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Volume 6 Supplement 3

AIDS Vaccine 2009

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P12-13. Structure-guided design and immunological characterization of immunogen constructs presenting the HIV-1 gp120 V3 loop on a CTB scaffold


The V3 loop is a major neutralizing determinant of the HIV-1 virus. Cholera toxin subunit B (CTB) is a highly immunogenic protein and it has been used in fusion constructs to enhance immunogenicity of target proteins. We hypothesized that a rationally designed immunogen, based on V3 and CTB, could induce high titers of Abs with binding mode and epitope specificity similar to known broadly neutralizing anti-V3 mAbs.


We used molecular modeling and available crystallographic structures of the V3 loop in the HIV-1 gp120 context, the V3 loop fragment bound to broadly neutralizing mAbs, as well as the structure of the CTB to design two novel V3-scaffold immunogen constructs: a full-length V3-CTB presenting the complete 35 amino-acid residue V3 loop in a structural context mimicking the V3 in gp120, and a short V3-CTB presenting a smaller segment of V3 in the conformation recognized by mAb 447-52D.


Antigenic properties were evaluated on a panel of 24 anti-V3 human mAbs. The full V3 construct was recognized with high affinity by the large majority of mAbs, with some preference by mAbs derived from clade B-infected individuals. Short V3 construct exhibited high affinity binding to mAb 447-52D and only a few additional mAbs. Immunogenicity of the constructs was evaluated in rabbits using a DNA prime/protein boost protocol. Boosting with the full-length V3-CTB resulted in serum anti-V3 titers that neutralized multiple HIV virus strains from various HIV-1 clades. Short V3-CTB construct was ineffective in boosting the Ab


The results suggest that while (1) a scaffold immunogen that presents a single epitope (designed to fit a single mAb) may result in a poor Ab response, (2) focusing the immune response on a specific immunogenic region, such as the V3 loop, can elicit a robust Ab response, and (3) the CTB scaffold can efficiently present V3

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Open Access This article is published under license to BioMed Central Ltd. This is an Open Access article is distributed under the terms of the Creative Commons Attribution 2.0 International License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Totrov, M., Jiang, X., Kong, X. et al. P12-13. Structure-guided design and immunological characterization of immunogen constructs presenting the HIV-1 gp120 V3 loop on a CTB scaffold. Retrovirology 6 (Suppl 3), P179 (2009).

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