B cell repertoire dynamics after sequential Hepatitis B vaccination, and evidence for cross-reactive B cell activation

Background: A diverse B cell repertoire is essential for recognition and response to infectious and vaccine antigens. High-throughput sequencing of B cell receptor (BCR) genes can now be used to study the B cell repertoire at great depth, and may shed more light on B cell responses than conventional immunological methods. Here, we use high-throughput BCR sequencing to provide novel insight into B cell dynamics following a primary course of Hepatitis B vaccination. Methods: Nine vaccine-naïve participants were administered three doses of Hepatitis B vaccine (month 0, 1 and 2 or 6). High throughput Illumina sequencing of the total BCR repertoire was combined with targeted sequencing of sorted vaccine antigen-enriched B cells to analyze the longitudinal response of both the total and vaccine-specific repertoire after each vaccine. ELISpot was used to determine vaccine-specific cell numbers following each vaccine. Results: Deconvoluting the vaccine-specific from total BCR repertoire showed that vaccine-specific sequence clusters comprised <0.1% of total sequence clusters, and had certain stereotypic features. The vaccine-specific BCR sequence clusters were expanded after each of the three vaccine doses, despite no vaccine-specific B cells being detected by ELISpot after the first vaccine dose. These vaccine-specific BCR clusters detected after the first vaccine dose had distinct properties compared to those detected after subsequent doses; they were more mutated, present at low frequency even prior to vaccination, and appeared to be derived from more mature B cells. Conclusions: These results demonstrate the high-sensitivity of our vaccine-specific BCR analysis approach, and suggest an alternate view of the B cell response to novel antigens. In the response to the first vaccine dose, many vaccine-specific BCR clusters appeared to largely derive from previously activated cross-reactive B cells that have low affinity for the vaccine antigen, and subsequent doses were required to yield higher affinity B cells