Nanobody Nb6 fused with porcine IgG Fc as the delivering tag to inhibit porcine reproductive and respiratory syndrome virus replication in porcine alveolar macrophages

Porcine reproductive and respiratory syndrome virus (PRRSV) is a highly contagious virus that has led to enormous economic loss worldwide because of ineffective prevention and treatment. In view of their minimized size, high target specificity and affinity, nanobodies have been extensively investigated as diagnostic tools and treatments of many diseases. Previously, a PRRSV Nsp9-specific nanobody (Nb6) was identified as a PRRSV replication inhibitor. When it was fused with cell-penetrating peptide (CPP) TAT, Nb6-TAT could enter the cells for PRRSV suppression. However, delivery of molecules by CPP lack cell specificity and have a short duration of action. PRRSV has a tropism for monocyte/macrophage lineage, which expresses high levels of Fc gamma receptors. Herein, we designed a nanobody containing porcine IgG Fc (Fc gamma) to inhibit PRRSV replication in PRRSV permissive cells. Fc gamma fused Nb6 chimeric antibody (Nb6-pFc) was assembled into a dimer with interchain disulfide bonds and expressed in a Pichia pastoris system. The results show that Nb6-pFc exhibits a well-binding ability to recombinant Nsp9 or PRRSV-encoded Nsp9 and that Fc gamma R-mediated endocytosis of Nb6-pFc into porcine alveolar macrophages (PAM) was in a dose-dependent manner. Nb6-pFc can inhibit PRRSV infection efficiently not only by binding with Nsp9 but also by upregulating proinflammatory cytokine production in PAM. Together, this study proposes the design of a porcine IgG Fc-fused nanobody that can enter PRRSV susceptible PAM via Fc gamma R-mediated endocytosis and inhibit PRRSV replication. This research reveals that nanobody-Fc gamma chimeric antibodies might be effective for the control and prevention of monocyte/macrophage lineage susceptible pathogeneses.

Automated summary

PRRSV is a highly contagious virus causing enormous economic loss globally. Nanobodies, with their small size and high specificity, have been studied as diagnostic tools and treatments for many diseases. A nanobody containing porcine IgG Fc was designed to inhibit PRRSV replication in susceptible cells, showing potential for controlling and preventing susceptible pathogeneses.