The IgM V H regions of the BCR of the antigen-specific IgM + B cell clones were sequenced. Overall, the BCR of HBsAg-specific and TT-specific B cell clones exhibited a V H sequence close to the germ-line sequence, although limited frequencies of somatic hyper-mutations were observed (Table S3 and Table S4 ). Somatic hyper-mutations were occasionally detected in all framework regions (FR) and complementary determining regions (CDR), and most of the BCR diversity was the result of Nadditions in the CDR3 region. Based on the BCR sequence, we observed that 12 out the 15 anti-HBsAg IgM + B cell clones were unique, as well as 5 out the 18 anti-TT IgM + B cell clones ( Table  S2, Table S3 and Table S4 ).