The augmentation of tumor-specific immunity by virus help. III. Enhanced generation of tumor-specific Lyt-1+2- T cells is responsible for augmented tumor immunity in vivo.

The role of vaccinia virus-reactive helper T cells (Th) in augmenting in vivo generation of antitumor protective immunity and the Ly phenotype mediating the enhanced in vivo tumor immunity were investigated. C3H/HeN mice were inoculated i.p. with viable vaccinia virus to generate vaccinia virus-reactive Th activity. The mice were subsequently immunized i.p. with virus-infected syngeneic X5563 and MH134 tumor cells, and spleen cells from these mice were tested for in vivo tumor neutralizing activity. Immunization of virus-primed mice with virus-uninfected tumor cells and of virus-unprimed mice with virus-infected tumor cells failed to result in in vivo protective immunity. In contrast, spleen cells from mice immunized with virus-infected tumor cells subsequent to virus-priming exhibited potent tumor-specific neutralizing activities. Such an augmented generation of in vivo protective immunity was accompanied by enhanced induction of tumor-specific cytotoxic T lymphocyte (CTL) and antibody activities in X5563 and MH134 tumor systems, respectively. However, analysis of the effector cell type responsible for in vivo tumor neutralization revealed that enhanced in vivo immunity was mediated by Lyt-1+2- T cells in both tumor systems. Moreover, the Lyt-1+2- T cells exerted their function in vivo under conditions in which anti-X5563 tumor-specific CTL or anti-MH134 tumor-specific antibody activity was not detected in recipient mice. These results indicate that augmenting the generation of a tumor-specific Lyt-1+2- T cell population is essential for enhanced tumor-specific immunity in vivo.