347 Shifting Pressure Affects the Frequency of CD8+ T-cell Escape Variants with Initiation of HAART J. Casazza*, M. Betts, B. Hill, J. Brenchley, D. Ambrozak, D. Douek, R. Koup Vaccine Res Ctr, NIH, Bethesda, MD
Background: In HAART-treated patients (pts), HIV is under pressure from the immune response and antiretroviral therapy. The varying pressures exerted by these 2 entities may be reflected in the viral quasispecies.
Method: Five (5) pts were screened for CD8+ T-cell responses to HIV using intracellular cytokine staining prior to or near initiation of HAART. Viral sequences within epitopes were determined by sequencing. If a sequence variant was identified, a peptide representing that variant was synthesized and tested for immune response at the date closest to the initial sequencing. Immune responses to variant peptides and viral sequences were followed both before and during therapy.
Results: In the 5 pts screened, 10 responses directed against optimized epitopes were identified. At 5 of these epitopes, plasma viral RNA sequencing revealed no evidence of escape from the CD8+ T-cell response. For the other 5 responses, either multiple viral sequences were identified at sites of CD8+ T-cell response or, in one case (pt 5, a recent seroconverter), only the non-consensus sequence TAFTIPST rather than TAFTIPSI (RT 128-135) was found. In each pt with multiple viral variants within epitopes, the CD8+ T-cell response was inversely correlated with the frequency of that viral strain in plasma, suggesting in vivo escape from the CD8+ T-cell response. In pt 5, approximately a 10-fold higher concentration of TAFTIPST was required to stimulate IFN-gamma production than for TAFTIPSI, indicating a significant viral escape at this epitope. With initiation of HAART, the frequency of the escape variant in plasma decreased to 0, leaving only the CD8+ T-cell-sensitive variant TAFTIPSI. This variant then escaped through a single nucleotide change leading to the sequence TAFTIPSM in 100% of the plasma virus. A similar shift was found in another epitope in this pt.
Conclusions: These data show that HAART primarily affects replicating virus (often escape variants from CD8+ T-cells) and can lead to re-emergence of CD8+ T-cell sensitive virus within the quasispecies. These data also suggest that new escape mutations may emerge during therapy.
