Assessment of bone marrow stem cell reserve and function and stromal cell function in patients with autoimmune cytopenias

To investigate whether bone marrow (BM) stem cell compartment and/or BM microenvironment are affected by the immune insult in autoimmune cytopenias (AICs), BM stem cell reserve and function and BM stromal function were studied in 15 AIC patients. Stem cells were evaluated by means of flow cytometry, clonogenic progenitor cell assays, long-term BM cultures (LTBMCs), and limiting dilution assay for quantification of long-term-culture initiating cells (LTC-ICs). Stromal cell function was assessed with the use of preformed irradiated LTBMCs from patients and normal controls, recharged with normal CD34(+) cells. AIC patients exhibited a high number of CD34(+), CD34(+)/CD38(+), and CD34(+)/CD38(-) cells; high frequency of granulocyte-macrophage colony forming units in the BM mononuclear cell fraction; high colony recovery in LTBMCs; and normal LTC-IC frequency. Patient BM stromal layers displayed normal hematopoietic-supporting capacity and increased production of granulocyte-colony stimulating factor. Data from this study support the concept that AIC patients with severe, resistant disease might be appropriate candidates for autologous stem cell transplantation.

T-cell depletion of bone marrow transplants for leukemia from donors other than HLA-identical siblings: advantage of T-cell antibodies with narrow specificities

T-cell depletion of donor marrow decreases graft-versus-host disease resulting from transplants from unrelated and human leukocyte antigen (HLA)-mismatched related donors. However, there are diverse strategies for T-cell-depleted transplantation, and it is uncertain whether any improve leukemia-free survival (LFS). To compare strategies for T-cell-depleted alternative donor transplants and to compare T-cell depleted with non-T-cell-depleted transplants, we studied 870 patients with leukemia who received T-cell-depleted transplants from unrelated or HLA-mismatched related donors from 1982 to 1994. Outcomes were compared with those of 998 non-T-cell-depleted transplants. We compared LFS using different strategies for T-cell-depleted transplantation considering T-cell depletion technique, intensity of pretransplant conditioning, and posttransplant immune suppression using proportional hazards regression to adjust for other prognostic variables. Five categories of T-cell depletion techniques were considered: narrow-specificity antibodies, broad-specificity antibodies, Campath antibodies, elutriation, and lectins. Strategies resulting in similar LFS were pooled to compare T-cell-depleted with non-T-cell-depleted transplants. Recipients of transplants T-cell depleted by narrow-specificity antibodies had lower treatment failure risk (higher LFS) than recipients of transplants T-cell depleted by other techniques. Compared with non-T-cell-depleted transplants (5-year probability +/- 95% confidence interval [CI] of LFS, 31% +/- 4%), 5-year LFS was 29% +/- 5% (P = NS) after transplants T-cell depleted by narrow-specificity antibodies and 16% +/- 4% (P <.0001) after transplants T-cell depleted by other techniques. After alternative donor transplantation, T-cell depletion of donor marrow by narrow-specificity antibodies resulted in LFS rates that were higher than those for transplants T-cell depleted using other techniques but similar to those for non-T-cell-depleted transplants. (Blood. 2000;95:3996-4003)

Clonal patterns of X-chromosome inactivation in female patients with aplastic anaemia studies using a novel reverse transcription polymerase chain reaction method

Conflicting results have been published on the frequency of clonal patterns of X-chromosome inactivation in female patients with aplastic anaemia. Previous studies have used DNA methylation to measure X-inactivation, but aberrant methylation is known to occur in some situations. We have developed a non-radioactive reverse transcription polymerase chain reaction (RT-PCR) method to study expression of the polymorphism at nt. 1311 of the G6PD gene at the RNA level. Using this, and a similar method for the iduronate-2-sulfatase (IDS) gene, we have re-evaluated X-inactivation in AA patients. 32/35 normal individuals showed polyclonal haemopoiesis. Patients with presumed clonal diseases showed both monoclonal and polyclonal patterns, consistent with previous reports. Overall, clonal patterns were observed in granulocytes of 10/26 AA patients (38%), a significantly higher proportion than in controls (p<0.01). Two cases showed discordance between lymphocytes and granulocytes, indicating clonality arising within the myeloid lineage. Eight cases showed clonal patterns in both myeloid and lymphoid cells, indicating the involvement of a pluripotent stem cell. Clonal patterns did not correlate with age, but there appeared to be an association with duration of disease. In PNH patients, CD59-negative cells showed clonal patterns of X-inactivation. In two cases, however, clonal patterns were also detected in CD59-positive cells.

Effects of antithymocyte globulin on bone marrow CD34+ cells in aplastic anaemia and myelodysplasia

The mechanism of action of antithymocyte globulin (ATG) in the treatment of aplastic anaemia (AA) and myelodysplastic syndromes (MDS) is poorly understood and may involve many different mechanisms. The aim of this in vitro study was to investigate further the effect of ATG on haemopoietic progenitor cells. A total of 16 patients (10 AA and 6 MDS) and 12 normal control subjects were studied. Purified bone marrow (BM) CD34+ cells were cultured in committed progenitor assay in the presence of ATG and autologous serum, then scored on day 14 for granulocyte-monocyte colony-forming units (CFU-GM) and erythroid colonies. ATG was found to be inhibitory to haemopoietic progenitor cells at high concentrations (1000 microg/ml and 100 microg/ml). This was confirmed by CD34-FITC and 7AAD staining of purified normal CD34+ cells after overnight incubation with ATG. In contrast, at lower doses (0.1-10 microg/ml), ATG produced an increase in colony growth in most normal, MDS and AA BM CD34+ cells. The greatest effect was in patients with non-severe AA, in whom the greatest increase in CFU-GM was seen at 0.5 microg/ml (P < 0.02) and 0.1 microg/ml (P = 0.02) and erythroid colonies at 0.1 microg/ml (P < 0.05). Serum ATG levels peaked during infusion to levels that were found to be toxic to haemopoietic progenitor cells in vitro and fell thereafter to levels that were associated with the highest colony numbers (0.1 and 0.5 microg/ml) in vitro. These results suggest that an increase in haemopoietic progenitor cells by ATG may be one of several important mechanisms for haematological recovery in AA and MDS.

N-RAS gene mutation in patients with aplastic anemia and aplastic anemia/ paroxysmal nocturnal hemoglobinuria during evolution to clonal disease

Long-term survivors of aplastic anemia (AA) have a high incidence of clonal disorders, in particular paroxysmal nocturnal hemoglobinuria (PNH), myelodysplastic syndromes (MDS), and acute nonlymphocytic leukemia. To investigate the potential involvement of N-RAS gene mutations in the predisposition to leukemic evolution, a subset of patients at potentially increased risk for clonal disease was selected based on evidence of existing clonal evolution. Nine patients showed a monoclonal pattern of X-chromosome inactivation, 18 demonstrated a PNH clone, and in 3 MDS developed during the course of this study. No mutations were detected during the aplastic phase of disease; 2 of 3 patients with MDS after AA also showed no mutations. However, in 1 patient in whom the disease transformed from AA/PNH to MDS, a mutation of GGT --> GAT at N-RAS codon 13 became detectable, whereas the PNH mutation disappeared. The authors conclude that N-RAS mutations are not an early event preceding transformation of AA or AA/PNH to leukemia. In a subset of patients, RAS mutations may occur at the time of evolution to MDS, but preexisting RAS mutations do not explain the propensity of AA to leukemogenesis. Although PNH is also associated with leukemia, this may arise in the non-PNH cells, indicating that PIG-A gene mutation is not per se oncogenic. (Blood. 2000;95:646-650)

Reduced TGF-beta1 in patients with aplastic anaemia in vivo and in vitro

Transforming growth factor beta (TGF-beta) 1 is a ubiquitous bifunctional cytokine implicated in the regulation of haemopoietic stem cells and bone marrow stromal cells. We analysed sera from 63 patients with aplastic anaemia and describe a significant reduction of TGF-beta1 that was directly related to their treatment status. Untreated patients (n = 35), patients who did not respond (n = 15) and those with a partial response (n = 23) to treatment had significantly lower TGF-beta1 than the normal control group (n = 55), P < 0.0001, P < 0.0001 and P = 0.002 respectively. Patients in complete remission (n = 15) exhibited TGF-beta1 serum levels comparable to the control group. In addition, there was a correlation (r = 0.83, P < 0.0001) between serum TGF-beta1 and platelet count at time of sample. We have demonstrated that the primary source of TGF-beta1 in peripheral blood mononuclear cell (PBMC) cultures was not CD3-positive cells. These data indicate aplastic anaemia is associated with a decreased TGF-beta1 expression in peripheral blood circulation, which may be a direct consequence of thrombocytopenia. In vitro stromal layers grown from aplastic patient bone marrow (n = 14) produced significantly lower levels of TGF-beta1 (P = 0.02) when compared to normal stroma (n = 15). In the aplastic anaemia bone marrow compartment we postulate that accessory cells down-regulate TGF-beta1 expression to allow stem cell cycling to counteract hypoplasia. As TGF-beta1 is important in the regulation of haemopoiesis, dysregulation of this cytokine in combination with previously described abnormal cytokine expression may contribute significantly to the pathophysiology of aplastic anaemia by exacerbating primary stem cell defects.

Epstein-Barr virus (EBV) associated B-cell lymphoproliferative disease following HLA identical sibling marrow transplantation for aplastic anaemia in a patient with an EBV seronegative donor

BACKGROUND

B-cell lymphoproliferative disorders (BLPD*) caused by Epstein-Barr virus (EBV) occurring after allogeneic bone marrow transplantation (BMT) are usually of donor origin. Treatment such as discontinuation of immunosuppression may be successful in some cases, but infusion of donor T cells results in successful eradication of EBV BLPD in most cases.

METHODS AND RESULTS

We report a case of EBV positive aggressive BLPD after HLA matched sibling BMT for aplastic anaemia. The tumour completely regressed after withdrawal of cyclosporin and donor lymphocyte infusion. However, although the tumor was of donor origin, the donor serum was negative for antibodies to EBV antigens and no EBV-specific cytotoxicity was detected in donor peripheral blood mononuclear cells. The recipient was seropositive for EBV before BMT.

CONCLUSIONS

We speculate that a 'second primary' EBV infection occurred involving donor cells in the recipient during BMT immunosuppression, with subsequent outgrowth of donor-derived BLPD. EBV infection may have been by an endogenous EBV isolate, from external sources, or from third party transfusions.

Clonal evolution of aplastic anaemia to myelodysplasia/acute myeloid leukaemia and paroxysmal nocturnal haemoglobinuria

Aplastic anaemia (AA) is a non-malignant haemopoietic disorder characterised by peripheral blood pancytopenia and a hypocellular bone marrow. Successful management of acquired AA including treatment with immunosuppressive agents, mainly antithymocyte globulin (ATG) and cyclosporin or allogeneic haemopoietic stem cell transplantation, has resulted in long-term survival of many patients. The later evolution of complicating clonal disorders such as paroxysmal nocturnal haemoglobinuria, myelodysplasia and acute myeloid leukaemia in patients treated with immunosuppressive therapy may be a manifestation of the natural history of the aplasia, the development of which may or may not be increased by immunosuppressive therapy. A persistent, profound deficiency and/or defect in the stem cell compartment, despite haematological recovery after immunosuppressive therapy, may create an unstable situation which predisposes to later clonal disorders. A review of the progression of AA to clonal disorders is now outlined.

Study of the association between cytochromes P450 2D6 and 2E1 genotypes and the risk of drug and chemical induced idiosyncratic aplastic anaemia

A genetic susceptibility to drug or chemical toxicity may provide a basis for an increased risk of idiosyncratic aplastic anaemia (AA). The cytochrome P450 enzymes are responsible for the metabolism of many drugs, some of which have been linked to AA. Mutations in the cytochrome P450 CYP2D6 gene result in absent or impaired enzyme activity in about 7% of Caucasians, whereas a specific mutation in the 5'-regulatory region of the CYP2E1 gene causes overexpression of the gene. We evaluated the frequency of allelic variants of CYP2D6 and CYP2E1 using allele-specific PCR amplification and restriction enzyme analysis of blood mononuclear cell DNA among 54 Caucasian AA patients. CYP2D6 and CYP2E1 were chosen because of the link between AA and the antipsychotic drug remoxipride (CYP2D6 substrate) and benzene (CYP2E1 substrate), respectively. Results were compared with 53 controls matched for age, sex and ethnicity. The percentage of AA patients homozygous for the CYP2D6*3, CYP2D6*4 alleles (poor metabolizer phenotype) and the CYP2E1 mutant allele (overexpression) was 0%, 4% and 0%, respectively, and the percentage of heterozygotes was 2%, 28% and 15%, respectively. For normal controls the corresponding results for homozygous mutants were 0%, 4% and 0% and for heterozygotes 4%, 25% and 6%, respectively. We concluded that there were no major differences in the frequencies of the genetic polymorphisms between this series of AA patients and controls, but due to the low number of cases with the poor metabolizer phenotype and those with a history of drug exposure, the power of the study was too low to disprove an interaction.

Bone marrow transplants for paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) is a rare clonal haematological disorder characterized by intravascular haemolysis and increased risk of thrombosis. PNH is associated with bone marrow failure syndromes including aplastic anaemia, myelodysplasia and leukaemia. Bone marrow transplants are sometimes used to treat PNH, but small series and reporting biases make assessment of transplant outcome difficult. The outcome of 57 consecutive allogeneic bone marrow transplants for PNH reported to the International Bone Marrow Transplant Registry (IBMTR) between 1978 and 1995 was analysed. The 2-year probability of survival in 48 recipients of HLA-identical sibling transplants was 56% (95% confidence interval 49-63%). Two recipients of identical twin transplants remain alive 8 and 12 years after treatment. One of seven recipients of alternative donor allogeneic transplants is alive 5 years after transplant. The most common causes of treatment failure were graft failure and infections. Our results indicate that bone marrow transplantation can restore normal bone marrow function in about 50% of PNH patients.

Abnormal cytogenetic clones in patients with aplastic anaemia: response to immunosuppressive therapy

We report the response to immunosuppressive therapy with antithymocyte globulin (ATG) and cyclosporin or oxymetholone in 13 cases of aplastic anaemia (AA) with an abnormal cytogenetic clone detected at or sometime after diagnosis. Blood and bone marrow examination showed no distinctive morphological features of myelodysplasia (MDS) at diagnosis. Haematological response occurred promptly in eight cases; the remainder responded after additional immunosuppression with or without oxymetholone. Three patients had a late relapse of AA, treated successfully by allogeneic bone marrow transplantation in one; the others responded to oxymetholone. Transformation to MDS or acute leukaemia was not observed after a median follow-up of 4.1 years (range 1.2-11.2). In four patients the cytogenetic clone disappeared after treatment.

The incidence and significance of fevers during treatment with antithymocyte globulin for aplastic anaemia

Antithymocyte globulin (ATG) is a foreign protein used widely to treat aplastic anaemia (AA). Febrile reactions occurring during its administration may be impossible to distinguish clinically from fever due to sepsis, and are therefore routinely treated with intravenous antibiotics after collection of blood cultures. A statistically highly significant difference was found in positive blood cultures between 39 AA patients who developed fever during ATG therapy, and 38 febrile neutropenic patients with acute leukaemia. suggesting that most fevers developing during ATG treatment are not due to infection. It may therefore be reasonable to consider early discontinuation of intravenous antibiotics in patients who are clinically stable and have no proven sepsis.

Progressive telomere shortening in aplastic anemia

Improved survival in aplastic anemia (AA) has shown a high incidence of late clonal marrow disorders. To investigate whether accelerated senescence of hematopoietic stem cells might underlie the pathophysiology of myelodysplasia (MDS) or paroxysmal nocturnal hemoglobinuria (PNH) occurring as a late complication of AA, we studied mean telomere length (TRF) in peripheral blood leukocytes from 79 patients with AA, Fanconi anemia, or PNH in comparison with normal controls. TRF lengths in the patient group were significantly shorter for age than normals (P < .0001). Telomere shortening was apparent in both granulocyte and mononuclear cell fractions, suggesting loss at the level of the hematopoietic stem cell. In patients with acquired AA with persistent cytopenias (n = 40), there was significant correlation between telomere loss and disease duration (r = -.685; P < .0001), equivalent to progressive telomere erosion at 216 bp/yr, in addition to the normal age-related loss. In patients who had achieved normal full blood counts (n = 20), the rate of telomere loss had apparently stabilised. There was no apparent association between telomere loss and secondary PNH (n = 13). However, of the 5 patients in the study with TRF less than 5.0 kb, 3 had acquired cytogenetic abnormalities, suggesting that telomere erosion may be relevant to the pathogenesis of MDS in aplastic anemia.

Deficiency of glycosylphosphatidyl inositol-anchored proteins in patients with aplastic anaemia does not affect response to immunosuppressive therapy

Deficient expression of glycosylphosphatidyl inositol (GPI)-anchored proteins in aplastic anaemia (AA) patients has previously been reported to be associated with a poor response to immunosuppressive (IS) therapy. Here we report the response to IS therapy of 111 patients with AA and correlate this with GPI-anchored protein expression on peripheral blood cells by flow cytometry. A GPI-anchored protein deficient population was identified in 15% (17/111) of patients with AA who had a negative Ham's test and no laboratory evidence of haemolysis. Patients were treated with antilymphocyte globulin and/or cyclosporin A, or oxymetholone. Bone marrow transplantation was performed in 12 patients, seven of whom had not responded to IS therapy. In patients tested for CPI-anchored protein expression prior to IS therapy there was no difference in response rate to IS therapy between AA patients with a GPI-anchored protein deficiency and those with normal GPI-anchored protein expression (50% response rate versus 75%, respectively). Survival in these two groups was similar at 90% with follow-up over 140 months from diagnosis. Eight of the 17 AA patients who developed a GPI-anchored protein-deficient population later went on to develop a positive Ham's test. From this study we demonstrate a lower incidence of GPI-anchored protein deficiency in AA patients compared with previous reports. In addition we have shown that the presence of a GPI-anchored protein-deficient cell population in patients with AA who have a negative Ham's test is not a poor prognostic factor in terms of response and survival after IS therapy.

Human immunodeficiency virus infection impairs hemopoiesis in long-term bone marrow cultures: nonreversal by nucleoside analogues

Hematologic abnormalities are often seen in patients infected with human immunodeficiency virus (HIV). The effect of HIV infection of bone marrow stroma on support of uninfected CD34 progenitor cells in long-term bone marrow culture (LTBMC) was investigated. Results show that HIV-infected bone marrow stroma was unable to adequately support CD34 progenitor cells in vitro. Zidovudine or didanosine was added to cultures in an attempt to reverse the suppressive effects exerted by HIV and to determine whether such suppression was mediated by transfer of HIV infection to progenitor cells. Didanosine failed to reduce the suppressive effects of HIV, whereas zidovudine compounded the observed suppression. HIV infection of bone marrow stroma, while reducing the production of nonadherent cells, did not increase apoptosis and cell death in such cells. In contrast, zidovudine enhanced apoptosis and cell death in nonadherent cells produced by both HIV-infected and control LTBMC.

Frequency of the G6PD nt 1311 C/T polymorphism in English and Iranian populations: relevance to studies of X chromosome inactivation

X chromosome inactivation is widely studied using DNA sequence polymorphisms and DNA methylation as a surrogate measure of inactivation, but the correlation of methylation with inactivation is not perfect. Thus, it may be better to study sequence polymorphisms expressed in the mRNA. A recent paper reported use of a silent C/T polymorphism at nt 1311 of the G6PD cDNA, and this polymorphism was reported to have a frequency of 40% in all ethnic groups. We have screened 218 English and 50 Iranian subjects by PCR and restriction digestion; 53/218 (24%) British and 22/50 (44%) Iranian subjects were heterozygous. Thus, X inactivation studies using this polymorphism may be useful in some populations, including Iran, but much less so in the UK.

Paroxysmal nocturnal haemoglobinuria due to an 88 bp direct tandem repeat insertion in the PIG-A gene

Paroxysmal nocturnal haemoglobinuria (PNH) is an acquired stem cell abnormality which frequently develops in patients with aplastic anaemia. The disease is due to somatic mutations in the PIG-A gene, and a variety of mutations have been reported. The majority are point mutations, or small insertions and deletions resulting in a frameshift. Previous insertions reported have all been within the range of 1-10 bp. We describe here a patient with PNH due to a large insertion of 88 bp; DNA sequencing showed this to be a tandem repeat of PIG-A sequences. The same mutation could be found in granulocytes and lymphocytes, indicating a pluripotent stem cell origin.

Bone marrow transplantation for severe aplastic anemia: has outcome improved?

Bone marrow transplants for severe aplastic anemia were first performed in the 1970s. Transplant regimens, supportive care, and patient selection have changed substantially since then. Our objective was to determine the impact of these changes on transplant outcome. We studied 1,305 recipients of HLA-identical sibling transplants for aplastic anemia between 1976 and 1992, reported to the IBMTR by 179 centers. We compared survival of transplants performed in three intervals (1976 through 1980 [n = 186], 1981 through 1987 [n = 648], and 1988 through 1992 [n = 471]) using Cox proportional hazards regression. Five-year survival (+/-95% confidence interval) increased from 48% +/- 7% in the 1976-1980 cohort to 66% +/- 6% in the 1988-1992 cohort (P < .0001). Risks of graft-versus-host disease (GVHD) and interstitial pneumonia decreased over time, but the risk of graft failure did not. Higher long-term survival resulted primarily from decreased mortality in the first 3 months posttransplantation. Late mortality risks were low and changed little over the intervals studied. In multivariate analysis, changes in transplantation strategies accounted for most but not all of the improved outcome. Use of cyclosporine to prevent GVHD was the most important factor. Changes in patient selection did not seem to explain improved survival. Survival after HLA-identical sibling bone marrow transplantations for aplastic anemia has improved since 1976. Changes in GVHD prophylaxis account for much of this improvement. Other changes may also operate.

Pilot study of HLA alloimmunization after transfusion with pre-storage leucodepleted blood products in aplastic anaemia

We have performed a pilot study to examine the incidence of alloimmunization using pre-storage leucocyte-depleted blood products (PLDP) in 16 previously transfused aplastic anaemia (AA) patients with no detectable HLA antibodies. A further eight AA patients with HLA antibodies received HLA-matched PLDP. Leucodepleted apheresed platelets were obtained using either Cobe spectra or Haemonetics system with an integral pall filter. Pall BPF4 filters were used for red cell preparation. Patients' sera were tested for HLA antibodies using lymphocytotoxicity (LCT). Patients who were HLA antibody negative by LCT at study entry were further tested with enzyme-linked immunoassay (ELISA). Out of 16 patients, two (12%) formed anti-HLA antibodies with a median follow-up of 9 months (range 1-15), but did not display platelet refractoriness to random donor platelets. Two patients were inadvertently transfused with non-leucodepleted blood products when later referred back to their local hospital. Both subsequently demonstrated HLA antibodies by LCT and became platelet refractory. These results contrast with a 50% incidence of HLA alloimmunization in a control group of AA patients transfused prior to this study with non-PLDP. HLA antibodies could no longer be detected by LCT in follow-up of three out of eight patients with HLA antibodies at study entry. Only one patient experienced non-haemolytic febrile transfusion reactions (NHFTR). We conclude that PLDP reduce the risk of alloimmunization even in previously transfused AA patients, PLDP are associated with a low incidence of NHFTR, and all new AA patients should receive PLDP from diagnosis.

Sustained remission of severe resistant autoimmune neutropenia with Campath-1H

We report the course of a patient with severe autoimmune neutropenia in whom only transient responses occurred with corticosteroids, antilymphocyte globulin and granulocyte-colony stimulating factor, and who was resistant to treatment with azathioprine, cyclosporin and intravenous immunoglobulin. A 10 d course of intravenous Campath-1H monoclonal resulted in a sustained haematological response. The long-lasting effect of Campath-1H may be due to its remarkable ability to induce a profound and prolonged peripheral blood T lymphopenia.

G-CSF-mobilized CD34 peripheral blood stem cells are significantly less apoptotic than unstimulated peripheral blood CD34 cells: role of G-CSF as survival factor

The mechanism of release of CD34+ cells into the peripheral blood (PB) after mobilization treatment with chemotherapy and/or growth factors is not clearly understood. Growth factors may induce increased proliferation and self renewal within the stem cell compartment. It is possible that they alter adhesion molecule profiles or other progenitor:stroma interactions, to allow release of these cells into the periphery. However, CD34+ cells are present in the PB under steady-state conditions, albeit in low number. Growth factors such as granulocyte colony-stimulating factor (G-CSF) may promote the survival of CD34+ cells in the PB by suppressing apoptosis. In order to test this hypothesis, we have quantitated apoptotic cells in the CD34+ fraction of peripheral blood stem cell (PBSC) collections, using two-colour flow cytometry, after staining with anti-CD34 antibody and the fluorescent DNA binding agent, 7-amino actinomycin D (7AAD). 7AAD differentially stains live, apoptotic and dead cells, due to the altered accessibility of DNA in each subpopulation. We have shown a significant reduction in the proportion of apoptotic cells in the CD34+ population mobilized by G-CSF compared to CD34+ cells in unstimulated PB, consistent with the theory that G-CSF is acting, at least in part, by suppressing apoptosis. In addition, we found that G-CSF mobilized CD34+ cells are less apoptotic than CD34+ cells of unstimulated normal bone marrow, indicating that, at the doses used, G-CSF is significantly altering the survival capacity of the mobilized cells.

Glycosylphosphatidyl-inositol (GPI)-linked protein deficiency on the platelets of patients with aplastic anaemia and paroxysmal nocturnal haemoglobinuria: two distinct patterns correlating with expression on neutrophils

Deficiencies in glycosylphosphatidyl-inositol (GPI)-linked proteins on erythrocytes and leucocytes in patients with paroxysmal nocturnal haemoglobinuria (PNH) are well known; however, expression on platelets in these patients is less well documented. We have studied CD55 and CD59 on the platelets of PNH and aplastic anaemia (AA) patients using flow cytometry. In all cases of PNH, CD55 and CD59 negative populations of platelets were detected with single or bimodal distribution and these results showed close correlation with the CD55 and CD59 patterns of neutrophils. Previous published studies have not demonstrated this distribution. We suggest that our findings may be due to the methodology used.

Liver function abnormality following treatment with antithymocyte globulin for aplastic anaemia

We have observed transient elevations of serum alanine transaminase (ALT) levels in patients with aplastic anaemia who have been treated with antithymocyte globulin (ATG). Out of 18 patient episodes analysed retrospectively over a 12 month period, 15 experienced increases in ALT levels with values ranging from 1.2 to 18.5 times the upper limit of normal. In 11 of 15 episodes this was transient with ALT values returning to normal by 30 days, but in two patients this persisted for 6 months, and in a further two, until death at 34 and 145 days from unrelated causes. There was no evidence of acute viral infection or reactivation and no other drug toxicity could be implicated. We conclude that this may represent either a non-specific binding effect of ATG to hepatocytes or infection with an unidentified agent.