Reconstitution of antigen presentation in HLA class I-negative cancer cells with peptide-β2m fusion molecules

Engineered MHC-peptide targets capable of inducing recognition by CTL may prove useful in designing vaccines for infectious disease and cancer. We tested whether peptides directly linked to β2-microglobulin (β2m) could complex with human HLA class I heavy chain, and could be recognized by human CTL, both as soluble reagents and as cell surface constituents. An HLA-A2-restricted peptide epitope was physically linked to the N terminus of human β2m. This fusion protein refolded efficiently in vitro with HLA-A2 heavy chain, and when multimerized, the resultant complexes ("fusamers") bound specifically to appropriate CTL clones. These fused peptide/MHC complexes were as efficient as standard tetrameric peptide/MHC complexes in recognizing antigen-specific CTL. When the fusion protein was delivered to target cells using a retroviral vector, these cells were recognized and killed by appropriate CTL clones. Efficient sensitization to CTL lysis was achieved in TAP-negative and β2m-negative cell lines, as well as in unmutated B cell lines, proving that such constructs may be effective in inducing CTL even when the MHC class I pathway has been disrupted. Specific peptides covalently linked to β2m and delivered via retroviral vectors may be useful reagents for in vivo priming of CTL against epitopes of clinical relevance.