Loss of human B cells bearing highly charged and highly hydrophobic amino acids in CDR-H3 at the pre B cell receptor stage (HEM2P.267)

Abstract Successive checkpoints in B cell development including differentiation in the bone marrow and the peripheral lymphoid organs control the composition and reactivity of the antibody repertoire. One of the first key checkpoints is testing of the efficiency of the heavy chain (HC) by forming a pre B cell receptor (pre BCR) composed of the newly generated μHCs and invariant surrogate light chains. Similar to mouse, human B cells with highly charged or highly hydrophobic antigen binding sites are rare in the mature B cell repertoire. Suppression of highly hydrophobic antigen binding sites in mouse reflects, in part, reduced use of RF2 due to Dμ protein containing preBCRs, but the mechanism(s) by which these clones are suppressed in human is unknown. We cloned and sequenced HC transcripts from early to late pre B cells in bone marrow samples obtained from healthy human donors and then used our bioinformatics approach to dissect and analyze the diversity of the third complementary determining region of the HC (CDR-H3). The prevalence of both highly hydrophobic and highly charged CDR-H3s dropped in the transition from early to late pre B cells. This suggests a novel mechanism of selection in human, where the pre BCR controls the passage of B cells based on their CDR-H3 amino acid content. These findings can help explain the diminished production of HIV neutralizing antibodies with abnormal highly charged or highly hydrophobic CDR-H3s due to their loss at the pre BCR stage.