Overcoming soluble target interference in an anti-therapeutic antibody screening assay for an antibody-drug conjugate therapeutic

Background: The standard safety evaluation of biotherapeutics includes assessment of immunogenicity. Anti-therapeutic antibodies (ATA) can be detected in serum using immunoassays with a bridging format. However, these assays can be subject to interference. Results: In the bridging ATA assay for 3A5 TDC, an antibody–drug conjugate that binds to the multimeric extracellular domain of MUC16 (CA125), soluble CA125 in the serum caused false-positive results by binding to the ATA assay reagents. This interaction was blocked by wheat germ agglutinin lectin as it binds to the glycans in CA125; thus, the specificity of the assay improved. Conclusion: The assay development and validation results showed that the addition of wheat germ agglutinin eliminates the interference from circulating CA125 without impacting the ability to detect ATA.