VSIR and graft versus host disease: While one study found that VISTA (PD-1H) expression on antigen-presenting cells (APCs) suppresses T cell activation and anti-VISTA mAb treatment exacerbates autoimmune encephalomyelitis (EAE), suggesting an immuno-inhibitory role for the molecule [9], another study found that treatment with mAb abolishes graft-vs-host disease (GVHD), suggesting a costimulatory role [10].