Complement dependent cytotoxicity (CDC) activity of a humanized anti Lewis-Y antibody: FACS-based assay versus the ‘classical’ radioactive method—Qualification, comparison and application of the FACS-based approach

The fully humanized Lewis-Y carbohydrate specific monoclonal antibody (mAb) IGN311 is currently tested in a passive immunotherapy approach in a clinical phase I trail and therefore regulatory requirements demand qualified assays for product analysis. To demonstrate the functionality of its Fc-region, the capacity of IGN311 to mediate complement dependent cytotoxicity (CDC) against human breast cancer cells was evaluated. The “classical” radioactive method using chromium-51 and a FACS-based assay were established and qualified according to ICH guidelines. Parameters evaluated were specificity, response function, bias, repeatability (intra-day precision), intermediate precision (operator–time different), and linearity (assay range).In the course of a fully nested design, a four-parameter logistic equation was identified as appropriate calibration model for both methods. For the radioactive assay, the bias ranged from −6.1% to −3.6%. The intermediate precision for future means of duplicate measurements revealed values from 12.5% to 15.9% and the total error (β-expectation tolerance interval) of the method was found to be <40%. For the FACS-based assay, the bias ranged from −8.3% to 0.6% and the intermediate precision for future means of duplicate measurements revealed values from 4.2% to 8.0%. The total error of the method was found to be <25%.The presented data demonstrate that the FACS-based CDC is more accurate than the radioactive assay. Also, the elimination of radioactivity and the ‘real-time’ counting of apoptotic cells further justifies the implementation of this method which was subsequently applied for testing the influence of storage at 4 °C and 25 °C (‘stability testing’) on the potency of IGN311 drug product. The obtained results demonstrate that the qualified functional assay represents a stability indicating test method.