DNA-based immunization for exploring the enlargement of immunological cross-reactivity against the lyssaviruses.

DNA-based immunization was used for studying the cross-reactivity of lyssavirus neutralizing antibodies and for exploring the induction of a wider range of protection against lyssaviruses. In order to immunize mice with homogeneous and chimeric genes of glycoproteins (G) from two divergent lyssaviruses, we used for the first time a new plasmid (pCI-neo) known to be a highly efficient vector for in vitro expression. The homogeneous plasmids pGPV and pGMok encoded the Pasteur virus (PV: genotype 1-GT-) and Mokola virus (Mok: GT 3) G, respectively. The chimeric pGMokPV encoded the NH2 part of GMok and the COOH part of GPV. These plasmids elicited full protection against intracerebral challenges with various lyssaviruses and a range of antigen-specific and non-specific immune responses. Virus neutralizing antibody (VNAb) levels were dose dependent and a single intramuscular (i.m.) injection of plasmids was sufficient to induce continuous high levels of VNAb. Production of antigen-specific T helper (Th), cytotoxic T cells (Tc) and non-specific natural killer cells was observed. Cross-reactivity studies showed that VNAb are obtained by immunizing with: (i) pGPV against GT 1 (classical rabies), GT 4 (Duvenhage: Duv), GT 5 (European Bat Lyssavirus: EBL-1) and GT 6 (European Bat Lyssavirus: EBL-2); (ii) pGMok against GT 2 (Lagos Bat: LB) and GT 3 (Mokola: Mok); (iii) pGMokPV against all GTs except GT 4 which is weakly neutralized. Therefore, the DNA-based immunization with the chimeric pGMokPV, could be very interesting to enlarge protection to all the lyssaviruses. According to the cross-reactivity of VNAb induced by the G genes, the lyssavirus GTs could be classified into two groups: the first including GT 1, 4, 5 and 6; the second including GT 2 and 3.