*Review* **Bioassay Development for Bispecific Antibodies—Challenges and Opportunities**

**Ames C. Register 1, Somayeh S. Tarighat <sup>2</sup> and Ho Young Lee 2,\***


**Abstract:** Antibody therapeutics are expanding with promising clinical outcomes, and diverse formats of antibodies are further developed and available for patients of the most challenging disease areas. Bispecific antibodies (BsAbs) have several significant advantages over monospecific antibodies by engaging two antigen targets. Due to the complicated mechanism of action, diverse structural variations, and dual-target binding, developing bioassays and other types of assays to characterize BsAbs is challenging. Developing bioassays for BsAbs requires a good understanding of the mechanism of action of the molecule, principles and applications of different bioanalytical methods, and phase-appropriate considerations per regulatory guidelines. Here, we review recent advances and case studies to provide strategies and insights for bioassay development for different types of bispecific molecules.

**Keywords:** bispecific antibodies; bioassays; mechanisms of action; binding assays; potency assays
