Drug–Fc conjugate CD388 targets influenza virus neuraminidase and is broadly protective in mice

The ability of influenza virus to undergo rapid antigenic shift to elude humoral immunity highlights the need for effective broad-spectrum influenza antivirals for treatment, prophylaxis and pandemic preparedness. Strategies providing durable, universal influenza protection in healthy and high-risk populations are urgently needed. Here we describe the design and preclinical characterization of CD388, a first-in-class antiviral drug-Fc conjugate (DFC), in mice and cynomolgus macaques. CD388 comprises a multivalent conjugate of the influenza virus neuraminidase inhibitor zanamivir, linked to a CH1-Fc hybrid domain of human IgG1 engineered for extended half-life. CD388 improves the antiviral activity of zanamivir, demonstrating potent, universal activity across influenza A and B viruses, including high pathogenicity and neuraminidase inhibitor resistant strains, a low potential for resistance development and potent efficacy in lethal mouse infection models. These results suggest that CD388 has the potential for universal prevention of influenza A and B in healthy and high-risk populations.