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330 Isolation of Epitopes Reactive with Antibody from HIV Viremia Controllers Using a Phage-Display Library
M. M. Berger*1, X.-Y. Jia1, M. M. Addo2, B. D. Walker2, R. D. Schrier3, J. G. Tilles1, and D. N. Forthal1
1Univ. of California, Irvine, USA; 2Massachusetts Gen. Hosp., Charlestown, USA; and 3Univ. of California, San Diego, USA
Background: HIV infection generally results in high levels of viremia and progressive disease. However, a small number of individuals (“viremia controllers”) sustains very low or undetectable viral loads in the absence of anti-retroviral therapy. In this study, we used a phage display library (PDL) to identify antibody epitopes that serologically distinguish viremia controllers from patients with progressive infection. Methods: Serum or plasma was collected from 23 never-treated HIV-infected viremia controllers (17 with plasma HIV RNA <50 copies/ml, and 6 with 50(3,000 copies/ml), from 25 patients with RNA levels >20,000 or AIDS (progressors), and from 18 uninfected controls. IgG from the viremia controllers was used to screen a 12-mer random peptide PDL. Oligonucleotides from captured phages were amplified and ligated into an expression vector for differential immunoscreening using pooled plasma from, alternatively, viremia controllers, progressors, and controls.
Results: Seven clones were isolated that reacted by immunoscreening exclusively with pooled plasma from viremia controllers. When individual plasma or serum samples were tested in an ELISA, 1 of these clones, HIVp5, differentiated viremia controllers from the other groups: HIVp5 reacted with 12 of 23 viremia controllers and with only 3 of 25 progressors (p = <0.01) and 1 of 18 uninfected controls. Viremia controllers had higher titers than progressors against a second clone, HIVp2, although similar proportions of patients from both groups reacted with HIVp2. The oligonucleotide inserts of HIVp5 and HIVp2 were sequenced, and the derived amino acid sequences showed some homology between HIVp5 and HIV Tat and between HIVp2 and HIV gp120.
Conclusions: Our results indicate that antibody from viremia controllers often recognize an HIV epitope that is infrequently recognized by antibody from patients with progressive infection. If these antibodies are biologically active in controlling viremia, their antigenic targets may be critical vaccine components. The use of phage display library panning combined with differential immunoscreening provides a powerful means of identifying antigens for the development of vaccines.
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