Cytolytic Perforin as an Adjuvant to Enhance the Immunogenicity of DNA Vaccines

Shrestha, Ashish C.; Wijesundara, Danushka K.; Masavuli, Makutiro G.; Mekonnen, Zelalem A.; Gowans, Eric J.; Grubor-Bauk, Branka

rDNA-PRF technology has been used in the development of HIV and HCV DNA vaccines [55, 57, 107] . Direct comparison of the effects of the cytolytic PRF and the apoptotic protein DTa on the immunogenicity of the HIV-1 Gag protein showed that PRF activated DCs more efficiently, as evidenced by the increase in frequency of cross-presenting DCs and upregulation of activation marker (CD80) [55] . In both DNA vaccines, PRF and DTa were driven by SV40 promoter. Immunization of mice with a DNA vaccine encoding proapoptotic DTa as an adjuvant in a HIV Gag DTa vaccine resulted in decreased DC activation, suggesting that DTa-induced apoptosis attenuated immune response [55] . Furthermore, improved protection in the mouse EcoHIV challenge model was achieved with rDNA-PRF encoding HIV Gag compared to protection levels in mice vaccinated with a canonical Gag DNA vaccine [57] . A rDNA-PRF vaccine encoding the HCV NS3 protein coexpressed with PRF was shown to increase NS3-specific CMI in mice and pigs, compared to NS3 coexpression with a proapoptotic protein, the rotavirus NSP4 protein [56] . NSP4 is an enterotoxin that elicits a proapoptotic effect by disrupting the mitochondrial membrane and activating caspase-3, -8, and -9 [108, 109] . This study showed that PRF coexpression induced cell death by necrosis, and thus enhanced NS3-specific immune responses, whereas, proapoptotic NSP4 reduced NS3-specific response [56] . Importantly, HCV NS3 PRF was more immunogenic than the canonical NS3 vaccine in pigs, demonstrating the translational potential of the cytolytic DNA vaccines in human clinical trials [56] . Likewise, we have shown that a multi-antigenic HCV DNA vaccine encoding genotype 3a proteins NS3, NS4A, NS4B, and NS5B coexpressed with PRF induced robust CMI against the range of HCV NS proteins, compared to coexpression with VSVG [57] . We also showed that multi-antigenic and multigenotypic (HCV genotype 1 and 3a) DNA cocktail vaccines encoding PRF can significantly increase the magnitude and breadth of CMI responses to NS3 and NS5B against both genotypes compared to those elicited by a single-genotype vaccine [107] .