Design and characterization of plasmids encoding antigenic peptides of Aha1 from Aeromonas hydrophila as prospective fish vaccines

•Antigenic Aeromonas hydrophila Aha1 peptides have potential for fish vaccination.•Aha1-based-pVAX-GFP vaccine candidates efficiently transfect CHO cells in 24 h.•PLGA-chitosan/pDNA nanoparticles and pDNA lipoplexes had similar transfection ability.•Nanoparticles demonstrated protection of DNA vaccines against enzymatic digestion.

The current investigation aimed at designing DNA vaccines against Aeromonas hydrophila infections. The DNA vaccine candidates were designed to express two antigenic outer membrane protein (Aha1) peptides and to be delivered by a nanoparticle-based delivery system. Gene sequences of conserved regions of antigenic Aha1 [aha1(211-381), aha1(211-381)opt, aha1(703-999) and aha1(703-999)opt] were cloned into pVAX-GFP expression vector. The selected DNA vaccine candidates were purified from E. coli DH5α and transfected into Chinese hamster ovary cells. The expression of the antigenic peptides was measured in cells along post-transfection time, through the fluorescence intensity of the reporter GFP. The lipofection efficiency of aha-pVAX-GFP was highest after 24 h incubation. Formulated PLGA-chitosan nanoparticle/plasmid DNA complexes were characterized in terms of size, size distribution and zeta potential. Nanocomplexes with average diameters in the range of 150-170 nm transfected in a similar fashion into CHO cells confirmed transfection efficiency comparable to that of lipofection. DNA entrapment and further DNase digestion assays demonstrated ability for pDNA protection by the nanoparticles against enzymatic digestion.