Patients with CD 45 negative multiple myeloma receiving high

CD45, the first receptor-like protein tyrosine phosphatase expressed on all nucleated hematopoietic cells, is a critical regulator of signaling thresholds in immune cells. Perturbation of its function may contribute to autoimmunity, immunodeficiency and malignancy. The expression of CD45 declines in vivo during normal plasma cell (PC) differentiation. Indeed, CD45 is brightly expressed in normal immature proliferative PC but weakly expressed in mature resting PC of the bone marrow. In all cases of MM, a small population of myeloma cells, which always corresponds to the most proliferative myeloma cells, presents bright expression of CD45. In the rest of myeloma cells, CD45 expression declines but remains detectable (CD45 positive MM) or becomes undetectable (CD45 negative MM). It has already been shown that CD45 negative MM correspond to those with myeloma cells circulating in the peripheral blood and/or to cases of advanced disease.