Vaccination of turkeys against Chlamydophila psittaci through optimised DNA formulation and administration

We have demonstrated that vaccination of turkeys with an unformulated DNA vaccine induces significant protection against Chlamydophila (Cp.) psittaci infections. Nevertheless, the immunogenicity of the DNA vaccine can still be improved by increasing translation and transfection efficiency. Therefore, the ompA codon was adapted to the codon usage in birds, resulting in pcDNA1/MOMP_opt. To increase gene transfer, polyplexes of pcDNA1/MOMP_opt–EGFP with different cationic polymers, such as linear and branched polyethyleneimine (lPEI and brPEI) and starburst PAMAM dendrimers, and lipoplexes with cationic DOTAP/DOPE liposomes were created. Transfection of lPEI and brPEI polyplexes with an N/P ratio of 8 resulted in the highest transfection efficiencies, but lPEI polyplexes were completely destroyed following nebulisation. Secondly, we examined the capacity of nebulised or intramuscularly (IM) administered brPEI-pcDNA1/MOMP_opt to induce a significant protective immune response in SPF turkeys experimentally infected with 10⁸ TCID₅₀ of a virulent Cp. psittaci strain. Results were compared to IM administration of naked plasmid DNA and to results of non-vaccinated animals. Intramuscular administration of brPEI-pcDNA1/MOMP_opt increased the immunogenicity of the Cp. psittaci DNA vaccine as compared to IM administration of pcDNA1/MOMP_opt or aerosol delivery of brPEI-pcDNA1/MOMP_opt. Improved immunogenicity was correlated with increased protection. Vaccinated groups were significantly protected against Cp. psittaci challenge.