Paroxysmal nocturnal hemoglobinuria and myelodysplastic sydromes: clonal expansion of PIG-A-mutant hematopoietic cells in bone marrow failure

Abstract

Editorials & Perspectives absence of a specific GPI-anchored protein? At the level of cell biology, do PNH clones persist for decades, and how does a single clone sustain virtually all hematopoietic activity? At the cellular level, what is the fate of all the proteins that are destined to be GPI-anchored but produced in an anchorless environment-are they degraded, digested, secreted or shed from the cell, and with what consequences? For what reason has evolution preserved the GPI-anchor for certain proteins? Indeed, we have little information on the biophysical differences and the functional consequences that result from a GPI-anchor attachment compared to the more conventional transmembrane configuration. GPIanchored proteins attach via a "fatty foot" to the surface but do not extend internally beyond the cell's membrane; they associate in cholesterol-rich, detergentinsoluble lipid raft structures and presumably must cooperate with other proteins in order to convey an internal signal after engaging a ligand. Paroxysmal nocturnal hemoglobinuria and bone marrow failurePerhaps the major focus of current research in PNH is the relationship of PNH and marrow failure in patients and the associated basic problem of PNH clonal expansion. Clinically, PNH has a strong relationship with aplastic anemia. Historically, some patients were recognized to have a mixture of the two diseases, manifesting both marrow failure and intravascular hemolysis. Many patients with PNH have low blood counts that cannot be attributed to peripheral destruction of cells and many younger PNH patients develop aplastic anemia. In patients first diagnosed with acquired aplastic anemia, PNH sometimes appeared to evolve after immunosuppressive treatment.The replacement of the cumbersome Ham test with flow cytometric assays for GPI-anchored proteins greatly simplified and quantified diagnostic testing for PNH, and also allowed a better description of the relationship between PNH and aplastic anemia. By flow cytometry investigation of granulocytes, expanded clones of PNH cells were observed in a large proportion of patients with aplastic anemia at the time of their presentation; if they recovered, the clone was apparent also in erythrocytes, having been obscured earlier by transfused blood cells. As described above, minute numbers of PNH granulocytes are present in normal individuals. At the time of diagnosis of aplastic anemia, between one third and one half of cases have elevated numbers of PNH granulocytes, but the proportion is usually much lower -just a small percentage of the total neutrophils -than in classical hemolytic PNH, in which the proportion of erythrocytes and granulocytes that lack GPI-anchored proteins is high, usually above 50%. In aplastic anemia the small clone may be stable in size for years, and in only a minority of cases does it increase to levels associated with frank hemolysis and anemia. The problem of clonal expansionThe PIG-A mutation alone is necessary but insufficient to explain PNH clonal expansion. In humans, PIG-A mu...

Paroxysmal nocturnal hemoglobinuria clones in severe aplastic anemia patients treated with horse anti-thymocyte globulin plus cyclosporine

“…5,6 The emergence of GPI-anchored protein-deficient cells primarily occurs in the setting of bone marrow failure, and about 40-50% of AA patients have a PNH clone detected at the time of diagnosis. 7 The mechanism by which the expansion of PNH cells occurs in AA remains unknown; one hypothesis is that the PNH cells have a proliferative advantage over non-PNH cells by an immune mechanism of selection. 7 Since 2000, all SAA treatment protocols at our institution included the measurement of PNH clones by flow cytometry in erythrocytes and granulocytes before and after IST.…”

“…7 The mechanism by which the expansion of PNH cells occurs in AA remains unknown; one hypothesis is that the PNH cells have a proliferative advantage over non-PNH cells by an immune mechanism of selection. 7 Since 2000, all SAA treatment protocols at our institution included the measurement of PNH clones by flow cytometry in erythrocytes and granulocytes before and after IST. In order to determine the evolution of PNH clones after IST, we conducted a retrospective analysis in 207 patients who were treated with horse anti-thymocyte globulin (h-ATG) plus cyclosporine (CsA) from 2000 to 2008 at the Clinical Center of the National Institutes of Health.…”

Frequency of Paroxysmal Nocturnal Hemoglobinuria Clone in Turkish Myelodysplastic Syndrome Group

“…Based on these data, we estimate that PNH, which has previously been linked with MDS and other bone marrow failure syndromes (2,5), occurs in approximately one-fifth of patients with MDS in Turkey.…”

“…However, PNH clone sizes can now be conveniently and accurately determined using modern flow cytometry methods (5,8,14). The pathogenesis of PNH leaves red cells, platelets and neutrophils vulnerable to attack by the complement system, with subsequent hemolysis and platelet activation resulting in severe end-organ damage and a high risk of thrombosis (15).…”

Flow cytometric analysis of CD 55 and CD 59 deficient cells in patients with Aplastic Anemia and their clinicohematological profile

“…Clones of glycosylphosphatidylinositolanchor protein-deficient cells characteristically seen in PNH are present in about 40-50% of patients with severe aplastic anemia. (2) Response to immunosuppressive therapy is better in this subset of patients and the bone marrow failure seen is less severe. (3,4) Flow cytometry has allowed for sensitive and precise measurement of glycosylphosphatidylinositol-anchor protein-deficient red blood cells and neutrophils in severe aplastic anemia.…”