Chaput et al. (2017) demonstrated that melanoma patients, whose baseline gut microbiota was driven by Faecalibacterium spp., had a lower frequency of regulatory T cells (Tregs) and α4+β7+CD4+ and α4+β7+CD8+ T cells before the anti-CTLA-4 therapy commencement compared to those with Bacteroides-driven gut microbiota, which was also associated with clinical benefit [37]. Here, CD4 is linked to melanoma.