To test whether CRC cell-derived CXCL1 is involved in P. anaerobius-induced MDSC migration, we silenced CXCL1, using small interfering RNA (siRNA) targeting CXCL1, in CRC cell lines (HCT116, Caco-2 and MC38) co-cultured with P. anaerobius (Extended Data Fig. 4d). This evidence concerns the gene CXCL1 and colorectal carcinoma.