We previously reported that HLA-unrestricted CTLs against MUC-1 were induced from colon cancer patients by stimulating peripheral blood lymphocytes (PBLs) with recombinant MUC-1 vaccinia virus (rVMUC-1). We have performed adoptive immunotherapy (AI) for two gastric and two colon cancer patients, using the rVMUC-1-stimulated T lymphocytes. A significant level of HLA-unrestricted cytotoxicity against MUC-1 was induced in the two colon cancer patients (pA and pB) during the first adoptive immunotherapy, but extremely reduced during the second AI. During the second stimulation phase, the rate of CD3+CD56+CD8+ cells were significantly increased and that of CD3+CD56-CD4+ cells were significantly decreased in the two colon cancer patients as compared to the first AI. CD3+CD56+CD8+ and CD3+CD56-CD4+ cells were isolated from the second AI of the colon cancer patient (pB) and designated as D856 and D4, respectively. The D4 cells demonstrated a high level of HLA-unrestricted CTL activity against MUC-1, but D856 cells did not. When D856 cells were mixed with D4 cells at a D856/D4 ratio of 1:3, 1:2, and 1:1 and used as effector cells, the HLA-unrestricted and MUC-1-specific CTL activity of D4 cells was suppressed in a D856/D4 ratio-dependent manner. Further, D856 cells were highly lytic for the D4 cells demonstrating HLA-unrestricted cytotoxicity against MUC-1. It is concluded that the reduction in HLA-unrestricted cytotoxicity against MUC-1 during the second AI is attributed to the D856 cells killing MUC-1-specific CTLs (D4). Thus, the CD3+CD56+ CD8+ cells seem likely to behave as a suppressor T cell.

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