The appendix orchestrates T-cell mediated immunosurveillance in colitis-associated cancer

Abstract Objective While appendectomy may reduce colorectal inflammation in patients with ulcerative colitis (UC), appendectomy has been suggested to be associated with an increased risk of colitis-associated cancer (CAC). The aim of this study was to explore the mechanism underlying the appendectomy-associated increased risk of CAC. Design Five-week-old male BALB/c mice underwent appendectomy, appendicitis induction or sham laparotomy. They were then exposed to azoxymethane/dextran sodium sulfate (AOM/DSS) to induce CAC. Mice were sacrificed 12 weeks later, and colons were taken for pathological analysis and immunohistochemistry (CD3 and CD8 staining). Human colonic tumors from 21 UC patients who underwent surgical resection for CAC were immunophenotyped and stratified according to the appendectomy status. Results While appendectomy significantly reduced colitis severity and increased CAC number, appendicitis induction without appendectomy led to opposite results. Intra-tumor CD3+ and CD8+ T-cell densities were lower after appendectomy and higher after appendicitis induction compared to the sham laparotomy group. Blocking lymphocyte trafficking to the colon with the anti-α4β7 integrin antibody or a sphingosine-1-phosphate receptor agonist suppressed the inducing effect of the appendectomy on tumors’ number and on CD3+/CD8+ intra-tumoral density. CD8+ or CD3+ T cells isolated from inflammatory neo-appendix and intravenously injected into AOM/DSS-treated recipient mice increased CD3+/CD8+ T-cell tumor infiltration and decreased tumor number. In UC patients with a history of appendectomy, intra-tumor CD3+ and CD8+ T-cell densities were decreased compared to UC patients without history of appendectomy. Conclusions In UC, appendectomy could suppress a major site of T-cell priming resulting in a less efficient CAC immunosurveillance. Significance of this study What is already known on this subject? The protective effect of preemptive appendectomy is currently investigated as a therapy for refractory ulcerative colitis (UC), with encouraging results. An increased risk of developing colitis-associated cancer (CAC) caused by this promising treatment has been identified. Since it is commonly accepted that CAC is related to colitis severity and extent, this finding is counterintuitive and the mechanisms of this paradoxical effect remain unknown. What are the new findings? In a mouse model of CAC, less extended colitis associated with an increased number of tumors was observed. Intra-tumor T-cell infiltration was significantly reduced after appendectomy. Blocking lymphocyte trafficking to the colon with current or experimental UC treatments mimicked the appendectomy-associated phenotype whereas neo-appendicitis or appendix-primed T-cell injection in recipient mice increased intra-tumor T-cell infiltration and strengthened protection against CAC. In UC patients with CAC, appendectomy was associated with a decreased intra-tumor T-cell infiltration. These findings suggest that, in UC, appendectomy could suppress a major site of T-cell priming in the colon, resulting in a reduced CAC immunosurveillance. How might it impact on clinical practice in the foreseeable future? This work emphasizes the fact that precautions will be necessary if appendectomy becomes an accepted therapeutic option for the treatment of refractory UC. Innovative cell-based therapies and immunotherapies, such as the administration of stimulated autologous appendicular T cells in patients with CAC are promising options.