Adjuvants may reduce in vivo transfection levels for DNA vaccination in mice leading to reduced antigen-specific CD8+ T cell responses.

Adjuvants for DNA vaccination are designed to promote transformation of transgenes into target cells and increase inflammation in the site of injection, with resultant immune cell recruitment. Numerous studies indicated cationic liposomes as effective adjuvants for DNA vaccination due to their ability to promote in vivo transfection and innate immune system activation. Commercial reagents as Adjuplex and in vivo-JetPEI are also intended to facilitate DNA vaccination. Here, we evaluate the adjuvant properties of cationic liposomes, Adjuplex and in vivo-JetPEI compared to injection of DNA without adjuvant. In mice vaccinated with piggyBac pDNA vaccines, we assessed in vivo antigen expression, innate immune responses in draining lymph nodes, and antigen-specific T cell responses in spleens and blood. Surprisingly, vaccination with DNA in PBS emerged as the most efficient in promoting in vivo transfection and consequent antigen expression, while the addition of adjuvant reduced the amount of antigen expressed. On the other hand, we discovered higher numbers of innate immune cells and activated dendritic cells in the lymph nodes of mice injected with adjuvants than those vaccinated in PBS. The analysis of eGFP-specific immune responses revealed that all the different immunizations induced functional antigen-specific T cells in spleens, although only T cells generated by non-adjuvant vaccination and Adjuplex were identified in the blood of vaccinated mice. These results provide insight into the effects of these 3 adjuvants and may facilitate appropriate use off adjuvants by researchers using DNA vaccines in laboratory animals.