HUMAN-IMMUNOGLOBULIN HEAVY-CHAIN MINILOCUS RECOMBINATION IN TRANSGENIC MICE - GENE-SEGMENT USE IN MU-TRANSCRIPTS AND GAMMA-TRANSCRIPTS

We (N.L. and L.D.T.) have introduced a human heavy-chain minilocus into mice transgenically. Constructs contain 2 heavy-chain variable (V(H); psiV(H)3-105 and V(H)5-251), 10 diversity (D), 6 heavy-chain joining (J(H)), and either constant (C)mu or Cmu and Cgamma gene segments. Several founder lines were established and studied before immunization. Seventy heavy-chain transcripts were cloned and sequenced from murine splenic B lymphocytes, and gene-segment use was assessed before and after class-switching. In general, the repertoire was ''fetal'' in appearance with little evidence of somatic mutation in any gene segment. The two V(H) gene segments were found rearranged to mu- and gamma-chain C segments, with a preference of V(H)5-251. We observed a preponderance of the most-J-proximal D gene (D(HQ52)) segments among the mu transcripts (44%). The JH gene-segment use mimics most patterns seen in human antibodies. Diversification in CDR3 was extensive and included clear examples of D inversions and D-D fusions. These data suggest that a human immunoglobulin minilocus can undergo recombinatorial processes in a manner analogous to that seen in the human fetal/preimmune repertoire. This model, in addition to providing a potential source of human monoclonal antibodies, is ideal for the study of further questions concerning immunoglobulin gene-segment recombination.