Reconstitution of antigen presentation in HLA class I-negative cancer cells with peptide- beta 2m 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 beta 2-microglobulin ( beta 2m) 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 beta 2m. 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 beta 2m-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 beta 2m and delivered via retroviral vectors may be useful reagents for in vivo priming of CTL against epitopes of clinical relevance.