U266/GFP-luciferase cells are derived from the human myeloma U266 cell line by stably integration of a constitutive GFP and Firefly luciferase stably expression construct. The U266 cells are an important tool in studying the pathogenesis, progression, and treatment of multiple myeloma, as well as for testing chemotherapies and immunotherapies, including monoclonal antibodies, immune checkpoint inhibitors, and CAR-T cell therapies. U266/GFP-luciferase cells stably express GFP and Firefly luciferase, can be used for in vitro assays and in vivo imaging.