Session 53Poster Presentations DNA Vaccines Session Day and Time: Thursday 1:30 - 3:30 pm Room: Hall D
447 Enhanced DNA Prime-protein Boost Vaccines Induce Potent and Protective Immune Responses Against HIV-1 S. Barnett*1, I. Srivastava1, L. Stamatatos2, J. zur Megede1, Y. Lian1, G. Otten1, D. Montefiori3, M. Lewis4, S. Engelbrecht5, E Janse van Rensburg5, G Widera6, D O'Hagan1, J Polo1, J Ulmer1, J Donnelly1 1Chiron Corp, Emeryville, CA; 2Seattle BioMed Res Inst, WA; 3Duke Univ, Durham, NC; 4Southern Res Inst, Gaithersburg, MD; 5Univ of Stellenbosch, Tygerberg, South Africa; and 6Genetronics, Inc, San Diego, CA
Background: Novel vaccine approaches will be required to induce potent and durable immunity against diverse HIV-1 strains.
Methods: Sequence-modified gene cassettes were constructed expressing the gag, pol, and env antigens derived from subtypes B and C HIV-1 strains. In addition to naked DNA, 2 different DNA vaccine delivery technologies were evaluated: 1) delivery of DNA adsorbed to cationic polylactide co-glycolide (PLG) microparticles, and 2) electroporation. Oligomeric env proteins derived from subtypes B and C HIV-1 strains ±V2 or V1V2 loop regions were purified and characterized. Rhesus macaques were immunized using DNA prime-protein boost regimens. Antigen-specific T-cell responses were measured by LPA, cytolytic assays, and intracellular cytokine staining. Humoral responses were evaluated by ELISA and neutralization assays using primary virus strains. Vaccine efficacy was determined by measurements of plasma RNA and CD4+ T-cell subsets after challenge with the pathogenic SHIVSF162P4.
Results: Sequence-modified subtype B and C HIV-1 gag, pol, and env antigens expressed at increased levels over the native forms and were highly immunogenic in mice, rabbits, and monkeys. DNA adsorption to PLG and electroporation of injected DNA were effective in enhancing B- and T-cell responses to HIV antigens in mice and macaques. Macaques primed with SF162 gp140 ± V2 loop DNA and boosted with oligomeric SF162 gp140delV2 protein exhibited neutralizing antibody responses to both the parental SF162 virus and to heterologous R5 primary virus isolates. These SF162-based env vaccines alone (in the absence of SIV gag or pol) were able to partially protect macaques against intravenous challenge with pathogenic SHIVSF162P4. While none of the animals was completely protected, peak viremia during the acute phase of infection was blunted, and virus loads during this period were found to inversely correlate with the degree of neutralizing antibody activity directed toward the challenge virus. Vaccinated animals also demonstrated lower set-point viremia, stable CD4+ T-cell levels, and lack of disease, as well as a more rapid development of neutralizing antibodies against the challenge virus as compared with unvaccinated controls.
Conclusions: Enhanced DNA delivery of improved HIV gag, pol, and env antigens combined with boosting using V2-deleted oligomeric env protein holds great promise for future clinical evaluation.
