Abstract
Influenza B virus (IBV) causes annual influenza epidemics around the world. Here we use an in vivo plasmablast enrichment technique to isolate a human monoclonal antibody, 46B8 that neutralizes all IBVs tested in vitro and protects mice against lethal challenge of all IBVs tested when administered 72 h post infection. 46B8 demonstrates a superior therapeutic benefit over Tamiflu and has an additive antiviral effect in combination with Tamiflu. 46B8 binds to a conserved epitope in the vestigial esterase domain of hemagglutinin (HA) and blocks HA-mediated membrane fusion. After passage of the B/Brisbane/60/2008 virus in the presence of 46B8, we isolated three resistant clones, all harbouring the same mutation (Ser301Phe) in HA that abolishes 46B8 binding to HA at low pH. Interestingly, 46B8 is still able to protect mice against lethal challenge of the mutant viruses, possibly owing to its ability to mediate antibody-dependent cellular cytotoxicity (ADCC).
Highlights
Influenza B virus (IBV) causes annual influenza epidemics around the world
Peripheral blood mononuclear cells were isolated from human blood or leukopak and mixed with IBV HA protein to activate antigen-specific cells prior to intrasplenic transplantation into severe combined immunodeficiency (SCID) mice for rapid expansion and enrichment of human plasmablasts
Individual IBV HA-specific plasmablasts were isolated from splenic cells of the SCID mice by flow cytometry and subjected to IgG cloning followed by Enzyme-linked immunosorbent assay (ELISA) screening of the cloned monoclonal antibodies (mAbs)
Summary
Influenza B virus (IBV) causes annual influenza epidemics around the world. Here we use an in vivo plasmablast enrichment technique to isolate a human monoclonal antibody, 46B8 that neutralizes all IBVs tested in vitro and protects mice against lethal challenge of all IBVs tested when administered 72 h post infection. 46B8 demonstrates a superior therapeutic benefit over Tamiflu and has an additive antiviral effect in combination with Tamiflu. 46B8 binds to a conserved epitope in the vestigial esterase domain of hemagglutinin (HA) and blocks HA-mediated membrane fusion. Upon Fab-mediated binding to viral antigens on the surface of infected cells, the fragment crystallisable (Fc) domain of IgG can provide protective activity in vivo by engaging host effector cells to kill virus-infected cells through antibody-dependent cellular cytotoxicity (ADCC) or complement-dependent cytotoxicity (CDC). Some stalk-binding mAbs are able to prevent HA activation, the cleavage of HA0 by host serine proteases into two-disulfide-linked subunits HA1 and HA2 (refs 13,14) Another broadly neutralising anti-IBV mAb, CR8071 binds to the vestigial esterase domain in HA head, representing a new class of neutralising epitopes on IBV HA that are highly conserved[9]. CR8071 is able to induce ADCC in vitro[15] Another antibody, 5A7 binds to the C terminus of HA1 in the stalk and partially protected mice (20% or 60%) from lethal IBV infection when administered 72 h post infection[10]. 5A7 was able to block both viral attachment and membrane fusion[10]
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