Cell Type-Specific Proteasomal Processing of HIV-1 Gag-p24 Results in an Altered Epitope Repertoire

Cell Type-Specific Proteasomal Processing of HIV-1 Gag-p24 Results in an Altered Epitope Repertoire ▿ Nicholas J. Steers 1 , 2 , Jeffrey R. Currier 1 , 2 , Gustavo H. Kijak 1 , 2 , Robert C. di Targiani 3 , Ashima Saxena 3 , Mary A. Marovich 2 , Jerome H. Kim 2 , Nelson L. Michael 2 , Carl R. Alving 2 and Mangala Rao 2 , * 1 Henry M. Jackson Foundation for the Advancement of Military Medicine, 1600 East Gude Drive, Rockville, Maryland 20850 2 U.S. Military HIV Research Program, Division of Retrovirology, Walter Reed Army Institute of Research, Rockville, Maryland 20850 3 Division of Bacterial and Rickettsial Diseases, Walter Reed Army Institute of Research, Silver Spring, Maryland 20910 ABSTRACT Proteasomes are critical for the processing of antigens for presentation through the major histocompatibility complex (MHC) class I pathway. HIV-1 Gag protein is a component of several experimental HIV-1 vaccines. Therefore, understanding the processing of HIV-1 Gag protein and the resulting epitope repertoire is essential. Purified proteasomes from mature dendritic cells (DC) and activated CD4 + T cells from the same volunteer were used to cleave full-length Gag-p24 protein, and the resulting peptide fragments were identified by mass spectrometry. Distinct proteasomal degradation patterns and peptide fragments were unique to either mature DC or activated CD4 + T cells. Almost half of the peptides generated were cell type specific. Two additional differences were observed in the peptides identified from the two cell types. These were in the HLA-B35-Px epitope and the HLA-B27-KK10 epitope. These epitopes have been linked to HIV-1 disease progression. Our results suggest that the source of generation of precursor MHC class I epitopes may be a critical factor for the induction of relevant epitope-specific cytotoxic T cells.