Generation of chimeric monoclonal antibodies from mice that carry human immunoglobulin Cγ1 heavy or Cκ light chain gene segments

Gene targeting in mouse embryonic stem (ES) cells was used to replace (i) the mouse immunoglobulin heavy chain (IgH) Cγ2a gene segment (mCγ2a) with the human Cγ1 gene segment (hCγ1), and (ii) the mouse immunoglobulin light chain (IgL) Cκ gene segment (mCκ) with its human counterpart (hCκ). ES cells carrying these gene conversions were used to generate chimeric mice that transmitted the human alleles through the germ line. Mice homozygous for both gene alterations were generated by breeding. Serum from homozygous mutant mice contained comparable amounts of antibodies with chimeric κ or mouse λ light chains but only small fractions of basal serum IgG or antibodies elicited against immunizing agents contained chimeric heavy chains. A relative increase in immunogen-specific hCγ1 antibodies was seen following immunization in combination with the saponin adjuvant QS-21. The effect of this was to shift the IgG1-dominated response to an IgG subclass profile that included significant amounts of IgG2a, IgG2b and IgG3 and chimeric IgG. The amounts of antibody secreted by hybridomas derived from mutant and wild-type mice were similar. Sequencing confirmed correct splicing of hCγ1 and hCκ gene segments to mouse J gene segments in hybridoma Ig gene transcripts. In conclusion, IgHhCγ1/IgLhCκ double mutant mice provide a useful animal model for deriving humanized antibodies with potential applications in immunotherapy and diagnostics in vivo as well as for investigating hCγ1 associated functions.