Preparation of F(ab')2 fragments from monoclonal mouse IgG1 suitable for use in radioimaging

Abstract

Monoclonal antibodies of IgG1 subclass raised against purified human prostate-specific acid phosphatase were subjected to different procedures to produce F(ab')2 fragments suitable for radioimaging of prostatic cancer, following derivatization and labeling with radionuclides. The main aim was to obtain highly purified fragments with preserved immunological activity. Optimized pepsin digestion led to the formation of mainly F(ab')2 and Fab fragments, and, following Sephacryl S-200 gel filtration, the yield of pure F(ab')2 fragments was 24 +/- 11% of the theoretical maximum. After papain digestion in the absence of thiols, no formation of Fab fragments was observed, and the F(ab')2 fragments formed could be efficiently separated from Fc fragments by chromatofocusing or ion exchange chromatography. The yield of F(ab')2 fragments from papain digestion was 50 +/- 5% of the theoretical maximum. Both the above procedures gave F(ab')2 fragments with immunoreactivity and affinity identical to those of the precursor IgG1, despite the fact that isoelectric focusing profiles of the two F(ab')2 preparations differed, suggesting different digestion sites.