Frequency of class I HLA-restricted anti-HIV CD8(+) T cells in individualsreceiving highly active antiretroviral therapy (HAART)

Peptide/MHC tetrameric complexes were used to enumerate the frequency of HL A class I-restricted epitope-specific CD8+ T cells in 18 HLA-A*0201 HIV T t ype 1-infected asymptomatic patients. HLA-A*0201 molecules were complexed t o HIV Gag p17 (amino- acids 77-85) and reverse transcriptase (amino acids 4 64-472) peptides, biotinylated, and bound to streptavidin-phycoerythrin to form tetramers, We show in this study that 17 of 18 HIV-1-infected asymptom atic patients have circulating frequencies of 1/50-1/1000 CD8(+) T cells th at recognize both Gag and Pol CTL epitopes or either epitope alone, The fun ctional nature of these cells is open to interpretation, as we show that de spite relatively high frequencies of fresh epitope-specific CD8(+) T cells, variant epitope sequences in viral plasma progeny were rare. In addition, the majority of tetramer-positive cells did not display discernible fresh C TL activity; only after restimulation with specific peptide in culture was there an expansion of epitope-specific CD8(+) cells, correlating with high CTL activity. These data suggest that fresh tetramer-stained cells probably represent memory precursors; we demonstrate, with the application of highl y active antiretroviral therapy, that the interruption of chronic antigenic stimulation causes significant reductions in the frequency of these cells in five of six patients. In conclusion, this study provides evidence that p ersistently replicating viral populations are probably required to maintain high frequencies of HIV-1 epitope-specific CD8(+) T cells in asymptomatic chronically infected individuals.