A novel method for quantitative measurement of a biomarker in the presence of a therapeutic monoclonal antibody directed against the biomarker

Therapeutic monoclonal antibodies (MoAb) have become important tools in the treatment of numerous diseases. Many of these MoAb are present in the blood at very high levels due to high dosing and long half-lives. Quantification of biomarkers bound by these therapeutic MoAb can be an important factor in determining efficacy and dosing requirements. However, quantitation of these biomarkers with reasonable accuracy can be very difficult to accomplish due to concomitant binding of the therapeutic MoAb. We describe here a novel method for quantifying total (free plus bound) biomarker concentration in the presence of high levels of therapeutic MoAb using a single non-competing MoAb in a capture/elution format. This assay has the capability to accurately detect and quantitate circulating ng/ml biomarker levels in the presence of 200 μg/ml or more of therapeutic MoAb.