IMPROVEMENT OF ANTIGEN-BINDING ABILITY OF HUMAN-ANTIBODIES BY LIGHT-CHAIN SHIFTING

Human HB4C5 hybridoma cells produce a lung cancer-specific IgM human m onoclonal antibody (mAb). HB4C5 human mAb cross-reacts with Candida cy tochrome c (Cyt c) and carboxypeptidase (Cpase). Concanavalin A (ConA) -resistant variants of HB4C5 cells loss the original light chain follo wed by expression of various new light chains at a high incidence (lig ht chain shifting) (Tachibana ef al., 1996). HTD8 cells, one of the Co nA-resistant variant subclones of HB4C5 cells, undergo the active ligh t chain shifting and produce various sublines, each of which stably se cretes new mAb consisting of a new light chain and a HB4C5 heavy chain . The new mAb exhibits altered antigen binding ability from that of th e original antibody. We could expect that HTD8 cells can be used as 'a light chain stem cell line' to improve antigen binding ability and sp ecificity of established human mAbs. A BD9D12 IgG human mAb recognizes lung cancer cells and cross-reacts with cytokeratin 8. Introduction o f the heavy chain gene of BD9D12 mAb into HTD8 cells resulted in estab lishment of various sublines which secreted various kinds of hybrid an tibodies consisting of different light chains derived from HTD8 subclo nes which underwent light chain shifting and a common IgG heavy chain derived from BD9D12. These hybrid antibodies exhibited different or im proved reactivities to Cyt, Cpase, cytokeratin 8 and various cancer ce lls from those of parental mAb, demonstrating that light chain shiftin g can be applied to improve the affinity and specificity of human mAb.