Second, rejection and/or reduced tumor growth were mediated by tumor-specific CD4+ TH and CD8+ CTL, because ablation of these subpopulations in vivo by injection of specific anti-CD4 or anti-CD8, but not by anti-B cell or anti-NK cell monoclonal antibodies, prevented the acquisition of protective immunity after injection of CIITA-expressing tumor cells. The gene discussed is CIITA; the disease is neoplasm.