TCR Vaccines against a Murine T Cell Lymphoma: A Primary Role for Antibodies of the IgG2c Class in Tumor Protection

Tumor-associated proteins can act as effective immunotherapeutic targets. Immunization with tumor TCR protein conjugated to the immunogenic protein keyhole limpet hemocyanin (KLH) protects mice from tumor challenge with the murine T cell lymphoma C6VL. The immune mechanisms responsible for this tumor protection are of interest for designing more effective vaccine strategies. Previous studies using depletion experiments had suggested a CD8-mediated component of protection induced by TCR-KLH vaccines. In this study we used CD8α knockout, μMT, and FcγR knockout mice to investigate the relative roles of CD8⁺ T cells and Ab in protective immunity induced by TCR-KLH immunization. We found that CD8⁺ T cells are not required for tumor protection, although they may contribute to protection. Vaccine-induced Abs are sufficient to mediate protection against this murine T cell lymphoma through an FcR-dependent mechanism. This was confirmed with Ab transfers, which protect challenged mice. Additionally, recombinase-activating gene 1^-/- splenocytes can mediate Ab-dependent cellular cytotoxicity against this tumor in the presence of bound anti-TCR Abs. IFN-γ knockout mice demonstrated a requirement for IFN-γ, probably via generation of IgG2c Abs, in vaccine-induced tumor protection. IFN-γ knockout mice were not protected by immunization and had a severe impairment in IgG2c Ab production in response to immunization. Although mock-depleted anti-TCR Abs could transfer tumor protection, IgG2c-deficient anti-TCR Abs were unable to transfer tumor protection to wild-type mice. These results suggest that TCR-KLH vaccine-induced tumor protection in the C6VL system is primarily attributable to the induction of IgG2c Abs and humoral immunity.