Mechanism of paroxysmal nocturnal hemoglobinuria clonal dominance: possible roles of different apoptosis and CD8 + lymphocytes in the selection of paroxysmal nocturnal hemoglobinuria clones

BACKGROUND AND OBJECTIVES Paroxysmal nocturnal hemoglobinuria (PNH), a clonal hematopoietic stem cell disorder, manifests when the PNH clone populates in the hematopoietic compartment. We explored the roles of different apoptosis of GPI+ and GPI- (glycosylphosphatidylinositol) cells and CD8+ lymphocytes in a selection of PNH clones. PATIENTS AND METHODS Granulocytes from PNH patients and normal controls were subjected to an apoptosis assay using annexin V. Hematopoietic cell in semisolid media were cultured with or without CD8 + lymphocytes. RESULTS In PNH, CD59 + granulocytes exhibited more apoptosis than their CD59- counterparts, after 0 or 4 hours in liquid growth culture system (mean [standard error of mean]: 2.1 (0.5) vs 1.2 (0.2), P = .01 at 0 hour and 3.4 [0.7] vs 1.8 [0.3], P = .03 at 4 hour, respectively). The presence of mononuclear cells (MNCs) rendered a greater difference in apoptosis. The percentages of apoptotic CD59 + granulocytes measured at 4 hours with or without MNC fraction were correlated with the sizes of PNH clones (r = 0.633, P = .011; and r = 0.648, P = .009; respectively). The autologous CD8 + lymphocytes inhibited CFU-GM and BFU-E colony formation in PNH patients when compared with normal controls (mean [SEM] of percentages of inhibition: 61.7 (10.4) vs 11.9 (2.0), P = .008 for CFU-GM and 26.1 (6.9) vs 4.9 (1.0), P = .037 for BFU-E). CONCLUSIONS Increased apoptosis of GPI + blood cells is likely to be responsible in selection and expansion of PNH clones. MNCs or possibly CD8 + lymphocytes may play a role in this phenomenon.