Evidence for immunosurveillance in intestinal premalignant lesions.

The immunosurveillance theory argues that the immune system recognizes tumour-specific antigens expressed by transformed cells, which results in the destruction of cancer precursors before they become clinically manifest. As a model for the development of cancer, we set out to study premalignant lesions and immune responses in sentinel lymph nodes from patients with long-standing ulcerative colitis and progression of mucosal dysplasia. Mesenteric lymph nodes draining dysplastic and normal intestinal segments were identified by sentinel node technique during surgery in 13 patients with ulcerative colitis who were subjected to colectomy because of intestinal dysplasia. T cells were extracted from the lymph nodes and analysed by flow cytometry, and lymphocyte proliferation assays were set up in the presence of extracts from dysplastic and normal intestinal mucosa. Increase in CD4/CD8 ratio was observed in sentinel lymph nodes draining dysplastic epithelium compared to normal mucosa. The increase in CD4(+) T cells in relation to CD8(+) T cells correlated with the degree of dysplasia reflected by a significant increase in the ratio against low-grade dysplasia compared to indefinite dysplastic lesions. The T-cell response was specific to antigens from dysplastic epithelial lining as seen in proliferation assays. The observation suggests an important surveillance role for the immune system against premalignant intestinal lesions in patients with long-standing ulcerative colitis.