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Antibody valency describes the antigen-binding capacity of an antibody in terms of total number of antigen-binding sites (Labrijn et al. 2019). For example, an IgG with two binding sites to one target antigen is a bivalent monospecific antibody. For bispecific antibodies, valency can be used to describe both the total number of antigen binding sites as well as the number of binding sites for each target antigen (Brinkmann and Kontermann 2017). As a parameter in Assess, valency describes the binding capacity of the antibody to its antigen(s). Valency can be set for each target of a bispecific separately.

Valency in Assess

Valency is defined as part of the drug design, and the impact of valency can be tested by varying this parameter.

Important Note

In Assess, valency also describes the stoichiometry of the interaction between drug and target. There are situations where the stoichiometry of the interaction should be considered.

For example, when the target is a soluble ligand that exists as a dimer. If both arms of a bivalent antibody bind to the same ligand dimer in a (1 drug):(1 ligand) stoichiometry, the effective valency of the antibody would be 1. If the arms of the bivalent antibody bind to two different ligand dimers in a (1 drug):(2 ligand) stoichiometry, the effective valency of the antibody would be 2. Once again, if stoichiometry is uncertain, testing the impact of varying this parameter can help determine if more characterization of a drug candidate is warranted.


  • Brinkmann, Ulrich, and Roland E. Kontermann. 2017. "The Making of Bispecific Antibodies." mAbs 9 (2): 182–212.
  • Labrijn, Aran F., Maarten L. Janmaat, Janice M. Reichert, and Paul W. H. I. Parren. 2019. "Bispecific Antibodies: A Mechanistic Review of the Pipeline." Nature Reviews. Drug Discovery 18 (8): 585–608.