Development of a Flow Cytometric Receptor Occupancy Assay for Clinical Analysis of Immune Checkpoint Inhibitor Therapeutics

PD-1 (CD279) is an immune checkpoint inhibitor that is expressed on the surface of T cells. Therapies inhibiting PD-1 interactions have become the most popular checkpoint inhibitor utilized in cancer immunotherapies. While treatments with anti-PD-1 can be highly effective, the combination of PD-1 with targeted treatment against other immune checkpoint molecules or costimulatory molecules has largely improved patient outcomes in the clinic.
The pharmacokinetics of these treatments, including the retention of therapies to their target molecules, have played a critical role in establishing effective dosing and treatment regimens. However, performing these assays can be costly, time-intensive to develop, and require specialized equipment and expertise. Here, Champions Oncology has established a receptor occupancy (RO) assay against PD-1 in a scalable fashion using high dimensional flow cytometry.

Flow cytometry is a powerful single-cell technique that allows for the interrogation of drug-target cell interactions at the single-cell level and has been utilized to evaluate receptor occupancy for several molecules, including PD-1. Champions Oncology has developed a panel that includes adrop-inchannel to evaluate both the receptor occupancy of PD-1 and the expression of other key checkpoint markers used in combination therapies. The receptor occupancy assay was evaluated for both assay sensitivity and reproducibility. This assay has been further developed to be scalable and stable for up to 48-72 hours on fresh whole blood samples. Collectively, this assay establishes the strength of the drug-target interaction, the sensitivity to which PD-1 interactions can be evaluated, and the flexible nature of the assay developed at Champions Oncology.