Antibody Repertoires Generated by VH Replacement and Direct VH to JH Joining

SummaryThe immunoglobulin heavy chain repertoire is generated by somatic rearrangement of variable (VH), diversity (DH), and joining (JH) elements. It can be further diversified by VH replacement, where nonrearranged VH genes invade preexisting VHDHJH joints. To study the impact and mechanism of VH replacement, we generated mice in which antibody production depends on the replacement of a nonproductive VHDHJH rearrangement inserted into its physiological position in the immunoglobulin heavy chain locus. In these mice a highly diverse heavy chain repertoire resulted from VH replacement and a second process of noncanonical V(D)J recombination, direct VH to JH joining. VH replacement rarely generated detectable sequence duplications but often proceeded through recombination between the conserved homologous sequences at the 3′ end of VH. Thus, VH 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.