Development of an edible rabies vaccine in maize using the Vnukovo strain

The objective of this study was to obtain transgenic maize expressing the rabies virus glycoprotein (G) of the Vnukovo strain and to evaluate its immunogenicity in mice, by the oral route. The ubiquitin maize promoter fused to the whole coding region of the rabies virus G gene, and a constitutive promoter from cauliflowermosaic virus (CaMV)were used. Maize embryogenic callus were transformed with the above construct by biolistics. Regenerated maize plants were recovered and grown in a greenhouse. The presence of the G gene and its product was detected by PCR and western blot, respectively. The amount of G protein detected in the grains was approximately 1% of the total soluble plant protein. Transformed kernels containing 50 microg of G protein were given once by the oral route in adult mice (BALB-C strain). Challenge was undertaken at 90-days post-vaccination using a lethal dose of a vampire bat rabies virus (100 LD 50% in mice); vampire bats are one of the main reservoirs in Latin America. The edible vaccine induced viral neutralizing antibodies (VNA) which, protected mice 100% against challenge. The control group did not survive. The G protein of the Vnukovo strain expressed in transgenic maize may be considered as an oral immunogen against rabies, conferring cross-protection.