Quantitative Cell-Based Bioassays to Advance Immunotherapy Programs Targeting Immune Checkpoint Receptors
Richard Somberg, Jamison Grailer, Julia Gilden, Pete Stecha, Denise Garvin, Jun Wang, Michael Beck, Jim Hartnett, Frank Fan, Mei Cong and Zhi-jie Jey Cheng
Promega Corporation, 2800 Woods Hollow Road, Madison, WI 53711, USA
The human immune system is comprised of a complex network of immune checkpoint receptors that are promising new immunotherapy targets for the treatment of a variety of cancers and autoimmune-mediated disorders. Immunotherapies designed to block co-inhibitory receptors (e.g. PD-1, CTLA-4) are showing unprecedented efficacy in the treatment of cancer. However, not all patients and tumor types respond to this approach. This has resulted in broadening of immunotherapy research programs to target additional co-inhibitory (e.g. LAG-3, TIGIT) and co-stimulatory (e.g. GITR, 4-1BB, OX40, CD40) receptors individually and in combination.
A major challenge in the development of biologics is access to quantitative and reproducible functional bioassays. Existing methods rely on primary cells and measurement of complex functional endpoints. These assays are cumbersome, highly variable and fail to yield data quality required for drug development in a quality-controlled environment. To address this need, we have developed a suite of cell line-based bioluminescent reporter bioassays for co-inhibitory and co-stimulatory immune checkpoint targets including PD-1, CTLA-4, GITR, 4-1BB, OX40, CD40 and more. These assays consist of stable cell lines that express luciferase reporters driven by response elements under the precise control of intracellular signals mediated by each immune receptor. These bioassays reflect mechanisms of action for the drug candidates designed for each immune checkpoint receptor and demonstrate high specificity, sensitivity and reproducibility. In summary, these reporter-based bioassays can serve as powerful tools in immunotherapy drug development for antibody screening, potency testing and stability studies.