Understanding the treatment benefit of hyperimmune anti-influenza intravenous immunoglobulin (Flu-IVIG) for severe human influenza

Background: Antibody-based therapies for respiratory viruses are of increasing importance. The INSIGHT006 trial administered anti-influenza hyperimmune intravenous immunoglobulin (Flu-IVIG) to patients hospitalised with influenza. Flu-IVIG treatment improved outcomes in patients with influenza B but showed no benefit for influenza A. Methods: To probe potential mechanisms of Flu-IVIG utility, sera collected from patients hospitalised with influenza A or B viruses (IAV or IBV) were analysed for antibody isotype/subclass and Fc-gamma receptor (FcgR) binding by ELISA, bead-based multiplex and NK cell activation assays. Results: Influenza-specific FcgR binding antibodies were elevated in Flu-IVIG infused IBV- and IAV-infected patients. In IBV-infected participants (n = 62), increased IgG3 and FcgR binding were associated with more favourable outcomes. Flu-IVIG therapy also improved the odds of a more favourable outcome in patients with low levels of anti-IBV Fc-functional antibody. Higher FcgR binding antibody was associated with less favourable outcomes in IAV-infected patients (n = 50), and Flu-IVIG worsened the odds of a favourable outcome in participants with low levels of anti-IAV Fc-functional antibody. Conclusion: These detailed serological analyses provide insights into antibody features and mechanisms required for a successful humoral response against influenza, suggesting that IBV-specific, but not IAV-specific, antibodies with Fc-mediated functions may assist in improving influenza outcome. This work will inform development of improved influenza immunotherapies.