OR9 A single amino acid residue within the HLA-B*35 heavy chain determines the immune dominance of peptides during hcmv infection

Abstract

Aim The crucial role of certain components of the peptide loading complex in selecting and loading peptides on HLA class I molecules makes the PLC an ideal target for viral immune escape mechanisms. The immune evasion strategy of HCMV prevents the presentation of viral antigens; consequently only PLC-independent HLA variants are able to constitutively present viral derived peptides. A problem in cellular therapy strategies is the emergence of antiviral T-cell anergy over time. The crucial question is at what stage of HCMV infection viral-peptides are preferentially presented over self-peptides. Two of those PLC-independent HLA molecules are the common variants B*35:01 and 35:08 distinguished by a single mismatch at residue 156, both of them have been described to present viral-peptides. The impact of the 156 mismatch on the selection and presentation of available viral peptides is not investigated, yet. Methods To analyze the competitive HLA-B*35:01 and B*35:08 restricted viral- and self-peptide repertoire in the presence of HCMV, we utilized soluble HLA technology. Soluble HLA complexes from HCMV infected BJ/sHLA cells were affinity purified. Kinetic of immune evasions was monitored by mRNA analysis. sHLA-B*35:01 or sHLA-B*35:08 restricted peptides were recovered and analyzed using nano-LC-ESI MS/MS technology. Results We found a distinct self-peptide pattern in the presence of HCMV for B*35 variants, the features and anchor motifs remained mainly unaltered in comparison to peptides recruited in the absence of HCMV. However, a different subset of viral peptides from the early to late phase of infection was recruited by B*35:01 and B*35:08. A high frequency and dominance of certain viral peptides over self-peptides was striking. Conclusion These findings explain the discrepancy between predicted and naturally presented immunogenic epitopes for establishing anti-viral effector cells. Furthermore, peptide prediction based on available peptide anchors as given in the databases might fail due to structural alteration of HLA variants and support the need of comprehensive peptide recruitment data for personalized and effective cellular therapies.