Used in immunological research to study T-cell activation and immune checkpoint pathways. Enables screening of therapeutic agents targeting the PD-1 pathway, such as antibodies or small molecules, by measuring NF-AT signaling as a readout of T-cell receptor activation. Commonly applied in drug discovery for cancer immunotherapy to assess the efficacy of PD-1 inhibitors in restoring T-cell function. Also utilized in evaluating the functional activity of biologics and in quality control during biopharmaceutical production.