Inhibition of HIV Envelope Glycoprotein-Mediated Syncytia Formation by Lectins

Objectives: Currently available therapies to treat HIV-1 infection cannot eradicate the virus, since the viral genome is integrated into host cell chromosomes. Our long-term goal is to use targeted cytotoxicity to specifically eradicate HIV-infected cells. Virus-producing cells express the envelope glycoproteins (gp120/gp41; Env) on the cell surface during assembly and budding. Macromolecules that can exclusively recognize Env may be useful as agents that can mediate the targeting of cytotoxic lipidic nanoparticles to HIV-infected cells. Since Env is heavily glycosylated, we examined the ability of carbohydrate-binding plant lectins and anti-gp120 antibodies to inhibit Env-mediated syncytia formation as a first step to identify molecules that may be used for targeting.

Methods: Anti-gp120 antibodies were obtained from the NIH AIDS Research and Reference Reagent Program. Lectins were a gift of Dr. Jan Balzarini (University of Leuven, Belgium). Both the plant lectins and the anti-gp120 compounds were tested for their ability to inhibit syncytia formation (cell-cell fusion) overnight between HIV Env-expressing TF228.1.16 cells and CD4-expressing SupT T-lymphocytic cells. The lectins were used at concentrations between 2-8 µg/mL, while the antibodies were tested at 5 and 10 µg/mL. Syncytia formation was monitored using phase contrast microscopy, and binding of the compounds to TF228.1.16 cells was monitored via fluorescence microscopy.

Results: The plant lectins Galanthus nivalis (snowdrop) agglutinin (GNA) and Hippeastrum hybrid (Amaryllis ) agglutinin (HHA) inhibited cell-cell fusion of TF228.1.16 cells with SupT cells at low concentrations. Urtica dioica agglutinin (UDA) was also inhibitory to fusion, but at higher concentrations. Conversely, none of the anti-gp120 antibodies inhibited fusion in any significant way.

Conclusion: GNA and HHA are highly inhibitory to Env-mediated fusion. These lectins may be useful in targeting lipidic nanoparticles (liposomes) specifically to HIV-infected cells.