Progressive Increase of Regulatory T Cells and Decrease of CD8+T Cells and CD8+T Cells/Regulatory T Cells Ratio during Colorectal Cancer Development

Background: We examined the distribution of CD8+ T cells and regulatory T cells (Tregs), measured the CD8+ T cell/Tregs ratio, investigated the relationship between Tregs and cyclooxygenase-2 (COX-2) expression during colorectal cancer (CRC) development. Methods: We performed immunohistochemical staining for CD8, forkhead box P3, E-cadherin, and COX-2 in 32 cases of invasive CRC, 10 cases of intramucosal CRC, 27 cases of high-grade tubular adenoma, 22 cases of low-grade tubular adenoma, and 32 cases of non-neoplastic conditions. Results: We observed a progressive increase in Tregs, and a decrease in CD8+ T cells and the CD8+ T cells/Tregs ratio during CRC development. The alterations were most severe in high-grade tubular adenoma and CRC. COX-2 expression was positively associated with Tregs infiltration. The degree of T cell infiltration differed among tumor compartment and the ratio in the tumor center was the lowest of all areas. The ratio and number of CD8+ T cells in the tumor center and the invasive front of invasive CRC were associated with gender, differentiation, node metastasis and tumor budding. Conclusions: Alteration in the distribution of both CD8+T cells and Tregs may contribute to the generation of an immune environment suitable for the development and progression of CRC.