A bivalent mammalian expression vector encoding two rabies glycoprotein genes induces enhanced immunity and protection

A bicistronic plasmid DNA vaccine encoding glycoprotein genes from CVS and ERA strains of rabies virus (RV) was constructed by subcloning of glycoprotein genes from recombinant pTargeT.rg.cvs and pTargeT.rg.era vectors into bicistronic pIRES mammalian expression vector. High level expression of the glycoprotein gene in MDCK cells was shown by indirect immunofluroscent antibody test (IFAT) and SDS-PAGE. The 4 week old mice vaccinated with the bicistronic plasmid DNA and booster immunization given on 14^th day after primary immunization showed 90% protection whereas protection was 80% in monocistronic DNA vaccine immunized group, when challenged with 20LD₅₀ of rabies virus CVS after 21^st day of booster immunization. Antibody titres in sera of dogs immunized with the bicistronic plasmid DNA vaccine revealed that there was seroconversion in vaccinated dogs on 14^th day of primary immunization and the significant increase in antibody titre was observed after booster immunization as determined by ELISA and mouse neutralization test. Higher level of antibody immune response was observed when dogs were also injected with plasmid encoding dog interleukin-2 along with the bicistronic vaccine. Lymphocyte proliferation test revealed that the bicistronic vaccine induced cell mediated immune response also. The results of the present study indicate that bicistronic plasmid DNA vaccine is capable of both humoral and cellular immune responses resulting in protective immunity in mice and dogs.