Flow cytometry can be a powerful tool for the evaluation of Receptor Occupancy (RO) to provide an assessment of the therapeutic binding to the target receptor. This can be evaluated using direct or indirect methods. Please inquire to start the scientific discussion.


Receptor occupancy assays are a method for identifying, and monitoring the binding of a therapeutic to its cellular target. These assays can be as simple as measuring the number of cell surface receptors bound by a therapeutic agent or highly complex such as measuring receptor dynamics, depending on the scientific questions being studied.  Evaluating receptor occupancy during the development of new biologic drugs is crucial not only for candidate selection in the early stages but also to confirm that the therapeutic is binding to its cellular target and establishing the dose or plasma concentration needed to reach a therapeutically-effective receptor occupancy level when combined with pharmacokinetic (PK) and pharmacodynamic (PD) data.

Flow cytometry, the leading technology for single cell multiplex analysis, is ideally suited for receptor occupancy assays, which are most often applied to the evaluation of therapies targeting peripheral blood cells. At Flow Contract Site Laboratory, LLC we provide custom developed receptor occupancy assays based on client defined parameters to identify the binding of therapeutic compound to its specific target.

Assessment of receptor occupancy by flow cytometry can take several approaches:

  • Free Receptor Assay– Shown in the Left Panel is an illustration of free receptors that are not occupied by biotherapeutic agent detected using either a fluorescently labeled competitive antibody or biotherapeutic agent.
  • Free and Total Receptor Assay– Shown in the Middle Panel is an illustration of free and total receptor assay design which depicts the total receptors available, recognized by a noncompetitive antibody bound to a different epitope on the receptor from the one recognized by the biotherapeutic agent. This design can be used determine the ratio of free (unoccupied) sites to total sites available.
  • Direct Assessment of Bound Receptor– Shown in the Right Panel is an illustration of direct assessment of bound receptor with biotherapeutic agent, typically detected with a fluorescently labeled anti-drug antibody.



This can be evaluated using direct or indirect methods. We can help you to move your novel biologic to the development of targeted drug. Please inquire to start the scientific discussion.


Litwin V, Green C, Stewart JJ (2016) Receptor occupancy by flow cytometry. Cytometry B Clin Cytom 90:108–109. doi: 10.1002/cyto.b.21364

Stewart JJ, Green CL, Jones N, Liang M, Xu Y, Wilkins D, Moulard M, Czechowska K, Lanham D, McCloskey TW, et al. Role of receptor occupancy assays by flow cytometry in drug development 2016;90:110–116.