cells. Lastly, when combined with the genetic deficiency of another checkpoint molecule, synergistic or additive immune activation was observed.