Objective:

To examine whether tumor-selective infiltration, activation, and cytotoxic activity of tumor infiltrating T lymphocytes (TIL) can be demonstrated in situ in colorectal cancer samples.

Summary Background Data:

Recent studies indicated a correlation between the presence of TIL and an improved prognosis in colorectal cancer. However, tumor-selective activation and cytotoxic activity of CD8+ TIL in situ in colorectal cancer patients have not yet been examined.

Methods:

Tumor samples from 49 patients and corresponding normal mucosa samples from 23 patients with colorectal cancer (UICC stages II–IV) were examined for TIL. Two-color fluorescence immunohistochemistry and multicolor flowcytometric (FACS) analysis were used for quantification of CD8+ T cells and measurement of their activation status (CD69-expression) and cytotoxic activity (CD107a-expression) in situ. Presence of tumor antigen-reactive T cells in tumor, blood, and bone marrow was evaluated by IFN-γ Elispot analysis.

Results:

While absolute numbers of CD8+ T cells were similar, CD4+ T helper cells were significantly increased in tumor tissue compared with normal mucosa. There was a significantly higher proportion of activated and cytotoxically active CD8+ TIL in colorectal cancer compared with normal mucosa. Increased activation, cytotoxic activity, and functional reactivity of TIL were correlated with the presence of functional tumor antigen-reactive T cells in the blood and bone marrow. The proportion of activated TIL decreased significantly with higher tumor stage.

Conclusions:

Tumor-selective activation and cytotoxic activity of CD8+ TIL and tumor-selective migration of CD4+ T helper cells were demonstrated in colorectal cancer for the first time. Our data support the immunogenicity of colorectal cancer and suggest clinical significance of tumor-specific immune responses.