308 Immune Selection by CTL is an Important Factor for Sequence Variation in HIV-1 Nef T. Harrer*, A. Goldwich, M. Schmitt, M. Bäuerle, S. Bergmann, M. Hamacher, J. R. Kalden, R. Müller, S. Kasten, T. Harrer Univ of Erlangen, Germany
Background: HIV-1-specific T-cells can select HIV-1 strains with escape mutations. However, it is still debated whether sequence variation in HIV-1-specific T-cell epitopes is predominantly caused by immune selection or by random mutational events. To investigate the influence of T-cell driven immune selection we analyzed in HIV-infected patients (pts) the occurrence of mutations in conserved epitopes in Nef.
Methods: Forty-three (43) HIV-1-infected pts were included in this study. Thirty-one (31) pts were on HAART and 12 without therapy. Proviral HIV-1 nef genes were analyzed by PCR-based sequencing from PBMC or PHA-stimulated PBMC. HLA class I typing was done by serologic standard assays and in a few pts also by genotypic analysis. Analysis of recognition of variant HIV strains by PBMC was performed by using synthetic peptides in a gamma-IFN ELISpot.
Results:The HLA A3 restricted nef epitope QVPLRMTYK (QK10) is a conserved CTL epitope within a functional domain of nef. It is overlapping with CTL epitopes restricted by HLA A11, B7 and B35. We observed aa substitutions within the QK10 epitope in 13 of the 43 pts. Ten (10) of these 13 pts with mutations were positive for at least 1 of the HLA A3, A11, B7, and B35 alleles (77%), whereas 3/13 (23%) were negative for these HLA alleles (p = 0.05). Of the 21/43 pts carrying at least 1 of the HLA A3, A11, B7, and B35 alleles 10 (47,6 %) showed mutations within the QK10 epitope in contrast to only 3 of the 22 HLA B A3/A11/B7/B35 negative pts (13,6%). Except for 1, all mutations strongly decreased recognition by QK10 specific CTL. A similar strong correlation between the occurrence of mutations within defined epitopes and the presence of the corresponding HLA alleles was found also for several other CTL epitopes such as the HLA B8 restricted epitope FLKEKGGL and the B7 restricted epitope FPVTPQVPL.
Conclusions: Our data strongly suggest that T-cells play an important role in the generation of sequence variation, at least in conserved functional important epitopes. Despite of the functional immune evasive properties of HIV nef, the immune system is able to select for mutations even in conserved sequence areas of nef, suggesting an important role of HIV-1 specific T-cells for the control of HIV-1.
