The invention provides agonistic anti-human VISTA antibodies and antibody fragments. These agonist antibodies and antibody fragments may be used to potentiate or enhance or mimic VISTA's suppressive effects on T cell immunity and thereby suppress T cell immunity. These agonist antibodies and antibody fragments are especially useful in the treatment of autoimmunity, allergy, inflammatory conditions, GVHD, sepsis and transplant recipients. Screening assays for identifying these agonists are also provided.
