Presentation clinical, haematological and immunophenotypic features of 1081 patients with GPI-deficient (paroxysmal nocturnal haemoglobinuria) cells detected by flow cytometry.

A retrospective analysis of presentation clinical, laboratory and immunophenotypic features of 1 081 patients with paroxysmal nocturnal haemoglobinuria (PNH) clones [glycosylphosphatidylinositol (GPI)-deficient blood cells] identified at our hospital by flow cytometry over the past 25 years was undertaken. Three distinct clusters of patients were identified and significant correlations between presentation disease type and PNH clone sizes were evident. Smaller PNH clones predominate in cytopenic and myelodysplastic subtypes; large PNH clones were associated with haemolytic, thrombotic and haemolytic/thrombotic subtypes. Rare cases with an associated chronic myeloproliferative disorder had either large or small PNH clones. Cytopenia was a frequent finding, highlighting bone marrow failure as the major underlying feature associated with the detection of PNH clones in the peripheral blood. Red cell PNH clones showed significant correlations between the presence of type II (partial GPI deficiency) red cells and thrombotic disease. Haemolytic PNH was associated with type III (complete GPI deficiency) red cell populations of >20%. Those with both haemolytic and thrombotic features had major type II and type III red cell populations. Distinct patterns of presentation age decade were evident for clinical subtypes with a peak incidence of haemolytic PNH in the 30-49 year age group and a biphasic age distribution for the cytopenia group.

Eculizumab prevents intravascular hemolysis in patients with paroxysmal nocturnal hemoglobinuria and unmasks low-level extravascular hemolysis occurring through C3 opsonization.

BACKGROUND: Paroxysmal nocturnal hemoglobinuria is an acquired hemolytic anemia characterized by intravascular hemolysis which has been demonstrated to be effectively controlled with eculizumab. However, lactate dehydrogenase levels remain slightly elevated and haptoglobin levels remain low in some patients suggesting residual low-level hemolysis. This may be due to C3-mediated clearance of paroxysmal nocturnal hemoglobinuria red blood cells through the reticuloendothelial system. DESIGN AND METHODS: Thirty-nine samples from patients not treated with eculizumab and 31 samples from patients treated with eculizumab were obtained (for 17 of these 31 samples there were also samples taken prior to eculizumab treatment). Membrane bound complement was assessed by flow cytometry. Direct antiglobulin testing was carried out using two methods. Lactate dehydrogenase was assayed to assess the degree of hemolysis. RESULTS: Three of 39 patients (8%) with paroxysmal nocturnal hemoglobinuria not on eculizumab had a positive direct antiglobulin test, while the test was positive in 21 of 31 (68%) during eculizumab treatment. Of these 21 patients who had a positive direct antiglobulin test during eculizumab treatment, 17 had been tested prior to treatment; only one was positive. Flow cytometry using anti-C3 monoclonal antibodies was performed on the 21 direct antiglobulin test-positive, eculizumab-treated patients; the median proportion of C3-positive total red blood cells was 26%. Among the eculizumab-treated patients, 16 of the 21 (76.2%) with a positive direct antiglobulin test received at least one transfusion compared with one of ten (10.0%) of those with a negative test (P<0.01). Among the eculizumab-treated patients, the mean hemoglobin value for the 21 with a positive direct antiglobulin test was 9.6+/-0.3 g/dL, whereas that in the ten patients with a negative test was 11.0+/-0.4 g/dL (P=0.02). CONCLUSIONS: These data demonstrate a previously masked mechanism of red cell clearance in paroxysmal nocturnal hemoglobinuria and suggests that blockade of complement at C5 allows C3 fragment accumulation on some paroxysmal nocturnal hemoglobinuria red cells, explaining the residual low-level hemolysis occurring in some eculizumab-treated patients.

Development and evaluation of a stabilized whole-blood preparation as a process control material for screening of paroxysmal nocturnal hemoglobinuria by flow cytometry.

BACKGROUND: Paroxysmal nocturnal hemoglobinuria (PNH) is a rare disorder in which correct diagnosis is essential for effective patient management. Demonstration of deficiency of glycosylphosphatidylinositol (GPI)-linked antigens from red cells and/or granulocytes by flow cytometry represents a highly specific diagnostic test for PNH. Currently, no external quality assessment (EQA) programme or reference material is available for whole-blood PNH testing (red cells and leucocytes) by flow cytometry. METHODS: In order to address this issue, we report the development of a stabilized whole-blood PNH sample. We present the results of a detailed time course study by flow cytometry that demonstrates the stability of GPI-linked antigen expression on granulocytes and red cells in a stabilized PNH peripheral blood sample, using a previously described method. RESULTS: The PNH cells, as well as the coexisting normal red cell and granulocyte populations, remained stable for up to 120 days, both in terms of immunophenotypic and light scatter characteristics. Subsequent samples were used for a PNH EQA programme and issued to 92 laboratories worldwide. CONCLUSIONS: This study has highlighted that PNH testing by flow cytometry has significant problems with regard to false-positive and -negative results. In addition, the variation in GPI-linked antigen detection methods has highlighted the urgent need for standardized protocols.

Protection of erythrocytes from human complement-mediated lysis by membrane-targeted recombinant soluble CD59: a new approach to PNH therapy.

Paroxysmal nocturnal hemoglobinuria (PNH) results from the expansion of a hematopoietic clone that is deficient in glycosylphosphatidylinositol-anchored molecules. PNH is characterized by chronic hemolysis with acute exacerbations due to the uncontrolled activity of complement on PNH cells, which lack the inhibitor of homologous complement, CD59. Symptoms include severe fatigue, hemoglobinuria, esophageal spasm, erectile dysfunction, and thrombosis. We report the use of a novel synthetically modified recombinant human CD59, rhCD59-P, a soluble protein that attaches to cell membranes. In vitro treatment of PNH erythrocytes with rhCD59-P resulted in levels of CD59 equivalent to normal erythrocytes and effectively protected erythrocytes from complement-mediated hemolysis. The administration of rhCD59-P to CD1 mice resulted in levels of CD59 on erythrocytes, which protected them from complement-mediated lysis. Thus, rhCD59-P corrects the CD59 deficiency in vitro and can bind to erythrocytes in an in vivo murine model, protecting the cells from the activity of human complement, and represents a potential therapeutic strategy in PNH.

Effect of eculizumab on hemolysis and transfusion requirements in patients with paroxysmal nocturnal hemoglobinuria.

BACKGROUND: Paroxysmal nocturnal hemoglobinuria (PNH) arises from a somatic mutation of the PIG-A gene in a hematopoietic stem cell and the subsequent production of blood cells with a deficiency of surface proteins that protect the cells against attack by the complement system. We tested the clinical efficacy of eculizumab, a humanized antibody that inhibits the activation of terminal complement components, in patients with PNH. METHODS: Eleven transfusion-dependent patients with PNH received infusions of eculizumab (600 mg) every week for four weeks, followed one week later by a 900-mg dose and then by 900 mg every other week through week 12. Clinical and biochemical indicators of hemolysis were measured throughout the trial. RESULTS: Mean lactate dehydrogenase levels decreased from 3111 IU per liter before treatment to 594 IU per liter during treatment (P=0.002). The mean percentage of PNH type III erythrocytes increased from 36.7 percent of the total erythrocyte population to 59.2 percent (P=0.005). The mean and median transfusion rates decreased from 2.1 and 1.8 units per patient per month to 0.6 and 0.0 units per patient per month, respectively (P=0.003 for the comparison of the median rates). Episodes of hemoglobinuria were reduced by 96 percent (P<0.001), and measurements of the quality of life improved significantly. CONCLUSIONS: Eculizumab is safe and well tolerated in patients with PNH. This antibody against terminal complement protein C5 reduces intravascular hemolysis, hemoglobinuria, and the need for transfusion, with an associated improvement in the quality of life in patients with PNH.

Development and progression of a Philadelphia-chromosome-negative acute myelocytic leukemia clone in a patient with Philadelphia-chromosome-positive chronic myelocytic leukemia.

We report a patient with typical Philadelphia-chromosome-positive chronic myelocytic leukemia who developed Philadelphia-chromosome-negative acute myelocytic leukemia following autologous stem cell transplantation. The implications of this observation for disease monitoring and treatment are discussed.

Early prediction of outcome and response to alemtuzumab therapy in chronic lymphocytic leukemia.

Alemtuzumab therapy is effective for some refractory chronic lymphocytic leukemia (CLL), but identifying responders requires at least 8 weeks of therapy. Early identification of nonresponders would minimize toxicity and/or facilitate more effective strategies. The aim of this study was to identify a minimally invasive method for early prediction of response and relapse. Flow cytometric monitoring was performed in 887 blood samples and 201 marrow samples from 43 patients undergoing intravenous alemtuzumab therapy. Although the absolute lymphocytosis was resolved in all patients by week 4, significant depletion of bone marrow tumor only occurred if circulating B-lymphocyte counts were persistently less than 0.001 x 10(9)/L, which was rare in nonresponders. The majority of patients (16/28) who did not benefit from a full course of therapy were identified with 100% positive predictive value using the following algorithm: peripheral B-cell count greater than 0.001 x 10(9)/L at week 2 with less than 1 log depletion of circulating B cells between weeks 2 and 4. Monitoring CLL levels after treatment identified patients at risk of early disease progression and could potentially improve patient management. During alemtuzumab therapy, bone marrow CLL depletion only occurs after abrogation of circulating tumor, requiring close monitoring of circulating B-cell levels. If validated in prospective studies, blood monitoring at 2 and 4 weeks may be used to optimize therapy.