Monoclonal antibodies (mAbs) targeting immune checkpoint pathways such as programmed cell death protein 1 (PD‐1)/PD‐L1 are central to modern immunotherapy, yet scalable methods to assess their functional blockade remain limited. We present a bead‐based flow cytometry assay for quantifying the inhibition of PD‐1/PD‐L1 interaction by antibodies. Recombinant human PD‐1 protein was conjugated to polystyrene beads, and its interaction with recombinant human PD‐L1 protein labeled with a fluorochrome was measured. The inhibitory activity of an anti‐PD‐L1 mAb was quantified based on their ability to disrupt this interaction. The assay was validated for intra‐ and inter‐assay precision, in addition, functionality was confirmed using a T cell coculture assay. The assay demonstrated dose‐dependent inhibition by the αPD‐L1 mAb, with a calculated mean IC 50 of 3.122 µg/mL. The method proved to be reproducible for the determination of antibody blocking activity, with relative standard deviation (RSD) < 20% between three independent runs. At the concentration approximating the IC 50 detected on the bead assay, the antibody significantly restored CD69 expression on the T cell surface ( p = 0.0001) in a coculture in vitro system. In addition, the methodology could successfully distinguish the blocking capacity of two anti‐PD‐L1 antibodies with different affinities. This high‐throughput compatible platform offers a reliable tool for screening PD‐1/PD‐L1 blocking antibodies, supporting immunotherapy discovery and development.
Pscheidt et al. (Thu,) studied this question.