Quantitative analysis of bone marrow CD34 cells in aplastic anemia and hypoplastic myelodysplastic syndromes

Comprehensive mapping of immune perturbations associated with aplastic anemia

BACKGROUND

Aplastic anemia (AA) is an immune-mediated syndrome characterized by bone marrow failure. Therefore, comprehending the cellular profile and cell interactions in affected patients is crucial.

METHODS

Human peripheral blood mononuclear cells (PBMCs) were collected from both healthy donors (HDs) and AA patients, and analyzed using multicolor flow cytometry. Utilizing the FlowSOM and t-SNE dimensionality reduction technique, we systematically explored and visualized the major immune cell alterations in AA. This analysis provided a foundation to further investigate the subtypes of cells exhibiting significant changes.

RESULTS

Compared to HDs, peripheral blood from patients with AA exhibits a marked reduction in CD56Dim natural killer (NK) cells, which also show diminished functionality. Conversely, an increase in NK-like CD56+ monocytes, which possess compromised functionality. Along with a significant reduction in myeloid-derived suppressor cells (MDSCs), which show recovery post-treatment. Additionally, MDSCs serve as effective clinical markers for distinguishing between acquired aplastic anemia (AAA) and congenital aplastic anemia (CAA). Our comprehensive analysis of correlations among distinct immune cell types revealed significant associations between NKBri cells and CD8+ T cell subsets, as well as between NKDim cells and CD4+ T cells, these results highlight the intricate interactions and correlations within the immune cell network in AA.

CONCLUSION

Our study systematically elucidates the pronounced immune dysregulation in patients with AA. The detailed mapping of the immune landscape not only provides crucial insights for basic research but also holds promise for enhancing the accuracy of diagnoses and the effectiveness of timely therapeutic interventions in clinical practice. Consequently, this could potentially reduce the high mortality rate associated with AA.

Guidelines for the diagnosis and management of adult aplastic anaemia: A British Society for Haematology Guideline

Pancytopenia with hypocellular bone marrow is the hallmark of aplastic anaemia (AA) and the diagnosis is confirmed after careful evaluation, following exclusion of alternate diagnosis including hypoplastic myelodysplastic syndromes. Emerging use of molecular cyto-genomics is helpful in delineating immune mediated AA from inherited bone marrow failures (IBMF). Camitta criteria is used to assess disease severity, which along with age and availability of human leucocyte antigen compatible donor are determinants for therapeutic decisions. Supportive care with blood and platelet transfusion support, along with anti-microbial prophylaxis and prompt management of opportunistic infections remain key throughout the disease course. The standard first-line treatment for newly diagnosed acquired severe/very severe AA patients is horse anti-thymocyte globulin and ciclosporin-based immunosuppressive therapy (IST) with eltrombopag or allogeneic haemopoietic stem cell transplant (HSCT) from a matched sibling donor. Unrelated donor HSCT in adults should be considered after lack of response to IST, and up front for young adults with severe infections and a readily available matched unrelated donor. Management of IBMF, AA in pregnancy and in elderly require special attention. In view of the rarity of AA and complexity of management, appropriate discussion in multidisciplinary meetings and involvement of expert centres is strongly recommended to improve patient outcomes.

Diagnostic Value of CD34 and CD117 Immunohistochemistry and Megakaryocyte Morphology in Myelodysplastic Syndromes: A Retrospective Case-control Study

This study evaluated the diagnostic value of CD34 and CD117 immunohistochemistry(IHC) and megakaryocyte morphology in Myelodysplastic syndromes (MDS). In this study, CD34-positive individual cells (Type I) and small clusters (Type II) were observed in most cases (91.2%). Type II CD34-positive was seen in 24 (49%) MDS cases, and positive percentage was higher than in acute myelogenous leukemia (AML) or aplastic anemia (AA). Type II CD117-positive were observed in 44 (89.8%) MDS cases and Type I were observed in 5 (10.2%) MDS. Type II CD117-positive percentage was higher than in AML or AA. Megakaryocyte counts were normal or increased in most MDS cases except one. Although megakaryocyte counts of AML and AA were predominantly decreased, Most MDS patients (81.6%) had abnormal megakaryocyte, whereas almost none of megakaryocyte abnormality was found in AML and AA. In conclusion, combined detection of CD34 and CD117 and observation of megakaryocyte count and morphology are useful for the diagnosis of MDS.

Diagnosis of immune pathophysiology in patients with bone marrow failure

Differential diagnosis of pancytopenia with bone marrow (BM) hypoplasia represented by aplastic anemia (AA) is often challenging for physicians, because no laboratory tests have been established, until recently, to distinguish immune-mediated BM failure, which includes acquired AA (aAA) and a subset of low-risk myelodysplastic syndrome (MDS), from non-immune BM failure, which is primarily caused by genetic abnormalities in hematopoietic stem cells (HSCs). HSCs of healthy individuals often undergo somatic mutations, and some acquire phenotypic changes that allow them to escape immune attack against themselves. Once an immune attack against HSCs occurs, HSCs that undergo somatic mutations survive the immune attack and continue to produce their progenies with the same genetic or phenotypic changes. The presence of mature blood cells derived from mutated HSCs in the peripheral blood serves as evidence of the immune-mediated destruction of HSCs. Glycosylphosphatidylinositol-anchored protein-deficient (GPI[-]) blood cells and HLA class I allele-lacking (HLA[-]) leukocytes are two major aberrant cell types that represent the immune mechanism underlying BM failure. This review focuses on the importance of identifying immune mechanisms using laboratory markers, including GPI(-) cells and HLA(-) leukocytes, in the management of BM failure.

Aplastic anemia and paroxysmal nocturnal hemoglobinuria in children and adults in two centers of Northern Greece

Bone marrow failure (BMF) syndromes are a group of various hematological diseases with cytopenia as a main common characteristic. Given their rarity and continuous progress in the field, we aim to provide data considering the efficiency and safety of the therapeutic methods, focusing on the treatment of aplastic anemia(AA) and paroxysmal nocturnal hemoglobinuria (PNH). We enrolled consecutive patients diagnosed with BMF in two referral centers of Northern Greece from 2008 to 2020. We studied 43 patients with AA (37 adults and 6 children/adolescents) and 6 with classical PNH. Regarding classical PNH, 4 patients have received eculizumab treatment with 1/4 presenting extravascular hemolysis. Among 43 patients with aplastic anemia, PNH clones were detected in 11. Regarding patients that did not receive alloHCT (n=15), 14/15 were treated with ATG and cyclosporine as first line, with the addition of eltrombopag in patients treated after its approval (n=9). With a median follow-up of 16.7 (1.8-56.2) months from diagnosis, 12/14 (85.7%) are alive (4-year OS: 85.1%). AlloHCT was performed in 28 patients. Five patients developed TA-TMA which did not resolve in 3/5 (all with a pre-transplant PNH clone). With the follow-up among survivors reaching 86.3 (6.3-262.4) months, 10-year OS was 56.9%, independently associated with PNH clones after adjusting for age (p=0.024). In conclusion, our real-world experience confirms that novel treatments are changing the field of BMF syndromes. Nevertheless, there is still an unmet need to personalize algorithms in this field.

Aplastic Anemia as a Roadmap for Bone Marrow Failure: An Overview and a Clinical Workflow

In recent years, it has become increasingly apparent that bone marrow (BM) failures and myeloid malignancy predisposition syndromes are characterized by a wide phenotypic spectrum and that these diseases must be considered in the differential diagnosis of children and adults with unexplained hematopoiesis defects. Clinically, hypocellular BM failure still represents a challenge in pathobiology-guided treatment. There are three fundamental topics that emerged from our review of the existing data. An exogenous stressor, an immune defect, and a constitutional genetic defect fuel a vicious cycle of hematopoietic stem cells, immune niches, and stroma compartments. A wide phenotypic spectrum exists for inherited and acquired BM failures and predispositions to myeloid malignancies. In order to effectively manage patients, it is crucial to establish the right diagnosis. New theragnostic windows can be revealed by exploring BM failure pathomechanisms.

A multicentre trial of intensive immunosuppressive therapy combined with umbilical cord blood for the treatment of severe aplastic anaemia

Immunosuppressive therapy (IST) is an effective treatment regimen for severe aplastic anaemia (SAA) patients without HLA-identical donors. This study further compared the outcomes between IST and IIST-UCB in SAA on the basis of research shown that IST combined with umbilical cord blood infusion (IIST-UCB) treated effectively. A total of 123 patients from 11 hospitals in China were enrolled. Sixty-nine patients in IIST-UCB group were treated with ATG + CsA + CTX combined with cord blood, while 54 patients in IST group with ATG + CsA. The overall remission rates (ORRs), complete remission (CR) rates and partial response (PR) rates of IIST-UCB group and IST group at 3 months were 69.67% vs 51.85% (P = .045), 21.74% vs 3.7% (P = .004) and 47.83% vs 48.15% (P = .972), respectively. After 6 months of treatment, they were 76.81% vs 57.41% (P = .022), 37.68% vs 11.11% (P = .001) and 39.13% vs 46.30% (P = .425), respectively. After 1 year of treatment, they were 85.51% vs 61.11% (P = .002), 59.42% vs 25.93% (P = .000) and 26.09% vs 35.19% (P = .275), respectively. The ORRs and CR rates of IIST-UCB group were both significantly higher than IST group after 3 months, 6 months and 1 year of treatment. The neutrophil granulocyte, platelet and haemoglobin recovery times of IIST-UCB group were significantly shorter than IST group. Compared with standard IST, IIST-UCB as an effective therapy for SAA patients without HLA-identical donors accelerated the haematopoietic reconstitution, resulting in higher early CR rates.

Measurement for the Area of Red Blood Cells From Microscopic Images Based on Image Processing Technology and Its Applications in Aplastic Anemia, Megaloblastic Anemia, and Myelodysplastic Syndrome

Background

Aplastic anemia (AA), megaloblastic anemia (MA), and myelodysplastic syndrome (MDS) were common anemic diseases. Sometimes it was difficult to distinguish patients with these diseases.

Methods

In this article, we proposed one measurement method for the area of red blood cells (RBCs) from microscopic images based on image processing technology and analyzed the differences of the area in 25 patients with AA, 64 patients with MA, and 68 patients with MDS.

Results

The area of RBCs was 44.19 ± 3.88, 42.09 ± 5.35, 52.87 ± 7.68, and 45.75 ± 8.07 μm2 in normal subjects, patients with AA, MA, and MDS, respectively. The coefficients of variation were 8.78%, 10.05%, 14.53%, and 14.00%, respectively, in these groups. The area of RBCs in patients with MA was significantly higher than normal subjects (p < 0.001). Compared with patients with AA and MDS, the area of RBCs in patients with MA was also significantly higher (p < 0.001). The results of correlation analysis between the area of RBCs and mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), MCH concentration (MCHC), and red cell distribution width showed no significant correlations (p > 0.05). The area under the curve (AUC) results of the Receiver Operating Characteristic (ROC) curves of RBCs area were 0.421, 0.580, and 0.850, respectively, in patients with AA (p = 0.337), MDS (p = 0.237), and MA (p < 0.001).

Conclusion

Identifying the area of RBCs in peripheral blood smears based on the image processing technology could achieve rapid and efficient diagnostic support for patients with MDS and MA, especially for patients with MA and in combination with MCV. However, a larger sample study is needed to find the cutoff area values.

Poly (A)-specific ribonuclease (PARN): More than just "mRNA stock clearing"

In eukaryotic cells, the balance between the synthesis and the degradation decides the steady-state levels of messenger RNAs (mRNA). The removal of adenosine residues from the poly(A) tail, called deadenylation, is the first and the most crucial step in the process of mRNA degradation. Poly (A)-specific ribonuclease (PARN) is one such enzyme that catalyses the process of deadenylation. Although PARN has been primarily known as the regulator of the mRNA stability, recent evidence clearly suggests several other functions of PARN, including a role in embryogenesis, oocyte maturation, cell-cycle progression, telomere biology, non-coding RNA maturation and ribosome biogenesis. Also, deregulated PARN activity is shown to be a hallmark of specific disease conditions. Pathogenic variants in the PARN gene have been observed in various cancers and inherited bone marrow failure syndromes. The focus in this review is to highlight the emerging functions of PARN, particularly in the context of human diseases.

Immunoexpression of CD34, CD117, and p53 in Hypocellular Bone Marrow Disorders

Objectives  Hypocellular bone marrow (BM) disorders comprise heterogeneous entities associated with peripheral cytopenias and decreased production of hematopoietic cells in BM. This study was undertaken to analyze immunohistochemical expression of CD34, CD117, and p53 in morphologically diagnosed patients of hypocellular BM (aplastic anemia [AA], hypocellular myelodysplastic syndrome [h-MDS], and hypocellular acute myeloid leukemia [h-AML]).

Materials and Methods  BM specimens were obtained from patients presenting with pancytopenia/bicytopenia. On 30 patients diagnosed as hypocellular BM, immunohistochemistry (IHC) for CD34, CD117, and p53 was performed.

Results  BM cellularity was < 30% in all (100%) patients. Blast count was increased in h-MDS and h-AML. Features of dysplasia were noted in six (20%) patients. Out of these, three patients were diagnosed as h-MDS having bilineage/trilineage dysplasia, and the other three patients were of AA (11.5% patients) displaying only dyserythropoiesis. On IHC, percentage of BM CD34+ cells was increased in h-MDS+ h-AML (3.87 ± 0.86) as compared with AA (0.19 ± 0.15) and controls (0.81 ± 0.21), p  = 0.01. Percentage of BM p53+ cells was also increased in h-MDS+ h-AML (2.9 ± 2.07) as compared with AA and controls, which did not show any p53+ cells, p  = 0.0. No statistically significant difference was observed in the expression of CD117 in h-MDS+ h-AML (4.95 ± 3.40) compared with AA (4.49 ± 1.07), p  = 0.99.

Conclusion  The study demonstrates the usefulness of CD34 and p53 immunoexpression as an important ancillary method in distinguishing various hypocellular BM disorders, especially h-MDS and AA. However, the role of CD117 remains unclear and needs to be evaluated further by larger studies.

Biology and clinical management of hypoplastic MDS: MDS as a bone marrow failure syndrome

Hypoplastic MDS is a subset of MDS characterized by marrow hypocellularity diagnosed in 10-15% of MDS patients. The pathogenesis of this disease shares features of aplastic anemia with activation of the effector T cells against hematopoietic stem and progenitor cells and high-risk MDS with acquisition of somatic mutations that provide survival and growth advantage of these cells in the inflammatory bone marrow microenvironment. Clonal evolution in hypoplastic MDS may be associated with accumulation of DNA damage and progression to AML while clonal hematopoiesis in aplastic anemia is strongly related to immune escape of the hematopoietic cells. Distinction of hypoplastic MDS from other acquired and inherited bone marrow failure syndromes is frequently challenging but it is critical for the appropriate clinical management of the patients. Treatment with immunosuppression is an important component of the clinical approach to patients with hypoplastic MDS while hypomethylating agents and early allogeneic bone marrow transplantation are also considerations in some patients. In this review, we summarize the current literature on the biology of hypoplastic MDS, the differences between this disease and other bone marrow failure syndromes, and the treatment algorithm for patients with this subtype of MDS.

Approach to the diagnosis of aplastic anemia

Establishing a diagnosis of aplastic anemia (AA) can be challenging, but it is absolutely critical to appropriate management, especially differentiating between acquired and inherited forms of the disease. The hematology field requires updated diagnostic guidelines to ensure that appropriate clinical pathways are pursued for patients and their safety. There are increasing clinical options for patients with immunosuppressive therapy and transplant once the diagnosis is made. In a case-based format, this review emphasizes the newer data on molecular (somatic and germline) findings in AA and how they are (or are not) helpful during diagnosis. There are key details on somatic mutation profiles and stated evidence where available for prognostic and treatment indications. Germline details of newer syndromes are also outlined, which make this review modern and reflect areas of uncertainty for clinicians.

Acquired severe aplastic anaemia: how medical therapy evolved in the 20th and 21st centuries

The progress in aplastic anaemia (AA) management is one of success. Once an obscure entity resulting in death in most affected can now be successfully treated with either haematopoietic stem cell transplantation (HSCT) or immunosuppressive therapy (IST). The mechanisms that underly the diminution of haematopoietic stem cells (HSCs) are now better elucidated, and include genetics and immunological alterations. Advances in supportive care with better antimicrobials, safer blood products and iron chelation have greatly impacted AA outcomes. Working somewhat 'mysteriously', anti-thymocyte globulin (ATG) forms the base for both HSCT and IST protocols. Efforts to augment immunosuppression potency have not, unfortunately, led to better outcomes. Stimulating HSCs, an often-sought approach, has not been effective historically. The thrombopoietin receptor agonists (Tpo-RA) have been effective in stimulating early HSCs in AA despite the high endogenous Tpo levels. Dosing, timing and best combinations with Tpo-RAs are being defined to improve HSCs expansion in AA with minimal added toxicity. The more comprehensive access and advances in HSCT and IST protocols are likely to benefit AA patients worldwide. The focus of this review will be on the medical treatment advances in AA.

Genetic Predisposition to Myelodysplastic Syndrome in Clinical Practice

Myelodysplastic syndromes (MDSs) are a heterogeneous group of marrow failure disorders that primarily affect older persons but also occur at a lower frequency in children and young adults. There is increasing recognition of an inherited predisposition to MDS as well as other myeloid malignancies for patients of all ages. Germline predisposition to MDS can occur as part of a syndrome or sporadic disease. The timely diagnosis of an underlying genetic predisposition in the setting of MDS is important. This article delineates germline genetic causes of MDS and provides a scaffold for the diagnosis and management of patients in this context.

Differences in the bone marrow histology between childhood myelodysplastic syndrome with multilineage dysplasia and refractory cytopenia of childhood without multilineage dysplasia

AIMS

Refractory cytopenia of childhood (RCC) is subdivided into myelodysplastic syndrome with multilineage dysplasia (MDS-MLD) and RCC without (w/o) multilineage dysplasia (RCC without MLD). Although RCC is a histomorphological distinct entity, the bone marrow (BM) histology of RCC is not yet characterised in relation to multilineage dysplasia. We investigated the BM histological features of RCC to clarify the characteristics of BM histology of MDS-MLD in childhood compared to RCC without MLD.

METHODS AND RESULTS

The BM histology and cytology in 60 RCC patients from the nationwide registry of Japanese Childhood AA-MDS Study Group were reviewed retrospectively. Although a thorough genetic assessment, including GATA2 and/or SAMD9, was not performed, inherited BM failure disorders were excluded by a cytogenetic test, a chromosome fragility test and a telomere length measurement along with careful clinical assessments. Among the 60 patients, 20 (33%) of MDS-MLD and 40 (67%) of RCC w/o MLD were classified according to their BM cytology. We then investigated the BM histological features and compared them between the two groups. The BM cellularity, distribution pattern of haematopoiesis, frequency of left-shifted granulopoiesis, numbers of micromegakaryocytes and p53 immunostaining-positive cells were significantly different between the groups. The BM histology of MDS-MLD in childhood showed higher cellularity, the more common occurrence of diffuse distribution pattern, more frequently left-shifted granulopoiesis and more micromegakaryocytes and p53 immunostaining-positive cells than RCC without MLD.

CONCLUSIONS

Our results showed that MDS-MLD in childhood had a characteristic BM histology compared to RCC without MLD. The clinical relevance of MDS-MLD in childhood needs to be evaluated.

Acquired and germline predisposition to bone marrow failure: Diagnostic features and clinical implications

Bone marrow failure and related syndromes are rare disorders characterized by ineffective bone marrow hematopoiesis and peripheral cytopenias. Although many are associated with characteristic clinical features, recent advances have shown a more complicated picture with a spectrum of broad and overlapping phenotypes and imperfect genotype-phenotype correlations. Distinguishing acquired from inherited forms of marrow failure can be challenging, but is of crucial importance given differences in the risk of disease progression to myelodysplastic syndrome, acute myeloid leukemia, and other malignancies, as well as the potential to genetically screen relatives and select the appropriate donor if hematopoietic stem cell transplantation becomes necessary. Flow cytometry patterns in combination with morphology, cytogenetics, and history can help differentiate several diagnostic marrow failure and/or insufficiency entities and guide genetic testing. Herein we review several overlapping acquired marrow failure entities including aplastic anemia, hypoplastic myelodysplasia, and large granular lymphocyte disorders; and several bone marrow disorders with germline predisposition, including GATA2 deficiency, CTLA4 haploinsufficiency, dyskeratosis congenita and/or telomeropathies, Fanconi anemia, Shwachman-Diamond syndrome, congenital amegakaryocytic thrombocytopenia, severe congenital neutropenia, and Diamond-Blackfan anemia with a focus on advances related to pathophysiology, diagnosis, and management.

A nationwide survey of hypoplastic myelodysplastic syndrome (a multicenter retrospective study)

Hypoplastic myelodysplastic syndrome (hMDS) is a distinct entity with bone marrow (BM) hypocellularity and the risk of death from BM failure (BMF). To elucidate the characteristics of hMDS, the data of 129 patients diagnosed between April 2003 and March 2012 were collected from 20 institutions and the central review team of the National Research Group on Idiopathic Bone Marrow Failure Syndromes, and compared with 115 non-hMDS patients. More RA and fewer CMMoL and RAEB-t in French-American-British (FAB) and more RCUD and MDS-U and fewer RCMD in World Health Organization (WHO) classifications were found in hMDS than non-hMDS with significant differences. The overall survival (OS) and AML progression-free survival (AML-PFS) of hMDS were higher than those of non-hMDS, especially in patients at age ≥50 and of lower risk in Revised International Prognostic Scoring System (IPSS-R). In competing risks analysis, hMDS exhibited decreased risk of AML-progression in lower IPSS or IPSS-R risk patients, and higher risk of death from BMF in patients at age ≥50. Poor performance status (PS ≥2) and high karyotype risks in IPSS-R (high and very high) were significant risk factors of death and AML-progression in Cox proportional hazards analysis.

Paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) is a clonal haematopoietic stem cell (HSC) disease that presents with haemolytic anaemia, thrombosis and smooth muscle dystonias, as well as bone marrow failure in some cases. PNH is caused by somatic mutations in PIGA (which encodes phosphatidylinositol N-acetylglucosaminyltransferase subunit A) in one or more HSC clones. The gene product of PIGA is required for the biosynthesis of glycosylphosphatidylinositol (GPI) anchors; thus, PIGA mutations lead to a deficiency of GPI-anchored proteins, such as complement decay-accelerating factor (also known as CD55) and CD59 glycoprotein (CD59), which are both complement inhibitors. Clinical manifestations of PNH occur when a HSC clone carrying somatic PIGA mutations acquires a growth advantage and differentiates, generating mature blood cells that are deficient of GPI-anchored proteins. The loss of CD55 and CD59 renders PNH erythrocytes susceptible to intravascular haemolysis, which can lead to thrombosis and to much of the morbidity and mortality of PNH. The accumulation of anaphylatoxins (such as C5a) from complement activation might also have a role. The natural history of PNH is highly variable, ranging from quiescent to life-threatening. Therapeutic strategies include terminal complement blockade and bone marrow transplantation. Eculizumab, a monoclonal antibody complement inhibitor, is highly effective and the only licensed therapy for PNH.

Distinct routes of lineage development reshape the human blood hierarchy across ontogeny

In a classical view of hematopoiesis, the various blood cell lineages arise via a hierarchical scheme starting with multipotent stem cells that become increasingly restricted in their differentiation potential through oligopotent and then unipotent progenitors. We developed a cell-sorting scheme to resolve myeloid (My), erythroid (Er), and megakaryocytic (Mk) fates from single CD34(+) cells and then mapped the progenitor hierarchy across human development. Fetal liver contained large numbers of distinct oligopotent progenitors with intermingled My, Er, and Mk fates. However, few oligopotent progenitor intermediates were present in the adult bone marrow. Instead, only two progenitor classes predominate, multipotent and unipotent, with Er-Mk lineages emerging from multipotent cells. The developmental shift to an adult "two-tier" hierarchy challenges current dogma and provides a revised framework to understand normal and disease states of human hematopoiesis.

Anemia of Central Origin

Hypoproliferative anemia results from the inability of bone marrow to produce adequate numbers of red blood cells. The list of conditions that cause hypoproliferative anemia is long, starting from common etiologies as iron deficiency to rarer diagnoses of constitutional bone marrow failure syndromes. There is no perfect diagnostic algorithm, and clinical data may not always clearly distinguish "normal" from "abnormal", yet it is important for practicing clinicians to recognize each condition so that treatment can be initiated promptly. This review describes diagnostic approaches to hypoproliferative anemia, with particular emphasis on bone marrow failure syndromes.

I walk the line: how to tell MDS from other bone marrow failure conditions

Myelodysplastic syndromes (MDS) are clonal hematopoietic stem cell disorders characterized by peripheral cytopenias and ineffective hematopoiesis. MDS is an example of an age-related malignancy and its increasing prevalence and incidence can be attributed to a greater life expectancy in developed countries. Although frequently encountered in hematology/oncology clinics, MDS may constitute a diagnostic challenge especially with equivocal bone marrow morphology. Certain syndromes of bone marrow failure (BMF) may mimic MDS and formulating a correct diagnosis is vital for adequate prognostication as well as therapeutic approaches. Metaphase karyotyping (MK) is a very important diagnostic tool and marker of prognosis and can be an indicator of response to certain therapies. Unfortunately, chromosomal abnormalities may only be found in approximately 50 % of patients with MDS. In this review, we discuss the diagnostic approaches to patients with pancytopenia with a particular focus on the growing number of somatic mutations through new molecular testing.

GATA2 deficiency-associated bone marrow disorder differs from idiopathic aplastic anemia

Germ-line GATA2 gene mutations, leading to haploinsufficiency, have been identified in patients with familial myelodysplastic syndrome/acute myeloid leukemia, monocytopenia and mycobacterial infections, Emberger syndrome, and dendritic cell, monocyte, B-, and NK-cell deficiency. GATA2 mutations have also been reported in a minority of patients with congenital neutropenia and aplastic anemia (AA). The bone marrow (BM) from patients with GATA2 deficiency is typically hypocellular, with varying degrees of dysplasia. Distinguishing GATA2 patients from those with AA is critical for selecting appropriate therapy. We compared the BM flow cytometric, morphologic, and cytogenetic features of 28 GATA2 patients with those of 32 patients being evaluated for idiopathic AA. The marrow of GATA2 patients had severely reduced monocytes, B cells, and NK cells; absent hematogones; and inverted CD4:CD8 ratios. Atypical megakaryocytes and abnormal cytogenetics were more common in GATA2 marrows. CD34(+) cells were comparably reduced in GATA2 and AA. Using these criteria, we prospectively identified 4 of 32 patients with suspected AA who had features suspicious for GATA2 mutations, later confirmed by DNA sequencing. Our results show that routine BM flow cytometry, morphology, and cytogenetics in patients who present with cytopenia(s) can identify patients for whom GATA2 sequencing is indicated.

CD34 and p53 immunohistochemical stains differentiate hypocellular myelodysplastic syndrome (hMDS) from aplastic anemia and a CD34 immunohistochemical stain provides useful survival information for hMDS

Background

The presence of significant dysplasia in bone marrow (BM) aspirates helps to distinguish between hypocellular myelodysplastic syndrome (hMDS) and aplastic anemia (AA). Occasionally, diluted BM aspirates make it difficult to recognize dysplastic changes and can also negatively affect the detection of cytogenetic abnormalities in hMDS. We evaluated the usefulness of CD34 and p53 immunoreactivity for discriminating between hMDS and AA and for estimating survival outcomes in hMDS patients.

Methods

BM clot section (BMC) or BM biopsy (BMB) specimens were obtained from 64 hMDS/AA patients (33 with hMDS and 31 with AA) and seven controls. Immunohistochemical (IHC) staining for CD34 and p53 was performed by using the EnVision detection system (Dako, Denmark). We compared the results of IHC staining, BM findings, and chromosomal analyses, and determined overall survival outcomes.

Results

The number of CD34- and p53-positive BM cells was higher among the patients with hMDS than among the patients with AA (P<0.001 and P=0.001, respectively). hMDS patients with increased CD34-positive cells had significantly poorer survival outcomes compared with those with normal number of CD34-positive cells (P=0.013).

Conclusions

CD34 and p53 IHC stains of BMC or BMB provide useful information for differentiating between hMDS and AA. CD34 IHC staining of BMC or BMB also provides useful information for estimating survival outcomes in hMDS patients.

The challenging world of cytopenias: distinguishing myelodysplastic syndromes from other disorders of marrow failure

Over the past decade, our understanding of bone marrow failure has advanced considerably. Marrow failure encompasses multiple overlapping diseases, and there is increasing availability of diagnostic tools to distinguish among the subtypes. Identification of genetic alterations that underlie marrow failure has also greatly expanded, especially for myelodysplastic syndromes. Molecular markers are increasingly used to guide the management of myelodysplasia and may distinguish this diagnosis from other marrow failure disorders. This review summarizes the current state of distinguishing among causes of marrow failure and discusses the potential uses of multiple diagnostic and prognostic indicators in the management of myelodysplastic syndromes and other bone marrow failure disorders.

Mesenchymal stem cells in immune-mediated bone marrow failure syndromes

Immune-mediated bone marrow failure syndromes (BMFS) are characterized by ineffective marrow haemopoiesis and subsequent peripheral cytopenias. Ineffective haemopoiesis is the result of a complex marrow deregulation including genetic, epigenetic, and immune-mediated alterations in haemopoietic stem/progenitor cells, as well as abnormal haemopoietic-to-stromal cell interactions, with abnormal release of haemopoietic growth factors, chemokines, and inhibitors. Mesenchymal stem/stromal cells (MSCs) and their progeny (i.e., osteoblasts, adipocytes, and reticular cells) are considered as key cellular components of the bone marrow haemopoietic niche. MSCs may interfere with haemopoietic as well as immune regulation. Evidence suggests that bone marrow MSCs may be involved in immune-mediated BMFS underlying pathophysiology, harboring either native abnormalities and/or secondary defects, caused by exposure to activated marrow components. This review summarizes previous as well as more recent information related to the biologic/functional characteristics of bone marrow MSCs in myelodysplastic syndromes, acquired aplastic anemia, and chronic idiopathic neutropenia.

Burst-forming unit-erythroid assays to distinguish cellular bone marrow failure disorders

Patients with cytopenias and a cellular bone marrow can be a diagnostic and therapeutic challenge. Previous reports suggested a role for progenitor assays for diagnosis and predicting response to therapy. We report the results of Burst-forming unit-erythroid (BFU-E) assays in 48 consultative cases of single or multilineage cytopenias with cellular marrows. The final diagnoses included 17 patients with myelodysplastic syndrome, 9 patients with pure red cell aplasia (non-large granular lymphocytosis [LGL] in etiology], 15 patients with LGL (eight of whom had a single-lineage cytopenia only, whereas the other seven had multilineage cytopenias), and 7 patients with cytopenias associated with systemic inflammation from autoimmune conditions. In this cohort, nonmalignant diseases were well-distinguished from myelodysplastic syndrome by BFU-E growth. Our data suggest that low BFU-E growth (less than 10 BFU-E per 10(5) marrow mononuclear cells) helps to exclude LGL, pure red cell aplasia, or cytopenias associated with systemic inflammation as a cause of pancytopenia with a sensitivity of 96.8%, specificity of 76.5%, and a predictive value of 88.2% (p = 0.0001). BFU-E growth also was examined to predict treatment response. Of the 29 patients in this cohort treated with immunosuppressive therapy, there was an 86% response rate with 25 responders (11 partial responses and 14 complete responses) and 4 nonresponders. This result correlated with higher BFU-E growth. Our results suggest that BFU-E assays are a useful adjunct in the diagnosis and management of cytopenias in the setting of a normocellular or hypercellular marrows.

Impaired immunomodulatory ability of bone marrow mesenchymal stem cells on CD4(+) T cells in aplastic anemia

Aplastic anemia (AA) is a marrow failure syndrome mediated by aberrant T-cell subsets. Mesenchymal stem cells (MSCs) play an important role in maintaining immune homeostasis through modulating a variety of immune cells. However, little is known about the immunomodulation potential of bone marrow MSCs (BM-MSCs) in AA. Here, we reported that BM-MSCs from AA patients were reduced in suppressing the proliferation and clonogenic potential of CD4(+) T cells and the production of tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ), which was associated with decreased prostaglandin E2 (PGE2). Meanwhile, BM-MSCs from AA patients were defective to promote CD4(+)CD25(+)FOXP3(+) regulatory T cells expansion through reduced transforming growth factor-β (TGF-β). No significant difference between AA and normal BM-MSCs was observed in affecting the production of interleukins (IL)-4, IL-10 and IL-17. Our data indicate that BM-MSCs were impaired in maintaining the immune homeostasis associated with CD4(+) T cells, which might aggravate the marrow failure in AA.

Diagnosis and treatment of acquired aplastic anaemia in adults: 142 cases from a multicentre, prospective cohort study in Shanghai, China

To improve diagnosis and therapy for aplastic anaemia (AA) in Shanghai, clinical and laboratory data for patients with AA (n = 142) and hypocellular myelodysplastic syndrome (MDS; n = 22) were comparatively analysed (follow-up 2 - 6 years). Red blood cell distribution width and absolute lymphocyte and reticulocyte counts were significantly different between the two groups. AA was diagnosed in 54.2% of patients using a single bone marrow aspirate smear plus peripheral haemogram results, and in 95.1% using an additional bone marrow biopsy; 4.9% required multiple-site bone marrow examination. Clonal chromosomal abnormalities occurred in 3.9% and 31.8% of patients with AA and MDS, respectively. In patients with severe AA, 12.0% received antithymocyte globulin (ATG) + cyclosporin A (CSA; effectiveness rate 77.8%; 5-year survival 74.1%), 45.3% received CSA + androgen therapy (effectiveness rate 58.8%; 5-year survival 76.5%) and 26.7% received androgen monotherapy (effectiveness rate 25.0%). Multivariate analysis of prognostic factors indicated that therapy regimen and blood platelet count affected survival. Peripheral blood smears, bone marrow spicule classification and biopsy are important diagnostic factors. Standardization of evidence-based therapy and promotion of ATG + CSA would improve general therapeutic effects in AA.

Clinical management of aplastic anemia

Acquired aplastic anemia is a potentially fatal bone marrow failure disorder that is characterized by pancytopenia and a hypocellular bone marrow. Hematopoietic stem-cell transplantation or bone marrow transplantation (BMT) is the treatment of choice for young patients who have a matched sibling donor. Immunosuppression with either anti-thymocyte globulin and cyclosporine or high-dose cyclophosphamide is an effective therapy for patients who are not suitable BMT candidates owing to age or lack of a suitable donor. Results of BMT from unrelated and mismatched donors are improving, but presently this treatment option is best reserved for those patients who do not respond, relapse or develop secondary clonal disorders following immunosuppressive therapy. Efforts are currently underway to both improve immunosuppressive regimens and to expand the application of BMT.

Long-term outcome of isolated thrombocytopenia accompanied by hypocellular marrow

Background

Hypocellularity of bone marrow (BM), not associated with significant dyshematopoiesis, is often found in patients with isolated thrombocytopenia, but its clinical implications have not been studied. We prospectively studied the clinical features and natural history of these patients.

Methods

Adults with isolated thrombocytopenia (platelet counts <100×10⁹/L) in the absence of dyshematopoiesis, cytogenetic abnormalities, or megakaryocytic hyperplasia and who had BM hypocellularity (below 30% in patients aged less than 60 years; below 20% in patients aged 60 years or more) were enrolled at Chungnam National University Hospital between January 2002 and December 2006. They were monitored regularly for changes in platelet counts or development of additional cytopenia.

Results

Twenty patients (17 men and 3 women) were enrolled in the study. The median age was 29 years (range, 18-70 years). At initial presentation, the platelet counts ranged from 12×10⁹/L to 99×10⁹/L (median, 63×10⁹/L) and were >50×10⁹/L in 16 patients (80%). BM cellularity ranged from 5% to 25% (median, 15%) and was ≤10% in 6 patients (30%). During the median 48-month follow-up (range, 12-90 months), platelet counts of 3 of the 20 patients recovered to normal levels (>150×10⁹/L) after 12, 56 and 66 months. Three patients developed pancytopenia after 11, 70 and 90 months. Two patients were consistent with moderate aplastic anemia, and 1 was confirmed as having refractory cytopenia with multilineage dysplasia. In the remainder of the patients, platelet counts remained unchanged.

Conclusion

Isolated thrombocytopenia accompanied by hypocellular marrow encompasses a group of heterogeneous conditions.

Apoptotic bone marrow CD34+ cells in cirrhotic patients

AIM: To access the frequency and level of apoptotic CD34+ cells isolated from the marrow fluid of patients with post-hepatitis cirrhosis.

METHODS: The frequency of bone marrow CD34+ cells and apoptotic bone marrow CD34+ cells in 31 in-patients with post-hepatitis cirrhosis (cirrhosis group), and 15 out-patients without liver or blood disorders (control group) was calculated by flow cytometry. Parameters were collected to evaluate liver functions of patients in cirrhosis group.

RESULTS: The percentage of normal bone marrow CD34+ cells was 6.30% ± 2.48% and 1.87% ± 0.53% (t = 3.906, P < 0.01) while that of apoptotic marrow CD34+ cells was 15.00% ± 15.81% and 5.73% ± 1.57% (t = 2.367, P < 0.05) in cirrhosis and control groups, respectively. The percentage of apoptotic marrow CD34+ cells was 6.25% ± 3.30% and 20.92 ± 18.5% (t = 2.409, P < 0.05) in Child-Pugh A and Child-Pugh B + C cirrhotic patients, respectively. The percentage of late apoptotic marrow CD34+ cells was positively correlated with the total bilirubin and aspartate aminotransferase serum levels in patients with cirrhosis.

CONCLUSION: The status of CD34+ marrow cells in cirrhotic patients may suggest that the ability of hematopoietic progenitor cells to transform into mature blood cells is impaired.

Comparison of immunological abnormalities of lymphocytes in bone marrow in myelodysplastic syndrome (MDS) and aplastic anemia (AA)

OBJECTIVE

The subsets and the polarization of lymphocytes in bone marrow from low-risk myelodysplastic syndrome (MDS) were studied and compared with those from patients with aplastic anemia (AA).

METHODS

A total of 34 patients with low-risk MDS (IPSS score< or =1.0) who presented abnormal chromosomes and 16 patients with AA were enrolled in this study. We determined T lymphocyte subsets, T cells polarization status, and the percentages of NK cells and of B lymphocytes in bone marrow and compared these parameters between the two groups of patients. As controls, 24 patients with high-risk MDS (IPSS score>1.0) presenting abnormal chromosomes and 22 healthy/benign hematologic disease subjects were used.

RESULTS

In low-risk MDS/AA patients, the percentage of CD3+ lymphocytes was significantly increased compared to controls (p=0.006 and p=0.001), while the percentage of CD19+ lymphocytes was significantly decreased (p<0.001 and p=0.002); there were no significant differences between MDS/AA and normal controls in other parameters; For low-risk MDS patients, the polarization status of bone marrow CD4+ cells toward Th1 (Th1/Th2) and of CD8+ cells toward Tc1 (Tc1/Tc2) was stronger than that for AA patients (p=0.05 and p<0.001). Other parameters did not show significant differences; Regardless of the predominance of CD4 or CD8 T cells, all patients with low-risk MDS were accompanied with elevated Tc1 polarization (Tc1/Tc2).

CONCLUSION

In both AA and MDS, the number of total T lymphocytes increased. However, polarization towards Th1 and Tc1 was obviously stronger in MDS patients than in AA patients. This might be related to T cell stimulation from the clones of malignant hematopoietic cells.

Abnormal immunity and stem/progenitor cells in acquired aplastic anemia

Acquired aplastic anemia (AA) is considered as an immune-mediated bone marrow failure syndrome, characterized by hypoplasia and pancytopenia with fatty bone marrow. Abnormal immunity is the major factor mediating the pathogenesis of acquired AA. Activated DCs might promote the polarization to Th1 cells, and activate CD8(+) T cells. A variety of immune molecules including IFN-gamma, TNF-alpha, MIP-1alpha and IL-2, 8, 12, 15, 17, 23, produced by them and stromal cells, compose a cytokine network to destruct stem/progenitor cells as well as hematopoietic stem/progenitor cells, mesenchymal stem cells (MSCs) and angioblasts/endothelial progenitor cells. Inversely, deficient MSCs, CD4(+)CD25(+) T cells, NK cells, NKT cells and early hematopoietic growth factors diminish the capacity of immune regulation and the support of hematopoiesis. As a result, stem/progenitor cells are significantly impaired to be disabled cells with markedly deficient proliferation, differentiation, induced apoptosis and dysfunctional response to growth factor stimuli, together with rare normal ones. Although some patients can be ameliorated by stem-cell transplantation or immunosuppressive therapy, more effective and convenient therapies such as patient-specific pluripotent iPS cells based on definite pathogenesis are expected.

Myelodysplastic syndromes

Session 4 of the 2007 Workshop of the Society for Hematopathology/European Association for Haematopathology was devoted to myelodysplastic syndromes (MDSs). Submitted cases highlighted important issues and difficulties in relation to the diagnosis and classification of MDS. Much of the discussion focused on the correlation, or lack of it, between morphologic examination and other diagnostic techniques, cytogenetics in particular. The cases included examples of isolated del(5q) chromosomal abnormality, including the "classical" 5q- syndrome and other myeloid neoplasms. Other cytogenetic abnormalities in MDSs and the role of cytogenetics in diagnosing MDSs were addressed. Particularly challenging is the correct identification of fibrotic subtypes of MDSs and their separation from subsets of acute myeloid leukemia with myelofibrosis such as acute panmyelosis with myelofibrosis. The association and eventual relation of MDSs (hypoplastic in particular) with aplastic anemia, paroxysmal nocturnal hemoglobinuria, and other nonneoplastic disorders were illustrated. Novel cytogenetic and molecular genetic approaches are likely to revolutionize the classification of MDSs. However, it is unlikely that these new techniques will be capable, on their own, of adequately stratifying patients for treatment purposes. At least for the foreseeable future, the diagnosis of MDS requires integration of morphologic, immunophenotypic, and genetic features in the light of patient history and clinical manifestations.

How I treat paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare clonal blood disorder that manifests with hemolytic anemia, bone marrow failure, and thrombosis. Many of the clinical manifestations of the disease result from complement-mediated intravascular hemolysis. Allogeneic bone marrow transplantation is the only curative therapy for PNH. Eculizumab, a monoclonal antibody that blocks terminal complement activation, is highly effective in reducing hemolysis, improving quality of life, and reducing the risk for thrombosis in PNH patients. Insights into the relevance of detecting PNH cells in PNH and other bone marrow failure disorders are highlighted, and indications for treating PNH patients with bone marrow transplantation and eculizumab are explored.

Diagnostic challenges in the myelodysplastic syndromes: the current and future role of genetic and immunophenotypic studies

Myelodysplastic syndromes (MDS) comprise a clinically and pathologically diverse collection of hematopoietic neoplasms, most commonly presenting with peripheral cytopenias typically in the context of bone marrow hypercellularity. Mechanistically, at least in the early phases of the disease, this apparently paradoxical picture is primarily due to ineffective hematopoiesis, which is accompanied by a variety of morphologic abnormalities in hematopoietic cells. The identification of recurrent, clinically relevant cytogenetic defects in MDS has spurred the research of molecular mechanisms that contribute to its inception as well as to the development of heterogeneous subtypes. Although conventional cytogenetic analyses remain a diagnostic mainstay in MDS, the application of contemporary techniques including molecular cytogenetics, microarray technologies and multiparametric flow cytometry may ultimately reveal new diagnostic parameters that are theoretically more objective and sensitive than current morphologic approaches. This review aims to outline the role of genetic and immunophenotypic studies in the evaluation of MDS, including findings that may potentially influence future diagnostic classifications, which could refine prognostication and ultimately facilitate the growth of targeted therapies.

The utility of flow cytometric immunophenotyping in cytopenic patients with a non-diagnostic bone marrow: a prospective study

Cytopenia is a common problem in hematology outpatient clinics and among hospitalized patients. A bone marrow (BM) aspirate and biopsy are often performed to rule out an infiltrative versus intrinsic BM process, such as myelodysplastic syndrome (MDS). We have previously described a flow cytometric (FCM) assay useful in diagnosing MDS and demonstrated its good correlation with "gold standard" morphologic and cytogenetic criteria. In this study, we prospectively tested the utility of the FCM assay in 102 cytopenic patients with BMs showing neither diagnostic morphological dysplasia nor abnormal cytogenetics. FCM, following our published criteria, was positive in 22 cases (21.6%), intermediate in 11 cases (10.8%) and negative in 69 cases (67.6%). With a median follow-up period of 11 months (range, 4-24 months), 12 (11.8%) patients were proven to have or/develop MDS or related BM diseases (group-1); 61 (59.8%) patients had their cytopenia(s) attributed to various medical causes (group-2). In the remaining 29 patients, the causes of cytopenia(s) were not found, and some had the features consistent with the recently defined clinical entity -- idiopathic cytopenia of uncertain significance. A positive FCM result was significantly more prevalent (9/12, 75%) in group-1 patients; while a negative FCM result was significantly more frequent in group-2 patients (4/61, 7%) (p<0.0001) with a positive predictive value of 69% and a negative predictive value of 95%. We conclude that FCM analysis of myelomonocytic maturation has diagnostic utility in cytopenic patients who have an inconclusive BM examination by morphologic and cytogenetic evaluation, and may therefore be a useful adjunct in clinical management of these patients.

Paroxysmal nocturnal hemoglobinuria: stem cells and clonality

Paroxysmal nocturnal hemoglobinuria is a clonal hematopoietic stem cell disease that manifests with intravascular hemolysis, bone marrow failure, thrombosis, and smooth muscle dystonias. The disease can arise de novo or in the setting of acquired aplastic anemia. All PNH patients to date have been shown to harbor PIG-A mutations; the product of this gene is required for the synthesis of glycosylphosphatidylinositol (GPI) anchored proteins. In PNH patients, PIG-A mutations arise from a multipotent hematopoietic stem cell. Interestingly, PIG-A mutations can also be found in the peripheral blood of most healthy controls; however, these mutations arise from progenitor cells rather than multipotent hematopoietic stem cells and do not propagate the disease. The mechanism of whereby PNH stem cells achieve clonal dominance remains unclear. The leading hypotheses to explain clonal outgrowth in PNH are: 1) PNH cells evade immune attack possibly, because of an absent cell surface GPI-AP that is the target of the immune attack; 2) The PIG-A mutation confers an intrinsic resistance to apoptosis that becomes more conspicuous when the marrow is under immune attack; and 3) A second mutation occurs in the PNH clone to give it an intrinsic survival advantage. These hypotheses may not be mutually exclusive, since data in support of all three models have been generated.

Histopathology in the diagnosis and classification of acute myeloid leukemia, myelodysplastic syndromes, and myelodysplastic/myeloproliferative diseases

In spite of the impressive advances in the area of molecular pathology, bone marrow morphology remains the diagnosis cornerstone to identify the various subtypes of myeloid neoplasms. Morphological examination of the bone marrow requires both bone marrow aspirate and bone marrow trephine biopsy. Immunohistochemistry of bone marrow biopsy with markers reactive in paraffin-embedded tissues represents a powerful diagnostic tool; its results can be easily correlated with those obtained by other techniques such as flow cytometry and genetic analysis, and above all, the clinical findings. The role of the bone marrow biopsy will be particularly stressed in this review article. Particular emphasis is being given to the correct identification of cases of myeloid neoplasms associated with myelofibrosis and for which the bone marrow biopsy represents the only available diagnostic mean. Moreover, the often low cellular yield of the bone marrow aspirate in these cases may also be insufficient to obtain adequate cytogenetic information. Such cases include two subtypes of acute myeloid leukemia which typically cause diagnostic difficulties: acute megakaryoblastic leukemia and acute panmyelosis with myelofibrosis (acute myelosclerosis). Acute myeloid leukemia with multilineage dysplasia, therapy-related myelodysplastic syndrome/therapy-related acute myeloid leukemia and de novo myelodysplastic syndromes (MDS) will also be discussed. The value of bone marrow biopsy in this group of disorders is generally well established. In MDS, in particular, bone marrow biopsy may help in confirming a suspected diagnosis by excluding reactive conditions in which dyshematopoietic changes may also be observed. It can increase the diagnostic accuracy and helps in refining the IPPS risk evaluation system. Among the alterations detected by bone marrow biopsy, a prognostically important finding is the presence of aggregates or clusters of immature myeloid precursor cells (myeloblasts and promyelocytes). These can also be identified by immunohistochemistry with CD34, an antigen expressed in progenitor and early precursor marrow cells, which can be used to demonstrate pathological accumulations of blasts in aggressive subtypes of myeloid neoplasms. Immunohistologic analysis is especially helpful in cases of MDS with fibrosis and cases with hypocellular marrows (hypoplastic MDS). In both of these variants, the presence of reticulin fibrosis or fatty changes in the bone marrow can make accurate disease characterization very difficult or impossible using bone marrow aspirates. Finally, the important group of the myelodysplastic/myeloproliferative disorders can only be accurately categorized by a careful multiparametric approach in which the bone marrow biopsy exerts a pivotal role.

PIG-A mutations in paroxysmal nocturnal hemoglobinuria and in normal hematopoiesis

PIG-A is an X-linked gene that is essential for the first step in the biosynthesis of glycosylphosphatidyl-inositol (GPI) anchors. A rare clonal hematopoietic stem cell disease, paroxysmal nocturnal hemoglobinuria (PNH), is caused by mutations in the PIG-A gene. PNH is an acquired disease that may arise de novo or emanate from aplastic anemia. PNH blood cells have an absence or marked deficiency of all GPI anchored proteins. Interestingly, rare GPI anchor deficient blood and marrow cells that harbor PIG-A mutations can also be found in most healthy controls. This review examines the clinical and biological relevance of PIG-A mutations in PNH, aplastic anemia and healthy controls.

New insights into paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is an uncommon intravascular hemolytic anemia that results from the clonal expansion of hematopoietic stem cells harboring somatic mutations in an X-linked gene, termed PIG-A. PIG-A mutations block glycosylphosphatidylinositol (GPI) anchor biosynthesis, resulting in a deficiency or absence of all GPI-anchored proteins on the cell surface. CD55 and CD59 are GPI-anchored complement regulatory proteins. Their absence on PNH red cells is responsible for the complement-mediated intravascular hemolysis. Intravascular hemolysis leads to release of free hemoglobin, which contributes to many of the clinical manifestations of PNH including fatigue, pain, esophageal spasm, erectile dysfunction and possibly thrombosis. Interestingly, rare PIG-A mutations can be found in virtually all healthy control subjects, leading to speculation that PIG-A mutations in hematopoietic stem cells are common benign events. However, negative selection of PIG-A mutant colony-forming cells with proaerolysin, a toxin that targets GPI-anchored proteins, reveals that most of these mutations are not derived from stem cells. Recently, a humanized monoclonal antibody directed against the terminal complement protein C5 has been shown to reduce hemolysis and greatly improve symptoms and quality of life for PNH patients.