An affinity column method for determination of the immunoreactivity of 131I-chimeric L6 monoclonal antibody and comparison to in vivo tumor localization.

An affinity column method was developed to determine the immunoreactivity of 131I-ChiL6 (chimeric L6 monoclonal antibody), a candidate for radioimmunotherapy. This method involved assessing the binding of the radiolabeled antibody to antigen containing membranes bound to a Reacti-gel agarose matrix. The immunoreactivity determined by the affinity column method correlated to other in vitro binding assays including the Lindmo infinite antigen excess method. In tumor-bearing mice which had been injected with 131I-ChiL6, which possessed high immunoreactivities (90-82%), a high tumor uptake (13.5-10.5% ID/g) was observed. A decrease in tumor uptake (5.2-4.8% ID/g) was observed with 131I-ChiL6 samples of low immunoreactivity (42% and 31%, respectively). While a moderate loss of immunoreactivity (4-18%) of the 131I-ChiL6 samples could be detected by the affinity column method, the loss of tumor uptake in vivo observed was not as significant. This method was found to be an efficient and sensitive method for detecting damage to the antibody during radiolabeling and applicable as a quality control method for clinical trials. This rapid method, compared to the other in vitro binding assays (including the Lindmo infinite antigen excess method) has distinct advantages as a quality control method since it requires less manipulation and can be semi-automated.