Persistent Antibody Clonotypes Dominate the Serum Response to Influenza over Multiple Years and Repeated Vaccinations.

Humans are repeatedly exposed to influenza virus via infections and vaccinations. Understanding how multiple exposures and pre-existing immunity impact antibody responses is essential for vaccine development. Given the recent prevalence of influenza H1N1 A/California/7/2009 (CA09), we examined the clonal composition and dynamics of CA09 hemagglutinin (HA)-reactive IgG repertoire over 5 years in a donor with multiple influenza exposures. The anti-CA09 HA polyclonal response in this donor comprised 24 persistent antibody clonotypes, accounting for 72.6% ± 10.0% of the anti-CA09 HA repertoire over 5 years. These persistent antibodies displayed higher somatic hypermutation relative to transient serum antibodies detected at one time point. Additionally, persistent antibodies predominantly demonstrated cross-reactivity and potent neutralization toward a phylogenetically distant H5N1 A/Vietnam/1203/2004 (VT04) strain, a feature correlated with HA stem recognition. This analysis reveals how "serological imprinting" impacts responses to influenza and suggests that once elicited, cross-reactive antibodies targeting the HA stem can persist for years.

Antibody-guided vaccine design: identification of protective epitopes.

In the last decade, progress in the analysis of the human immune response and in the isolation of human monoclonal antibodies have provided an innovative approach to the identification of protective antigens which are the basis for the design of vaccines capable of eliciting effective B-cell immunity. In this review we illustrate, with relevant examples, the power of this approach that can rapidly lead to the identification of protective antigens in complex pathogens, such as human cytomegalovirus and Plasmodium falciparum, and of conserved sites in highly variable antigens, such as influenza hemagglutinin and HIV-1 Env. We will also discuss how the genealogical analysis of antigen-stimulated B cell clones provides the basis to delineate the best suitable prime-boost vaccination strategy for the induction of broadly neutralizing antibodies.