Mucosal Immune Environment in Colonic Carcinogenesis: CD80 Expression on Epithelial Cell Peaks in Dysplasia and Its Inhibition Leads to Carcinogenesis Progression

Background A significantly higher expression of the co-stimulatory molecule CD80 in ulcerat- ive colitis (UC) and dysplasia suggesting the presence of an immunosurveillance against cancerogenesis was recently observed. The aims of this study were to verify this hypothesis exploring the interplay between epithelium and CD8 T cell in human colonic carcinogenesis and evaluating the effect of CD80 signalling inhibition. Patients and methods Twenty nine patients diagnosed with UC, UC with colonic dysplasia, colonic adenoma, or colonic cancer were recruited at the moment of colonic resection. Mucosal samples were obtained during the colectomy and included specimens from healthy, dysplastic and neoplastic colon. Single cell suspensions were obtained by enzymatic digestion of mucosal specimens and subjected to Fluorescence-Activated Cell Sorting (FACS) to determine the proportion of epithelial cells (Cytokeratine 20, Cyt-20+) acting as antigen presenting cells (expressing CD80, CD40, HLA I or HLA II) and the proportion of CD8+ T cells activated (positive for CD28, CD38 or CD69). The second part of the study involved a mouse model of inflammation-related colon carcinogenesis with azoxymethane (AOM) and dextran sodium sulfate-induced (DSS). After the injection of AOM mice received 3 or 5 cycles of 3% DSS in their drinking water, each cycle consisted of 5 days of treatment followed by 14 days of rest. Animals were randomized to receive monoclonal anti-CD80 antibodies (10 ug/mouse) or isotype control, and sacrificed after 28 days. Results The proportion of Cyt-20+ CD80+ and Cyt-20+ HLA II+ cells was higher in dysplasia than in non dysplastic colonic tissue (p=0.03 and p=0.07, respectively). The proportion of Cyt-20+ CD80+ and Cyt-20+ CD40+ cells was higher in dysplasia than in invasive adenocarcinoma (p=0.07 and p=0.04, respectively). The proportion of CD8+ T cell expressing CD28 and CD38 was higher in dysplastic mucosa than in the mucosa with no neoplastic changes (p=0.01 and p=0.01, respectively). In mice that received anti-CD80 antibodies after AOM and 3 cycles of DSS inflammation was significantly inhibited (p=0.01) while high grade dysplasia extension was significantly higher than in mice that received a control antibody (p=0.01). The extension of low grade dysplasia was similar in the two groups. Conclusion This study confirmed that the proportion of epithelial cells acting as antigen presenting cells peaks in the dysplastic colonic mucosa and it is associated to activation of mucosal CD8+ T cell. CD80 inhibition increased high grade dysplasia extension without influencing the low grade dysplasia one. All together these data confirm the hypo- thesis that an active immunosurveillance mechanism centred on CD80 signalling is implicated in controlling the colonic carcinogenesis progression at the passage from low to high grade dysplasia.