CLONING AND EXPRESSION OF THE RECOMBINANT FAB FRAGMENT OF MONOCLONAL-ANTIBODY K1 THAT REACTS WITH MESOTHELIN PRESENT ON MESOTHELIOMAS AND OVARIAN CANCERS

The monoclonal antibody (MAb) KI recognizes an approximate 40 kDa glyc oprotein, mesothelin, that is present on the surface of human mesothel ial cells, mesotheliomas and ovarian cancers, We have cloned the cDNAs encoding the variable regions of MAb KI and constructed plasmids for expression of recombinant KI(FAb), Recombinant FAb was produced in Esc herichia coli in inclusion bodies that were solubilized and refolded t o active protein, Binding of KI MAb and FAb was compared by radioactiv e binding and competition assays and by surface plasmon resonance (BIA core), Recombinant KI(FAb) binds to cells expressing KI-antigen with a similar affinity as papain derived FAb from KI(IgG) and with a 4- to 10-fold reduced affinity compared with bivalent IgG, The cloned FAb ca n be used to make higher affinity antibodies and immunoconjugates that could be useful for various types of immunotherapies. (C) 1997 Wiley- Liss, Inc.