Induction of antitumor immunity by CTL epitopes genetically linked to membrane-anchored β₂-microglobulin

Level and persistence of antigenic peptides presented by APCs on MHC class I (MHC-I) molecules influence the magnitude and quality of the ensuing CTL response. We recently demonstrated the unique immunological properties conferred on APCs by expressing β₂-microglobulin (β₂m) as an integral membrane protein. In this study, we explored membrane-anchored β₂m as a platform for cancer vaccines using as a model MO5, an OVA-expressing mouse B16 melanoma. We expressed in mouse RMA-S cells two H-2K^b binding peptides from MO5, OVA_257-264, and TRP-2_181-188, each genetically fused with the N terminus of membranal β₂m via a short linker. Specific Ab staining and T cell hybridoma activation confirmed that OVA_257-264 was properly situated in the MHC-I binding groove. In vivo, transfectants expressing both peptides elicited stronger CTLs and conferred better protection against MO5 than peptide-saturated RMA-S cells. Cells expressing OVA_257-264/ β₂m were significantly superior to OVA_257-264-charged cells in their ability to inhibit the growth of pre-established MO5 tumors. Our results highlight the immunotherapeutic potential of membranal β₂m as a universal scaffold for optimizing Ag presentation by MHC-I molecules.