Annual and Interim Progress Report Summaries
Principal Investigator: Susan Zolla-Pazner
Project: The V3 Loop: A Conserved Structure of gp 120 that can Induce Broadly Neutralizing Antibodies Against HIV-1
Submitted April 30, 2010 (Interim Report)
Overall activities:
During the initial 3 years of our project, we have demonstrated that an immune response focused on V3 results in the induction of antibodies (Abs) that neutralize viruses from several HIV-1 subtypes. Our immune focusing strategy is based on DNA gp120 priming and V3-protein scaffold boosting. To this end, four generations of V3-scaffold proteins have been designed using an interdisciplinary and integrated approach which includes immunology, virology and computational structural biology. The current 2-year project aims to:
a) optimize the V3 design of multivalent scaffolds, synthesize them, and use them as immunogens
b) test the capacity of the immunogens, individually and as cocktails, to induce neutralizing Ab responses in the rabbit model.
The underlying hypothesis of the work is that using this DNA prime/protein boost approach, with gp120 DNA as the prime and V3-scaffold immunogens or a cocktail of V3-scaffold immunogens as the boost, will focus the immune response on conformational V3 epitopes and induce cross-clade neutralizing Abs against HIV. This would be the first step in developing recombinant immunogens that can focus the immune response on several epitopes in the Envelope of HIV, resulting in an effective protective vaccine.
Recent findings:
The rational design of V3 immunogens is based on the identification on several V3 crystal structures of conserved elements that are targeted by broadly neutralizing human anti-V3 monoclonal antibodies. In the past 6 months, we have reported the ability of six anti-V3 human monoclonal antibodies to display cross-clade neutralizing activities. Hence, 56 (57%) out of 98 viruses pseudotyped with HIV envelopes of subtypes A, AG, B, C, and D can be neutralized by one or more anti-V3 monoclonal antibodies. When the Tier 1 viruses are excluded from this analysis, significant neutralization is detected by one or more anti-V3 monoclonal antibodies against 46/88 (52%) viruses from the different subtypes. This work was conducted in collaboration with the Ab-VIMC and the VISC. The paper reporting these data was recently published (Hioe, et al, PLoS One, 2010).
The cross-reactivity of anti-V3 monoclonal antibodies is now supported by the identification of conserved elements within the V3 crown from the crystallographic structures of V3 bound by several neutralizing anti-V3 monoclonal antibodies, and by bioinformatics analyses of these V3 structures. Hence, the crown of the V3 loop adopts a nearly universal beta-hairpin conformation regardless of its amino acid sequence. This crown can be divided into four different zones, of which three are mainly conserved (the arch, the band, and the hydrophobic face). The most variable amino acids within the V3 crown are restricted to a small zone on the surface of one face of the beta-hairpin loop (the hydrophilic face). These findings were recently published (Burke, et al, Structure, 2009; Jiang, et al, Nat Struct Mol Biol, 2010; Almond, et al, AIDS Res Hum Retroviruses, 2010).