Detection of Antidrug Antibodies Against Antibody-drug Conjugates by Solid-phase Extraction with Acid Dissociation in Cynomolgus Monkey Serum

The formation of antidrug antibodies (ADAs) against antibody-drug conjugates (ADCs) can trigger a humoral immune response and change drug exposure. Although the immunogenicity assessment of an ADC drug in nonclinical nonhuman primates may not directly translate to potential immunogenicity in humans, the nonclinical ADA assay facilitates understanding the pharmacokinetic profiles of biotherapeutics. The immune response against the human IgG4 monoclonal antibody-based ADC was suspected in cynomolgus monkey serum after intravenous administration at 1.5 mg/kg. However, the conventional bridging format ADA assay presented unique challenges for the ADC molecules due to the interaction of ADC-based capture and detection reagents, which generated high background noise. Solid-phase extraction with acid dissociation (SPEAD) sample treatment allowed the selective ADA transfer to a second plate for detection while avoiding the interaction between the capture and detection reagents. The signal-to-noise ratio in the ADA assay for ADCs was notably improved with SPEAD sample treatment compared with the results from the bridging assay. Importantly, the rapid drug clearance of the ADC molecules at the later time points was well correlated with the signal-to-noise ratio of the ADA assay in monkey serum, suggesting the validity of the results. Hence, we demonstrated the utility of the SPEAD sample treatment to mitigate the critical reagent interaction that triggered the unexpectedly high background in the ADA assay. SIGNIFICANCE STATEMENT: A fit-for-purpose antidrug antibody screening assay for the human IgG4 monoclonal antibody-based antibody-drug conjugate (ADC) molecule by solid-phase extraction with acid dissociation was developed to mitigate the high background noise due to the interaction of capture and detection ADCs. A positive antidrug antibody signal was observed in the monkey serum sample, which is in line with the significant decrease in the plasma concentration of ADCs at the later time points.