Antibody Repertoires Generated by V sub(H) Replacement and Direct V sub(H) to J sub(H) Joining

The immunoglobulin heavy chain repertoire is generated by somatic rearrangement of variable (V sub(H)), diversity (D sub(H)), and joining (J sub(H)) elements. It can be further diversified by V sub(H) replacement, where nonrearranged V sub(H) genes invade preexisting V sub(H)D sub(H)J sub(H) joints. To study the impact and mechanism of V sub(H) replacement, we generated mice in which antibody production depends on the replacement of a nonproductive V sub(H)D sub(H)J sub(H) rearrangement inserted into its physiological position in the immunoglobulin heavy chain locus. In these mice a highly diverse heavy chain repertoire resulted from V sub(H) replacement and a second process of noncanonical V(D)J recombination, direct V sub(H) to J sub(H) joining. V sub(H) replacement rarely generated detectable sequence duplications but often proceeded through recombination between the conserved homologous sequences at the 3' end of V sub(H). Thus, V sub(H) replacement is an efficient mechanism of antibody diversification, and its impact on the overall antibody repertoire could be greater than anticipated because it frequently leaves no molecular footprint.