Alteration of HIV epitope processing and presentation by HIV protease inhibitors

Background Epitopes displayed by MHC-I come from the multistep degradation of proteins by intracellular peptidases such as proteasome and aminopeptidases or cathepsins in the exogenous pathway. We hypothesize that due to structural homologies HIV protease inhibitors (PIs) used in antiretroviral therapies may affect activities of cellular peptidases involved in epitope processing and may affect epitope presentation to immune cells. Methods Using a fluorogenic assay the effect of 5 HIV-1 PIs (Ritonavir, Saquinavir, Nelfinavir, Indinavir, Atazanavir) on proteasome, aminopeptidase and cathepsin activities was tested in PBMCs from at least 6 healthy donors. Using PBMC cytosol as a source of peptidases and HPLC and mass spectrometry to define and quantify the degradation products, the effect of HIV PIs on HIV peptide processing kinetics and HIV epitope half-life was assessed. Finally we assessed the impact of PIs on the endogenous processing and presentation of epitopes by infected cells to CD8 T cells using a fluorescence-based cytotoxicity assay. Results HIV PIs variably altered proteasome, post-proteasomal aminopeptidases and cathepsin activities. Depending on the PI, some activities were inhibited (from 1.1 to 5 folds, p