Role of Helper T-Lymphocytes in Rejection of UV-induced Murine Skin Cancers¹

The purpose of this study was to examine the role of helper T-lymphocytes (Th) in the immunological rejection of UV-induced tumors. Mice repeatedly exposed to UV radiation develop suppressor T-lymphocytes that facilitate the growth of UV-induced tumors by interfering with host immunity. These suppressor cells specifically blocked the generation of antitumor Th, suggesting that Th may be important in the immunological rejection of UV-induced tumors. The Th activity generated by a UV-induced tumor that grows progressively in normal mice was compared with that generated by a highly antigenic, regressor clone of the same tumor. The regressing tumor cell line generated a much higher amount of Th activity than the parental, progressor tumor cell line. The amount of Th activity generated by a highly antigenic, UV-induced tumor injected into normal mice, in which it regresses, was compared to the Th activity in UV-irradiated mice, in which the tumor grows progressively. Again, tumor regression was associated with a higher amount of Th activity, and this increased activity was detectable in the environment of the regressing tumor. Lyt-1⁺ cells containing Th activity mediated the regression of a UV-induced tumor when injected with the tumor cells s.c. into immunosuppressed mice. Lyt-1^- cells were cytotoxic to tumor cells in vitro but were unable to cause tumor rejection in vivo. These studies suggest that Th play a central role in the immunological rejection of UV-induced tumors.