The Effect of Immune Imprinting: Epitope-level Analyses of Antibody Responses to Influenza Immunization Using Phage Display

Background: Each year influenza viruses cause widespread infections during the winter months in the northern and southern hemisphere. Although existing antiviral drugs can shorten the duration of disease and reduce the risk of complications, disease prevention by vaccination is still the best option to reduce the burden of disease. Annual vaccination against seasonal influenza is recommended for individuals at risk, i.e. people above 65 years of age, pregnant women, immunocompromised patients and health care workers. However, vaccine effectiveness is low, usually only between 40-60%, depending on the antigenic match between the vaccine and the circulating influenza virus strains of a given year, on the health status of the patient and on the exposure history of each individual. The first strains encountered during childhood can cause immune imprinting, leading to skewed subsequent immune responses towards antigenic structures that are closely related to the imprinting strain. First reports that link the exposure history of patients to vaccine effectiveness date back to the 1940s and 50s. However, epitope-level analyses of antibody repertoires of individual patients that could identify imprinting strains and determine the individual exposure history have been hampered by a lack of appropriate methods. Existing methods include enzyme-linked immunosorbent assays (ELISA) using recombinant hemagglutinin (HA) proteins as antigens, hemagglutination inhibition assay (HAI) or microneutralisation assay (MN). However, these methods either have a low specificity due to the high cross reactivity of HA proteins (ELISA) or are not suitable to simultaneously detect antibodies against hundreds of influenza virus strains (HAI, MN). New serological methods are urgently needed to gain a more comprehensive picture of the exposure history of patients.Methods: In a pilot phase, we have adopted the phage immunoprecipitation sequencing (PhIP-Seq) technology to determine the humoral immune response after influenza vaccination to thousands of linear peptides derived from the HA protein of H3N2 strains. In this study, we will study the effect of different imprinting virus strains on the humoral immune response after vaccination in healthy adults and immunocompromised patients (ICP).Significance: The effect of exposure history and immune imprinting on vaccine effectiveness and susceptibility to influenza virus infections has been increasingly recognized in the past years. This will be the first study to determine exposure history and the imprinting virus strain through sophisticated state-of-the-art serological methods. These results will help to devise new vaccination strategies and identify immunity gaps, particularly for immunocompromised patients, which take the individual exposure history of individuals into account. This information will leave us better prepared for seasonal and pandemic influenza outbreaks will help to adapt public health measures, and decrease the burden of disease.