CD 200 - A useful marker in chronic B lymphoprolipherative disorders

Background: The diagnosis and management of the patients with chronic lymphoproliferative diseases have become dependent on immunological criteria. Flow cytometry immunophenotyping is used for rapid and specific diagnosis but there are cases when we are not facing a typical immunophenotype, so there is a constant need to find new markers and new combinations of markers that would allow the improvement and the development of our diagnosis. Aim: Our aim was to evaluate CD 200 expression in different B-cell chronic lymphoproliferative disorders. CD200 is a membrane glycoprotein belonging to the immunoglobulin superfamily and the over-expression of CD200 has been reported in a number of malignancies, including CLL, as well as on cancer stem cells. Methods: We analyzed the CD200 expression in 122 patients diagnosed with chronic lymphoproliferative disorders (100 patients with CLL, 10 patients with splenic marginal zone lymphoma (SMZL), 10 patients with MCL and 2 patients with hairy cell leukemia), in the Department of Hematology of the University Emergency Hospital, Bucharest. We performed immunophenotypical analysis of peripheral blood and bone marrow aspiration on BD FACS Calibur flowcytometer. Results: CD200 was brightly expressed in all 100 CLL patients (100%). In SMZL patients, CD200 was dim positive (40%-60%), in patients with HCL. CD200 was also bright positive (96% and 97%) and in patients with MCL CD200 was negative (1-10%); CD 200 was significantly higher in CLL patients compared with other B-cell chronic lymphoproliferative disorders. We found 14 patients with CD19, CD5 positive population and CD23- , but with high expression of CD 200. Cyclin D1 was negative on bone marrow biopsy in 13/14 of these patients. (1/14 patients were without bone marrow involvement); Conclusions: CD200 has a great impact in diagnosing B- chronic lymphoproliferative disorders, especially when we want to determine the origin of a CD19, CD5 positive population and distinguish between CLL and MCL. CD 23 is a reliable marker in those cases, but, as we showed, CD23 might have a lower specificity than CD200 for CLL. We added CD200 in our panels in order to diagnose chronic lymphoproliferative disorders, not to replace CD 23, but to improve and save time in our diagnostic process. The high expression of CD200 in CLL and HCL could open the option for new- targeted therapy (anti-CD200).