Complementing nuclear with DNA vaccine technologies for improving animal health: The Philippine experience

Full text: Immunization with 'naked DNA' (or DNA vaccines) coding for protein antigens can protect livestock against pathogens without the disadvantages associated with traditional vaccines. Advantages associated with DNA immunization are cheap production, heat stability, amenable to genetic manipulation, mimic viral infection, absence of requirement for a coldchain, and no risk of reversion to pathogenicity. These gene-(expression/cloning) plasmid constructs have been amplified in a bacterial host, purified and administered into the target animal. The gene is expressed in the host and the antigen that is produced induces an immune response. We evaluated chicken egg-yolk polyclonal antibodies response (chIgY) by radioimmunoassay (RIA) after direct intramuscular inoculation of a plasmid expression vector pRc/CMV-HBs(S). Elevated levels of the polyclonal antibodies were observed after 6 weeks. Aliquots of chIgY were coated on beads for RIA and results were comparable with immunized sera. Antibodies for RIA sourced from chicken egg yolks and produced through DNA-mediated vaccination may be a cheaper and much less invasive alternative to serum-derived antibodies. Results from this preliminary experiment may help improve cost-effectiveness of RIA using DNA vaccine and chicken yolk antibody technologies. For these vaccines however, virtually all recommended immunizations would require parenteral administration, which would be too tedious for this reason, alternatives to injections are being sought. The development and application of controlled and intelligent delivery depot systems for DNA vaccines have been studied. We have encapsulated pCMVSPORT- β-gal, our reporter construct, in K-carrageenan-PVP-modified microspheres: IP20 (for stomach sensitive) and IP18 (for intestine sensitive) and chitosan microspheres. The DNA-loaded polymers were delivered as feeds to the model animals, Oreochormis niloticus (fish) and ICR mice. The gills, stomach, small intestine, spleen were then stained with X-gal to observe β-galactosidase activity. Intense staining was observed in the stomach regions with IP20 and chitosan, while minimal staining was observed with IP18. Spleen and other tissues did not express β-galactosidase activity. Our report is an evidence for successful gene delivery capabilities of radiation-synthesized microspheres in both fish and mouse models. (author)