OR8 HIV Infection leads to the presentation of unexpectedly long peptides by HLA-A11:01

Vaccines for HIV-1 have proven ineffective due to the inability of the immune response to cope with HIV-1 diversity/antigenic variation. We proposed to identify host (human) ligands uniquely presented by Class I HLA during infection as these host targets are not likely to mutate. Deep Ligand Sequencing (DLS) was used to determine changes in the class I HLA presented host ligand repertoire after HIV-1 infection of CD4+T cells. In this manner we identified host-derived ligands that mark the surface of HIV infected cells. Soluble class I HLA-A*11:01 (sHLA) was harvested from HIV-1 (NL4–3)-infected and uninfected human CD4+SUP-T1 cells. Ligands from both infected and uninfected cells were purified and then fractionated by high pH HPLC. NanoLC-MS ligand fragment spectra were collected on all peptide containing fractions. Ligand sequences were determined from tandem MS spectra (DDA & DIA) using PEAKS v7.0 and Protein Pilot v4.5 at a 1% FDR. Ligand intensity data was extracted from the DIA spectra using Peakview v2.1 and the SWATH microapp. Normalization and log fold increase were determined using Excel. Quantitative values were obtained for a total of 5222 distinct HLA-A11 ligands from both infected and uninfected cells. Strikingly, over half of the ligands (55%) were unique to HIV-1 infected cells. These unique host ligands were significantly longer than the ligands found in uninfected cells with an average length of 12.2 amino acids as compared to 10.6 amino acids for uninfected ligands. Although ligands were longer, there were no significant changes in motif, and there was no difference in the source proteins providing peptides. Our group and others have previously reported long (>11 aa) HIV-1 peptide ligands that are recognized by CTL. Here, we observe a significant shift in the length of the host ligand repertoire as well. This suggests that HIV alters the antigen processing pathway to increase ligand length, possibly by inhibition of host cell peptidases. Since HLA-A11 is more permissive in binding longer ligands, we are able to observe this shift in length. However, with allomorphs like HLA-A2 that are not as length permissive, this could represent an immune escape mechanism for HIV. This ability to bind long ligands may partially explain why HLA-A11 is considered a correlate of protection. W.H. Hildebrand:Consultant; Company/Organization; Pure MHC, LLC.