MHC class II-transfected tumor cells directly present antigen to tumor- specific CD4⁺ T lymphocytes

We have developed and shown to be efficacious an immunotherapeutic strategy to enhance the generation of tumor-specific CD4⁺ T helper lymphocytes. The approach uses autologous tumor cells genetically modified to express syngeneic MHC class II genes as cell-based immunogens and is based on the hypothesis that tumor cells directly present tumor Ags to CD4⁺ T cells. Since the conventional pathway for CD4⁺ T cell activation is indirect via professional APC, induction of immunity following immunization with class II- transfected tumor cells was examined in bone marrow chimeric mice. Both tumor and host-derived cells are APC for tumor Ags, suggesting that the efficacy of tumor cell vaccines can be significantly improved by genetic modifications that enhance tumor cell Ag presentation.