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73 Isolation and Characterization of Multi-Clade V3-Specific Antibodies from Sera of Infected Humans That Effectively Neutralize Primary Isolates of HIV-1
C. Krachmarov1, W. Honnen1, S. Kayman1, M. Gorny2, S. Zolla-Pazner2,3, and A. Pinter*1
1Publ. Hlth. Res. Inst.; 2New York Univ. Sch. of Med.; and 3VA Med. Ctr., New York, NY, USA
Background: Whereas the V3 domain is a potent neutralization target for HIV-1, the heterogeneity of this domain, particularly in viruses from geographically diverse regions, is believed to be a major limitation in the effectiveness of V3 as a vaccine target. To explore this, native consensus V3 domains of clade A and clade B gp120s were expressed as fusion glycoproteins and used to isolate and characterize V3-specific antibodies from sera of US and African patients infected with clade B and clade A isolates, respectively.
Methods: V3-specific antibodies were immunoaffinity purified from sera of HIV-1 patients infected with clade B (US) or clade A (Cameroon) virus, using fusion proteins produced in mammalian cells that expressed either the clade B or clade A consensus V3 domain in native, glycosylated form. Eluted antibodies were analyzed by ELISA and immunoprecipitation and titered for neutralizing activity against primary HIV-1 isolate Envs using pseudotyped luciferase-encoding virions.
Results: Ninety-five percent of the US sera and 88% of the African sera tested reacted with the clade B V3 fusion protein, with considerably higher avidities than with synthetic V3 peptides of related sequences. The majority of the African sera, but none of the clade B sera, also recognized the clade A V3 protein. Thus, the African but not the US sera possessed either antibodies against V3 epitopes conserved across clade A and B or multiple antibodies with divergent V3 specificities. Antibodies immunoaffinity purified from both clade A and clade B sera on the clade B V3 protein possessed potent neutralization activity against some primary clade B HIV-1 isolates, in a number of cases giving 90% neutralization at concentrations of a few micrograms per milliliter.
Conclusions: The cross-clade neutralizing activity of V3 antibodies isolated from Africans infected with clade A viruses suggests that V3 sequence diversity may not preclude the generation of cross-protective antibody responses directed against this domain. Studies are ongoing to determine the frequency and breadth of such V3-targeted cross-neutralizing responses and to better characterize the epitopes involved.
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