Combined effects of IL-12 and electroporation enhances the potency of DNA vaccination in macaques

Abstract

DNA vaccines are a promising technology. Historically, however, the ability of DNA vaccines to induce high response rates and strong immune responses, especially antibody responses, in non-human primates and human clinical trials has proven suboptimal. Here, we performed a pilot study in rhesus macaques to evaluate whether we could improve the immunogenicity of DNA vaccines through the use of adjuvant technology and improved delivery systems. The study consisted of four groups of animals that received: DNA by intramuscular (IM) injection, DNA with plasmid-encoded IL-12 by IM injection, DNA by IM injection with in vivo electroporation (EP), and DNA with IL-12 by IM EP. Each group was immunized three times with optimized HIV gag and env constructs. Vaccine immunogenicity was assessed by IFNgamma ELISpot, CFSE proliferation, polyfunctional flow cytometry, and antibody ELISA. Similar to previous studies, use of IL-12 as an adjuvant increased the gag and env-specific cellular responses. The use of EP to enhance plasmid delivery resulted in dramatically higher cellular as well as humoral responses. Interestingly, the use of EP to administer the DNA and IL-12 adjuvant combination resulted in the induction of higher, more efficient responses such that a 10-fold increase in antigen-specific IFNgamma(+) cells compared to IM DNA immunization was observed after a single immunization. In addition to increases in the magnitude of IFNgamma production in the initial and memory responses, the combined approach resulted in enhancements in the proliferative capacity of antigen-specific CD8(+) T cells and the amount of polyfunctional cells capable of producing IL-2 and TNFalpha in addition to IFNgamma. These data suggest that adjuvant and improved delivery methods may be able to overcome previous immunogenicity limitations in DNA vaccine technology.