Establishing Tyro3, Axl, and Mertk Chinese hamster ovary (CHO) reporter cell lines for cancer immunology and therapeutic applications.

Tyro-3, Axl, and Mertk (abbreviated TAM receptors or TAMs), have well established functions in efferocytosis, the process by which apoptotic cells are engulfed by phagocytic cells such as macrophages and dendritic cells. In addition to their roles in efferocytosis, TAMs are also pleiotropic immune modulators that dampen inflammation and promote immune resolution and tolerance. Mice lacking one or more of the TAM receptors in various murine models leads to chronic inflammation and in some cases autoimmunity and chronic disease. In recent years, TAMs have emerged as important contributors in cancer, functioning both as oncogenic tyrosine kinases as well as immune modulators. Many recent studies indicate that TAM inhibitors, including monoclonal antibodies, kinase inhibitors, decoy receptors and ligands, and small molecular wedge inhibitors have therapeutic potential in cancer biology and immunotherapy. Here, we report the development and characterization of two type of TAM reporter lines that can be adapted to screen a wide range of TAM inhibitor types. The first involves TAM-IFN-γR1 chimeric CHO lines, where the extracellular domain of human TAM receptors is fused with the transmembrane and intracellular signaling domains of the human IFN-γ receptor chain. The second type of TAM reporter line described is the EGFR-TAM chimeric CHO lines, which involves fusing the extracellular domain of the EGFR receptor with the transmembrane and intracellular tyrosine kinase domains and cytosolic tail of TAM receptors. With minimal adaptation, both lines can be adopted for high throughput screening with immune-oncology applications.