Preparation of a pure 99mTc-F(ab')2 radioimmunoconjugate by direct labeling methods

Intact IgG and Fab' can be labeled directly with 99mTc to give quantitative incorporation of radioactivity into the protein. With F(ab')2 the reductive conditions yield a mixture of 99mTc-F(ab')2 and 99mTc-Fab'. We now report a direct labeling method to produce only 99mTc-F(ab')2 in quantitative yield and contaminated with 99mTc-Fab'. The properties, stability and biodistribution of the 99mTc-F(ab')2 have been compared to 99mTc-Fab'. This new technology will allow us to compare technetium direct-labeled IgG, F(ab')2 and Fab' derivatives of the same antibody for radioimmunodetection.