Contribution of Vh gene replacement to the primary B cell repertoire.

V(H) replacement has been proposed as one way to modify unwanted antibody specificities, but analysis of this mechanism has been limited without a dynamic cellular model. We describe a human cell line that spontaneously undergoes serial V(H) gene replacement mediated by cryptic recombination signal sequences (cRSS) located near the 3' end of V(H) genes. Recombination-activating gene products, RAG-1 and RAG-2, bind and cleave the cRSS to generate DNA deletion circles during the V(H) replacement process. A V(H) replacement contribution to normal repertoire development is revealed by the identification of V(H) replacement "footprints" in IgH sequences and double-stranded DNA breaks at V(H) cRSS sites in immature B cells. Surprisingly, the residual 3' sequences of replaced V(H) genes contribute charged amino acids to the CDR3 region, a hallmark of autoreactive antibodies.