Human immunoglobulin heavy-chain minilocus recombination in transgenic mice: gene-segment use in mu 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 (VH; psi VH3-105 and VH5-251), 10 diversity (D), 6 heavy-chain joining (JH), and either constant (C)mu or C mu and C gamma 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 VH gene segments were found rearranged to mu- and gamma-chain C segments, with a preference of VH5-251. We observed a preponderance of the most-J-proximal D gene (DHQ52) 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.