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 beta(2)-microglobulin (beta(2)m) as an integral membrane protein. In this study, we explored membrane-anchored beta(2)m 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 beta(2)m 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)/beta(2)m 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 beta(2)m as a universal scaffold for optimizing Ag presentation by MHC-I molecules.