Intraepithelial CD8+ T-cell-count becomes a prognostic factor after a longer follow-up period in human colorectal carcinoma: possible association with suppression of micrometastasis

Abstract

T-cell infiltration into human cancer tissues can be a manifestation of host immune responses to cancer cells. The present study was undertaken to explore the clinicopathological significance of intraepithelial CD8(+) T cells using 371 consecutively sampled human colorectal carcinomas. By univariate analysis, we noted that the survival curves by intraepithelial CD8(+) T cells became separated only after 1 to 2 years postoperation. Multivariate analyses revealed that the beneficial effect of this factor becomes significant only after a longer (more than 2 year), but not after a shorter (less than 2 year) follow-up period. Furthermore, the number of intraepithelial CD8(+) T cells was significantly higher in patients alive for more than 5 years than in patients who either died of cancer after a curative operation or patients who underwent a noncurative operation. Patients' cancer-specific death long after a curative operation is thought to be caused by the growth of micrometastases in other organs or near the primary sites. The effects of intraepithelial CD8(+) T cells, therefore, may be mediated by suppression of micrometastasis, rather than suppression of growth in the primary tumour. In conclusion, our data support a hypothesis on the presence of systemic immunosurveillance against micrometastasis of cancer cells.

Figure 1

Immunohistochemical results. Cases with median (A) and highly abundant (B) intraepithelial CD8⁺ T cells in colorectal carcinoma. Scale bar, 50 μm.

Figure 2

Distribution histogram of the number of intraepithelial CD8⁺ T cells in colorectal carcinoma (A), showing a distinct asymmetric pattern. Cancer-specific survival curves by intraepithelial CD8⁺ T cells in all patients (divided into two at the median) (B). The longitudinal axis, cancer-specific cumulative survival rate. The horizontal axis, years after operation. Note an inverse correlation between the number of intraepithelial CD8⁺ T cells and the stages (C), depicted by Box–Whisker plot showing 25 percentile, median, and 75 percentile.

Figure 3

Morphometric results of the number of intraepithelial CD8⁺ T cells among different groups. The longitudinal axis, the number of intraepithelial CD8⁺ T cells. A, Patients alive for more than 5 years (stage I excluded). B, Patients who died of the primary disease after curative operation (stages II and III). C, patients who received noncurative operation (stage IV+stage III with unresectable lymph node metastasis). We excluded cases positive for cancer cells at the resection margins. Overall differences, P<0.0005 (Kruskal–Wallis).

Figure 4

Double staining for CD8 (red) and Ki-67 (brown) (A). Green arrows indicate double positive cells (nucleus labelled in brown, cell surface in red). Red arrows indicate CD8+ T cells without labelling for Ki67. Arrowheads indicate single positivity for Ki-67 in cancer cells. Scale bar, 20 μm. Comparison of the labelling index of Ki-67 between intraepithelial and peritumoral CD8⁺ T cells (B).