ABSTRACT
Fc effector function is one of the main mechanisms of action (MoA) for therapeutic monoclonal antibodies (mAbs). Quantitative measurement of antibody-dependent cellular cytotoxicity (ADCC) is critically required for understanding the Fc function in mAb drug development. Despite the increasing interest and clinical success of the mAb therapeutic, it has been highly challenging to measure their ADCC activity in a reproducible and quantitative manner due to the lack of consistency in current methods that are based on primary PBMCs or NK cells and use tedious assay procedures. To improve ADCC assay precision so they can be validated as potency assay in cGMP laboratories, we developed reporter based ADCC bioassays using engineered effector cell line stably expressing a luciferase reporter and FcγRIIIa (V or F variant) to replace primary PBMC to overcome the assay variation. The ADCC reporter bioassays have been validated according to ICH guidelines by many laboratories and are demonstrated to be suitable for product release and stability studies in a quality-controlled environment. For early research and antibody characterization, we developed an improved PBMC ADCC assay using ADCC-prequalified PBMCs and engineered HiBiT target cells so they can measure the target specific lysis in ADCC. The PBMCs used in the study are isolated from prescreened blood donors and QC tested in ADCC assay. When HiBiT target cells are incubated with an antibody and PBMCs, HiBiT are released to the culture medium where it binds to LgBiT in the detection reagent to form a functional NanoBiT luciferase to generate luminescence signal. This new PBMC ADCC bioassay is simple, homogenous, highly sensitive, and gives a robust assay window. We demonstrate that it can quantitatively measure the potency for mAb drugs in cancer immunotherapy (e.g., rituximab, trastuzumab), and for anti-SARS-CoV-2 spike antibodies in antiviral drug development. Additionally, it shows antibody potency comparable with the ADCC reporter bioassay. In summary, the new PBMC ADCC bioassay using HiBiT target cells can be a valuable tool for early antibody discovery and characterization and also for method bridging study with ADCC reporter bioassay.