Abnormal Phenotype of Bone Marrow Plasma Cells in Patients with Chronic Myeloid Leukemia Undergoing Therapy with Imatinib

Imatinib induces several effects on the immune system, including hypogammaglobulinemia and has been associated with multiple myeloma in some patients. We studied the phenotype of plasma cells from patients with chronic myeloid leukemia (CML) undergoing therapy with Imatinib mesylate (Glivec). Bone marrow samples from 30 CML patients were evaluated and plasma cells were identified by multiparametric flow cytometry. In 21 patients an abnormal plasma cell phenotype, characterized by the absence of CD19, was registered, with 12 patients expressing also the CD56 molecule. A significant correlation between abnormal plasma cell phenotype and reduced gamma-globulin levels was found. Immunofixation was always negative. Therapy with Imatinib for CML seems to induce a plasma cell phenotype with the same characteristics as monoclonal gammapathies. These findings deserve further studies and suggest to monitor plasma protein electrophoresis and gamma-globulin levels in all patients treated with Imatinib.