Development of functional anti-Gn nanobodies specific for SFTSV based on next-generation sequencing and proteomics

The Neutralizing Monoclonal Antibodies against SFTS Group Bandaviruses Suggest New Targets of Specific or Broad-Spectrum Antivirals

Severe fever with thrombocytopenia syndrome virus (SFTSV), Heartland virus (HRTV) and Guertu virus (GTV) belong to the severe fever with thrombocytopenia syndrome/Heartland group of genus Bandavirus in the family Phenuiviridae of order Bunyavirales. Severe fever with thrombocytopenia syndrome virus and HRTV, identified from ticks from Asia and America, respectively, are important pathogens causing severe febrile diseases in humans. Guertu virus, closely related to these two viruses, is a potential pathogen, but no confirmed infection has been identified. So far, human-derived neutralizing monoclonal antibodies (mAbs) against SFTSV have been identified as having a great potential to be developed as antivirals; however, there is still a lack of neutralizing mAbs to GTV and HRTV. In this study, five neutralizing the mAbs against GTV and HRTV were obtained by hybridoma screening technology, four of which (14B4, 14D8, and 20D4 derived from GTV, and 27C8 derived from HRTV) showed cross reactivity and neutralization to all three viruses, and one derived from HRTV (10D6) neutralized HRTV specifically. The possible mechanisms of mAbs cross neutralization among the three viruses are discussed by analyzing their glycoprotein (GP) sequences and structures. Generating these neutralizing mAbs provides important antiviral candidates against GTV, HRTV, and SFTSV despite their differential activities, and their protective effect could be further evaluated in virus-infected mice. Their differential neutralizing efficiency and specificity further suggested that the three viruses share common mechanisms on the basis of GP functioning, and that HRTV poses a unique mechanism that differs from the other viruses. These findings shed light on developing broad-spectrum antiviral strategies against bandaviruses and promoting an understanding of the bandavirus infection process.

Development of functional anti-Gn nanobodies specific for SFTSV based on next-generation sequencing and proteomics

Severe fever with thrombocytopenia syndrome (SFTS) is an acute infectious disease caused by novel bunyavirus (SFTSV), with a mortality rate of 6.3% ~ 30%. To date, there is no specific treatment for SFTS. Previously, we demonstrated that SFTSV surface glycoprotein (Glycoprotein N, Gn) was a potential target for the development of SFTS vaccine or therapeutic antibodies, and anti-Gn neutralizing antibodies played a protective role in SFTS infection. Compared with traditional antibodies, nanobodies from camelids have various advantages, including small molecular weight, high affinity, low immunogenicity, convenient production by gene engineering, etc. In this study, we combined next-generation sequencing (NGS) with proteomics technology based on affinity purification-mass spectrometry (AP-MS) and bioinformatics analysis to high-throughput screen monoclonal anti-Gn nanobodies from camel immunized with Gn protein. We identified 19 anti-Gn monoclonal nanobody sequences, of which six sequences were selected for recombinant protein expression and purification. Among these six anti-Gn nanobodies, nanobody 57,493 was validated to be highly specific for Gn. The innovative high-throughput technical route developed in this study could also be expanded to the production of nanobodies specific for other viruses like SARS-CoV-2.