VHSV G glycoprotein major determinants implicated in triggering the host type I IFN antiviral response as DNA vaccine molecular adjuvants

We have recently identified the two major determinants of the glycoprotein G of the viral hemorrhagic septicaemia rhabdovirus (gpG_VHSV), peptides p31 and p33 implicated in triggering the host type I IFN antiviral response associated to these rhabdoviral antigens. With the aim to investigate the properties of these viral glycoprotein regions as DNA molecular adjuvants, their corresponding cDNA sequences were cloned into a plasmid (pMCV1.4) flanked by the signal peptide and transmembrane sequences of gpG_VHSV. In addition, a plasmid construct encoding both sequences p31 and p33 (pMCV1.4-p31 + p33) was also designed. In vitro transitory cell transfection assays showed that these VHSV gpG regions were able to induce the expression of type I IFN stimulated genes as well as to confer resistance to the infection with a different fish rhabdovirus, the spring viremia of carp virus (SVCV). In vivo, zebrafish intramuscular injection of only 1 μg of the construct pMCV1.4-p31 + p33 conferred fish protection against SVCV lethal challenge up to 45 days post-immunization. Moreover, pMCV1.4-p31 + p33 construct was assayed for molecular adjuvantcity's for a DNA vaccine against SVCV based in the surface antigen of this virus (pAE6-G_SVCV). The results showed that the co-injection of the SVCV DNA vaccine and the molecular adjuvant allowed (i) a ten-fold reduction in the dose of pAE6-Gsvcv without compromising its efficacy (ii) an increase in the duration of protection, and (iii) an increase in the survival rate. To our knowledge, this is the first report in which specific IFN-inducing regions from a viral gpG are used to design more-efficient and cost–effective viral vaccines, as well as to improve our knowledge on how to stimulate the innate immune system.