Human monoclonal ScFv specific to NS1 protein inhibits replication of influenza viruses across types and subtypes

Currently, there is a need of new anti-influenza agents that target influenza virus proteins other than ion channel M2 and neuraminidase. Non-structural protein-1 (NS1) is a highly conserved multifunctional protein which is indispensable for the virus replication cycle. In this study, fully human single chain antibody fragments (HuScFv) that bound specifically to recombinant and native NS1 were produced from three huscfv-phagemid transformed Escherichia coli clones (nos. 3, 10 and 11) selected from a human ScFv phage display library. Western blot analysis, mimotope searching/epitope identification, homology modeling/molecular docking and phage mimotope ELISA inhibition indicated that HuScFv of clone no. 3 reacted with NS1 R domain important for host innate immunity suppression; HuScFv of clone nos. 10 and 11 bound to E domain sites necessary for NS1 binding to the host eIF4GI and CPSF30, respectively. The HuScFv of all clones could enter the influenza virus infected cells and interfered with the NS1 activities leading to replication inhibition of viruses belonging to various heterologous A subtypes and type B by 2-64-fold as semi-quantified by hemagglutination assay. Influenza virus infected cells treated with representative HuScFv (clone 10) had up-expression of IRF3 and IFN-β genes by 14.75 and 4.95-fold, respectively, in comparison with the controls, indicating that the antibodies could restore the host innate immune response. The fully human single chain antibodies have high potential for developing further as a safe (adjunctive) therapeutic agent for mitigating, if not abrogating, severe symptoms of influenza.