Validated detection of anti-GD2 antibody ch14.18/CHO in serum of neuroblastoma patients using anti-idiotype antibody ganglidiomab.

Human/mouse chimeric monoclonal antibody (mAb) ch14.18 is directed against disialoganglioside GD2 and has demonstrated activity and efficacy in high-risk neuroblastoma (NB). For the purpose of industrial production, ch14.18 was manufactured in Chinese hamster ovarian cells (ch14.18/CHO) in order to facilitate clinical trials in Europe. To determine immunopharmacological effects of ch14.18 in preclinical models and clinical trials, a validated method of quantitative detection of ch14.18/CHO in serum is an important tool. We recently described the generation and characterization of ganglidiomab, a monoclonal anti-idiotype Ab (AIT) of ch14.18 (Lode et al., 2013), which was used to establish quantitative and validated enzyme-linked immunosorbent assay (ELISA) methods using ganglidiomab as a capture mAb. With these ELISA methods, we first demonstrated binding of ch14.18/CHO to ganglidiomab to a similar extent as to the nominal antigen GD2 and in contrast to GD1b and GM2 precursor and metabolite gangliosides, used as negative controls. In order to determine both low (0.5–3.1μg/ml) and high levels of ch14.18/CHO (1.0–25μg/ml) in the serum of NB patients treated with ch14.18/CHO, we established two ELISA methods with high and low sensitivity using 1/1001, and 1/5126 sample dilutions, respectively. For validation, we used a set of tailored quality controls (QC) containing distinct concentrations of ch14.18/CHO (1.0, 2.0, 7.0, and 20.0μg/ml). We determined the limit of detection (LOD) for both ELISA methods to be 0.50μg/ml for the high sensitivity and 1.02μg/ml for low sensitivity ELISA. The within-assay precision was 12% for high and 4% for low sensitivity ELISA, and the coefficients of variation (CV) were under 20% for all assays (3% for QC-1.0, 5% for QC-2.0, 7% for QC-7, and 3% for QC-20). With this method, we showed that neither eight freeze–thaw cycles nor storage at room temperature for up to 168h affected ch14.18/CHO stability in serum. Finally, we analyzed ch14.18 Ab serum levels in selected NB patients receiving ch14.18/CHO as a continuous or bolus infusion with a peak concentration at the last day of Ab application (17.14±7.20mg/ml with continuous and 19.78±2.26mg/ml with bolus infusion).