Accurate quantification of anti-drug antibodies against each unique Fab of a bispecific antibody using an ECL bridging assay

To develop an anti-drug antibody (ADA) assay for a bispecific antibody (bsAb) we will refer to as Drug-1, and to quantify the ADAs against each specific fragment antigen-binding (Fab) site of Drug-1.
Here we use two additional unlabeled monoclonal antibodies (mAbs) Drug-2 & Drug-3 in an ADA confirmation assay format. Drugs-2 & −3 have the same targets as the two Fabs of Drug-1, facilitating our aim to measure and quantify the anti-drug Abs against each specific Fab of Drug-1 by signal inhibition.
By using the combination of a screening and a dual confirmation assay format, we were able to accurately quantify the ADAs against each specific Fab of the bsAb Drug-1.
Many new medicines are biologics – they’re made from proteins similar to those our bodies make. Most biologics are antibodies. To make antibody medicines, scientists give living cells (usually CHO cells) the antibody’s genetic instructions. The cells then produce the antibody and add small changes like those that happen in humans. Most antibodies bind to one target. Bispecific antibodies are different because they have two separate binding parts (called Fabs) and can attach to two different targets at the same time. Because biologics are large proteins, the immune system can see them as foreign and make anti-drug antibodies (ADAs). Regulators require testing to see if patients make ADAs and whether those ADAs affect safety or how well the drug works. We developed a test that: Detects all ADAs a patient makes against a bispecific antibody, Identifies which of the two Fabs the ADAs bind to, and Measures how much binds to each Fab. This ADA information, together with safety and efficacy data, can help decide whether and how to use those Fabs in future drug projects.