Hematopoietic cell destruction by immune mechanisms in acquired aplastic anemia

Single-cell RNA sequencing depicts metabolic changes in children with aplastic anemia

Introduction

Aplastic anemia (AA) is a bone marrow hematopoietic failure syndrome mediated by immune cells. The mechanism of this immune disorder is not well understood and therapeutic strategies still need to be improved.

Methods

Studies have found that abnormalities in metabolisms promote the survival of AA cells. In recent years, an increasing number of studies have reported the immunosuppressive therapy for the treatment of AA. In this study, we analyzed the transcriptome of AA from peripheral blood compared with healthy donors by single-cell sequencing and identified the affected metabolic pathways including lysine degradation. We demonstrated that the metabolic abnormalities of T lymphocytes mainly focus on glycolysis/gluconeogenesis. In addition, the metabolic abnormalities of natural killer cells concentrated in oxidative phosphorylation.

Results

The key genes involved in abnormal metabolic processes were Neustein neurotrophic factor (NENF), inositol polyphosphate-4-phosphatase type II B (INPP4B), aldo-keto reductase family 1, member C3 (AKR1C3), and carbohydrate (N-acetylglucosamine-6-O) sulfotransferase 2 (CHST2) by differential gene expression analysis.

Discussion

Molecule interaction analysis showed that tumor necrosis factor superfamily, member 12 (TNFSM12) in tumor necrosis factor (TNF) signaling was broadly activated in AA. In conclusion, we suppose that the treatment of the immune cells’ abnormal metabolic pathway may contribute to the development of novel strategies to treat AA.

Differences in the Differentiation Potential and Relative Levels of Gene Expression in the Bone Marrow-Derived Fibroblast Colony-Forming Units in Patients during the Onset of Aplastic Anemia Depending on the Disease Severity

The differentiation potential of individual clones of fibroblast CFU (CFU-F) was studied and the relative expression level of genes was analyzed in the culture of CFU-F from the bone marrow in patients with non-severe and severe forms of aplastic anemia at the onset of the disease. The differentiation potential of CFU-F clones was determined by the relative expression of marker genes using quantitative PCR. In aplastic anemia, the ratio of CFU-F clones with different differentiation potential changes, but the molecular mechanisms of this phenomenon are different in non-severe and severe aplastic anemia. In the culture of CFU-F in non-severe and severe aplastic anemia, the relative expression level of genes associated with the maintenance of the hematopoietic stem cell in the bone marrow niche changes, but the decrease in the expression of immunoregulatory genes occurs in severe form only, which may reflect differences in the pathogenesis of non-severe and severe aplastic anemia.

Hepatitis-associated aplastic anemia

Hepatitis-associated aplastic anemia (HAAA) is a rare illness, characterized by onset of pancytopenia with a hypoplastic bone marrow that traditionally occurs within 6 months of an increase in serum aminotransferases. HAAA is observed in 1% to 5% of all newly diagnosed cases of acquired aplastic anemia. Several hepatitis viruses have been linked to the disease, but in many cases no specific virus is detected. The exact pathophysiology is unknown; however, immune destruction of hematopoietic stem cells is believed to be the underlying mechanism. HAAA is a potentially lethal disease if left untreated. Management includes immunosuppression with antithymocyte globulin and cyclosporine and allogeneic hematopoietic stem cell transplantation.

Better Failure-Free Survival and Graft-versus-Host Disease-Free/Failure Free Survival with Fludarabine-Based Conditioning in Stem Cell Transplantation for Aplastic Anemia in Children

BACKGROUND

This study aimed to assess the outcome of stem cell transplantation (SCT), including overall survival (OS), failure-free survival (FFS) and graft-versus-host disease (GvHD)-free/failure-free survival (GFFS), and to analyze prognostic factors in children with aplastic anemia (AA).

METHODS

From 1991 to 2018, 43 allogeneic SCT recipients were enrolled in the study to investigate the demographic characteristics, survival outcomes and prognostic factors.

RESULTS

With the median follow-up of 7.1 years, the estimated 10-year OS, FFS, GFFS were 86.0%, 60.5%, and 51.2%, respectively. Matched related donors (MRD, n = 28) showed better 10-year OS than unrelated donors (n = 15) (96.4% vs. 66.7%; P = 0.006). Engraftment failure was seen in 13 patients (30.2%). Donor-type aplasia was seen in 13.8% (4/29) after fludarabine (Flu)-based conditioning (Flu-group), while in 42.6% (6/14) after cyclophosphamide (Cy)-based regimen (Cy-group) (P = 0.035). Six patients died. The 10-year OS in Cy-group was 92.9% (n = 14, all MRD), while that of Flu-group was 82.1% (n = 29; P = 0.367). But Flu-group tended to have better FFS and GFFS than Cy-group, although Flu-group had less MRDs (41.4% vs. 100%; P = 0.019), and higher proportion of previous immunosuppressive treatment (IST; 62% vs. 21.4%, P = 0.012). In MRD transplants, OS was similar between Flu-group (100%, n = 14) and Cy-group (92.9%, n = 14), while FFS (100.0% vs. 42.9%; P = 0.001) and GFFS (85.7% vs. 35.7%; P = 0.006) were significantly better in Flu-group. Stem cell sources, irradiation in the conditioning, and method of GvHD prophylaxis did not significantly influence the outcome.

CONCLUSION

This study reviewed SCT outcomes for pediatric AA with changes of transplant strategies over the last 25 years. The FFS and GFFS were higher in Flu-group than in Cy-group, especially in matched related transplantation. Graft failure including donor-type aplasia remains troublesome even with Flu-based conditioning. Further refinement of transplant strategies to ensure better quality-of-life should be pursued.

Pathogenesis of aplastic anemia

Aplastic anemia (AA) is a rare and life-threatening bone marrow failure (BMF) that results in peripheral blood cytopenia and reduced bone marrow hematopoietic cell proliferation. The symptoms are similar to myelofibrosis, myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) making diagnosis of AA complicated. The pathogenesis of AA is complex and its mechanism needs to be deciphered on an individualized basis. This review summarizes several contributions made in trying to understand AA pathogenesis in recent years which may be helpful for the development of personalized therapies for AA.

Panaxdiol Saponins Component Promotes Hematopoiesis and Modulates T Lymphocyte Dysregulation in Aplastic Anemia Model Mice

OBJECTIVE

To investigate the potential efficacy of panaxadiol saponins component (PDS-C) in the treatment of aplastic anemia (AA) model mice.

METHODS

Totally 70 mice were divided into 7 groups as follows: normal, model, low-, medium-, high-dose PDS-C (20, 40, 80 mg/kg, namely L-, M-, H-PDS-C), cyclosporine (40 mg/kg), and andriol (25 mg/kg) groups, respectively. An immune-mediated AA mouse model was established in BALB/c mice by exposing to 5.0 Gy total body irradiation at 1.0 Gy/min, and injecting with lymphocytes from DBA mice. On day 4 after establishment of AA model, all drugs were intragastrically administered daily for 15 days, respectively, while the mice in the normal and model groups were administered with saline solution. After treatment, the peripheral blood counts, bone marrow pathological examination, colony forming assay of bone marrow culture, T lymphocyte subpopulation analysis, as well as T-bet, GATA-3 and FoxP3 proteins were detected by flow cytometry and Western blot.

RESULTS

The peripheral blood of white blood cell (WBC), platelet, neutrophil counts and hemoglobin (Hb) concentration were significantly decreased in the model group compared with the normal group (all P<0.01). In response to 3 dose PDS-C treatment, the WBC, platelet, neutrophil counts were significantly increased at a dose-dependent manner compared with the model group (all P<0.01). The myelosuppression status of AA was significantly reduced in M-, H-PDS-C groups, and hematopoietic cell quantity of bone marrow was more abundant than the model group. The colony numbers of myeloid, erythroid and megakaryocytic progenitor cells in the model group were less than those of the normal mice in bone marrow culture, while, PDS-C therapy enhanced proliferation of hematopoietic progenitor cells by significantly increasing colony numbers (all P<0.01). Furthermore, PDS-C therapy increased peripheral blood CD3⁺ and CD3⁺CD4⁺ cells and reduced CD3⁺CD8⁺ cells (P<0.05 or P<0.01). Meanwhile, PDS-C treatment at medium- and high doses groups also increased CD4⁺CD25⁺FoxP3⁺ cells, downregulated T-bet protein expression, and upregulated GATA-3 and FoxP3 protein expressions in spleen cells (P<0.05).

CONCLUSION

PDS-C possesses dual activities, promoting proliferation hematopoietic progenitor cells and modulating T lymphocyte immune functions in the treatment of AA model mice.

Evaluating and monitoring bone marrow hypoplasia in adults with aplastic anemia via high-resolution iliac magnetic resonance imaging in the current era

The diagnosis and monitoring of aplastic anemia (AA) rely heavily on a complete blood count (CBC), and multiple-site bone marrow (BM) aspirations and biopsies. However, these approaches have certain limitations. We aimed to assess high-resolution magnetic resonance imaging (MRI) as a complementary approach for evaluating BM hypoplasia and monitoring treatment response in adults with AA in the current era.Twelve newly diagnosed AA patients and 12 sex- and age-matched healthy controls were enrolled in this study from January 2017 to August 2018. A bilateral iliac 3.0T MRI was used to collect data for each subject, and the signal intensity on the T1-weighted images (T1WIs) were expressed as a contrast-to-noise ratio (CNR). The MRI, CBC, and BM biopsy data were analyzed and compared.A qualitative analysis identified a significant difference in MRI signal characteristics between the AA group and the healthy control group. The clinical classifications of very severe aplastic anemia (VSAA) and severe aplastic anemia (SAA) corresponded to pattern I and pattern II on the MR images, respectively. However, this imaging classification did not correlate with the biopsy-based BM cellularity measure. A quantitative analysis showed a significantly higher signal intensity in AA patients than in controls. A within-group comparison revealed that more severe types of AA, based on the clinical classification, corresponded to stronger signals. Notably, MRI could detect treatment response earlier than CBC, regardless of whether there were improvements in hematopoiesis.MRI can be used to predict the therapeutic effects in patients with AA and is an important complementary tool for evaluating and monitoring BM hypoplasia.

Interleukin-18 plays a dispensable role in murine and likely also human bone marrow failure

Interleukin-18 (IL-18), also known as interferon-gamma (IFN-γ)-inducing factor, is involved in Th1 responses and regulation of immunity. Accumulating evidence implicates IL-18 in autoimmune diseases, but little is known of its role in acquired aplastic anemia (AA), the immune-mediated destruction of bone marrow (BM) hematopoietic stem and progenitor cells (HSPCs). IL-18 protein levels were significantly elevated in sera of severe AA (SAA) patients, including both responders and nonresponders assayed before treatment, and decreased after treatment. IL-18 receptor (IL-18R) was expressed on HSPCs. Co-culture of human BM CD34⁺ cells from healthy donors with IL-18 upregulated genes in the helper T-cell and Notch signaling pathways and downregulated genes in the cell cycle regulation, telomerase, and IL-6 signaling pathways. Plasma IL-18 levels were also elevated in murine models of immune-mediated BM failure. However, deletion of IL-18 in donor lymph node cells or deletions of either IL-18 or IL-18R in recipients did not attenuate elevations of circulating IFN-γ, tumor necrosis factor-alpha, or IL-6, nor did they alleviate BM failure. In summary, our findings suggest that, although increased circulating IL-18 is a feature of SAA, it may reflect an aberrant immune response but be dispensable to the pathogenesis of AA.

Value of systemic PET/CT in the diagnosis and differential diagnosis of aplastic anemia

The aim of the present study was to investigate the value of systemic [¹⁸F]fluorodeoxyglucose positron emission tomography (PET)/computed tomography (CT) in the diagnosis and differential diagnosis of aplastic anemia (AA). Systemic PET/CT imaging results of 24 patients diagnosed with AA in The First Affiliated Hospital of Sun Yat-Sen University between May 2011 and August 2014 were retrospectively analyzed and compared with results from healthy individuals and patients with acute leukemia (AL) or myelodysplastic syndrome (MDS) in the same period to summarize the PET/CT characteristics of patients with AA. Systemic PET/CT manifestations of the 24 patients with AA were classified into three types: Normal bone marrow metabolism, hypometabolism and hypometabolism complicated by focal hyperproliferation. Focal hyperproliferation was frequently identified in the vertebral body, breast bones and iliac bones. Bone marrow maximum standardized uptake values (SUV) of AA were associated, to certain extents, with the degree of proliferation and the bone marrow T/B cell ratio. The overall bone marrow SUV of AA were lower compared with those of healthy individuals and AL or patients with MDS, indicating hypometabolism. Considering the T/B cell ratio, systemic PET/CT manifestations of patients with AA are able to predict treatment responses to certain degrees. Systemic PET/CT is highly valuable in the diagnosis and differential diagnosis of AA, and may also indicate treatment responses.

Circulating exosomal microRNAs in acquired aplastic anemia and myelodysplastic syndromes

Exosomal microRNAs modulate cancer cell metabolism and the immune response. Specific exosomal microRNAs have been reported to be reliable biomarkers of several solid and hematologic malignancies. We examined the possible diagnostic and prognostic values of exosomal microRNAs in two human bone marrow failure diseases: aplastic anemia and myelodysplastic syndromes. After screening 372 microRNAs in a discovery set (n=42) of plasma exosome samples, we constructed a customized PCR plate, including 42 microRNAs, for validation in a larger cohort (n=99). We identified 25 differentially expressed exosomal microRNAs uniquely or frequently present in aplastic anemia and/or myelodysplastic syndromes. These microRNAs could be related to intracellular functions, such as metabolism, cell survival, and proliferation. Clinical parameters and progression-free survival were correlated to microRNA expression levels in aplastic anemia and myelodysplastic syndrome patients before and after six months of immunosuppressive therapy. One microRNA, mir-126-5p, was negatively correlated with a response to therapy in aplastic anemia: patients with higher relative expression of miR-126-5p at diagnosis had the shortest progression-free survival compared to those with lower or normal levels. Our findings suggest utility of exosomal microRNAs in the differential diagnosis of bone marrow failure syndromes. (Registered at clinicaltrials.gov identifiers: 00260689, 00604201, 00378534, 01623167, 00001620, 00001397, 00217594).

Deep sequencing and flow cytometric characterization of expanded effector memory CD8+CD57+ T cells frequently reveals T-cell receptor Vβ oligoclonality and CDR3 homology in acquired aplastic anemia

Oligoclonal expansion of CD8⁺ CD28⁻ lymphocytes has been considered indirect evidence for a pathogenic immune response in acquired aplastic anemia. A subset of CD8⁺ CD28⁻ cells with CD57 expression, termed effector memory cells, is expanded in several immune-mediated diseases and may have a role in immune surveillance. We hypothesized that effector memory CD8⁺CD28⁻CD57⁺ cells may drive aberrant oligoclonal expansion in aplastic anemia. We found CD8⁺CD57⁺ cells frequently expanded in the blood of aplastic anemia patients, with oligoclonal characteristics by flow cytometric Vβ usage analysis: skewing in 1–5 Vβ families and frequencies of immunodominant clones ranging from 1.98% to 66.5%. Oligoclonal characteristics were also observed in total CD8⁺ cells from aplastic anemia patients with CD8⁺CD57⁺ cell expansion by T-cell receptor deep sequencing, as well as the presence of 1–3 immunodominant clones. Oligoclonality was confirmed by T-cell receptor repertoire deep sequencing of enriched CD8⁺CD57⁺ cells, which also showed decreased diversity compared to total CD4⁺ and CD8⁺ cell pools. From analysis of complementarity-determining region 3 sequences in the CD8⁺ cell pool, a total of 29 sequences were shared between patients and controls, but these sequences were highly expressed in aplastic anemia subjects and also present in their immunodominant clones. In summary, expansion of effector memory CD8⁺ T cells is frequent in aplastic anemia and mirrors Vβ oligoclonal expansion. Flow cytometric Vβ usage analysis combined with deep sequencing technologies allows high resolution characterization of the T-cell receptor repertoire, and might represent a useful tool in the diagnosis and periodic evaluation of aplastic anemia patients. (Registered at clinicaltrials.gov identifiers: 00001620, 01623167, 00001397, 00071045, 00081523, 00961064)

Efficacy and safety of combined immunosuppressive therapy plus umbilical cord blood infusion in severe aplastic anemia patients: A cohort study

The present study aimed to evaluate the efficacy and safety of combined immunosuppressive therapy (IST) plus umbilical cord blood infusion (UCBI) in severe aplastic anemia (SAA) patients. A total of 68 patients with SAA were enrolled in the current prospective cohort study and divided into the IST (n=35; positive control) and IST+UCBI (n=33; experimental) groups according to the treatment conditions. Patients in the IST group were treated with rabbit antithymocyte globulin (r-ATG) at a dose of 2.5 mg/kg through intravenous infusion once a day for five days. This was combined with oral cyclosporine A (CsA) at a dose of 3–5 mg/kg twice a day for 2 years. Patients in the IST+UBCI group were treated with r-ATG and CsA at the same doses and frequencies as the IST group plus one UCBI 1 day after the final treatment with r-ATG. At 6 months post treatment, the complete response and overall response rate (ORR) of the IST+UCBI group were markedly higher compared with those in the IST group. Furthermore, patients in the IST+UCBI group achieved absolute neutrophil count (ANC) and platelet count responses more rapidly as compared with the IST group. However, no difference in the hemoglobin (Hb) response was identified between the two groups. In addition, SAA patients achieved responses in the ANC and platelet count more rapidly in comparison with very severe aplastic anemia (VSAA) patients, while the number of days to Hb responses were similar in the SAA and VSAA patients. Multivariate logistic regression analysis also revealed that IST+UCBI treatment was an independent predicting factor for patients achieving complete response or partial response, whereas VSAA was an independent predictor of a worse ORR. Platelet and reticulocyte were also independent predicting factors. Finally, the survival of patients was similar between the groups, and no difference in the safety of the treatment was observed. In conclusion, combined IST plus UCBI treatment may be applied as an effective and safe therapy for SAA patients.

Protective Effects of Chronic Intermittent Hypobaric Hypoxia Pretreatment against Aplastic Anemia through Improving the Adhesiveness and Stress of Mesenchymal Stem Cells in Rats

Aplastic anemia (AA) is a common malignant blood disease, and chronic intermittent hypobaric hypoxia (CIHH) has a beneficial effect against different diseases. The aim of the present study was to investigate the protective effect of CIHH against AA and underlying mechanisms. 5-Fluorouracil and busulfan treatment induced AA model in rats with reduction of hematological parameters and bone marrow tissue injury and decrease of the colony numbers of progenitor cells. CIHH pretreatment significantly reduced the incidence rate of AA and alleviated above symptoms in AA model. The adhesive molecules of bone marrow mesenchymal stem cells (BMMSCs) in AA model, VLA-4, VCAM-1, and ICAM-1 were upregulated, and those of CD162 and CD164 were downregulated by CIHH pretreatment. The expressions of HIF-1α and NF-κB in BMMSCs were also decreased through CIHH pretreatment. Overall, the results demonstrated for the first time that CIHH has an anti-AA effect through improving the adhesiveness and stress of mesenchymal stem cells in rats. CIHH could be a promising and effective therapy for AA.

The clinical relevance and prognostic significance of microsomal epoxide hydrolase gene polymorphisms and their susceptibility to acquired aplastic anemia: an Egyptian study

BACKGROUND

Microsomal epoxide hydrolase enzyme (mEPHX) is involved in xenobiotics detoxification. Two variants of mEPHX, Tyr113His and His139Arg, have been described. Both may lead to acquired aplastic anemia (AA).

OBJECTIVES

Assessing mEPHX genetic polymorphisms and detecting their impact on susceptibility and prognosis in Egyptian AA patients.

PARTICIPANTS AND METHODS

mEPHX 113 and 139 genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in 100 patients with AA and 100 control subjects.

RESULTS

Both mEPHX Tyr113His and His139Arg gene polymorphisms were associated with increased risk of developing AA, and have a significant impact of bad prognosis (p value < 0.01).

CONCLUSIONS

These mEPHX gene polymorphisms can be considered as risk factors and predictive molecular markers for prognosis in AA patients.

Impaired Autophagy in Adult Bone Marrow CD34+ Cells of Patients with Aplastic Anemia: Possible Pathogenic Significance

Aplastic anemia (AA) is a bone marrow failure syndrome that is caused largely by profound quantitative and qualitative defects of hematopoietic stem and progenitor cells. However, the mechanisms underlying these defects remain unclear. Under conditions of stress, autophagy acts as a protective mechanism for cells. We therefore postulated that autophagy in CD34⁺ hematopoietic progenitor cells (HPCs) from AA patients might be impaired and play a role in the pathogenesis of AA. To test this hypothesis, we tested autophagy in CD34⁺ cells from AA samples and healthy controls and investigated the effect of autophagy on the survival of adult human bone marrow CD34⁺ cells. We found that the level of autophagy in CD34⁺ cells from AA patients was significantly lower than in age/sex-matched healthy controls, and lower in cases of severe AA than in those with non-severe AA. Autophagy in CD34⁺ cells improved upon amelioration of AA but, compared to healthy controls, was still significantly reduced even in AA patients who had achieved a complete, long-term response. We also showed that although the basal autophagy in CD34⁺ cells was low, the autophagic response of CD34⁺ cells to “adversity” was rapid. Finally, impaired autophagy resulted in reduced differentiation and proliferation of CD34⁺ cells and sensitized them to death and apoptosis. Thus, our results confirm that autophagy in CD34⁺ cells from AA patients is impaired, that autophagy is required for the survival of CD34⁺ cells, and that impaired autophagy in CD34⁺ HPCs may play an important role in the pathogenesis of AA.

Characterization of bone marrow mesenchymal stromal cells in aplastic anaemia

In aplastic anaemia (AA), haemopoietic activity is significantly reduced and generally attributed to failure of haemopoietic stem cells (HSC) within the bone marrow (BM). The regulation of haemopoiesis depends on the interaction between HSC and various cells of the BM microenvironment, including mesenchymal stromal cells (MSC). MSC involvement in the functional restriction of HSC in AA is largely unknown and therefore, the physical and functional properties of AA MSC were studied in vitro. MSC were characterized by their phenotype and ability to form adherent stromal layers. The functional properties of AA MSC were assessed through proliferative, clonogenic and cross-over culture assays. Results indicate that although AA MSC presented typical morphology and distinctive mesenchymal markers, stromal formation was reduced, with 50% of BM samples failing to produce adherent layers. Furthermore, their proliferative and clonogenic capacity was markedly decreased (P = 0·03 and P = 0·04 respectively) and the ability to sustain haemopoiesis was significantly reduced, as assessed by total cell proliferation (P = 0·032 and P = 0·019 at Week 5 and 6, respectively) and clonogenic potential of HSC (P = 0·02 at Week 6). It was concluded that the biological characteristics of AA MSC are different from those of control MSC and their in vitro haemopoiesis-supporting ability is significantly reduced.

Aberrant overexpression of CD14 on granulocytes sensitizes the innate immune response in mDia1 heterozygous del(5q) MDS

The myelodysplastic syndromes (MDSs) include a spectrum of stem cell malignancies characterized by an increased risk of developing acute myeloid leukemia. Heterozygous loss of chromosome 5q (del[5q]) is the most common cytogenetic abnormality in MDS. DIAPH1 is localized to 5q31 and encodes one of the formin proteins, mDia1, which is involved in linear actin polymerization. Mice with mDia1 deficiency develop hematologic features with age mimicking human myeloid neoplasm, but its role in the pathogenesis of MDS is unclear. Here we report that mDia1 heterozygous and knockout mice develop MDS phenotypes with age. In these mice, CD14 was aberrantly overexpressed on granulocytes in a cell-autonomous manner, leading to a hypersensitive innate immune response to lipopolysaccharide (LPS) stimuli through CD14/Toll-like receptor 4 signaling. Chronic stimulation with LPS accelerated the development of MDS in mDia1 heterozygous and knockout mice that can be rescued by lenalidomide. Similar findings of CD14 overexpression were observed on the bone marrow granulocytes of del(5q) MDS patients. Mechanistically, mDia1 deficiency led to a downregulation of membrane-associated genes and a specific upregulation of CD14 messenger RNA in granulocytes, but not in other lineages. These results underscore the significance of mDia1 heterozygosity in deregulated innate immune responses in del(5q) MDS.

Ezh2 regulates transcriptional and posttranslational expression of T-bet and promotes Th1 cell responses mediating aplastic anemia in mice

Acquired aplastic anemia (AA) is a potentially fatal bone marrow (BM) failure syndrome. IFN-γ-producing Th1 CD4(+) T cells mediate the immune destruction of hematopoietic cells, and they are central to the pathogenesis. However, the molecular events that control the development of BM-destructive Th1 cells remain largely unknown. Ezh2 is a chromatin-modifying enzyme that regulates multiple cellular processes primarily by silencing gene expression. We recently reported that Ezh2 is crucial for inflammatory T cell responses after allogeneic BM transplantation. To elucidate whether Ezh2 mediates pathogenic Th1 responses in AA and the mechanism of Ezh2 action in regulating Th1 cells, we studied the effects of Ezh2 inhibition in CD4(+) T cells using a mouse model of human AA. Conditionally deleting Ezh2 in mature T cells dramatically reduced the production of BM-destructive Th1 cells in vivo, decreased BM-infiltrating Th1 cells, and rescued mice from BM failure. Ezh2 inhibition resulted in significant decrease in the expression of Tbx21 and Stat4, which encode transcription factors T-bet and STAT4, respectively. Introduction of T-bet but not STAT4 into Ezh2-deficient T cells fully rescued their differentiation into Th1 cells mediating AA. Ezh2 bound to the Tbx21 promoter in Th1 cells and directly activated Tbx21 transcription. Unexpectedly, Ezh2 was also required to prevent proteasome-mediated degradation of T-bet protein in Th1 cells. Our results demonstrate that Ezh2 promotes the generation of BM-destructive Th1 cells through a mechanism of transcriptional and posttranscriptional regulation of T-bet. These results also highlight the therapeutic potential of Ezh2 inhibition in reducing AA and other autoimmune diseases.

Bone marrow mesenchymal stem cells from patients with aplastic anemia maintain functional and immune properties and do not contribute to the pathogenesis of the disease

Aplastic anemia is a life-threatening bone marrow failure disorder characterized by peripheral pancytopenia and marrow hypoplasia. The majority of cases of aplastic anemia remain idiopathic, although hematopoietic stem cell deficiency and impaired immune responses are hallmarks underlying the bone marrow failure in this condition. Mesenchymal stem/stromal cells constitute an essential component of the bone marrow hematopoietic microenvironment because of their immunomodulatory properties and their ability to support hematopoiesis, and they have been involved in the pathogenesis of several hematologic malignancies. We investigated whether bone marrow mesenchymal stem cells contribute, directly or indirectly, to the pathogenesis of aplastic anemia. We found that mesenchymal stem cell cultures can be established from the bone marrow of aplastic anemia patients and display the same phenotype and differentiation potential as their counterparts from normal bone marrow. Mesenchymal stem cells from aplastic anemia patients support the in vitro homeostasis and the in vivo repopulating function of CD34(+) cells, and maintain their immunosuppressive and anti-inflammatory properties. These data demonstrate that bone marrow mesenchymal stem cells from patients with aplastic anemia do not have impaired functional and immunological properties, suggesting that they do not contribute to the pathogenesis of the disease.

Pancytopenia in children: A 6-year spectrum of patients admitted to Pediatric Department of Rehman Medical Institute, Peshawar

Objective: To determine the various spectrum of pancytopenia with its frequency on the basis of bone marrow examination in children from 6 months to 14 years.

Methods: A retrospective descriptive study was carried out at Department of Pediatric Rehman Medical Institute Peshawar from January 2006 to December 2012. A total of 205 patient’s age between 6 months and 14 years, fulfilling the inclusion and exclusion criteria were included in the study. Complete blood count, peripheral smear, bone marrow examination and Serum vitamin B12 level was done in all the cases.

Results: Out of 14642 patients admitted to the Pediatric department during the study period, 205 (1.4%) patients were pancytopenic on their peripheral blood smear. Male outnumbered female with a ratio of 1.8:1. 42.5% of the patients were in the age group of 1 month to 5 years. Common etiological pattern identified were Aplastic anemia 58(28.3%), Hematological malignancies 49 (23.9%), megaloblastic anemia 40 (19.5%), idiopathic thrombocytopenic purpura 16 (7.8%), iron deficiency anemia 9 (4.4%), hemolytic anemia 7 (3.41%), Visceral leishmaniasis 6 (2.93%), hypersplenism 5 (2.44%), malaria 5 (2.44%), anemia of chronic disorder 4 (1.95%), Myelodisplastic syndrome 3 (1.46%), Niemen pick disease 2 (0.97%) and Gaucher disease in 1(0.49%). Common clinical presentations were fever, pallor, body aches, petechial hemorrhages and epistaxis.

Conclusion: Pancytopenia is one of the importance occurrences in pediatric patients. Acute leukemia and bone marrow failure are the most common causes yet megaloblastic anemia and infections are the treatable and reversible causes of pancytopenia.

Next-generation-sequencing-spectratyping reveals public T-cell receptor repertoires in pediatric very severe aplastic anemia and identifies a β chain CDR3 sequence associated with hepatitis-induced pathogenesis

Current diagnostic approaches that characterize T-cell deficiency by analyzing diversity of T-cell receptor sequences effectuate limited informational gain about the actual restrictiveness. For deeper insight into T-cell receptor repertoires we developed next-generation-sequencing-spectratyping, which employs high coverage Roche/454 sequencing of T-cell receptor (β)-chain amplicons. For automated analysis of high-throughput-sequencing data, we developed a freely available software, the TCR profiler. Gene usage, length, encoded amino acid sequence and sequence diversity of the complementarity determining region 3 were determined and comprehensively integrated into a novel complexity score. Repertoires of CD8(+) T cells from children with idiopathic or hepatitis-induced very severe aplastic anemia (n=7), children two months after bone marrow transplantation (n=7) and healthy controls (children n=5, adults n=5) were analyzed. Complexity scores clearly distinguished between healthy and diseased, and even between different immune deficiency states. The repertoire of aplastic anemia patients was dominated by public (i.e. present in more than one person) T-cell receptor clonotypes, whereas only 0.2% or 1.9% were public in normal children and adults, respectively. The CDR3 sequence ASSGVGFSGANVLT was highly prevalent in 3 cases of hepatitis-induced anemia (15-32% of all sequences), but was only low expressed in idiopathic aplastic anemia (2-5%, n=4) or healthy controls (<1%). Fifteen high frequent sequences were present exclusively in aplastic anemia patients. Next-generation-sequencing-spectratyping allows in-depth analysis of T-cell receptor repertoires and their restriction in clinical samples. A dominating clonotype was identified in hepatitis-induced anemia that may be associated with disease pathogenesis and several aplastic-anemia-associated, putatively autoreactive clonotypes were sequenced.

Antithymocyte globulin/antilymphocyte globulin plus kidney-nourishing Chinese medicinal: effect on severe aplastic anemia

OBJECTIVE

To explore the effect of antithymocyte globulin (ATG)/antilymphocyte globulin (ALG) plus kidney-nourishing Chinese medicinal (KNCM) on severe aplastic anemia (SAA).

METHODS

Twenty-five subjects of severe aplastic anemia were treated with ATG/ALD plus KNCM between 1992 and 2009, and the clinical data before and after treatment were collected and analyzed.

RESULTS

Of the 25 patients, 9 were nearly cured, 6 were improved, 5 were in remission, and 5 failed. The overall effective rate was 80.0%. The 3-year, 5-year, 10-year, 15-year survival rate were respectively 98.6%, 97.3%, 97.3%, 67.5%, and median survival time was 180 months. Compared to the conditions before administering the medication of ATG/ ALG plus KNCM, after 2 weeks, reticulocyte was first improved (P = 0.001); one month later, followed by palette (P = 0.037); two months later, by neutrophil cell in peripheral blood (P = 0.001); three months later, then by the hemoglobin (P = 0.012). By conducting 1-year follow-up, 1 case of complication--paroxysmal nocturnal hemoglobinuria (PNH) was identified and the patient still alive today.

CONCLUSION

ATG/ALG plus KNCM had better effect on SAA and could improve patients' survival rate.

Response of paroxysmal nocturnal hemoglobinuria clone with aplastic anemia to rituximab

Paroxysmal nocturnal hemoglobinuria is caused by expansion of a hematopoietic stem cell clone with an acquired somatic mutation in the PIG-A gene. This mutation aborts the synthesis and expression of the glycosylphosphatidylinositol anchor proteins CD55 and CD59 on the surface of blood cells, thereby making them more susceptible to complement-mediated damage. A spectrum of disorders occurs in PNH ranging from hemolytic anemia and thrombosis to myelodysplasia, aplastic anemia and, myeloid leukemias. Aplastic anemia is one of the most serious and life-threatening complications of PNH, and a PNH clone is found in almost a third of the cases of aplastic anemia. While allogeneic bone marrow transplantation and T cell immune suppression are effective treatments for aplastic anemia in PNH, these therapies have significant limitations. We report here the first case, to our knowledge, of PNH associated with aplastic anemia treated with the anti-CD20 monoclonal antibody rituximab, which was associated with a significant reduction in the size of the PNH clone and recovery of hematopoiesis. We suggest that this less toxic therapy may have a significant role to play in treatment of PNH associated with aplastic anemia.

Intrinsic impairment of CD4+CD25+ regulatory T cells in acquired aplastic anemia

Acquired aplastic anemia (AA) is an immune-mediated bone marrow (BM) failure attacked by autoreactive effector T cells and BM is the main target organ. CD4+CD25+ regulatory T cells (Tregs) were believed to control development and progression of autoimmunity by suppressing autoreactive effector T cells, but little was known regarding the function of Tregs in AA. Our study demonstrated that both peripheral blood (PB) and BM had decreased frequencies of Tregs, accompanied with a reversed lower ratio of Treg frequencies between BM and PB in AA. PB Tregs in AA had impaired migratory ability because of lower CXCR4 (but not for CXCR7) expression. Interestingly, we first showed that impairment of Treg-mediated immunosuppression was intrinsic to Tregs, rather than resistance of effector T cells to suppression in AA by coculture assays and criss-cross experiments in vitro. Furthermore, Tregs in AA were less able to inhibit interferon-γ production by effector T cells. Defective immunosuppression by Tregs could contribute to impaired hematopoiesis conducted by effector T cells in vitro. Our study provided powerful evidence that impairment of Tregs played a critical role in the pathophysiology of AA. Thus, patients with AA might greatly benefit from a Treg-oriented immunosuppressive strategy.

Experimental bone marrow failure in mice ameliorated by OCH via tippling the balance of released cytokines from Th1 to Th2

BACKGROUND

OCH was reported to stimulate natural killer T (NKT) cells to produce predominantly T helper type 2 (Th2) cytokines. The present study was attempted to evaluate potential protection of OCH on acquired bone marrow failure syndromes (BMFS) in mice model.

METHODS

BMFS in mice model was established by exposure to sublethal irradiation followed by infusion with 5 × 10(6) B6 lymph nodes cells. Mice were injected intraperitoneally (I.P.) with either OCH or α-galactosylceramide (α-GC) at a dose of 100 µg kg(-1) twice a week for two weeks after post-irradiation. The control mice were I.P. with vehicle alone (10% dimethyl sulfoxide in phosphate-buffered saline). Meanwhile, anti-interleukin-4 (anti-IL-4) monoclonal antibody (mAb) (500 µg/animal) was given I.P. 2 hours prior to vehicle or OCH administration. Both interferon-γ (IFN-γ) and IL-4 levels in the serum were measured by enzyme-linked immunosorbent assay. Colony-forming unit-granulocyte-macrophage (CFU-GM) by bone marrow (BM) mononuclear cells was counted. The percentage of NKT cell in BM cells and intracellular cytokines were determined by flow cytometry.

RESULTS

The treatment of OCH in vivo decreased the IFN-γ/IL-4 ratio in the serum, and increased the transformation of NKT cells into NKT2 cells. The treatment of OCH in vitro increased the colonies of CFU-GM.

CONCLUSION

Our data suggests that OCH ameliorated immune-mediated BMFS in CByB6F1 mice via activation of NKT cells, and shifting the balance from Th1 to Th2.

Soluble PD-1 is associated with aberrant regulation of T cells activation in aplastic anemia

Engagement of the membrane program death-1 (PD-1) receptor by its ligands suppresses T cell proliferation and cytokine production. Aberrant over-expression of costimulatory molecules, including PD-1, has been associated with persistent activation of self-reactive T cells in autoimmune diseases. However, the mechanism underlying the dysfunction of PD-1 in the regulation of T-cell activation in such diseases remains unclear. Here, we report the overexpression of CD4(+) and CD8(+) T cell PD-1 and elevated serum levels of soluble PD-1 in aplastic anemia (AA) patients. Detailed characterization of soluble PD-1 revealed that it corresponded to an alternative splice variant PD-1Deltaex3, which lacks the transmembrane domain but has a soluble extracellular domain of the PD-1 molecule. In a further study, PD-1 fusion protein displayed the ability of increasing the proliferation of T cells in vitro, which suggested that soluble PD-1 might serve as an autoimmune antibody to block the function of membrane-bound PD-1 on T cells and lead to aberrant T cell proliferation. Our study revealed a novel pathogenic pathway in which the function of overexpressed PD-1 to restrict over-self-reaction is counteracted by the excessive production of soluble PD-1.

Primitive Sca-1 Positive Bone Marrow HSC in Mouse Model of Aplastic Anemia: A Comparative Study through Flowcytometric Analysis and Scanning Electron Microscopy

Self-renewing Hematopoietic Stem Cells (HSCs) are responsible for reconstitution of all blood cell lineages. Sca-1 is the “stem cell antigen” marker used to identify the primitive murine HSC population, the expression of which decreases upon differentiation to other mature cell types. Sca-1⁺ HSCs maintain the bone marrow stem cell pool throughout the life. Aplastic anemia is a disease considered to involve primary stem cell deficiency and is characterized by severe pancytopenia and a decline in healthy blood cell generation system. Studies conducted in our laboratory revealed that the primitive Sca-1⁺ BM-HSCs (bone marrow hematopoietic stem cell) are significantly affected in experimental Aplastic animals pretreated with chemotherapeutic drugs (Busulfan and Cyclophosphamide) and there is increased Caspase-3 activity with consecutive high Annexin-V positivity leading to premature apoptosis in the bone marrow hematopoietic stem cell population in Aplastic condition. The Sca-1^bright, that is, “more primitive” BM-HSC population was more affected than the “less primitive” BM-HSC Sca-1^dim population. The decreased cell population and the receptor expression were directly associated with an empty and deranged marrow microenvironment, which is evident from scanning electron microscopy (SEM). The above experimental evidences hint toward the manipulation of receptor expression for the benefit of cytotherapy by primitive stem cell population in Aplastic anemia cases.

Fanconi anemia proteins and endogenous stresses

Each of the thirteen identified Fanconi anemia (FA) genes is required for resistance to DNA interstrand crosslinking agents, such as mitomycin C, cisplatin, and melphalan. While these agents are excellent tools for understanding the function of FA proteins in DNA repair, it is uncertain whether a defect in the removal of DNA interstrand crosslinks (ICLs) is the basis for the pathophysiology of FA. For example, DNA interstrand crosslinking agents induce other types of DNA damage, in addition to ICLs. Further, other DNA-damaging agents, such as ionizing or ultraviolet radiation, activate the FA pathway, leading to monoubiquitination of FANCD2 and FANCI. Also, FA patients display congenital abnormalities, hematologic deficiencies, and a predisposition to cancer in the absence of an environmental source of ICLs that is external to cells. Here we consider potential sources of endogenous DNA damage, or endogenous stresses, to which FA proteins may respond. These include ICLs formed by products of lipid peroxidation, and other forms of oxidative DNA damage. FA proteins may also potentially respond to telomere shortening or replication stress. Defining these endogenous sources of DNA damage or stresses is critical for understanding the pathogenesis of deficiencies for FA proteins.We propose that FA proteins are centrally involved in the response to replication stress, including replication stress arising from oxidative DNA damage.

Changes in cytokine profile pre- and post-immunosuppression in acquired aplastic anemia

Cytokine expression assessed by flow cytometry in 53 acquired aplastic anemia patients before and after combined immunosuppression (EBMT WPSAA protocols) showed that CD3(+) marrow cells containing TNF-alpha, IFN-gamma and IL4 were similar in subjects with disease at onset (DO) and responsive to treatment who had more CD3(+)/TNF-alpha(+) and CD 3(+)/IFN-gamma(+) cells than normal controls. In vitro block of TNF-alpha and/or IFN-gamma significantly increased BFU-e over baseline in 28 patients. In responsive to treatment patients only TNF-alpha block significantly incremented colonies over normal controls. Absolute marrow CD3(+)/TNF-alpha(+) and CD3(+)/IFN-gamma(+) cells prospectively tested in a group of 21 subjects declined significantly more in Responders than in Non Responders to immunosuppression at Response Evaluation Time respect to Diagnosis. Both in Responders and in Non Responders these cells remained higher than in normal controls. This study suggests that immunosuppression does not fully clear excess TNF-alpha and IFN-gamma from marrow of patients with good outcome and raises the hypothesis that additional cytokine blockade might be useful in immunosuppression for acquired aplastic anemia.

Advances in the understanding of congenital amegakaryocytic thrombocytopenia

Congenital amegakaryocytic thrombocytopenia (MIM #604498) is an extremely rare inherited bone marrow failure syndrome, usually presenting as a severe thrombocytopenia at birth due to ineffective megakaryocytopoiesis and no characteristic physical anomalies. Usually the isolated thrombocytopenia progresses to pancytopenia during the first years of life. The only curative therapy to date is haematopoietic stem cell transplantation. Most of the cases of congenital amegakaryocytic thrombocytopenia are caused by defective expression or function of the thrombopoietin receptor due to homozygous or compound heterozygous mutations in the gene MPL. The essential roles of thrombopoietin as a lineage specific regulator of platelet production and as a regulator of haematopoietic stem cell function are reflected in the haematological defects seen in affected individuals.

Aplastic anemia

PURPOSE OF REVIEW

Most acquired aplastic anemia is the result of immune-mediated destruction of hematopoietic stem cells causing pancytopenia and an empty bone marrow, which can be successfully treated with either immunosuppressive therapy or hematopoietic stem-cell transplantation.

RECENT FINDINGS

In aplastic anemia, oligoclonally expanded cytotoxic T cells induce apoptosis of hematopoietic progenitors. T-bet, a transcription factor that binds to the interferon-gamma promoter region, is upregulated in aplastic anemia T cells. Regulatory T cells are significantly reduced in patients' peripheral blood and in an aplastic anemia murine model, infusion of regulatory T cells ameliorates disease progression. In a minority of cases, loss-of-function mutations in telomerase complex genes may underlie disease development. Long-term survival, once strongly linked to response to immunosuppressive therapy, can now be achieved even among nonresponders due to significant advances in supportive care and better salvage treatments.

SUMMARY

Evidence has accumulated in the recent years further corroborating an immune-mediated process underlying aplastic anemia pathogenesis. Hematopoietic stem-cell transplantation from a matched sibling donor is preferred for children and young adults with severe aplastic anemia, and immunosuppressive therapy is employed when hematopoietic stem-cell transplantation is not feasible due to age, lack of a histocompatible sibling, co-morbidities, or by patient choice.

Elevated expression of IL-12 and IL-23 in patients with aplastic anemia

Aplastic anemia (AA), which is characterized by hypocellular bone marrow (BM) and blood pancytopenia, was considered as a T-helper1 (Th1) mediated disease. Interleukin (IL)-12 and IL-23 produced by antigen presenting cells are essential for inducing and sustaining Th1 effector cells via different pathways. However, less is known with regard to the levels of expression and synthesis of these two cytokines in patients with AA. This was determined in the current study in 26 patients with AA as well as in 20 healthy controls. Our results showed that IL-12 p40, IL-12 p35 and IL-23 p19 gene expression can be detected in all samples both from the patients and the controls, using real-time reverse transcription polymerase chain reaction. Furthermore, an increased expression of IL-12 p40, IL-12 p35 and IL-23 p19 mRNA was observed in bone marrow mononuclear cells and peripheral blood mononuclear cells of patients with AA compared with the corresponding one in normal controls. Higher levels of IL-12 and IL-23 were also found in BM plasma and PB plasma in patients with AA than in normal controls. Therefore, the augmented expression of IL-12 and IL-23 in patients with AA may play an important role in the pathogenesis of this disease.

Prospective multicenter trial comparing repeated immunosuppressive therapy with stem-cell transplantation from an alternative donor as second-line treatment for children with severe and very severe aplastic anemia

We conducted a prospective multicenter study to compare the efficacy of repeated immunosuppressive therapy (IST) with stem-cell transplantation (SCT) from an alternative donor in children with acquired aplastic anemia (AA) who failed to respond to an initial course of IST. Patients with severe (n = 86) and very severe disease (n = 119) received initial IST consisting of antithymocyte globulin (ATG) and cyclosporine. Sixty patients failed to respond to IST after 6 months from the initial IST and were eligible for second-line treatment. Among them, 21 patients lacking suitable donors received a second course of IST. Three patients developed an anaphylactoid reaction to ATG and could not complete the second IST. A trilineage response was seen in only 2 of 18 (11%) evaluable patients after 6 months. Thirty-one patients received SCT from an alternative donor. At 5 years from the initiation of second-line therapy, the estimated failure-free survival (FFS), defined as survival with response, was 83.9% (+/- 16.1%, SD) in the SCT group compared with 9.5% (+/- 9.0%) in the IST group (P = .001). These results suggest that SCT from an alternative donor offers a better chance of FFS than a second IST in patients not responding to an initial IST.

Inflammatory reactive oxygen species-mediated hemopoietic suppression in Fancc-deficient mice

Patients with the genomic instability syndrome Fanconi anemia (FA) commonly develop progressive bone marrow (BM) failure and have a high risk of cancer. Certain manifestations of the disease suggest that the FA immune system is dysfunctional and may contribute to the pathogenesis of both BM failure and malignancies. In this study, we have investigated inflammation and innate immunity in FA hemopoietic cells using mice deficient in Fanconi complementation group C gene (Fancc). We demonstrate that Fancc-deficient mice exhibit enhanced inflammatory response and are hypersensitive to LPS-induced septic shock as a result of hemopoietic suppression. This exacerbated inflammatory phenotype is intrinsic to the hemopoietic system and can be corrected by the re-expression of a wild-type FANCC gene, suggesting a potential role of the FANCC protein in innate immunity. LPS-mediated hemopoietic suppression requires two major inflammatory agents, TNF-alpha and reactive oxygen species. In addition, LPS-induced excessive accumulation of reactive oxygen species in Fancc(-/-) BM cells overactivates the stress kinase p38 and requires prolonged activation of the JNK. Our data implicate a role of inflammation in pathogenesis of FA and BM failure diseases in general.

Inflammatory ROS promote and cooperate with the Fanconi anemia mutation for hematopoietic senescence

The proinflammatory cytokine tumor necrosis factor alpha (TNFalpha) inhibits hematopoietic stem cell (HSC) expansion, interferes with HSC self-renewal and compromises the ability of HSC to reconstitute hematopoiesis. We have investigated mechanisms by which TNFalpha suppresses hematopoiesis using the genomic instability syndrome Fanconi anemia mouse model deficient for the complementation-group-C gene (Fancc). Examination of senescence makers, such as senescence-associated beta-galactosidase, HP1-gamma, p53 and p16(INK4A) shows that TNFalpha induces premature senescence in bone marrow HSCs and progenitor cells as well as other tissues of Fancc-/- mice. TNFalpha-induced senescence correlates with the accumulation of reactive oxygen species (ROS) and oxidative DNA damage. Neutralization of TNFalpha or deletion of the TNF receptor in Fancc-/- mice (Fancc-/-;Tnfr1-/-) prevents excessive ROS production and hematopoietic senescence. Pretreatment of TNFalpha-injected Fancc-/- mice with a ROS scavenger significantly reduces oxidative base damage, DNA strand breaks and senescence. Furthermore, HSCs and progenitor cells from TNFalpha-treated Fancc-/- mice show increased chromosomal aberrations and have an impaired oxidative DNA-damage repair. These results indicate an intimate link between inflammatory reactive oxygen species and DNA-damage-induced premature senescence in HSCs and progenitor cells, which may play an important role in aging and anemia.

Current concepts in the pathophysiology and treatment of aplastic anemia

Aplastic anemia, an unusual hematologic disease, is the paradigm of the human bone marrow failure syndromes. Almost universally fatal just a few decades ago, aplastic anemia can now be cured or ameliorated by stem-cell transplantation or immunosuppressive drug therapy. The pathophysiology is immune mediated in most cases, with activated type 1 cytotoxic T cells implicated. The molecular basis of the aberrant immune response and deficiencies in hematopoietic cells is now being defined genetically; examples are telomere repair gene mutations in the target cells and dysregulated T-cell activation pathways. Immunosuppression with antithymocyte globulins and cyclosporine is effective at restoring blood-cell production in the majority of patients, but relapse and especially evolution of clonal hematologic diseases remain problematic. Allogeneic stem-cell transplant from histocompatible sibling donors is curative in the great majority of young patients with severe aplastic anemia; the major challenges are extending the benefits of transplantation to patients who are older or who lack family donors. Recent results with alternative sources of stem cells and a variety of conditioning regimens to achieve their engraftment have been promising, with survival in small pediatric case series rivaling conventional transplantation results.

Chemokine expression in human erythroid leukemia cell line AS-E2: macrophage inflammatory protein-3alpha/CCL20 is induced by inflammatory cytokines

OBJECTIVE

Normal and malignant hematopoietic cells are shown to express and secrete various cytokines and chemokines, some of which are believed to play an important role in normal and abnormal hematopoiesis in an autocrine/paracrine manner. To explore the possibility of a cytokine/chemokine network participating in the pathophysiology of anemic disorders, we evaluated the ability of inflammatory cytokines to induce chemokine expression using erythroid progenitor cells.

METHODS

Erythropoietin-dependent human leukemia cell line AS-E2 was used as a model of erythroid colony-forming unit (CFU-E) cells. The expression of mRNA of 8 chemokines was examined using RT-PCR, before and after TNF-alpha, IFN-gamma, and IL-1beta stimulation. For MIP-3alpha, the promoter activity was analyzed by luciferase assay and secretion was confirmed by ELISA. The expression of CCR6, the specific receptor for MIP-3alpha, was analyzed by RT-PCR and flow cytometry.

RESULTS

Unstimulated AS-E2 cells constitutively expressed transcripts for MCP-4, IP-10, PF-4, IL-8, and MIP-3alpha. Stimulation with TNF-alpha, IFN-gamma, and IL-1beta upregulated MIP-3alpha mRNA expression and induced its protein secretion. Luciferase assay revealed that these cytokines could upregulate promoter activity of the MIP-3alpha gene, possibly through the NF-kappaB pathway. CCR6 mRNA was detected and its intracellular expression was confirmed.

CONCLUSION

These data suggest that inflammatory cytokine-stimulated erythroid progenitors secrete MIP-3alpha, which may function in an autocrine/paracrine manner. Furthermore, the existence of intracellular CCR6 suggests the involvement in cytokine signaling of a MIP-3alpha-dependent internal autocrine mechanism. These mechanisms may play a role in pathophysiology of anemic disorders, such as secondary anemia and bone marrow failure syndromes.

T-bet, a Th1 transcription factor, is up-regulated in T cells from patients with aplastic anemia

In aplastic anemia, immune destruction of hematopoietic cells results in bone marrow failure. Type 1 cytokines, especially IFN-gamma, have been implicated in the pathophysiology of T-cell-mediated, Fas-mediated stem cell apoptosis of hematopoietic cells. Here, we show that the transcription factor T-bet (T-box expressed in T cells) is increased in T cells from patients with aplastic anemia. Patients' T-bet bound directly to the proximal site of the IFN-gamma promoter without any prior stimulation, in contrast to healthy controls. Increased levels of Itk kinase participated in T-bet up-regulation and active transcription of the IFN-gamma gene observed in these patients. Blocking PKC-, a kinase that lies downstream of Itk kinase, decreased T-bet protein and IFN-gamma intracellular levels. These data suggest that the increased IFN-gamma levels observed in aplastic anemia patients are the result of active transcription of the IFN-gamma gene by T-bet. Blocking the transcription of the IFN-gamma gene with kinase inhibitors might lead to the development of novel therapeutic agents for patients with aplastic anemia and other autoimmune diseases.

A probable role for trail-induced apoptosis in the pathogenesis of marrow failure. Implications from an in vitro model and from marrow of aplastic anemia patients

Aplastic anemia (AA) is a syndrome of hematopoietic failure involving increased apoptosis of stem cells. In order to investigate the molecular mechanisms participated in the process of marrow failure, we created an in vitro model of hematopoietic cell suppression, by continuous addition of TNF-alpha and IFN-gamma in an vitro long-term bone marrow culture system. An up-regulation of Fas expression was observed in CD34+ cells in cytokine treated cultures, compared to controls. This was accompanied by significant TRAIL and decreased caspase 3 mRNA expression, whereas the expression of Bcl-2 family members was low (Bcl-xl) or absent (Bcl-2, Bax). The expression of these apoptotic genes was also investigated in aplastic anemia patients. Apart from Fas mRNA expression in total marrow and/or CD34+ cells, TRAIL mRNA expression was found only in CD34+ cells in active disease while in total marrow cell compartment this remains a constant finding even in patients in remission. The above data are in agreement with previous studies proposing a major role for the extrinsic apoptosis pathway in the pathogenesis of aplastic anemia and additionally introduce TRAIL as a probable important molecule in the process.

Autoimmune hepatitis type 1 and primary biliary cirrhosis have distinct bone marrow cytokine production

We have recently reported differences in the hematopoiesis between autoimmune hepatitis type 1 (AIH-1) and primary biliary cirrhosis (PBC). In view of the notion that cytokines are regulators of hematopoiesis, we investigated in our tertiary center the cytokine production in the bone marrow (BM) of the same consecutive cohort of patients (13 AIH-1, 13 PBC, 10 healthy and 7 patients with cirrhosis due to chronic hepatitis B). Interferon-gamma (IFN-gamma), interleukin-4 (IL-4), interleukin-10 (IL-10), tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta (TGF-beta) were determined in the supernatants of long-term BM cultures by ELISAs. IL-4, TNF-alpha and TGF-beta were found significantly increased in the BM of PBC patients compared to AIH-1 and both control groups. AIH-1 patients had significantly higher BM IL-10 compared to PBC patients and higher IL-10, IL-4 and TNF-alpha compared to controls. BM IFN-gamma was significantly higher in PBC and AIH-1 patients compared to controls. In AIH-1 patients, IL-10 was positively correlated with CD34+, CD34+/CD38- and CD34+/CD38+ cell proportions. In conclusion, the BM cytokine microenvironment of PBC and AIH-1 patients differs significantly compared to that of healthy individuals and cirrhotic patients of non-autoimmune etiology. Differences were also found between patients with PBC and AH-1. The implication of BM in the pathogenesis of autoimmune liver diseases is possible and needs further investigation.

ADP-ribosyl cyclases generate two unusual adenine homodinucleotides with cytotoxic activity on mammalian cells

ADP-ribosyl cyclases are ubiquitous enzymes responsible for synthesis from NAD(+) of the intracellular calcium-releasing signal molecules cyclic ADP-ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP(+)). Here, we show that cyclases from lower and higher Metazoa also synthesize three adenylic dinucleotides from cADPR and adenine: diadenosine diphosphate and two isomers thereof. These dinucleotides are present and metabolized in mammalian cells and affect intracellular calcium and cell proliferation. The diadenosine diphosphate isomers are naturally occurring nucleotides containing an N-glycosidic bond different from the usual C1'-N9. The identification of these members of the family of NAD(+)-derived, calcium-active nucleotides opens new areas of investigation into their functional cooperation with cADPR and NAADP(+) and into their involvement in the physiology and pathology of calcium-controlled cell functions.

Tumor necrosis factor-alpha inhibits hTERT gene expression in human myeloid normal and leukemic cells

Telomerase catalytic subunit (hTERT) has been shown to play a critical role not only in telomere homeostasis but also in cellular survival, DNA repair, and genetic stability. In a previous study, we described that tumor necrosis factor-xalpha (TNFxalpha) induced in the leukemic KG1 cells a senescence state characterized by decreased hTERT activity followed by prolonged growth arrest, increasedx beta-galactosidase activity, telomere shortening, and major chromosomal instability. Interestingly, granulocyte-macrophage colony-stimulating factor (GM-CSF) abrogated all these events. In the present study, we show for the first time that TNFxalpha acts by inhibiting the hTERT gene in both normal CD34x+ cells and fresh leukemic cells. Using KG1 cells as a representative cellular model, we show that TNFxalpha induced sphingomyelin hydrolysis, ceramide production, and c-Jun N-terminal kinase (JNK) activation, all of which are critical components of TNFxalpha signaling, resulting in hTERT gene inhibition. Moreover, we provide evidence that the protective effect of GM-CSF is related to its capacity to interfere with both ceramide generation and ceramide signaling. Negative regulation of the hTERT gene may represent one mechanism by which TNFxalpha interferes with normal hemopoiesis.

Expression of interferon-gamma and tumor necrosis factor-alpha in bone marrow T cells and their levels in bone marrow plasma in patients with aplastic anemia

Immune-mediated stem cell damage has been postulated to be responsible for disease initiation and progression in aplastic anemia (AA). It is hypothesized that T lymphocytes play a major role in destroying the bone marrow (BM) stem cells of AA patients by infiltrating the BM and secreting excessive levels of anti-hematopoietic cytokines, interferon-gamma (IFN-gamma), and tumor necrosis factor-alpha (TNF-alpha). We undertook this study to assess the pathogenic significance of anti-hematopoietic cytokines such as IFN-gamma and TNF-alpha in BM T cells and plasma of AA patients. Significantly elevated levels of IFN-gamma and TNF-alpha were found in the BM plasma of AA patients compared to controls (p=0.05 and 0.006, respectively). Intracellular IFN-gamma and not TNF-alpha in BM CD3+ T cells of AA patients was significantly higher compared to controls (p=0.04 and p=0.2, respectively). A follow-up analysis of expression of these cytokines in BM T cells and their levels in BM plasma in five AA patients before and 180 days (6 months) after antithymocyte globulin (ATG) and cyclosporin A (CsA) therapy showed a decline 180 days after therapy compared to pre-therapy. We thus conclude that increased production of both IFN-gamma and TNF-alpha in the BM may contribute to disease pathogenesis in AA and ATG therapy may induce hematological remission by suppressing the elevated levels of IFN-gamma and TNF-alpha in AA BM.