Antibody-Mediated Suppression Regulates the Humoral Immune Response to Influenza Vaccination in Humans.

Background: Preexisting immunity, including memory B cells and preexisting antibodies, can modulate antibody responses to influenza in vivo to antigenically related antigens. We investigated whether preexisting hemagglutination inhibition (HAI) antibodies targeting the K163 epitope on the hemagglutinin (K163 antibodies) could affect antibody responses following vaccination with A/California/07/2009-like A(H1N1)pdm09 influenza viruses in humans.

Methods: Pre- and postvaccination sera collected from 300 adults (birth years, 1961-1998) in 6 seasons (2010-2016) were analyzed by HAI assays with 2 reverse genetics viruses and A(H1N1) viruses circulated from 1977 to 2018. Antibody adsorption assays were used to verify the preexisting K163 antibody-mediated suppression effect.

Results: Preexisting K163 antibody titers ≥80 affected HAI antibody responses following influenza vaccination containing A/California/07/2009-like antigens. At high K163 antibody concentrations (HAI antibody titers ≥160), all HAI antibody responses were suppressed. However, at moderate K163 antibody concentrations (HAI antibody titer, 80), only K163 epitope-specific antibody responses were suppressed, and novel HAI antibody responses targeting the non-K163 epitopes were induced by vaccination. Novel antibodies targeting non-K163 epitopes cross-reacted with newly emerging A(H1N1)pdm09 strains with a K163Q mutation rather than historic 1977-2007 A(H1N1) viruses.

Conclusions: K163 antibody-mediated suppression shapes antibody responses to A(H1N1)pdm09 vaccination. Understanding how preexisting antibodies suppress and redirect vaccine-induced antibody responses is of great importance to improve vaccine effectiveness.