Tag-lite cells transiently expressing the Chemokine CXCR4 receptor labeled with Terbium for use in receptor binding applications. The cells are provided ready to use..CXCR4 is a receptor for the C-X-C chemokine CXCL12/SDF-1. Compelling evidences suggest that CXCR4 is nvolved in hematopoiesis and in cardiac ventricular septum formation. The receptor also plays an essential role in vascularization of the gastrointestinal tract. CXCR4 acts as a coreceptor for human immunodeficiency virus-1/HIV-1. Cells expressing the CXCR4 receptor are provided pre-labeled with Terbium, and can be used to conduct receptor binding studies on the aforementioned receptor..