Mature dendritic cells make clusters with T cells in the invasive margin of colorectal carcinoma.

Dendritic cells (DCs) take up tumour-specific antigen and migrate to regional lymph nodes to generate anti-tumour immunity. Although DC infiltration within human tumour tissue has been reported, the subset distribution has not been fully investigated. This study used immunohistochemistry to investigate DC subset distribution in colorectal adenocarcinoma. DCs expressing CD83, which are considered to be mature DCs, were present mainly in the invasive margin of cancer stroma. CD83(+) DCs in the invasive margin formed clusters with lymphocytes, the majority of which were CD45RO(+) T cells. The number of CD4(+) T cells was greater than that of CD8(+) T cells in these DC-lymphocyte clusters. The elongated cytoplasmic processes of CD83(+) DCs engulfed CD4(+) T cells. DCs that express CD1a were located throughout tumour tissue. Although the number of CD1a(+) DCs was almost the same as that of CD83(+) DCs in the invasive margin of cancer stroma, CD1a(+) DCs were mostly scattered and rarely formed clusters with lymphocytes. DCs that expressed both CD1a and CD83 were rare. Moreover, about 20% of lymphocytes in DC-lymphocyte clusters were positive for Ki-67, and CD83(+) DCs were attached to Ki-67(+) cells. CD83(+) DCs were also present in T-cell areas that had a distinctive structure involving the presence of B-cell lymphoid follicles. These results suggest that in the invasive margin of the colorectal cancer stroma, mature CD83(+) DCs form clusters with T cells to promote T-cell activation for the generation of tumour-specific immunity.