Is there an advantage to including the nucleoprotein in a rabies glycoprotein subunit vaccine?

The PV rabies (genotype 1) G and N proteins were produced by recombinant baculoviruses in insect cells. We tested the ability of recombinant antigens to synergistically induce an immune response and, particularly, to broaden the spectrum of Lyssavirus-neutralizing antibodies produced. Cell-free preparations of recombinant proteins caused an immune response. Recombinant rabies G protein (RRG) from infected cell extract or supernatant induced virus neutralizing antibodies (VNAb) against rabies CVS virus (genotype 1) and in a less extent against European Bat Lyssavirus-1 (EBL-1: genotype 5) Recombinant rabies N protein (RRN) induced antibodies that reacted with the rabies virus ribonucleoprotein (RNP) and primed mice for both the production of VNAb induced by inactivated and purified rabies virus and the protection conferred by RNP. RRN also had an adjuvant effect on VNAb production induced by RRG when the two recombinant proteins were physically associated either encapsulated in liposomes or subjected to ultrasound treatment. However, there was no increase in production of VNAb directed against EBL-1 although classical vaccines (genotype 1) induce partial protection against this virus. Thus, beside its adjuvant effect there is some doubt as to whether including rabies N protein in a rabies subunit vaccine containing the recombinant G protein would be advantageous. (C) 1999 Elsevier Science Ltd. All rights reserved.