CD4⁺ T cells in the absence of the CD8⁺ cytotoxic T cells are critical and sufficient for NKT cell-dependent tumor rejection

NKT cells perform crucial roles in tumor surveillance, functioning as regulators of early host response. In this study, we have assessed the effects of NKT activation at the time of tumor Ag immunization, and have evaluated the contributions of CD4⁺ and CD8⁺ T cells in tumor rejection during adaptive immune response against live tumor cells. Our data indicate that CD4⁺ T cells play critical roles, not only in assisting CTL, but also in the orchestration of host response against the tumor. The CD4 ⁺ T cells were found to reject the transplanted tumor cells very efficiently under conditions in which the CTLs were removed either genetically, or via the action of anti-CD8 Ab in mice that had been immunized with tumor extracts and α-galactosylceramide. Immunization resulted in an NKT cell-dependent antitumor adaptive immune response, which was associated with both CD4⁺ T cells and cytokine IFN-γ.