CCR9 and neoplasm: A. muciniphila can produce inosine, induce the expression of TH1 regulatory genes in CD4+ T cells (Zhang et al., 2019), and reverse PD-1 blockade by IL-12 from dendritic cells, increasing the recruitment of CCR9+ CXCR3+ CD4+ T lymphocytes to the tumor microenvironment to kill tumor cells (Routy et al., 2018b).