CTLA4 and neoplasm: To address the question of whether T cell inhibitory receptors or ligands, such as PD-1, CTLA-4 and PD-L1, were responsible for the impaired OVA-CD8+ T cell function and resumed tumor growth, we next evaluated whether antibody therapy targeting these molecules would enhance the efficacy of MS-OVA therapy in B16-OVA tumor-bearing mice.