The genetic engineering of an immunoglobulin construct with the variable region of a mouse monoclonal antibody (mAb) and the constant region of a human immunoglobulin has resulted in the development and production of chimeric mouse/human mAbs with improved biologic activity, long residence times and reduced immunogenicity (Morrison et al., 1984, Morrison, 1985). In an attempt to further reduce immunogenicity, recombinant DNA technology has been used to generate “humanized” mAbs with mouse sequences largely confined to the hypervariable regions.