CTLA4 and colitis: Bacteroides inoculation in GF and antibiotic-treated specific-pathogen-free mice treated with anti-CTLA-4 showed decreased tumors and a reduced incidence of colitis, which is the side effect of anti-CTLA-4 treatment, revealing that Bacteroides was the causation for the treatment effect, whereas mice without inoculation had markedly reduced efficacy of anti-CTLA-4 treatment [89–91].