314 Underestimation of HIV-1 Specific T-cell Responses Directed Against the Autologous Virus using HIV-1 Clade B Consensus Sequences M. Altfeld*, M. M. Addo, P. K. Lee, R. Shankarappa, C. Brander, T. Allen, A. Rathod, X. G. Yu, J. Harlow, K. O’Sullivan, M. N. Johnston, D. Strick, J. I. Mullins, E. S. Rosenberg, B. D. Walker AIDS Res Ctr, MGH, Boston, MA
Background: The definition of the correlates of protective immunity in HIV requires the determination of the real breadth and magnitude of responses directed against the virus. Comprehensive screening approaches using overlapping peptides spanning the entire expressed HIV sequence of viral reference strains or consensus sequences have shown strong and broadly directed T-cell responses against HIV, but failed to demonstrate an inverse correlation to HIV viral load. This may partially be due to the underestimation of the T-cell response directed against the autologous virus.
Method: HIV-specific T-cell responses were characterized using overlapping peptides spanning HIV clade B consensus sequences in 54 infected individuals, using an IFN-g ELISpot assay. In a subset of 12 individuals, the autologous virus sequences were determined and sets of overlapping peptides corresponding to autologous HIV Tat, Vpr, and p24-Gag sequences were tested for recognition by T-cells in 6 individuals.
Results: The comprehensive characterization of HIV-specific immune responses in the 54 subjects demonstrated broadly directed (median 14 epitopic regions, range 2-42) and strong (median 4,245 SFC/Mill, range 280-25,860) virus-specific T-cell responses, but no correlation of these responses to viral load or CD4 counts. Clustering of virus-specific T-cell responses was observed in conserved regions of the genome, while more variable regions were rarely targeted. Subsequent studies comparing the recognition of overlapping peptides spanning the HIV-1 clade B consensus and autologous virus sequences of Tat, Vpr, and p24-Gag demonstrated broader, significantly stronger and higher avidity T-cell responses directed against the autologous virus than against peptide sets based on consensus sequences. Under-estimation was more pronounced for the proteins with higher sequence variability (Tat and Vpr) compared to the more conserved protein p24-Gag.
Conclusion: These data indicate that the breadth, magnitude and avidity of HIV-1-specific T-cell responses can be significantly underestimated using HIV-1 clade B consensus sequences, in particular within more variable proteins of the HIV-1 genome. The assessment of HIV-1-specific T-cell responses directed against the autologous virus may help to determine the true correlates of protective immunity in HIV-1 infection.
