T Regulator Cells (T_reg) In Patients with Myelofibrosis

Abstract 5051

Primary myelofibrosis (PMF) and myelofibrosis post essential thrombocytosis (MF-ET) or myelofibrosis post polycythemia vera (MF-PV) have been reported to be associated with autoimmune phenomenon, such as Coomb positive anemia, lupus anticoagulant, positive ANA and the presence of circulating immune complex etc. Regulatory T cells (T_reg) also have known to play important roles in modulating immune responses. Therefore we studied T_reg cells in 25 patients with MF including PMF (12), MF-ET (8), MF-PV (5) and compared with other MPD including ET (7), PV (8), and normal volunteer controls (17). Mononuclear cells (MNC) were separated from peripheral blood. 10⁶ MNCs were stained for flow cytometry analysis using T_reg Detection Kit from Miltenyi Biotec Inc (Auburn, CA). The numbers of T_reg was calculated as the percentage of positive CD4⁺ CD25⁺ FoxP3⁺ T cells (T_reg) from the numbers of gated CD4⁺ cells. T_reg function was evaluated by XTT cell proliferation assay (Invitrogen) with ratios of T_reg vs. T-effector cells (CD4⁺ CD25^-) at 1:1, 1:2, 1:4, and 0:1 in the presence of anti-CD3 CD28 microbeads (Invitrogen). The results (mean ± SE) showed numbers of T_reg cells in MF were 0.73 + 0.08, other MPD were 1.37 ± 0.22, and normal controls were 0.96 ± 0.27 (p=NS). T_reg function was evaluated in 12 patients with MF and 6 normal volunteer controls. Four MF patients were found to have significant lower values than controls. We concluded that in MF, quantitatively T_reg were not different from other MPD or normal controls but T_reg dysfunction was observed in 30–40 % of MF patients. This could explain why some patients with MF are prone to develop autoimmune phenomenon. Further studies with more patients are in progress.