Method for the preparation of bispecific F(ab')2mu fragments from mouse monoclonal antibodies of the immunoglobulin M class and characterization of the fragments.

Bispecific F(ab')2mu fragments (Bs F(ab')2mu) binding simultaneously both sialyl Lewis A antigen (SLA) and human carcinoembryonic antigen (CEA) were prepared by disulfide bond exchange between F(ab')2mu fragments derived from IgM monoclonal antibodies (mAbs) against SLA and CEA, and were purified to homogeneity in a one-step procedure of hydrophobic interaction HPLC. The final yield of Bs F(ab')2mu from F(ab')2mu fragments was 70-78%, and the purity was higher than 98%. The immunoreactivities of the Bs F(ab')2mu fragments against SLA and CEA were almost the same as those of the respective parental F(ab')2mu fragments. The dissociation constant (0.17 microM) of the Bs F(ab')2mu for CEA was in good agreement with that of the parental F(ab')2mu fragments. Although the number of applications of IgM mAbs is restricted because of the large molecular mass and low solubility, Bs F(ab')2mu might, nevertheless, be a useful tool for immunotherapy and immunodiagnosis.