For practical application, microbicides must be available in massive amounts, and must be produced cost- effectively. These requirements might eliminate recombinant proteins from consideration as costs of production in cell-based fermentation systems are prohibitively high. We developed a practical solution by expressing and purifying recombinant forms of the algal lectin Griffithsin (GRFT), the most potent HIV-1 entry inhibitor yet described, from tobacco leaf tissues. GRFT has no known homologs in vertebrates, and hence has the potential to be immunogenic and thus possibly to induce an inflammatory response incompatible with its use as a microbicide. This is a theoretical concern that applies to most, if not all, peptide-based microbicides, and it is of vital importance to the field that this phenomenon be investigated more thoroughly. We will generate a mutant of GRFT that lacks lectin activity to allow us to answer the question whether lectin activity plays a role in induction of mucosal inflammatory responses. We will use a comprehensive mouse vaginal administration model, developed by our consultant and collaborator Dr. Betsy Herold, to evaluate the mucosal toxicity of hydroxyethylcellulose-formulated GRFT. Toxicology endpoints will include histology, measurement of molecular markers of inflammation, and phenotypes of leukocyte infiltrate in vaginal tissues. Since immunogenicity of protein microbicides is a concern, we will also measure immune responses to the vaginal microbicide in animals in which we have intentionally raised an anti-GRFT immune response. We will use Dr. Herold's elegant mouse genital herpes simplex virus (HSV) infectivity assay that functions as a surrogate measurement of microbicide safety. Susceptibility to challenge with HSV-2 in animals treated with GRFT will inform us whether the complex of biological responses to treatment with GRFT can increase susceptibility to infection with HSV-2, and hence to possible enhanced susceptibility to HIV-1 infection in humans. We will also study the mechanism of resistance to GRFT in a mutant HIV-1 Clade C virus that we isolated in a selection experiment. Collectively, the data that we generate in the course of this research will provide a comprehensive assessment of the utility of GRFT as a component of a vaginal microbicide to prevent HIV-1 transmission. ? ?
In the absence of an effective vaccine against HIV, there is an urgent need for alternative strategies to prevent sexual transmission of HIV, such as vaginally-applied microbicidal gels.
We aim to answer the question whether proteins called lectins, which bind the sugar structures found on the surface of the AIDS virus, generate an inflammatory response when administered in the vagina of mice. These studies will provide important information that will help determine whether lectins have acceptable toxicity profiles to justify further development as microbicides. ? ? ? ?
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