Antibody Expression from the Core Region of the Human IgH Locus Reconstructed in Transgenic Mice Using Bacteriophage P1 Clones

Mice carrying transgenic human immunoglobulin gene miniloci can be used for the production of human monoclonal antibodies. The human variable region (V) gene segments in these miniloci undergo productive rearrangement in mouse lymphoid tissue to yield a population of B lymphocytes expressing a repertoire of antibodies. Many of the miniloci studied to date have included only a small number of germline gene segments in an artificially compact configuration. Here we describe the use of the bacteriophage P1 cloning system to create mice carrying the core region of the human immunoglobulin heavy chain (IgH) locus. Three P1 clones carrying overlapping regions of the human IgH locus (spanning the five J_H-proximal V_Hsegments, the entire D_Hand J_Hclusters, and the Cμ and Cδ constant regions) were injected into mouse eggs and appear to have reconstituted the core region of the locus (>180 kb) following homologous recombination with each other. While this translocus yielded a titer of serum immunoglobulin similar to that obtained with a smaller plasmid-based minilocus, the P1-based locus gave rise to substantially greater diversification by somatic hypermutation. Such diversification is important for obtaining high-affinity antibodies. The results show the usefulness of the P1 system in facilitating the manipulation and recreation of large transgenes.