CTLA4 and colitis: In another study, vancomycin supplementation to mice before administration of anti-CTLA-4 antibodies and dextran sulfate sodium (a colitogen to model blockade-induced colitis) provoked a more severe and largely fatal form of the disease, implicating the role of gram-positive bacteria in mitigating CTLA-4 blockade-induced colitis.31 Of note, oral gavage of a mixture of four gram-positive Bifidobacterium species could ameliorate the immunopathology associated with CTLA-4 blockade by upregulating T cell-mediated metabolic processing, thereby rescuing mice from vancomycin-induced dysbiosis.