2005. Effect of plasmid backbone modification by different human CpG motifs on the immunogenicity of DNA vaccine vectors

Abstract: DNA vaccines, in general, have been found to be poorly immunogenic in nonhuman pri-mates and humans as compared with mice. As the immunogenicity of DNA plasmids relies, to a large extent, on the presence of CpG motifs as built in adjuvants, we addressed the issue of poor immuno-genicity by inserting recently identified CpG oligo-nucleotides (ODN) optimal for human (K-type or D-type CpG ODN) into the backbone of plasmid VR1020. We found that plasmid DNA containing K-type CpG motifs or D-type CpG motifs signifi-cantly enhanced the up-regulation of surface mol-ecules and production of interleukin-6 from hu-man peripheral blood mononuclear cells (PBMC) and stimulated monocytes to develop into function-ally mature dendritic cells (DC) compared with unmodified plasmid. Monocyte maturation into DC was through plasmacytoid DC present in the cul-ture. It is interesting that the K-type CpG motif-modified plasmid stimulated significant levels of interferon (IFN)- and IFN- from human PBMC. Immunization of mice with D-type CpG motif-mod-ified plasmid, encoding Plasmodium falciparum surface protein 25, yielded enhanced antigen-spe-cific antibodies. Taken together, these results sug-gest that insertion of immunomodulatory human CpG motifs into plasmid DNA can improve immu