There is a need for new approaches for the control of influenza given the burden caused by annual seasonal outbreaks, the emergence of viruses with pandemic potential, and the development of resistance to current antiviral drugs. We show that multivalent biologics, engineered using carbohydrate-binding modules specific for sialic acid, mask the cell-surface receptor recognized by the influenza virus and protect mice from a lethal challenge with 2009 pandemic H1N1 influenza virus. The most promising biologic protects mice when given as a single 1-μg intranasal dose 7 d in advance of viral challenge. There also is sufficient virus replication to establish an immune response, potentially protecting the animal from future exposure to the virus. Furthermore, the biologics appear to stimulate inflammatory mediators, and this stimulation may contribute to their protective ability. Our results suggest that this host-targeted approach could provide a front-line prophylactic that has the potential to protect against any current and future influenza virus and possibly against other respiratory pathogens that use sialic acid as a receptor.

The influenza A virus genome comprises eight segments of negative-sense RNA that encode up to 12 proteins. RNA segment 2 encodes three proteins, PB1, PB1-F2 and N40, that are translated from the same mRNA by ribosomal leaky scanning and reinitiation. PB1 is a subunit of the trimeric viral RNA polymerase. PB1-F2 has been reported to be a potential virulence factor, and has been shown to be involved in a number of activities including induction of apoptosis, regulation of virus replication and modulation of the immune response. No function has yet been ascribed to N40, which represents an N-terminally deleted form of PB1. Previous studies on PB1-F2 function mainly used viruses genetically engineered to prevent PB1-F2 expression by mutation of the PB1-F2 start codon. However, ablation of the start codon was shown to increase the expression level of the downstream protein N40. In the present study, we generated recombinant A/WSN/33 viruses carrying different combinations of PB1-F2- and N40-knockout mutations. Overexpression of N40 in a PB1-F2-deficient background had a detrimental effect on virus growth in vitro and in vivo. However, ablation of PB1-F2 or N40 expression individually was not disadvantageous for the virus. Primer-extension analyses revealed an increase in vRNA production by viruses that overexpressed N40. Our data suggest that the observed attenuation of mutant viruses in vitro and in vivo results from these changes in transcription and replication.