Dysbiosis in pre-cancerous mucosa may drive immune dysfunction: a study of immune system: microbiota interaction in familial adenomatous polyposis

Objectives: Familial adenomatous polyposis (FAP) is a condition caused by a constitutional pathogenic variant of the adenomatous polyposis coli (APC) gene that results in intestinal adenoma formation and colorectal cancer (CRC), necessitating pre-emptive colectomy. We sought to examine interaction between the mucosal immune system and commensal bacteria in FAP to test for immune dysfunction that might accelerate tumorigenesis. Methods: Colonic biopsies were obtained from macroscopically normal mucosal tissue from 14 healthy donors and 13 patients with FAP during endoscopy or from surgical specimens. Intraepithelial and lamina propria lymphocytes were phenotyped. Intraepithelial microbes were labelled with anti-IgA/IgG and analyzed by flow cytometry. Results: Proportions of resident memory CD103-expressing CD8+ and {gamma}{delta} T cell receptor+ intraepithelial lymphocytes were dramatically reduced in both left and right colon of patients with FAP compared to healthy controls. In lamina propria, T-cells expressed less CD103 and CD4+ CD103+ cells expressed less CD73 ectonucleotidase. IgA coating of epithelia-associated bacteria, IgA+ peripheral B cells and CD4 T-cell memory responses to commensal bacteria were increased in FAP. Conclusions: Loss of resident memory T-cells and {gamma}{delta} T-cells in mucosal tissue of patients with FAP accompanies intestinal microbial dysbiosis previously reported in this pre-cancerous state and suggests impaired cellular immunity and tumor surveillance. This may lead to barrier dysfunction, possible loss of regulatory T-cell function and excess IgA antibody secretion. Our data are the first to implicate mucosal immune dysfunction as a contributing factor in this genetically driven disease and identify potentially critical pathways in the etiology of CRC.