A Novel Cre Recombinase-Mediated Minicircle DNA (CRIM) Vaccine Provides Partial Protection against Newcastle Disease Virus.

Minicircle DNA (mcDNA), which contains only the necessary components for eukaryotic expression and is thus smaller than traditional plasmids, has been designed for application in genetic manipulation. In this study, we constructed a novel plasmid containing both the Cre recombinase under the phosphoglycerate kinase (PGK) promoter and recombinant and sites located outside the cytomegalovirus (CMV) expression cassette. The strictly controlled synthesis of Cre recombinase maintained the complete form of the plasmid , whereas the production of Cre transformed the parental plasmid to mcDNA after transfection. The newly designed re ecombinase-mediated cDNA platform, named CRIM, significantly increased the nuclear entry of mcDNA, followed by increased production of mRNA and protein, using enhanced green fluorescent protein (EGFP) as a model. Similar results were also observed in chickens when the vaccine was delivered by the regulated-delayed-lysis strain χ11218, where significantly increased production of EGFP was observed in chicken livers. Then, we used the HN gene of genotype VII Newcastle disease virus as an antigen model to construct the traditional plasmid pYL43 and the novel mcDNA plasmid pYL47. After immunization, our CRIM vaccine provided significantly increased protection against challenge compared with that of the traditional plasmid, providing us with a novel mcDNA vaccine platform. Minicircle DNA (mcDNA) has been considered an attractive alternative to DNA vaccines; however, the relatively high cost and complicated process of purifying mcDNA dramatically restricts the application of mcDNA in the veterinary field. We designed a novel mcDNA platform in which the complete plasmid could spontaneously transform into mcDNA In combination with the regulated-delayed-lysis strain, the newly designed mcDNA vaccine provides us with an elegant platform for veterinary vaccine development.