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179 Qualitatively Different Immune Responses Induced by Monomeric and Oligomeric Forms of Env Glycoprotein from HIV-1SF162 in Prime-Boost Regimen
I. Srivastava, E. Kan*, A. Fong, Y. Lian, L. Stamatatos, J. Ulmer, and S. Barnett
Chiron Corp., Emeryville, CA, USA and Aaron Diamond AIDS Res. Inst., New York, NY, USA
Background: A significant emphasis of our work on the development of an HIV vaccine has been toward the evaluation and comparison of monomeric (gp120) and oligomeric (o-gp140) forms of the HIV-1 envelope proteins for their relative abilities to induce functional neutralizing antibody responses.
Methods: To expose potential conformational and neutralizing epitopes, we introduced V2 loop deletions in both gp120 and o-gp140 and then compared their relative ability to induce high avidity and primary isolate neutralizing antibodies in DNA prime and o-gp140DV2 protein boost regimen. Toward this end, we designed a strategy to stabilize gp140 in oligomeric conformation and developed stable CHO cell lines expressing o-gp140 +/( V2 loop in higher concentrations. Furthermore, we purified o-gp140DV2 SF162 proteins to homogeneity and demonstrated that they bind to sCD4 and have glycosylation profiles similar to that obtained for the native env protein. Groups of 4 rabbits were immunized with gp120+/( V2 loop and o-gp140 +/( V2 loop 3 times with 1 mg of plasmid DNA followed by 2 boosts with 50 mug of purified o-gp140DV2 SF162 protein adjuvanted in MF59.
Results: All the animals induced Env-specific antibodies post DNA but the titers were significantly enhanced after the protein boost. The gp140 immunized animals had a higher proportion of antibodies directed toward conformational epitopes as compared with the gp120 group, whereas the gp120 immunized animals had more antibodies directed against the V3 loop. As expected, antibodies induced after DNA immunization exhibited relatively lower avidity, however the antibody avidity increased significantly after the protein boost. Anti-env antibodies with the highest avidity and neutralizing activity were induced by gp140 (+/( V2 loop) primed animals. Interestingly, gp140DV2 primed animals also had the highest proportion of antibodies directed against the CD4 binding site.
Conclusions: This information will aid in the rational design of novel immunogens capable of inducing high avidity and primary isolate neutralizing antibody responses.
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