Protection of mice with vaccinia virus recombinants that express the rabies nucleoprotein

The role of rabies virus nucleoprotein (N) in protection against rabies was examined with recombinant vaccinia viruses expressing the N of the Challenge Virus Standard strain. Two chimeric plasmids were constructed with the open reading frame of the N gene placed downstream of the vaccinia P7.5 promoter (early/late class) or the vaccinia P11 promoter (late class), with each expression cassette flanked by vaccinia thymidine kinase (TK) sequences to enable marker rescue by TK insertional inactivation. Two recombinants were isolated that expressed the rabies N in infected cells as determined by radioimmunoprecipitation and immunofluoresence microscopy with an anti-N monoclonal antibody. Two groups of 25 ICR mice inoculated intradermally with the recombinants and challenged with 75 MFPLD50 of street rabies virus showed high survival ratios (22/25 and 21/25). Intramuscular inoculation, however, was not protective against 25 MFPLD50. The intradermally vaccinated mice developed non-neutralizing antibodies against rabies N.