Induction of high-grade tumor-specific immunity in a host using a cytotoxic T-lymphocyte clone specific for a stable tumor antigen on murine leukemia L1210.

T-cell clone K4L, the cell surface phenotypes of which were Thy-1+, Lyt-1-, Lyt-2+, and L3T4-, was established from the spleen cells of a murine leukemia L1210-immune mouse. Clone K4L was specific for antigen B on L1210, and this antigen was different from antigen A for which the previously reported T-cell clone K7L was specific. K4L possessed cytotoxicity and tumor growth-inhibitory activity against both L1210 and antigen A loss variant, L1210-K7L-, but not against syngeneic tumor P388 or L5178Y. Previously we showed that antigen A was lost frequently for generation of antigen loss variants. In contrast, antigen B was barely found to be lost. When mice were inoculated with L1210 plus a moderate dose of K4L, the tumor grew after initial suppression but this newly emerging tumor was K4L sensitive and was ultimately rejected. The mice initially given L1210 plus K4L attained a high-grade tumor-specific immunity for rejecting the subsequently challenged high-dose (10(7) cells) L1210. This immunity did not involve any bystander antitumor activity against the third party P388 lymphoma that was injected together with L1210 but accompanied the increase in the L1210-specific cytotoxic T-lymphocyte activity. Evidence was provided that the live L1210, the outgrowth of which was inhibited by K4L, induced an effective immune response of radiation-sensitive host lymphocytes including L3T4+ helper T-cells. Taken together, our results show a novel strategy for inducing high-grade host-dependent antitumor immunity by use of a cytotoxic T-lymphocyte clone specific for a stable tumor-specific transplantation antigen.