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42 Improved Efficacy of DNA Vaccination Using a New Generation of Optimized HIV and SIV Plasmids
G. N. Pavlakis1, M. Rosati1, P. Eyler1, A. Valentin1, H. Trivedi1, A. Biragyn1, L. W. Kwak1, P. Markham2, R. Woodward 2, A. von Gegerfelt1, N. Miller3, and B. K. Felber1
1NCI at Frederick, MD, USA; 2Advanced BioScience Labs, Inc., Kensington, MD, USA; and 3NIAID, NIH, Bethesda, MD, USA
Background: Multiple point mutations in the gag, pol, and env coding regions of lentiviral mRNAs are necessary to improve expression. The mutations act mainly at the level of mRNA transport and stability. Improved expression vectors for SIV and HIV proteins were used in vaccination experiments in mice and macaques to measure cellular and humoral immune responses. Improved expression led to better immunogenicity, but antibody production was still poor. Therefore, we constructed several vectors expressing secreted or intracellular forms of gag and env proteins.
Results: Expression and immunogenicity of secreted and intracellular forms of antigens were compared with the native forms of antigens using similar expression vectors. We found that combinations of different forms of antigens resulted in improved immunogenicity. Fusions of gag to MCP-3 chemokine stimulated a strong humoral immune response. Antibody titers of >1:1,000 were observed in vaccinated macaques. This was far superior to the antibody responses observed with the unmodified gag sequence. Macaques vaccinated with some combinations developed both strong humoral and cellular immune responses. Such combinations may overcome some limitations of DNA vaccines in primates, namely, the poor ability to elicit humoral immune responses. Studies are in progress to evaluate whether optimization of both the dosage and the form of antigen will improve vaccination results against HIV and SIV.
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