Assay pH and critical reagent optimization in measuring concentrations of a monoclonal antibody and its target

Aim: To mitigate assay interference in the drug and target assays to support the development of monoclonal antibody REGN-Z. Results: Mild acidic assay conditions and capture and detection antibodies with different affinities and t_1/2 under different assay pHs were used to mitigate interference in the total drug and total target assays. A free target assay was also developed using a lower-affinity capture antibody with a much slower association and dissociation rate. The impact of sample incubation, dilution and storage on the accurate detection of the free target was also evaluated. Conclusion: The total drug, total and free target assays can accurately quantitate drug and target concentrations when tested with a subset of clinical study samples.