Increased sensitivity to complement of megakaryocyte progenitors in paroxysmal nocturnal haemoglobinuria

Efficacy and safety of eculizumab in children and adolescents with paroxysmal nocturnal hemoglobinuria

BACKGROUND

Paroxysmal nocturnal hemoglobinuria (PNH) is rare in children, but represents a similarly serious and chronic condition as in adults. Children with PNH frequently experience complications of chronic hemolysis, recurrent thrombosis, marrow failure, serious infections, abdominal pain, chronic fatigue, and decreased quality of life with reduced survival. The terminal complement inhibitor eculizumab is proven to be effective and safe in adults and approved by the FDA for treatment of PNH.

PROCEDURE

This 12-week, open-label, multi-center phase I/II study evaluated pharmacokinetics, pharmacodynamics, efficacy, and safety in seven children with PNH 11-17 years of age. Eculizumab was intravenously administered at 600 mg weekly for 4 weeks, 900 mg in week 5, and 900 mg every 2 weeks thereafter (http://clinicaltrials.gov NCT00867932).

RESULTS

Eculizumab therapy resulted in complete and sustained inhibition of hemolysis in all participants with a reduction of lactate dehydrogenase to normal levels. All hematological parameters stabilized. No definitive, study drug-related adverse events were observed. Only one severe SAE of hospitalization due to aplastic anemia occurred, which was not study drug-related.

CONCLUSION

Eculizumab appears to be a safe and effective therapy for children with PNH.

Thrombosis in paroxysmal nocturnal hemoglobinuria

The most frequent and feared complication of paroxysmal nocturnal hemoglobinuria (PNH) is thrombosis. Recent research has demonstrated that the complement and coagulation systems are closely integrated with each influencing the activity of the other to the extent that thrombin itself has recently been shown to activate the alternative pathway of complement. This may explain some of the complexity of the thrombosis in PNH. In this review, the recent changes in our understanding of the pathophysiology of thrombosis in PNH, as well as the treatment of thrombosis, will be discussed. Mechanisms explored include platelet activation, toxicity of free hemoglobin, nitric oxide depletion, absence of other glycosylphosphatidylinositol-linked proteins such as urokinase-type plasminogen activator receptor and endothelial dysfunction. Complement inhibition with eculizumab has a dramatic effect in PNH and has a major impact in the prevention of thrombosis as well as its management in this disease.

A new aspect of the molecular pathogenesis of paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal hematologic disorder which is manifest by complement-mediated hemolysis, venous thrombosis, and bone marrow failure. Complement-mediated hemolysis in PNH is explained by the deficiency of glycosylphosphatidylinositol (GPI)-anchored proteins, CD55 and CD59 on erythrocyte surfaces. All the PNH patients had phosphatidylinositol glycan-class A (PIG-A) gene abnormalities in various cell types, indicating that PIG-A gene mutations cause the defects in GPI-anchored proteins that are essential for the pathogenesis of PNH. In addition, a PIG-A gene abnormality results in a PNH clone. Bone marrow failure causes cytopenias associated with a proliferative decrease of its hematopoietic stem cells and appears to be related to a pre-leukemic state. Although it is unclear how a PNH clone expands in bone marrow, it is considered that the most important hypothesis implicates negative selection of a PNH clone, but it does not explain the changes in the clinical features at the terminal stage of PNH. Recently, it has been suggested that an immune mechanism, in an HLA-restricted manner, plays an important role in the occurrence or selection of a PNH clone and GPI may be a target for cytotoxic-T lymphocytes. Also, it has been indicated that the Wilms' tumor gene (WT1) product is related to a PNH clone, but the significance of WT1 expression is not clear because of the functional diversity of the gene. To elucidate this problem, it is important to know the pathophysiology of bone marrow failure in detail and how bone marrow failure affects hematopoietic stem cells and immune mechanisms in bone marrow failure syndromes.

Phenotypes and phosphatidylinositol glycan-class A gene abnormalities during cell differentiation and maturation from precursor cells to mature granulocytes in patients with paroxysmal nocturnal hemoglobinuria

To define the phosphatidylinositol glycan-class A (PIG-A) gene abnormality in precursor cells and the changes of expression of glycosylphosphatidylinositol-anchored protein and contribution of paroxysmal nocturnal hemoglobinuria (PNH) clones with PIG-A gene abnormalities among various cell lineages during differentiation and maturation, we investigated CD59 expression on bone marrow CD34(+) cells and peripheral granulocytes from 3 patients with PNH and the PIG-A gene abnormalities in the CD59(-), CD59(+/-), and CD59(+) populations by nucleotide sequence analyses. We also performed clonogeneic assays of CD34(+)CD59(+) and CD34(+)CD59(-) cells from 2 of the patients and examined the PIG-A gene abnormalities in the cultured cells. In case 1, the CD34(+) cells and granulocytes consisted of CD59(-) and CD59(+) populations and CD59(-), CD59(+/-), and CD59(+) populations, respectively. Sequence analyses indicated that mutation 1-2 was in the CD59(+/-) granulocyte population (20 of 20) and the CD34(+)CD59(-) population (2 of 38). In cases 2 and 3, the CD34(+) cells and granulocytes consisted of CD59(+) and CD59(-) cells. Sequence analyses in case 3 showed that mutation 3-2 was not in CD34(+)CD59(-) cells and was present in the CD59(-) granulocyte population. However, PIG-A gene analysis of cultured CD34(+)CD59(-) cells showed that they had the mutation. This analysis also revealed that there were some other mutations, which were not found in CD34(+)CD59(-) cells and CD59(-) or CD59(+/-) granulocytes in vivo, and that sometimes they were distributed specifically among different cell lineages. In conclusion, our findings suggest that PNH clones might contribute qualitatively and quantitatively differentially to specific blood cell lineages during differentiation and maturation of hematopoietic stem cells.

Granulocytes from patients with paroxysmal nocturnal hemoglobinuria and normal individuals have the same sensitivity to spontaneous apoptosis

OBJECTIVE

The aim of this study was to determine whether granulocytes from patients with paroxysmal nocturnal hemoglobinuria (PNH) are more or less intrinsically sensitive to spontaneous apoptosis than granulocytes from healthy individuals. Resistance to apoptosis has been suggested as an explanation for the proliferation or selection of PNH clones.

PATIENTS AND METHODS

Peripheral blood granulocytes from five patients with PNH, five patients with myelodysplastic syndrome (MDS), and five healthy volunteers were cultured in the absence of serum. Spontaneous apoptosis of the granulocytes was assessed every 6 hours by flow cytometry. The expression levels of CD16b, CD95, and granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor also were studied by flow cytometry, and caspase-3 activity was measured by fluorometry.

RESULTS

There were no significant differences in the proportion or absolute numbers of apoptotic and apoptotic/dead granulocytes between the cells from PNH patients and healthy individuals, whereas those from MDS patients showed significantly lower frequencies of apoptotic granulocytes compared with normal controls. The proportion of CD16b(-) granulocytes was not significantly different among the three groups during in vitro culture. CD95 and GM-CSF receptor was not significantly increased in cultured granulocytes or noncultured granulocytes from, respectively, patients with PNH and normal controls. Caspase-3 activity significantly decreased in cultured granulocytes from MDS patients, but not in granulocytes from PNH patients.

CONCLUSIONS

Granulocytes from PNH patients did not display a reduced sensitivity to spontaneous apoptosis, suggesting that the apoptosis of blood cells in PNH may not be an important factor in proliferation or selection of PNH clones. These findings are in agreement with the normal lifespan of granulocytes in vivo.

In vitro proliferation and differentiation of megakaryocytic progenitors in patients with aplastic anemia, paroxysmal nocturnal hemoglobinuria, and the myelodysplastic syndromes

It has previously been shown that patients with aplastic anemia (AA) have a stem cell defect both of proliferation and differentiation. This has been shown by long-term bone marrow (BM) culture, long-term initiating cell assays, and committed progenitor assays. We present, for the first time, data on megakaryocyte (Mk) colony formation from purified BM CD34(+) cells from patients with AA. The results are compared with those from normal controls and from patients with paroxysmal nocturnal hemoglobinuria (PNH) and the myelodysplastic syndromes (MDSs). Those treated for AA had previously received immunosuppression (antithymocyte globulin and/or cyclosporin). No patients had received bone marrow transplantation. A total of 13 AA patients (five untreated, eight treated), six PNH, six MDS, and 13 normal donors were studied. BM CD34(+) cells were purified by indirect labeling and then cultured in a collagen-based Mk assay kit (MegaCult-C, StemCell Technologies). The cultures were fixed on day 12, and the Mk colonies were identified by the alkaline phosphatase anti-alkaline phosphatase technique using the monoclonal antibody CD41 (GP IIb/IIIa). The slides were scored for Mk colony-forming units (CFU-Mks) (3-20 and >20 cells), Mk burst-forming units (BFU-Mks) (>50 cells), and mixed colonies. The results show that total Mk colony formation in AA was significantly lower than in normal donors (p<0.0001), both in untreated patients/nonresponders to treatment (p = 0.0001) and in complete/partial responders (p<0.002). There was no significant difference in Mk colony formation in treated and untreated patients (p = 0.05). Patients with AA had a lower total colony formation than PNH patients (p = 0.0002). PNH patients exhibited lower colony formation than normal controls (p = 0.03), as shown by MDS patients, although the considerable number of variables resulted in a lack of statistically significant difference from normal controls (p = 0.2). We have now shown that Mk colony formation from purified BM CD34(+) cells is significantly reduced, supporting previous evidence that AA results from a stem cell defect.

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.

Hematopoietic progenitor cells in the blood and bone marrow in various hematologic disorders

Hematopoietic progenitor cells are present in the blood and the bone marrow. Changes in the numbers of hematopoietic progenitor cells reflect alteration of pluripotent stem cells. We discuss such changes in common hematologic diseases including aplastic anemia, paroxysmal nocturnal hemoglobinuria (PNH) and thalassemia. In aplastic anemia, the numbers of burst forming units-erythroid (BFU-E) and colony-forming units-granulocyte-macrophage (CFU-GM) are much decreased; the decrease still exists after recovery from therapy. In PNH, the numbers of progenitor cells are low, even in the presence of marrow hypercellularity. In thalassemia, the numbers of progenitor cells are much increased; more pronounced in splenectomized patients.

Relationship Between the Phenotypes of Circulating Erythrocytes and Cultured Erythroblasts in Paroxysmal Nocturnal Hemoglobinuria

To investigate erythropoiesis in paroxysmal nocturnal hemoglobinuria (PNH), we studied the expression of glycosylphosphatidylinositol (GPI)-anchored membrane proteins on circulating erythrocytes and erythroblasts obtained by erythropoietic cell culture in nine patients with this disease. One-color and two-color flow cytometric analyses were performed using monoclonal antibodies for decay-accelerating factor (DAF ) and/or CD59/membrane attack complex-inhibitory factor (MACIF). In addition, terminal deoxynucleotidyl transferase–mediated dUTP-biotin nick end-labeling (TUNEL) analysis was performed to assess apoptosis of erythroblasts from six patients. On flow cytometric analysis, cases 1 to 6 had positive and negative erythrocyte populations, case 7 intermediate and negative populations, case 8 positive, intermediate, and negative populations, and case 9 a single double-negative population. In addition, cases 1 to 6 and 8 had positive, intermediate, and negative erythroblast populations, while cases 7 and 9 had intermediate and negative populations. The percentage of double-negative erythrocytes showed a significant correlation with that of double-negative erythroblasts (r = .741, P < .05). In seven of nine patients, more erythroblasts than erythrocytes were negative for the two membrane proteins. Also, some patients with an intermediate population of erythrocytes did not necessarily show an increase of PNH II erythroblasts. Apoptosis of PNH erythroblasts was also detected, but the percentage of apoptotic cells in PNH patients showed no difference from that in healthy volunteers. These findings suggest that the final phenotype of mature erythrocytes in PNH is determined during maturation from erythroblasts to erythrocytes by the disappearance or persistence of PNH II erythroblasts. In addition, PNH erythroblasts in vitro may be partly lost by apoptosis, but apoptosis does not play an important role in determining GPI-linked protein expression.

Relationship Between the Phenotypes of Circulating Erythrocytes and Cultured Erythroblasts in Paroxysmal Nocturnal Hemoglobinuria

To investigate erythropoiesis in paroxysmal nocturnal hemoglobinuria (PNH), we studied the expression of glycosylphosphatidylinositol (GPI)-anchored membrane proteins on circulating erythrocytes and erythroblasts obtained by erythropoietic cell culture in nine patients with this disease. One-color and two-color flow cytometric analyses were performed using monoclonal antibodies for decay-accelerating factor (DAF ) and/or CD59/membrane attack complex-inhibitory factor (MACIF). In addition, terminal deoxynucleotidyl transferase–mediated dUTP-biotin nick end-labeling (TUNEL) analysis was performed to assess apoptosis of erythroblasts from six patients. On flow cytometric analysis, cases 1 to 6 had positive and negative erythrocyte populations, case 7 intermediate and negative populations, case 8 positive, intermediate, and negative populations, and case 9 a single double-negative population. In addition, cases 1 to 6 and 8 had positive, intermediate, and negative erythroblast populations, while cases 7 and 9 had intermediate and negative populations. The percentage of double-negative erythrocytes showed a significant correlation with that of double-negative erythroblasts (r = .741, P &lt; .05). In seven of nine patients, more erythroblasts than erythrocytes were negative for the two membrane proteins. Also, some patients with an intermediate population of erythrocytes did not necessarily show an increase of PNH II erythroblasts. Apoptosis of PNH erythroblasts was also detected, but the percentage of apoptotic cells in PNH patients showed no difference from that in healthy volunteers. These findings suggest that the final phenotype of mature erythrocytes in PNH is determined during maturation from erythroblasts to erythrocytes by the disappearance or persistence of PNH II erythroblasts. In addition, PNH erythroblasts in vitro may be partly lost by apoptosis, but apoptosis does not play an important role in determining GPI-linked protein expression.

Impaired Hematopoiesis in Paroxysmal Nocturnal Hemoglobinuria/Aplastic Anemia Is Not Associated With a Selective Proliferative Defect in the Glycosylphosphatidylinositol-Anchored Protein-Deficient Clone

Paroxysmal nocturnal hemoglobinuria (PNH) results from somatic mutations in the PIG-A gene, leading to poor presentation of glycosylphosphatidylinositol (GPI)-anchored surface proteins. PNH frequently occurs in association with suppressed hematopoiesis, including frank aplastic anemia (AA). The relationship between GPI-anchored protein expression and bone marrow (BM) failure is unknown. To assess the hematopoietic defect in PNH, the numbers of CD34+ cells, committed progenitors (primary colony-forming cells [CFCs]), and long-term culture-initiating cells (LTC-ICs; a stem cell surrogate) were measured in BM and peripheral blood (PB) of patients with PNH/AA syndrome or patients with predominantly hemolytic PNH. LTC-IC numbers were extrapolated from secondary CFC numbers after 5 weeks of culture, and clonogenicity of LTC-ICs was determined by limiting dilution assays. When compared with normal volunteers (n = 13), PNH patients (n = 14) showed a 4.7-fold decrease in CD34+ cells and an 8.2-fold decrease in CFCs. LTC-ICs in BM and in PB were decreased 7.3-fold and 50-fold, respectively. Purified CD34+ cells from PNH patients had markedly lower clonogenicity in both primary colony cultures and in the LTC-IC assays. As expected, GPI-anchored proteins were decreased on PB cells of PNH patients. On average, 23% of monocytes were deficient in CD14, and 47% of granulocytes and 58% of platelets lacked CD16 and CD55, respectively. In PNH BM, 27% of CD34+ cells showed abnormal GPI-anchored protein expression when assessed by CD59 expression. To directly measure the colony-forming ability of GPI-anchored protein-deficient CD34+ cells, we separated CD34+ cells from PNH patients for the GPI+ and GPI− phenotype; CD59 expression was chosen as a marker of the PNH phenotype based on high and homogeneous expression on fluorescent staining. CD34+CD59+ and CD34+CD59− cells from PNH/AA patients showed similarly impaired primary and secondary clonogeneic efficiency. The progeny derived from CD34+CD59− cells were both CD59− and CD55−. A very small population of CD34+CD59− cells was also detected in some normal volunteers; after sorting, these CD34+CD59− cells formed normal numbers of colonies, but their progeny showed lower CD59 levels. Our results are consistent with the existence of PIG-A–deficient clones in some normal individuals. In PNH/AA, progenitor and stem cells are decreased in number and function, but the proliferation in vitro is affected similarly in GPI-protein–deficient clones and in phenotypically normal cells. As measured in the in vitro assays, expansion of PIG-A– clones appears not be caused by an intrinsic growth advantage of cells with the PNH phenotype.

Megakaryocyte progenitors in paroxysmal nocturnal haemoglobinuria are sensitive to complement

We have investigated growth in vitro of bone marrow megakaryocytic progenitors (CFU-Mk) in 7 patients with paroxysmal nocturnal haemoglobinuria (PNH) to determine the sensitivity of CFU-Mk to complement. Bone marrow light density mononuclear cells were exposed to fresh or heat-inactivated AB human serum in the presence of medium or isotonic sucrose solution. We found that the proliferative activity of bone marrow CFU-Mk in PNH patients was significantly lower than in controls. In addition, the number of CFU-Mk in PNH bone marrow cells exposed to isotonic sucrose and complement was reduced to 25% of that in PNH cells exposed to isotonic sucrose without complement. In conclusion, our finding showed an increased sensitivity of CFU-Mk in PNH bone marrow cells to complement, supporting the hypothesis that the PNH defect is present at the level of CFU-Mk.

Trisomy 8 detection in granulomonocytic, erythrocytic and megakaryocytic lineages by chromosomal in situ suppression hybridization in a case of refractory anaemia with ringed sideroblasts complicating the course of paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) was diagnosed in a 20-year-old male patient who suffered from anaemia since the age of 11. Eighteen years after diagnosis, PNH transformed into refractory anaemia with ringed sideroblasts (RARS). Trisomy 8 was observed in 27%, 45% and 53% of the bone marrow metaphase cells analysed in 1987, 1988 and 1990 respectively. In order to determine which bone marrow cell lineages were affected by trisomy 8 and at which stage of stem cell differentiation, MAC (Morphology, Antibody, Chromosomes) and CISS (Chromosomal In Situ Suppression) hybridization techniques were combined. The MAC technique enables karyotypic analysis of morphologically and immunologically classified mitotic cells. CISS hybridization makes it possible to detect individual chromosomes and chromosome aberrations using recombinant DNA libraries from sorted human chromosomes. Trisomy 8 was detected in granulomonocytic (50.6%), erythrocytic (67.2%) and megakaryocytic (one megakaryocyte with trisomy 8, one normal) lineages, providing evidence for the occurrence of trisomy 8 in early haematopoietic cell precursors, at the GEMM or pluripotent level. Cytogenetic and clinical data suggest that the sideroblastic clone originated from a mutation affecting a cell of the PNH clone, progressively replaced by the PNH/RARS clone, due to proliferative advantage.