Background: Nucleic acid vaccines adjuvanted with lipid nanoparticles (LNPs) are a simple and effective means of protection against infectious diseases through the delivery of antigen(s) that elicit(s) specific immunity. DNA vaccines are not commercially available for poultry mainly due to low protective efficacy and the associated production cost. Methods: We introduced here a novel nanoadjuvant system (namely, QTAP) comprising DOTAP and Quil-A for efficient delivery of plasmid DNA (pDNA) constructs into cells and boosting immune responses of chickens. Variable QTAP-pDNA-LNPs formulas were investigated for their physicochemical characteristics, cellular transfection, and in vivo efficacy in a vaccine/challenge model using pDNA encoding both S and N proteins of avian Infectious Bronchitis Virus (IBV). Results: Under electron microscopy, all LNP formulas were spherical in shape and had an overall size range of 45.4-376.3 nm. The formula with the smallest size had the lowest pDNA encapsulation and the highest polydispersity index (PDI). On the contrary, formulas with larger sizes and lower PDI values encapsulated a higher concentration of plasmid payload. Interestingly, the high-payload vaccine formula was stable at both 25 °C and 4 °C for up to 6 weeks of storage, but its gene expression dropped beyond this point at both temperatures. Following immunization of chickens, all groups were challenged with a virulent IBV. Surprisingly, both formulas were able to reduce the IBV viral shedding, indicating their effectiveness even when low concentrations of pDNA were incorporated in LNPs. However, pre-challenge sera from immunized chicks did not elicit IBV-specific antibodies, compared to birds immunized with a commercial live-attenuated IBV vaccine. Conclusions: This study suggests that the QTAP nanoadjuvant system is a safe and effective adjuvant for DNA immunization in poultry that could also be further developed for commercialization.
