Preferential induction of cross-group influenza A hemagglutinin stem–specific memory B cells after H7N9 immunization in humans
Antigenic drift and shift of influenza strains underscore the need for broadly protective influenza vaccines. One strategy is to design immunogens that elicit B cell responses against conserved epitopes on the hemagglutinin (HA) stem. To better understand the elicitation of HA stem–targeted B cells to group 1 and group 2 influenza subtypes, we compared the memory B cell response to group 2 H7N9 and group 1 H5N1 vaccines in humans. Upon H7N9 vaccination, almost half of the HA stem–specific response recognized the group 1 and group 2 subtypes, whereas the response to H5N1 was largely group 1–specific. Immunoglobulin repertoire analysis of HA-specific B cells indicated that the H7N9 and H5N1 vaccines induced genetically similar cross-group HA stem–binding B cells, albeit at a much higher frequency upon H7N9 vaccination. These data suggest that a group 2–based stem immunogen could prove more effective than a group 1 immunogen at eliciting broad cross-group protection in humans.