Assessment of antibody-dependent cellular cytotoxicity (ADCC) during human influenza infection, vaccination and immunotherapy

© 2018 Dr Hillary VandervenDespite the availability of influenza vaccines and antiviral therapies, human influenza virus infections cause approximately half a million deaths and five million cases of severe illness each year. Seasonal influenza vaccines provide protective immunity by inducing neutralising antibodies against the influenza envelope proteins: hemagglutinin (HA) and neuraminidase (NA). Neutralising antibodies induced by seasonal influenza vaccination are primarily strain-specific and are susceptible loss of antigen recognition by the gradual accumulation of minor mutations over time (antigenic drift). Additionally, seasonal influenza vaccines are not protective against novel, reassortant influenza viruses with pandemic potential. In addition to neutralisation, influenza antibodies have non-neutralising Fc-mediated effector functions, such as antibody-dependent cellular cytotoxicity (ADCC). In this thesis, we studied the ADCC activity of influenza-specific human antibodies through the use of biochemical, effector cell activation and killing assays. We found that most healthy and influenza-infected humans had antibodies against the highly conserved internal influenza proteins nucleoprotein (NP) and matrix protein 1 (M1). M1- and NP-specific human antibodies were capable of cross-linking Fc gamma receptors (FcγRs) and activating natural killer (NK) cells, suggesting ADCC as a possible mechanism of heterosubtypic influenza immunity. We found that HA antibodies with Fc-mediated effector functions were generated earlier than neutralising antibodies in humans with severe avian and seasonal influenza infections. At later time points post-infection, humans who survived severe H7N9 infection demonstrated significantly higher levels of FcγR cross-linking antibodies (with ADCC-mediating potential) than humans who succumbed to infection. Collectively, human survivors of severe influenza rapidly produced cross-reactive ADCC antibodies, which could promote influenza virus clearance and recovery from infection. We found that the majority of older adults (≥65 years) had HA-specific ADCC antibodies against seasonal vaccine strains of influenza prior to immunisation with a trivalent influenza vaccine (TIV). The TIV-induced ADCC response closely mirrored hemagglutination inhibition (HAI) antibody titres in older adults, but baseline ADCC activity was not predictive of vaccine responsiveness. Finally, we showed that anti-influenza hyperimmune intravenous immunoglobulin G (Flu-IVIG) contained higher concentrations of influenza-specific ADCC antibodies than standard IVIG preparations, and passive infusion of Flu-IVIG into influenza-infected patients resulted in a transient increase in influenza-specific ADCC antibodies. Overall, we demonstrated that influenza-specific ADCC antibodies are inducible by influenza infection, seasonal influenza vaccination and passive infusion in humans. Human ADCC studies have important implications for the future of universal influenza vaccine and immunotherapy design