Bacterial-driven inflammation and mutant BRAF expression combine to promote murine colon tumorigenesis that is sensitive to immune checkpoint therapy.

Colorectal cancer (CRC) is multi-faceted with subtypes defined by genetic, histological, and immunologic features which are potentially influenced by inflammation, mutagens, and/or microbiota. CRCs with activating mutations in BRAF are associated with distinct clinical characteristics though the pathogenesis is not well understood. The Wnt-driven multiple intestinal neoplasia (MinApc[triangle]716/+) enterotoxigenic Bacteroides fragilis (ETBF) murine model is characterized by IL-17-dependent, distal colon adenomas. Herein, we report that addition of the BRAFV600E mutation to this model results in emergence of a distinct locus of mid-colon tumors. In ETBF-colonized BRAFV600ELgr5CreMin (BLM) mice, tumors have similarities to human BRAFV600E tumors, including histology, CpG island DNA hypermethylation, and immune signatures. In comparison to Min ETBF tumors, BLM ETBF tumors are infiltrated by CD8+ T cells, express interferon-gamma signatures, and are sensitive to anti-PDL1 treatment. These results provide direct evidence for critical roles of host genetic and microbiota interactions in CRC pathogenesis and sensitivity to immunotherapy.