Heavy Chain CDR 3 and Junctional Length Biases in Human Antibody Repertoires Associated with Heavy and Light Chain Germline Utilization

Antibody variable domain sequence diversity is generated by recombination of germline segments. The third complementarity-determining region of the heavy chain (CDR H3) is the region of highest sequence diversity and is formed by the joining of heavy chain VH, DH and JH germline segments combined with random nucleotide trimming and additions between these segments. We show that CDR H3 length distribution is biased in human antibody repertoires as a function of VH, VL and JH germline segment utilization. Most length biases are apparent in the naive B cell compartment, with a significant bias towards shorter CDR H3 sequences observed in association with a subset of VH and VL germlines in the antigen experienced compartment. Similar biases were not observed in nonproductive heavy chain recombination products, indicating selection of the repertoire during B cell maturation as a major driver of the length biases. Some VH-associated CDR H3 length biases are dependent on utilization of specific JH germline segments in a manner not directly linked to JH segment length in the germline, but are rather associated with selection of differentially trimmed JH segments in the naive compartment. In addition, DH segment and N-region random nucleotide insertion lengths within CDR H3 in the naive compartment were also biased by specific VH/JH germline combinations, indicating a complex set of constraints between germline segments selected during repertoire maturation. Our findings reveal biases in the antibody diversity landscape shaped by VH, VL, and JH germline features with implications for mechanisms of naive and immune repertoire selection.