DNA-BASED IMMUNIZATION FOR EXPLORING THE ENLARGEMENT OF IMMUNOLOGICALCROSS-REACTIVITY AGAINST THE LYSSAVIRUSES

DNA-based immunization was used for studying the cross-reactivity of l yssavirus 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. T he homogeneous plasmids pGPV and pGMok encoded the Pasteur virus (PV: genotype 1 -GT-) and Mokola virus (Mok: GT 3) G, respectively. The chi meric pGMokPV encoded the NH2 part of GMok and the COOH part of GPV. T hese plasmids elicited full protection against intracerebral challenge s with various lyssaviruses and a range of antigen-specific and non-sp ecific immune responses. Virus neutralizing antibody (VNAb) levels wer e dose dependent and a single intramuscular (i.m.) injection of plasmi ds was sufficient to induce continuous high levels of VNAb. Production of antigen-specific T helper (Th), cytotoxic T cells (Tc) and non-spe cific natural killer cells was observed. Cross-reactivity studies show ed that VNAb are obtained by immunizing with: (i) pGPV against GT 1 (c lassical 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 al l GTs except GT 4 which is weakly neutralized. Therefore, the DNA-base d immunization with the chimeric pGMokPV, could be very interesting to enlarge protection to all the lyssaviruses. According to the cross-re activity of VNAb induced by the G genes, the lyssavirus GTs could be c lassified into two groups: the first including GT 1, 4, 5 and 6; the s econd including GT 2 and 3. (C) 1998 Elsevier Science Ltd. All rights reserved.