[Effects of adult thymectomy on the growth of 203-glioma in mice--analysis of T cell subpopulation in tumor immunology].

The effects of adult thymectomy in C 57 BL/6 mice on in vivo and in vitro responses to syngeneic methylcholanthrene-induced glioma (203-glioma) were investigated in order to analyse the role of T cell subpopulation in relation to the antitumor immunity. The tumor growth in adult mice thymectomized 3 weeks before subcutaneous inoculation of tumor cells was significantly suppressed. On the other hand, in mice thymectomized 7 or 10 weeks before tumor cell inoculation, the tumor growth was enhanced resulting in shorter mean survival time. The cytotoxic activity of the regional lymph node T cells in the former mice was increased from the beginning after tumor cell inoculation with peak observed on day 14 and maintained for about 4 weeks, while it was extremely decreased in the latter mice. The marked enhancement of cytotoxic activity in the former mice is probably due to a reduced proportion of short-lived T lymphocyte population after adult thymectomy. In contrast, the low level of cytotoxic activity in the latter mice may be due to a gradual reduction of long-lived T lymphocyte population in addition to short-lived T lymphocyte population after adult thymectomy. The cytotoxic activity was specific for 203-glioma cells and almost completely eliminated with anti-Thy-1 monoclonal antibody and complement. The surface markers of these killer T cells were checked with the results that in normal mice Lyt-1-.2.3+ and Lyt-1+.2.3+ cells participate in cytotoxic reaction. In mice thymectomized 3-10 weeks before tumor cell inoculation, however, Lyt-1+.2.3+ killer T cells were not detected suggesting strongly that the progenitors of Lyt-1+.2.3+ killer T cells are short-lived cells in contrast to those of Lyt-1-.2.3+ killer T cells which survive more than 10 weeks after adult thymectomy. The tumor growth was also significantly suppressed by the intravenous adoptive transfer of sensitized lymphocytes obtained from mice thymectomized 3 weeks before tumor cell inoculation. This effect of tumor suppression was disappeared by the pretreatment of infused lymphocytes with anti-Thy-1 monoclonal antibody and complement. These evidences may suggest that in tumor bearing mice short-lived suppressor T cells or their precursors exist and regulate the growth and differentiation of killer T cells and that adult thymectomy affects immunoregulation, possibly by altering the generation of suppressor T cells.