Intranasal administration of a pan-reactive influenza antibody reveals Fc-independent mode of protection 2259232

Abstract Introduction Monoclonal antibodies protect through two core mechanisms: their antigen-binding fragment (Fab) directly binds and neutralizes viral antigens, while the fragment crystallizable domain (Fc) engages Fcγ receptors to activate immune effector functions. We investigated and segregated the relative contribution of each antibody domain to immune protection by comparing peripheral/systemic versus local/mucosal delivery within a mouse model of antibody prophylaxis against influenza virus Methods We performed intranasal versus intravenous delivery of CR9114, the broadest known human influenza antibody, which engages a conserved epitope on the hemagglutinin stem to provide protection against both influenza A and influenza B viruses within pre-clinical challenge models. Mice received either wild-type CR9114, Fc-silenced mutants (LALA, N297Q), or the bivalent antigen-binding F(ab’)₂ fragment alone (no Fc domain) 24 hours before lethal challenge with influenza A/H1N1, A/H3N2, A/H5N1, B/Yamagata, or B/Victoria viruses. Survival and weight change were measured to determine protection and median effective doses (ED50). Results Intranasal delivery of CR9114 resulted in an increase in potency against lethal influenza A/H1N1, A/H5N1, A/H3N2, B/Yam and B/Vic compared to intravenous administration, up to 50-fold. Systemic protection required an intact Fc domain, whereas intranasal protection remained strong even with Fc-silenced or Fc-depleted formats. The F(ab’)₂ fragment alone conferred full prophylaxis when delivered locally but was ineffective systemically. Conclusion These findings reveal that the route of antibody delivery determines its mechanism of protection. Local mucosal delivery achieves potent Fc-independent immunity, which was also seen in the absence of conventional neutralization activity, offering a new strategy for antibody-based prevention of influenza and other respiratory infections. Funding Source Leyden Laboratories B.V. Topic Categories Mucosal and Regional Immunology (MUC)