In mouse tumor model, Routy et al. revealed that oral supplementation with A. muciniphila after fecal microbiome transplantation in mice not responding to therapy restored the efficacy of PD-1 blockade in an interleukin-12-dependent manner by recruitment of CCR9 + CXCR3 + CD4 + T lymphocytes into tumor beds. The gene discussed is CCR9; the disease is neoplasm.