CTLA4 and colitis: Assessment of fecal microbiota composition by 16S rRNA gene sequencing revealed that the abundance of the phylum Bacteroidetes was negatively associated with anti-CTLA4–associated colitis, in which patients enriched are less likely to develop colitis perhaps due to expression of polysaccharide A can induce Tregs to prevent colitis; while patients enriched in Faecalibacterium genus and phylum Firmicutes are more likely to develop colitis, although with longer PFS and OS (23, 41).