Immunophenotypic discrepancies between granulocytic and erythroid lineages in peripheral blood of patients with paroxysmal nocturnal haemoglobinuria

Laboratory studies for paroxysmal nocturnal hemoglobinuria, with emphasis on flow cytometry

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare acquired clonal hematopoietic stem cell disorder caused by somatic mutations in the PIG-A gene, leading to the production of blood cells with absent or decreased expression of glycosylphosphatidylinositol-anchored proteins, including CD55 and CD59. Clinically, PNH is classified into three variants: classic (hemolytic), in the setting of another specified bone marrow disorder (such as aplastic anemia or myelodysplastic syndrome) and subclinical (asymptomatic). PNH testing is recommended for patients with intravascular hemolysis, acquired bone marrow failure syndromes and thrombosis with unusual features. Despite the availability of consensus guidelines for PNH diagnosis and monitoring, there are still discrepancies on how PNH tests are carried out, and these technical variations may lead to an incorrect diagnosis. Herein, we provide a brief historical overview of PNH, focusing on the laboratory tests available and on the current recommendations for PNH diagnosis and monitoring based in flow cytometry.

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.

A cohort study of the nature of paroxysmal nocturnal hemoglobinuria clones and PIG-A mutations in patients with aplastic anemia

BACKGROUND

Paroxysmal nocturnal hemoglobinuria (PNH) is characterized by the clonal expansion of blood cells, which are deficient in glycosylphosphatidylinositol anchored proteins (GPI-APs). As PNH frequently occurs during the clinical course of acquired aplastic anemia (AA), it is likely that a process inducing bone marrow failure in AA is responsible for the selection of GPI-AP deficient blood cells or PNH clone.

OBJECTIVE

To explore the nature and mutation of a PNH clone in AA.

METHODS

We performed regular repeated flow cytometric analyses of CD59 expression on peripheral blood cells from a cohort of 32 patients with AA. Mutation of phosphatidylinositol glycan class A (PIG-A) was also studied.

RESULTS

Fifty-one episodes of occurrences of CD59 negative granulocytes out of a total cohort 167 flow cytometric analyses (31%) were observed in 22 patients (69%). CD59 negative erythrocytes were less apparent than the granulocytes. Repeated occurrences of PNH clones were observed in 16 patients. Most of the emerging PNH clones were transient in nature. They were more frequently detected during episodes of lower white blood cell and platelet counts. Persistence and expansion of the GPI-AP deficient blood cell populations to the level of clinical PNH were seen in only four patients (12.5%). Analysis of PIG-A gene demonstrated eight mutations among the four patients, with two and four independent mutations in two patients.

CONCLUSIONS

Our study indicates that PIG-A mutations of hematopoietic stem cells with resultant PNH clones, are relatively common among AA patients. It also supports the hypothesis of selection of the PNH clone by a process or condition associated with or responsible for bone marrow failure in AA. However, there must be an additional factor favoring expansion or growth of the clone to the level of clinical or florid PNH.

Plasmatic coagulation and fibrinolytic system alterations in PNH

Paroxysmal nocturnal haemoglobinuria (PNH) is characterized pathophysiologically by intravascular lysis of blood cells and clinically by thromboembolic events, often atypical in localization. In this study, we examined the plasmatic coagulation system of PNH patients to investigate a potential relation between coagulation alterations and disease intensity (PNH clone size). We found evidence for both an increase in procoagulant and in fibrinolytic activity, resulting in increased fibrin generation and turnover. Whereas a positive association of the procoagulant potential with PNH clone size was notable, fibrinolytic activity showed an inverse association with clone size. As a possible cause, a growing impairment of fibrinolytic activation and/or an increasing displacement of fibrinolytic activity is assumed. These mechanisms are most likely caused by the detachment of the glycosyl-phosphatidyl-inositol-anchored urokinase plasminogen activator receptor from cell surfaces, causing a progressive resistance to fibrinolytic stimuli, together with a probable shift of the fibrinolytic potential from cell surfaces to soluble, circulating complexes, resulting in a cellular fibrinolysis-steal phenomenon. Together, these processes are accused of mediating an increased thrombophilic risk in PNH. As hereditary prothrombogenic defects were found more frequently in patients suffering ischaemic complications, genetic thrombophilia seems to confer an additional thromboembolic risk in PNH, and should therefore be screened for.

Diagnostic significance of measurement of the receptor for urokinase-type plasminogen activator on granulocytes and in plasma from patients with paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired stem cell disorder characterized by the deficiency of all proteins anchored to the membrane by the glycosyl-phosphatidylinositol (GPI) anchor. The receptor for urokinase-type plasminogen activator (uPAR) also is attached to the cell membrane by a GPI anchor, and that soluble uPAR (suPAR) is present in plasma. In the present study, we measured uPAR, CD55, and CD59 on granulocytes by means of flow cytometry and suPAR in plasma by means of immunoradiometric assay. The subjects were 20 patients with PNH, 59 other patients with anemia, and 21 healthy individuals. In patients with PNH, both the mean fluorescence intensity and the positive percentage of fluorescence-activated granulocytes of uPAR, CD55, and CD59 were remarkably decreased, whereas in patients with other forms of anemia, except 2 patients with aplastic anemia, the results were not altered in comparison with those for the healthy individuals. The level of uPAR was reduced to the same extent as were those of CD55 and CD59 on the PNH-affected granulocytes. Some peak shape abnormalities (double peaks, peak tailing, or both) in the histogram of fluorescence intensity were also found in patients with PNH. The suPAR concentration of PNH plasma was 4.04+/-2.47 ng/mL, which was higher than that of the healthy individuals, 1.73+/-0.96 ng/mL (P < .01). The positive percentage of fluorescence-activated granulocytes was inversely associated with the plasma suPAR level in patients with PNH (r = -0.79, P < .01). Our data suggest that measurement of uPAR on granulocytes by means of flow cytometry and of suPAR in plasma by means of immunoradiometric assay are specific techniques for the diagnosis of PNH.

Clinical paroxysmal nocturnal hemoglobinuria is the result of expansion of glycosyl-phosphatidyl-inositol-anchored protein-deficient clone in the condition of Deficient Hematopoiesis

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired, clonal hematopoietic stem cell disorder in which PIG-A, gene essential for the biosynthesis of the glycosyl-phosphatidyl-inositol (GPI) anchor, is somatically mutated. Absence of GPI-linked proteins from the surface of blood cells is characteristic of the PIG-A mutant (PNH) clone and is also accountable fo certain manifestations, such as intravascular hemolysis. It is unclear how the PNH clone expands and comes to dominate hematopoiesis. In this study, CD34+ cells--committed progenitors (colony-forming cells) representing immature hematopoietic stem cells--and reticulocytes representing the differentiated erythroid cells were quantitated in peripheral blood of patients with PNH. Compared with normal controls (n = 29), CD34+ cell levels were significantly lower in PNH patients who did not have preexisting aplastic anemia (AA) (n = 12) (2.47+/-1.23 versus 4.68+/-1.05 x 106/L, mean +/- standard error; P = .022). PNH patients with precedent aplastic anemia (AA+/PNH) showed markedly low CD34+ cell levels compared with normal control subjects (0.6+/-0.29 versus 4.68+/-1.05 x 10(6)/L; P = .0001). In addition, colony-forming cells from PNH patients were significantly decreased compared with those from normal volunteers (erythroid burst-forming units, 2.8+/-1.2 versu 25.6+/-6.2/5 x 10(5) mononuclear cells; P = .0006; and granulocyte/macrophage colony-forming units, 1.2+/-0.5 versus 13.3+/-3.0/ 5 x 10(5) mononuclear cells; P = .0006). These findings occur in both aplastic and hemolytic types of PNH, suggesting hematopoietic failure in PNH. On the contrary, the numbers of reticulocytes and the reticulocyte production index of PNH patients were significantly higher than those of normal persons and comparable to those from patients with autoimmune hemolytic anemia, indicating accelerating erythropoiesis in PNH. The degree of reticulocytosis correlated well with the proportion of CD59- (PNH) reticulocytes. All of the findings suggest that in the condition of deficient hematopoiesis, the PNH clone arising from the mutated hematopoietic stem cell expands and maintains a substantial proportion of the patient's hematopoiesis.