GTX65633-pro CD137L protein (DDDDK tagged) binding to CD137 transfected cells. HEK 293 cells were transiently transfected with a construct encoding full-length mouse CD137. At 48hrs after transfection, the transfectants were incubated with 0.5 or 5μg/ml GTX65633 CD137L protein (DDDDK tagged) and followed by flow cytometry analysis with anti-DDDDK anibody.