GM-CSF fused with GP3 and GP5 of porcine reproductive and respiratory syndrome virus increased the immune responses and protective efficacy against virulent PRRSV challenge

Porcine reproductive and respiratory syndrome virus (PRRSV) has recently caused catastrophic losses in swine industry worldwide. Current vaccination strategies only provide a limited protection against PRRSV infection. This study was aimed to construct the recombinant adenovirus co-expressing GP3 and GP5 of highly pathogenic PRRSV fused with swine granulocyte-macrophage colony stimulating factor (GM-CSF) (rAd-GF35), and to detect the immune response in mice and pigs. The results showed that the rAd-GF35 could induce significantly higher PRRSV-specific neutralizing antibodies than the recombinant adenovirus only expressing GP3 and GP5 (rAd-GP35). Moreover, the fusion of GM-CSF markedly increased the secretion of IFN-γ and IL-4 in PRRSV-stimulated mice lymphocytes culture and pigs sera. Following challenge with PRRSV, piglets inoculated with recombinant rAd-GF35 had lighter clinical signs, lower viremia and less gross lesion of lungs, as compared to that of rAd-GP35 immunized group. It demonstrated that GM-CSF fused with GP3 and GP5 of PRRSV could significantly enhance the humoral and cellular immune responses and provide protection against PRRSV challenge in pigs. The recombinant adenovirus rAd-GF35 might be an attractive candidate vaccine for the prevention and control of highly pathogenic PRRSV infection.