Immunization with envelope glycoprotein gp120 of HIV-1 has met limited success, due to poor immunogenicity in primates and man and due to variability in the virus. Previous work from this lab has identified a site in the carboxyl third of gp120, near the CD4 binding site, as an important target for neutralizing antibodies against HIV-1. Because this site is conversed among diverse HIV-1 isolates, it is an attractive target for vaccines, since antibodies to this site may potentially protect against a broad range of HIV-1 strains. In an attempt to increase the immunogenicity of this site on gp120 without destroying the protein conformation it depends on, we have designed a series of conjugate vaccines in which the gp120 is linked to a stronger immunogen via its carbohydrate sidechains. To this end, we have devised a novel heterobifunctional crosslinker, which links carbohydrate sidechains on the glycoprotein to SH groups on the carrier protein. Model reactions indicate high yield reactions of the crosslinker at both ends under mild conditions. Using protein antigens, coupling efficiency of >90% has been achieved between gp120 and HBsAg, tetanus toxoid, and inactivated poliovirus vaccine. Each conjugate has been used to immunize rabbits, and the resulting antibodies will be tested for the ability to neutralize virus homologous to the envelope used in the vaccine as well as other HIV-1 isolates with divergent envelopes, as a marker of antibodies to the conserved neutralizing site. In this way, we hope to develop conjugates with increased vaccine potency and with the ability to elicit broadly reactive neutralizing antibodies in man.
