CTLA4 and colitis: In an effort to provide mechanistic evidence for the microbiota-ICB colitis connection, Wang et al. (19) recently administered a neutralizing anti-CTLA antibody to DSS-treated mice, and they found that compared with mice receiving the isotype-treatment, anti-CTLA-4 blockade led to more severe colitis that was further aggravated following pretreatment with the antibiotic vancomycin, suggesting a mitigating effect of the Gram-positive components of the microflora.