Rabies DNA vaccine encoding lysosome‐targeted glycoprotein supplemented with Emulsigen‐D confers complete protection in preexposure and postexposure studies in BALB/c mice

Abstract

The worldwide incidence of rabies and the inability of currently used vaccination strategies to provide highly potent and cost-effective therapy indicate the need for an improved rabies vaccine. Thus, DNA vaccine based on lysosome-targeted glycoprotein of the rabies virus was evaluated in BALB/c mice. It imparted partial protection (60%) against challenge with 20 LD(50) of the challenge virus standard (CVS) strain of rabies virus. To improve the outcome of vaccination, to ultimately enhance the immune response, we investigated different routes for DNA vaccine delivery, varied doses of DNA, and the influence of adjuvant supplementation. The highest immune response pertaining to IgG antibody titer, with a predominantly IgG1/IgG2a subclass distribution, effective cellular immunity, and a high level of rabies virus neutralizing antibodies (RVNAs) was attained by the optimized DNA vaccine formulation comprising intramuscular administration of 100 microg of DNA vaccine supplemented with Emulsigen-D. In preexposure prophylaxis, a 3-dose regimen of this formulation generated a high RVNA titer (32 IU/ml) and conferred complete protection against challenge with 20 LD(50) of CVS. For postexposure efficacy analysis, rabies was experimentally induced with 50 LD(50) of CVS. Subsequent therapy with 5 doses of the formulation completely prevented rabies in BALB/c mice, which maintained protective RVNA titers of 4 IU/ml. The World Health Organization recommended rabies protective titer threshold is 0.5 IU/ml. Thus, this optimized DNA vaccine formulation provides an avenue for preventing and controlling rabies.