Efficacy of particle-based DNA delivery for vaccination of sheep against FMDV.

As an alternative strategy to classical inactivated viral vaccine against FMDV, naked DNA vaccine is attractive because of safety, flexibility and low cost. However DNA vaccination is usually poorly efficient in target species. Indeed we found that naked DNA plasmids encoding for P1-2A3C3D and GM-CSF proteins did not induce any detectable immunity against FMDV in sheep. Interestingly, we demonstrate herein that formulations of DNA on poly(D,L-lactide-co-glycolide) (PLG) or in lipofectin triggered divergent types of immune responses: PLG stimulated a T cell response and could elicit significant neutralising antibody titers, whereas lipofectin generated even higher antibody titers but no significant T cell response. The DNA/PLG regimen used in five sheep protected against clinical symptoms and viraemia and prevented the carrier state in four of them. Thus formulated DNA can be remarkably efficient against FMDV in a ruminant species that is usually refractory to DNA vaccination.