We examined the effects of a biological response modifier, lentinan, on tumor-infiltrating lymphocytes in advanced colon cancer. The subjects were 57 curatively resected patients with Dukes' B or C colon cancer, which was histologically diagnosed as well differentiated or moderately differentiated adenocarcinoma. The control group (n=29) did not receive any preoperative treatment. In the lentinan-treated group, lentinan was administered intravenously at 2 weeks and 1 week before surgery at a dose of 2mg (n=10), 4mg (n=8), or 8mg (n=10) each time.
The number of tumor-infiltrating lymphocytes increased depending on the dose of lentinan, and there was a significant difference between the control group and the patients given 4mg or 8mg of lentinan (P<0.05). Comparison of the subsets of tumor-infiltrating lymphocytes showed no difference in CD4
+ cells between the groups. However, CD8
+ cells showed a dose-dependent increase with lentinan treatment and there was a significant difference between the control group and patients given 8mg of lentinan (P<0.05). In addition, the number of emperipoletic lymphocytes detected by light microscopy at all lentinan doses was significantly higher than in the control group (P<0.05). Emperipoletic lymphocytes were mainly CD8
+ T cells, but a few were CD4
+, with the latter being almost all detected around ducts lined with cancer cells. The emperipoletic CD8
+ cells were confirmed to be cytotoxic T lymphocytes by double staining with CD8 and CD11b.
When cytotoxic T lymphocytes, natural killer cells, and other killer cells attack cancer cells, they must make contact with the tumor cell membrane. Detection of emperipoletic lymphocytes at the light microscopic level means that these lymphocytes are in contact with the cell membrane or have penetrated into cancer cells.
Therefore, the finding that emperipolesis was significantly enhanced by lentinan supports the role of killer cells in the antitumor effect of this agent.
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