The GITR Bioassays (Cat.# J2272, JA2291, JA2295), are bioluminescent cell-based assays that overcome the limitations of existing assays and can be used to measure the potency and stability of ligands or agonist antibodies that can bind and activate GITR. The assay consists of a genetically engineered Jurkat T cell line that expresses human GITR and a luciferase reporter driven by a response element that can respond to GITR ligand/agonist antibody stimulation. The GITR Effector Cells are provided in thaw-and-use format as cryopreserved cells that can be thawed, plated and used in an assay without the need for cell culture and propagation.Alternatively, the GITR Bioassay, Propagation Model (Cat.# J2272), provides GITR Effector Cells in Cell Propagation Model (CPM) format, as cryopreserved cells that can be thawed, propagated and banked for long-term use.The GITR Bioassay should be conducted with FcγRIIb CHO-K1 Cells (Cat.# JA2251, JA2255) to test whether agonist antibodies activate GITR in an FcγRIIb-dependent manner. FcγRIIb CHO-K1 cells may be required to crosslink agonist antibodies but are not required for testing ligands. It is recommended that, when screening for agonist antibodies of costimulatory immune checkpoints, you perform the assay both with and without FcγRIIb CHO-K1 Cells to ascertain the need for these cells in enhancing the effect of the agonist antibodies raised against the costimulatory immune checkpoint targets.The GITR Bioassay reflects the mechanism of action (MOA) of biologics designed to activate GITR. Specifically, GITR-mediated luminescence is detected following the addition of GITR agonist antibodies and GITR ligand, respectively. The bioassay is prequalified according to ICH guidelines and shows the precision, accuracy and linearity required for routine use in potency and stability studies. The assay can be performed in a one-day or two-day time frame depending on antibody properties. The bioassay workflow is simple and robust, and compatible with both 96-well and 384-well plate formats used for antibody screening in early drug discovery. In addition, the bioassay can be used with up to 100% human serum (in antibody samples), indicating potential for further development into a neutralizing antibody bioassay.