Abnormal T-cell repertoire is consistent with immune process underlying the pathogenesis of paroxysmal nocturnal hemoglobinuria

A Journey from Blood Cells to Genes and Back

I was attracted to hematology because by combining clinical findings with the use of a microscope and simple laboratory tests, one could often make a diagnosis. I was attracted to genetics when I learned about inherited blood disorders, at a time when we had only hints that somatic mutations were also important. It seemed clear that if we understood not only what genetic changes caused what diseases but also the mechanisms through which those genetic changes contribute to cause disease, we could improve management. Thus, I investigated many aspects of the glucose-6-phosphate dehydrogenase system, including cloning of the gene, and in the study of paroxysmal nocturnal hemoglobinuria (PNH), I found that it is a clonal disorder; subsequently, we were able to explain how a nonmalignant clone can expand, and I was involved in the first trial of PNH treatment by complement inhibition. I was fortunate to do clinical and research hematology in five countries; in all of them, I learned from mentors, from colleagues, and from patients.

Evaluating ravulizumab for the treatment of children and adolescents with paroxysmal nocturnal hemoglobinuria

INTRODUCTION

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare acquired clonal stem cell disease harvesting a somatic mutation in the phosphatidylinositol glycan class A (PIG-A) gene. This mutation results in a deficiency in cell membrane complement regulators leading to activation of the terminal complement pathway, clinically presenting as hemolytic anemia and thrombosis, and frequently associated with bone marrow failure. This condition was historically managed with supportive care and bone marrow transplant.

AREAS COVERED

This paper will review primary data on the pharmacology, efficacy, and safety of ravulizumab in the pediatric/adolescent population gathered from literature search from PubMed, abstracts from annual meetings, and medication package inserts. Eligible clinical trials identified on the clinicaltrials.gov website are also briefly discussed.

EXPERT OPINION

: The discovery of eculizumab, a monoclonal antibody against complement protein 5, has revolutionized the PNH landscape, with decreased hemolysis and risk of thrombosis, improved quality-of-life, and has become the standard of care. Ravulizumab, a longer-acting C5-inhibitor with 4 times the half-life of eculizumab, was recently approved for pediatric patients with PNH. Ravulizumab is effective, safe, and has the potential to improve quality of life further. In addition, ongoing clinical trials using second-generation complement inhibitors may provide promising new interventions in PNH.

Pegcetacoplan for Paroxysmal Nocturnal Hemoglobinuria

Approximately a third of patients with paroxysmal nocturnal hemoglobinuria (PNH) remain transfusion dependent or have symptomatic anemia despite treatment with a C5 inhibitor. Pegcetacoplan inhibits complement proximally at the level of C3 and is highly effective in treating persistent anemia resulting from C3-mediated extravascular hemolysis. We describe the rationale for C3 inhibition in the treatment of PNH and discuss preclinical and clinical studies using pegcetacoplan and other compstatin derivatives. We propose an approach for sequencing complement inhibitors in PNH.

The predictive value of PNH clones, 6p CN-LOH, and clonal TCR gene rearrangement for aplastic anemia diagnosis

Acquired aplastic anemia (AA) is a life-threatening bone marrow aplasia caused by the autoimmune destruction of hematopoietic stem and progenitor cells. There are no existing diagnostic tests that definitively establish AA, and diagnosis is currently made via systematic exclusion of various alternative etiologies, including inherited bone marrow failure syndromes (IBMFSs). The exclusion of IBMFSs, which requires syndrome-specific functional and genetic testing, can substantially delay treatment. AA and IBMFSs can have mimicking clinical presentations, and their distinction has significant implications for treatment and family planning, making accurate and prompt diagnosis imperative to optimal patient outcomes. We hypothesized that AA could be distinguished from IBMFSs using 3 laboratory findings specific to the autoimmune pathogenesis of AA: paroxysmal nocturnal hemoglobinuria (PNH) clones, copy-number-neutral loss of heterozygosity in chromosome arm 6p (6p CN-LOH), and clonal T-cell receptor (TCR) γ gene (TRG) rearrangement. To test our hypothesis, we determined the prevalence of PNH, acquired 6p CN-LOH, and clonal TRG rearrangement in 454 consecutive pediatric and adult patients diagnosed with AA, IBMFSs, and other hematologic diseases. Our results indicated that PNH and acquired 6p CN-LOH clones encompassing HLA genes have ∽100% positive predictive value for AA, and they can facilitate diagnosis in approximately one-half of AA patients. In contrast, clonal TRG rearrangement is not specific for AA. Our analysis demonstrates that PNH and 6p CN-LOH clones effectively distinguish AA from IBMFSs, and both measures should be incorporated early in the diagnostic evaluation of suspected AA using the included Bayesian nomogram to inform clinical application.

Immunologic effects on the haematopoietic stem cell in marrow failure

Acquired bone marrow failure (BMF) syndromes comprise a diverse group of diseases with variable clinical manifestations but overlapping features of immune activation, resulting in haematopoietic stem and progenitor cells (HSPC) damage and destruction. This review focuses on clinical presentation, pathophysiology, and treatment of four BMF: acquired aplastic anaemia, large granular lymphocytic leukaemia, paroxysmal nocturnal haemoglobinuria, and hypoplastic myelodysplastic syndrome. Autoantigens are speculated to be the inciting event that result in immune activation in all of these diseases, but specific pathogenic antigens have not been identified. Oligoclonal cytotoxic T cell expansion and an active role of proinflammatory cytokines, primarily interferon gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α), are two main contributors to HSPC growth inhibition and apoptosis in BMF. Emerging evidence also suggests involvement of the innate immune system.

Analysis of TET2 mutations in paroxysmal nocturnal hemoglobinuria (PNH)

Background

Large clonal populations of cells bearing PIG-A mutations are the sine qua non of PNH, but the PIG-A mutation itself is insufficient for clonal expansion. The association between PNH and aplastic anemia supports the immune escape model, but not all PNH patients demonstrate a history of aplasia; therefore, second genetic hits driving clonal expansion have been postulated. Based on the previous identification of JAK2 mutations in patients with a myeloproliferative/PNH overlap syndrome, we considered TET2 as a candidate gene in which mutations might be contributing to clonal expansion.

Methods

Here we sequenced the TET2 and JAK2 genes in 19 patients with large PNH clones.

Results

We found one patient with a novel somatic nonsense mutation in TET2 in multiple hematopoietic lineages, which was detectable upon repeat testing. This patient has had severe thromboses and has relatively higher peripheral blood counts compared with the other patients—but does not have other features of a myeloproliferative neoplasm.

Conclusions

We conclude that mutations in TET2 may contribute to clonal expansion in exceptional cases of PNH.

Features, reason for testing, and changes with time of 583 paroxysmal nocturnal hemoglobinuria clones from 529 patients: a multicenter Italian study

In this study, we aimed at disclosing the main features of paroxysmal nocturnal hemoglobinuria (PNH) clones, their association with presentation syndromes, and their changes during follow-up. A large-scale, cooperative collection (583 clones from 529 patients) of flow cytometric and clinical data was entered into a national repository. Reason for testing guidelines were provided to the 41 participating laboratories, which followed the 2010 technical recommendations for PNH testing by Borowitz. Subsequently, the 30 second-level laboratories adopted the 2012 guidelines for high-resolution PNH testing, both upon order by the local clinicians and as an independent laboratory initiative in selected cases. Type3 and Type2 PNH clones (total and partial absence of glycosyl-phosphatidyl-inositol-anchor, respectively) were simultaneously present in 54 patients. In these patients, Type3 component was sevenfold larger than Type2 (p < 0.001). Frequency distribution analysis of solitary Type3 clone size (N = 442) evidenced two discrete patterns: small (20% of peripheral neutrophils) and large (> 70%) clones. The first pattern was significantly associated with bone marrow failure and myelodysplastic syndromes, the second one with hemolysis, hemoglobinuria, and thrombosis. Pediatric patients (N = 34) showed significant preponderance of small clones and bone marrow failure. The majority of PNH clones involved neutrophils, monocytes, and erythrocytes. Nevertheless, we found clones made exclusively by white cells (N = 13) or erythrocytes (N = 3). Rare cases showed clonal white cells restricted only to monocytes (6 cases) or neutrophils (3 cases). Retesting over 1-year follow-up in 151 cases showed a marked clone size increase in 4 cases and a decrease in 13, demonstrating that early breaking-down of PNH clones is not a rare event (8.6% of cases). This collaborative nationwide study demonstrates a clear-cut difference in size between Type2 and Type3 clones, emphasizes the existence of just two classes of PNH presentations based on Type3 clone size, depicts an asymmetric cellular composition of PNH clones, and documents the possible occurrence of changes in clone size during the follow-up.

Expanding Complement Therapeutics for the Treatment of Paroxysmal Nocturnal Hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is widely regarded as an archetypal complement-mediated disorder that has propelled complement drug discovery in recent decades. Its pathology is driven by chronic complement dysregulation resulting from the lack of the glycosyl phosphatidyl inositol-linked regulators DAF and CD59 on susceptible erythrocytes. This complement imbalance fuels persistent C3 activation on affected erythrocytes, which culminates in chronic complement-mediated intravascular hemolysis. The clinical application of eculizumab, a humanized anti-C5 antibody that blocks terminal pathway activation, has led to drastic improvement of therapeutic outcomes but has also unveiled hitherto elusive pathogenic mechanisms that are now known to contribute to the clinical burden of a significant proportion of patients with PNH. These emerging clinical needs have sparked a true resurgence of complement therapeutics that offer the promise of even more effective, disease-tailored therapies for PNH. Here, we review the current state of complement therapeutics with a focus on the clinical development of C3-targeted and alternative pathway-directed drug candidates for the treatment of PNH. We also discuss the relative advantages and benefits offered by each complement-targeting approach, including translational considerations that might leverage a more comprehensive clinical intervention for PNH.

Lessons learned from bone marrow failure in systemic lupus erythematosus: Case reports and review of the literature

OBJECTIVE

In the present review, four new cases of bone marrow failure are presented and the potential contribution of systemic lupus erythematosus (SLE) is discussed. Furthermore, a comprehensive literature review of cases of autoimmune myelofibrosis (AIMF), aplastic anemia (AA), and paroxysmal nocturnal hemoglobinuria (PNH) with concurrent SLE aims to allow their direct comparison. Based on a clearer characterization of reported cases and our own experience, diagnostic and therapeutic strategies of these disorders in SLE are proposed based on lessons learned from the present and previous cases.

METHODS

A literature search was done in PubMed, accessed via the National Library of Medicine PubMed interface (http://www.ncbi.nlm.nih.gov/pubmed). Using PubMed, a Boolean search of the literature was performed by crossing the keywords "systemic lupus erythematosus," AND ["bone marrow fibrosis" or "bone marrow failure" or "myelofibrosis" or "aplastic anemia" or "paroxysmal nocturnal hemoglobinuria"].

RESULTS

After a stringent selection of previous cases with a clear diagnosis of SLE, we summarized in the present review 31 cases of AIMF, 26 cases of AA, and 3 cases of PNH. In addition, four new cases illustrate the problem of attribution of bone marrow failure to SLE.

CONCLUSIONS

The attribution of SLE to bone marrow failure is challenging due to a lack of biomarkers, which complicates treatment decisions. Autoimmune myelofibrosis is likely underreported, but corticosteroids and intravenous immunoglobulin appear to be effective immediate therapies. In AA attributable to SLE, a serum inhibitor of bone marrow precursors should be tested, since plasma exchange has been universally successful in these cases, and a PNH clone should be tested for in the setting of ongoing hemolysis, as complement inhibition may be effective. Further research is warranted to elucidate pathophysiological mechanisms of bone marrow failure in SLE.

T Cell Transcriptomes from Paroxysmal Nocturnal Hemoglobinuria Patients Reveal Novel Signaling Pathways

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare acquired disorder originating from hematopoietic stem cells and is a life-threating disease characterized by intravascular hemolysis, bone marrow (BM) failure, and venous thrombosis. The etiology of PNH is a somatic mutation in the phosphatidylinositol glycan class A gene (PIG-A) on the X chromosome, which blocks synthesis of the glycolipid moiety and causes deficiency in GPI-anchored proteins. PNH is closely related to aplastic anemia, in which T cells mediate destruction of BM. To identify aberrant molecular mechanisms involved in immune targeting of hematopoietic stem cells in BM, we applied RNA-seq to examine the transcriptome of T cell subsets (CD4⁺ naive, CD4⁺ memory, CD8⁺ naive, and CD8⁺ memory) from PNH patients and healthy control subjects. Differentially expressed gene analysis in four different T cell subsets from PNH and healthy control subjects showed distinct transcriptional profiles, depending on the T cell subsets. By pathway analysis, we identified novel signaling pathways in T cell subsets from PNH, including increased gene expression involved in TNFR, IGF1, NOTCH, AP-1, and ATF2 pathways. Dysregulation of several candidate genes (JUN, TNFAIP3, TOB1, GIMAP4, GIMAP6, TRMT112, NR4A2, CD69, and TNFSF8) was validated by quantitative real-time RT-PCR and flow cytometry. We have demonstrated molecular signatures associated with positive and negative regulators in T cells, suggesting novel pathophysiologic mechanisms in PNH. These pathways may be targets for new strategies to modulate T cell immune responses in BM failure.

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.

Minor populations of paroxysmal nocturnal hemoglobinuria-type cells in patients with chronic idiopathic neutropenia

Chronic idiopathic neutropenia (CIN) is an acquired disorder of granulopoiesis characterized by increased apoptosis of the bone marrow (BM) granulocytic progenitor cells under the influence of pro-inflammatory mediators and oligoclonal/monoclonal T-lymphocytes. Because patients with immune-mediated BM failure display frequently paroxysmal nocturnal hemoglobinuria (PNH)-type cells in the peripheral blood (PB), we investigated the possible existence of PNH-type cells in 91 patients with CIN using flow cytometry. The patients displayed increased proportions of PNH-type glycophorin A⁺ /CD59^dim and glycophorin A⁺ /CD59^- red blood cells (RBCs), FLAER^- /CD24^- granulocytes, and FLAER^- /CD14^- monocytes, compared to controls (n = 55). A positive correlation was found between the proportions of PNH-type RBCs, granulocytes, and monocytes and an inverse correlation between the number of PB neutrophils and the proportions of PNH-type cell populations. The number of patients, displaying percentages of PNH-type cells above the highest percentage observed in the control group, was significantly increased among patients with skewed compared to those with normal T-cell receptor repertoire suggesting that T-cell-mediated immune processes underlie the emergence of PNH-type cells in CIN. Our findings suggest that patients with CIN display PNH-type cells in the PB at a high frequency corroborating the hypothesis that CIN belongs to the immune-mediated BM failure syndromes.

IFN-γ causes aplastic anemia by altering hematopoietic stem/progenitor cell composition and disrupting lineage differentiation

Aplastic anemia (AA) is characterized by hypocellular marrow and peripheral pancytopenia. Because interferon gamma (IFN-γ) can be detected in peripheral blood mononuclear cells of AA patients, it has been hypothesized that autoreactive T lymphocytes may be involved in destroying the hematopoietic stem cells. We have observed AA-like symptoms in our IFN-γ adenylate-uridylate-rich element (ARE)-deleted (del) mice, which constitutively express a low level of IFN-γ under normal physiologic conditions. Because no T-cell autoimmunity was observed, we hypothesized that IFN-γ may be directly involved in the pathophysiology of AA. In these mice, we did not detect infiltration of T cells in bone marrow (BM), and the existing T cells seemed to be hyporesponsive. We observed inhibition in myeloid progenitor differentiation despite an increase in serum levels of cytokines involved in hematopoietic differentiation and maturation. Furthermore, there was a disruption in erythropoiesis and B-cell differentiation. The same phenomena were also observed in wild-type recipients of IFN-γ ARE-del BM. The data suggest that AA occurs when IFN-γ inhibits the generation of myeloid progenitors and prevents lineage differentiation, as opposed to infiltration of activated T cells. These results may be useful in improving treatment as well as maintaining a disease-free status.

A paroxysmal nocturnal haemoglobinuria progress with waldenström macroglobulinemia along with T cell monoclonal expansion

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired hematopoietic stem cell clinical disease, which has been reported associated with T cell monoclonal expansion and plasma cell dyscrasias. There we reported a case with a 20-year clinical history of PNH. Lately diagnosis of Waldenström macroglobulinemia with the offered evidences of bone marrow examination, flow cytometry and immunofixation electrophoresis. T cell monoclonal expansion was established by polymerase chain reaction. Meanwhile the decreased expression of CD55 and CD59 on neutrophils and erythrocyte were obvious observed. Here we describe the diagnostic evaluation of this patient and provide a brief review of such clonal disorder.

Complement in paroxysmal nocturnal hemoglobinuria: exploiting our current knowledge to improve the treatment landscape

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare hematological disorder associated with an acquired deficiency in glycophosphatidylinositol-anchor biosynthesis that renders erythrocytes susceptible to complement attack. Intravascular hemolysis via the membrane attack complex is a clinical hallmark of the disease, and C5 blockade is currently the only approved treatment for PNH. However, residual anemia is an emerging observation for many PNH patients receiving anti-C5 treatment. A range of complement-targeted therapeutic approaches, encompassing surface-directed inhibition of C3 convertases, blockade of membrane attack complex assembly or C3 interception using peptidic inhibitors, has yielded promising results and offers leverage for even more effective treatment of PNH. This article discusses recent advances in this rapidly evolving field, integrating critical perspectives from preclinical PNH models and diverse complement modulation strategies with genetic insights and therapy response profiles. It also evaluates the relative efficacy, limitations and benefits afforded by C3 or C5 inhibition in the context of PNH therapeutics.

Paroxysmal nocturnal hemoglobinuria clones in children with acquired aplastic anemia: a multicentre study

A multicentre study evaluating the presence of glycosil phosphatidyl-inositol (GPI)-negative populations was performed in 85 children with acquired aplastic anemia (AA). A GPI-negative population was observed in 41% of patients at diagnosis, 48% during immune-suppressive therapy (IST), and 45% in patients off-therapy. No association was found between the presence of a GPI-negative population at diagnosis and the response to IST. In addition, the response rate to IST did not differ between the patients who were GPI-positive at diagnosis and later developed GPI-negative populations and the 11 patients who remained GPI-positive. Two patients with a GPI-negative population >10%, and laboratory signs of hemolysis without hemoglobinuria were considered affected by paroxysmal nocturnal hemoglobinuria (PNH) secondary to AA; no thrombotic event was reported. Excluding the 2 patients with a GPI-negative population greater than 10%, we did not observe a significant correlation between LDH levels and GPI-negative population size. In this study monitoring for laboratory signs of hemolysis was sufficient to diagnose PNH in AA patients. The presence of minor GPI-negative populations at diagnosis in our series did not influence the therapeutic response. As occasionally the appearance of a GPI-negative population was observed at cyclosporine (CSA) tapering or AA relapse, a possible role of GPI-negative population monitoring during IST modulation may need further investigation.

T-large granular lymphocyte leukemia: current molecular concepts

T-large granular lymphocyte (T-LGL) leukemia is a chronic and often indolent T cell lymphoproliferation characterized by extreme expansion of a semi-autonomous cytotoxic T lymphocyte (CTL) clone. Clinically, T-LGL can be associated with various cytopenias; neutropenia constitutes the most frequent manifestation. LGL clone represents a pathologic counterpart of the cytotoxic effector T cell but an abnormal memory CD8 cell seems to provide the supply of the matured LGL population. Analysis of clonal T cell receptor (TCR) rearrangement and complementarity determining region 3 (CDR3) of the TCR beta-chain is a useful tool to investigate clonal expansions, track the frequency of expanded clones and also clinically useful to monitor the response to therapy. The lessons learned from molecular analysis of clonal repertoire support a clinically-derived conclusion that the LGL clone arises in the context of an initially polyclonal immune response or an autoimmune process. Consequently, specific manifestations of T-LGL may be a result of the recognition spectrum of the transformed clone and the cytokines it produces. Due to the often monoclonal manifestation, T-LGL constitutes a suitable model to investigate polyclonal CTL-mediated processes. Application of new technologies, including TCR repertoire analysis by sequencing, clonotypic quantitative PCR and VB flow cytometry facilitate clinical diagnosis and may allow insights into the regulation of TCR repertoire and consequences resulting from the contraction of clonal diversity.

Mechanism of paroxysmal nocturnal hemoglobinuria clonal dominance: possible roles of different apoptosis and CD8+ lymphocytes in the selection of paroxysmal nocturnal hemoglobinuria clones

BACKGROUND AND OBJECTIVES

Paroxysmal nocturnal hemoglobinuria (PNH), a clonal hematopoietic stem cell disorder, manifests when the PNH clone populates in the hematopoietic compartment. We explored the roles of different apoptosis of GPI+ and GPI- (glycosylphosphatidylinositol) cells and CD8+ lymphocytes in a selection of PNH clones.

PATIENTS AND METHODS

Granulocytes from PNH patients and normal controls were subjected to an apoptosis assay using annexin V. Hematopoietic cell in semisolid media were cultured with or without CD8+ lymphocytes.

RESULTS

In PNH, CD59+ granulocytes exhibited more apoptosis than their CD59- counterparts, after 0 or 4 hours in liquid growth culture system (mean [standard error of mean]: 2.1 (0.5) vs 1.2 (0.2), P=.01 at 0 hour and 3.4 [0.7] vs 1.8 [0.3], P=.03 at 4 hour, respectively). The presence of mononuclear cells (MNCs) rendered a greater difference in apoptosis. The percentages of apoptotic CD59+ granulocytes measured at 4 hours with or without MNC fraction were correlated with the sizes of PNH clones (r=0.633, P=.011; and r=0.648, P=.009; respectively). The autologous CD8+ lymphocytes inhibited CFU-GM and BFU-E colony formation in PNH patients when compared with normal controls (mean [SEM] of percentages of inhibition: 61.7 (10.4) vs 11.9 (2.0), P=.008 for CFU-GM and 26.1 (6.9) vs 4.9 (1.0), P=.037 for BFU-E).

CONCLUSIONS

Increased apoptosis of GPI+ blood cells is likely to be responsible in selection and expansion of PNH clones. MNCs or possibly CD8+ lymphocytes may play a role in this phenomenon.

Glycosylphosphatidylinositol-specific, CD1d-restricted T cells in paroxysmal nocturnal hemoglobinuria

The mechanism of bone marrow failure (BMF) in paroxysmal nocturnal hemoglobinuria (PNH) is not yet known. Because in PNH the biosynthesis of the glycolipid molecule glycosylphosphatidylinositol (GPI) is disrupted in hematopoietic stem and progenitor cells by a somatic mutation in the PIG-A gene, BMF might result from an autoimmune attack, whereby T cells target GPI in normal cells, whereas PIG-A mutant GPI-negative cells are spared. In a deliberate test of this hypothesis, we have demonstrated in PNH patients the presence of CD8(+) T cells reactive against antigen-presenting cells (APCs) loaded with GPI. These T cells were significantly more abundant in PNH patients than in healthy controls; their reactivity depended on CD1d expression and they increased upon coculture with CD1d-expressing, GPI-positive APCs. In GPI-specific T cells captured by CD1d dimer technology, we identified, through global T-cell receptor α (TCRα) analysis, an invariant TCRVα21 sequence, which was then found at frequencies higher than background in the TCR repertoire of 6 of 11 PNH patients. Thus, a novel, autoreactive, CD1d-restricted, GPI-specific T-cell population, enriched in an invariant TCRα chain, is expanded in PNH patients and may be responsible for BMF in PNH.

Paroxysmal nocturnal hemoglobinuria and the complement system: recent insights and novel anticomplement strategies

Paroxysmal nocturnal hemoglobinuria (PNH) is a hematological disorder characterized by complement-mediated hemolytic anemia, thrombophilia, and bone marrow failure. PNH is due to a somatic, acquired mutation in the X-linked phosphatidylinositol glycan class A (PIG-A) gene, which impairs the membrane expression on affected blood cells of a number of proteins, including the complement regulators CD55 and CD59. The most evident clinical manifestations of PNH arise from dysregulated complement activation on blood cells; in fact, the hallmark of PNH is chronic, complement-mediated, intravascular hemolysis, which results in anemia, hemoglobinuria, fatigue, and other hemolysis-related disabling symptoms. In addition, the peculiar thromboembolic risk typical of PNH patients is thought as secondary to the complement-mediated hemolysis itself and/or to a complement-mediated activation of platelets. Thus, as a complement-mediated disease, PNH was an appropriate medical condition to develop and to investigate therapeutical complement inhibitors. Indeed, the first complement inhibitor eculizumab, a humanized anti-C5 monoclonal antibody, has been proven safe and effective for the treatment of PNH patients. Chronic treatment with eculizumab results in sustained control of intravascular hemolysis, leading to hemoglobin stabilization and transfusion independence in more than half of the patients. However, recent observations have demonstrated that residual anemia may persist in some patients regardless of sustained fluid-phase terminal complement inhibition. Indeed, persistent dysregulated activation of the early phases of the complement cascade on PNH erythrocytes may lead to progressive C3 deposition on affected cells, which become susceptible to subsequent extravascular hemolysis through the reticuloendothelial system. These findings have renewed the interest for the development of novel complement inhibitors which aim to modulate early phases of complement activation, more specifically at the level of C3 activation. As proof of principle of this concept, an anti-C3 monoclonal antibody has been proven effective in vitro to prevent hemolysis of PNH erythrocytes. More intriguingly, a human fusion protein consisting of the iC3b/ C3d-binding region of complement receptor 2 and of the inhibitory domain of the CAP regulator factor H has been recently shown effective in inhibiting, in vitro, both intravascular hemolysis of and surface C3-deposition on PNH erythrocytes, and is now under investigation in phase 1 clinical trials.

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.

Killer immunoglobulin-like receptors (KIR) and their HLA-ligands in Italian paroxysmal nocturnal haemoglobinuria (PNH) patients

Paroxysmal nocturnal haemoglobinuria (PNH) is a haematopoietic disorder characterized by expansion of phosphatidylinositol glycan-A-defective progenitor(s). Immune-dependent mechanisms, likely involving a deranged T cell-dependent autoimmune response, have been consistently associated with the selection/dominance of PNH precursors. Natural killer (NK) lymphocytes might participate in PNH pathogenesis, but their role is still controversial. NK activity is dependent on the balance between activating and inhibiting signals. Key component in such regulatory network is represented by killer immunoglobulin-like receptors (KIR). KIR are also involved in the regulation of adaptive cytotoxic T cell response and associated with autoimmunity. This study investigated on the frequency of KIR genes and their known human leukocyte antigen (HLA) ligands in 53 PNH Italian patients. We observed increased frequency of genotypes characterized by ≤2 activating KIR as well as by the presence of an inhibitory/activating gene ratio ≥3.5. In addition, an increased matching between KIR-3DL1 and its ligand HLA-Bw4 was found. These genotypes might be associated with lower NK-dependent recognition of stress-related self molecules; this is conceivable with the hypothesis that an increased availability of specific T cell targets, not cleared by NK cells, could be involved in PNH pathogenesis. These data may provide new insights into autoimmune PNH pathogenesis.

Seroreactivity to LGL leukemia-specific epitopes in aplastic anemia, myelodysplastic syndrome and paroxysmal nocturnal hemoglobinuria: results of a bone marrow failure consortium study

Large granular lymphocyte (LGL) leukemia is characterized by clonal expansion of antigen-activated cytotoxic T cells (CTL). Patients frequently exhibit seroreactivity against a human T-cell leukemia virus (HTLV) epitope, BA21. Aplastic anemia, paroxysmal nocturnal hemoglobinuria and myelodysplastic syndrome are bone marrow failure diseases that can also be associated with similar aberrant CTL activation (LGL-BMF). We identified a BA21 peptide that was specifically reactive with LGL leukemia sera and found significantly elevated antibody reactivity against the same peptide in LGL-BMF sera. This finding of shared seroreactivity in LGL-BMF conditions and LGL leukemia suggests that these diseases might share a common pathogenesis.

Frequent loss of HLA alleles associated with copy number-neutral 6pLOH in acquired aplastic anemia

Idiopathic aplastic anemia (AA) is a common cause of acquired BM failure. Although autoimmunity to hematopoietic progenitors is thought to be responsible for its pathogenesis, little is known about the molecular basis of this autoimmunity. Here we show that a substantial proportion of AA patients harbor clonal hematopoiesis characterized by the presence of acquired copy number-neutral loss of heterozygosity (CNN-LOH) of the 6p arms (6pLOH). The 6pLOH commonly involved the HLA locus, leading to loss of one HLA haplotype. Loss of HLA-A expression from multiple lineages of leukocytes was confirmed by flow cytometry in all 6pLOH(+) cases. Surprisingly, the missing HLA-alleles in 6pLOH(+) clones were conspicuously biased to particular alleles, including HLA-A*02:01, A*02:06, A*31:01, and B*40:02. A large-scale epidemiologic study on the HLA alleles of patients with various hematologic diseases revealed that the 4 HLA alleles were over-represented in the germline of AA patients. These findings indicate that the 6pLOH(+) hematopoiesis found in AA represents “escapes” hematopoiesis from the autoimmunity, which is mediated by cytotoxic T cells that target the relevant auto-antigens presented on hematopoietic progenitors through these class I HLAs. Our results provide a novel insight into the genetic basis of the pathogenesis of AA.

Eculizumab treatment modifies the immune profile of PNH patients

Paroxysmal Nocturnal Haemoglobinuria (PNH) is due to pathological expansion of a stem progenitor bearing a somatic mutation of PIG-A gene involved in the biosynthesis of the glycosyl-phosphatidyl-inositol (GPI) anchor. Numerous data suggest a role for immune-mediated mechanisms in the selection/expansion of GPI-defective clone. Haemolytic anaemia in PNH is dependent on the effect of complement against GPI-defective red cells. Eculizumab, an anti-C5 monoclonal antibody, is dramatically effective in controlling haemolysis and thrombosis, in reducing fatigue and in improving quality of life of patients. However, this therapy presents new challenges that need to be properly faced. Here, we report the decrease in B, Natural Killer (NK) and regulatory T cells (Treg), an altered cytokine profile of invariant-NKT cells (NKTi) and the increasing of C-X-C chemokine receptor type 4 (CXCR4) receptor in PNH patients before the Eculizumab therapy. Treatment significantly affects some of these alterations: after Eculizumab, the number of B lymphocytes, the cytokine secretion of NKTi and CXCR4 expression on CD8 T cells became similar to healthy donors. No effects were observed on NK and Treg. The amplitude of the GPI-defective compartment remained unchanged.

The patterns of MHC association in aplastic and non-aplastic paroxysmal nocturnal hemoglobinuria

The deficiency of glycosyl-phosphatidylinositol (GPI)-anchored proteins in plasma membranes of PIG-A gene mutated hematopoietic stem cells (HSCs) is so far insufficient to explain the domination of paroxysmal nocturnal hemoglobinuria (PNH) clone over the normal HSC. We attempted to elucidate possible link between MHC and initial severe aplastic anemia (ISAA/PNH) type and non-aplastic (n/PNH) outcome of PNH. In 50 PNH patients assigned as ISAA/PNH (n = 13), n/PNH (n = 33) or nonassigned (n = 4) and 200 ethnically matched controls we analyzed MHC associations. Our data confirmed strong associations of DRB1*15:01 (RR = 3.51, p = 0.0011) and DQB1*06:02 (RR = 7.09, p = 0.000026) alleles, especially with n/PNH subtype. B*18:01 allele was associated with increased risk of ISAA/PNH subtype (RR = 5.25, p = 0.0028). We conclude that both class II and class I MHC alleles are associated with different subsets of PNH. Clonal selection of PIG-A mutated cells with cognate metabolic block is associated with MHC class II alleles DRB1*15:01 and DQB1*06:02 independent from initial severe AA clone selection. MHC class I molecule B*18:01 can additionally influence the domination of PNH clone in PNH subjects with initial severe aplastic anemia.

GPI-anchored protein-deficient T cells in patients with aplastic anemia and low-risk myelodysplastic syndrome: implications for the immunopathophysiology of bone marrow failure

Glycosylphosphatidylinositol-anchored protein-deficient (GPI-AP(-) ) T cells can be detected in some patients with bone marrow failure (BMF), but the link between these cells and BMF pathophysiology remains to be elucidated. To clarify the significance of GPI-AP(-) T cells in BMF, peripheral blood from 562 patients was examined for the presence of CD48(-) CD59(-) CD3(+) cells using high-resolution flow cytometry (FCM), and the GPI-AP(-) T cells were characterized with regard to their phenotype and sensitivity to inhibitory molecules, including herpesvirus entry mediator (HVEM) and a myelosuppressive cytokine, TGF-β. A multi-lineage FCM analysis detected CD48(-) CD59(-) CD3(+) T cells in 72 (12.8%) of the patients, together with GPI-AP(-) myeloid cells. Unexpectedly, 12 patients (10 with aplastic anemia and 2 with myelodysplastic syndrome-refractory anemia, 2.1%), who showed clinical features similar to those of other BMF patients with GPI-AP(-) myeloid cells, such as a good response to immunosuppressive therapy, displayed 0.01-0.3% GPI-AP(-) cells exclusively in T cells. The CD48(-) CD59(-) T cells consisted of predominantly effector memory (EM) and terminal effector cells, while CD48(-) CD59(-) T cells from non-BMF patients who had received anti-CD52 antibody only showed EM and central memory phenotypes. TGF-β and HVEM capable of inhibiting T-cell proliferation via its GPI-AP CD160 ligation suppressed the in vitro proliferation of GPI-AP(+) T cells more potently than that of GPI-AP(-) T cells from the same patients. The presence of GPI-AP(-) T cells, as well as GPI-AP(-) myeloid cells, may therefore reflect the immunopathophysiology of BMF in which cytokine-mediated suppression of hematopoietic stem cells via GPI-AP-type receptors takes place.

NKG2D-mediated immunity underlying paroxysmal nocturnal haemoglobinuria and related bone marrow failure syndromes

It is considered that a similar immune mechanism acts in the pathogenesis of bone marrow (BM) failure in paroxysmal nocturnal haemoglobinuria (PNH) and its related disorders, such as aplastic anaemia (AA) and myelodysplastic syndromes (MDS). However, the molecular events in immune-mediated marrow injury have not been elucidated. We recently reported an abnormal expression of stress-inducible NKG2D (natural-killer group 2, member D) ligands, such as ULBP (UL16-binding protein) and MICA/B (major histocompatibility complex class I chain-related molecules A/B), on granulocytes in some PNH patients and the granulocyte killing by autologous lymphocytes in vitro. The present study found that the expression of NKG2D ligands was common to both granulocytes and BM cells of patients with PNH, AA, and MDS, indicating their exposure to some incitement to induce the ligands. The haematopoietic colony formation in vitro by the patients' marrow cells significantly improved when their BM cells were pretreated with antibodies against NKG2D receptor, suggesting that the antibodies rescued haematopoietic cells expressing NKG2D ligands from damage by autologous lymphocytes with NKG2D. Clinical courses of patients with PNH and AA showed a close association of the expression of NKG2D ligands with BM failure and a favourable response to immunosuppressive therapy. We therefore propose that NKG2D-mediated immunity may underlie the BM failure in PNH and its-related marrow diseases.

Glycosylphosphatidylinositol-anchored protein deficiency confers resistance to apoptosis in PNH

OBJECTIVE

Investigate the contribution of PIG-A mutations to clonal expansion in paroxysmal nocturnal hemoglobinuria (PNH).

MATERIALS AND METHODS

Primary CD34+ hematopoietic progenitors from PNH patients were assayed for annexin-V positivity by flow cytometry in a cell-mediated killing assay using autologous effectors from PNH patients or allogeneic effectors from healthy controls. To specifically assess the role of the PIG-A mutation in the development of clonal dominance and address confounders of secondary mutation and differential immune attack that can confound experiments using primary cells, we established an inducible PIG-A CD34+ myeloid cell line, TF-1. Apoptosis resistance was assessed after exposure to allogeneic effectors, NK92 cells (an interleukin-2-dependent cell line with the phenotype and function of activated natural killer [NK] cells), tumor necrosis factor (TNF)-alpha, and gamma-irradiation. Apoptosis was measured by annexin-V staining and caspase 3/7 activity.

RESULTS

In PNH patients, CD34+ hematopoietic progenitors lacking glycosylphosphatidylinositol (GPI)-anchored proteins (GPI-AP(-)) were less susceptible than GPI-AP+ CD34+ precursors to autologous (8% vs 49%; p < 0.05) and allogeneic (28% vs 58%; p < 0.05) cell-mediated killing from the same patients. In the inducible PIG-A model, GPI-AP(-) TF-1 cells exhibited less apoptosis than induced, GPI-AP+ TF-1 cells in response to allogeneic cell-mediated killing, NK92-mediated killing, TNF-alpha, and gamma-irradiation. GPI-AP(-) TF-1 cells maintained resistance to apoptosis when effectors were raised against GPI-AP(-) cells, arguing against a GPI-AP being the target of immune attack in PNH. NK92-mediated killing was partially inhibited with blockade by specific antibodies to the stress-inducible GPI-AP ULBP1 and ULBP2 that activate immune effectors. Clonal competition experiments demonstrate that the mutant clone expands over time under proapoptotic conditions with TNF-alpha.

CONCLUSION

PIG-A mutations contribute to clonal expansion in PNH by conferring a survival advantage to hematopoietic progenitors under proapoptotic stresses.

Neutral evolution in paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria is an acquired hematopoietic stem cell (HSC) disorder characterized by the partial or complete deficiency of glycosyl-phosphatidylinositol (GPI)-linked membrane proteins, which leads to intravascular hemolysis. A loss of function mutation in the PIG-A gene, required for GPI biosynthesis, explains how the deficiency of many membrane proteins can result from a single genetic event. However, to date the mechanism of expansion of the GPI(-) clone has not been fully understood. Two hypotheses have been proposed: A selective advantage of GPI(-) cells because of a second mutation or a conditional growth advantage of GPI(-) cells in the presence of an immune attack on normal (GPI(+)) HSCs. Here, we explore a third possibility, whereby the PNH clone does not have a selective advantage. Simulations in a large virtual population accurately reproduce the known incidence of the disease; and the fit is optimized when the number of stem cells is decreased, reflecting a component of bone marrow failure in PNH. The model also accounts for the occurrence of spontaneous cure in PNH, consequent on clonal extinction. Thus, a clonal advantage may not be always necessary to explain clonal expansion in PNH.

Paroxysmal nocturnal hemoglobinuria: significant association with specific HLA-A, -B, -C, and -DR alleles in an Italian population

Paroxysmal nocturnal hemoglobinuria (PNH) is characterized by the expansion of a PIG-A mutated hematopoietic stem cell. An immune-mediated origin has been suggested for this disease. Because HLA genes represent a susceptibility factor for autoimmunity, we investigated HLA genotype in 42 Italian PNH patients compared with 301 control subjects of the same ethnic origin. A significantly increased frequency of the HLA class I alleles A*0201 (p < 0.05), B*1402 (p < 0.001), and Cw*0802 (p < 0.005), and of the HLA class II DRB1*1501 (p < 0.01) with the linked DQB1*0602 (p </= 0.05) and DRB1*01 (p </= 0.05) with the linked DQB1*0501 (p </= 0.01) alleles, has been observed. Notably, a fourfold increase of the haplotype B*1402, Cw*0802 (p < 0.0005) and a 15-fold increase of the Mediterranean haplotype A*33, B*1402, Cw*0802, DRB1*0102, DQB1*0501 (p < 0.005) was also revealed. This association may provide new insights into the autoimmune pathogenesis of PNH.

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.

Paroxysmal nocturnal hemoglobinuria in children

Paroxysmal nocturnal hemoglobinuria (PNH), an acquired hematologic disorder characterized by intravascular hemolysis, nocturnal hemoglobinuria, thrombotic events, serious infections, and bone marrow failure, is very rare in children. PNH is caused by a somatic mutation of the phosphatidylinositol glycan (GPI) complementation class A (PIGA) gene, followed by a survival advantage of the PNH clone, which results in a deficiency of GPI-anchored proteins on hematopoietic cells. Currently, immunophenotypic GPI-linked anchor protein analysis has replaced the acid Ham and sucrose lysis test, as it provides a reliable diagnostic tool for this disease. The presence of PNH clones should be considered in every child with an acquired bone marrow failure syndrome, for example (hypoplastic) myelodysplastic syndrome and aplastic anemia, and/or unexpected serious thrombosis. Treatment of PNH in children is dependent on the clinical presentation. In cases of severe bone marrow failure, stem cell transplantation should be seriously considered as a therapeutic option even if no matched sibling donor is available. This article reviews the reported cases of PNH in children using the recently published guidelines for classification, diagnostics, and treatment.

The pathophysiology of paroxysmal nocturnal hemoglobinuria

The molecular basis of PNH is known. Somatic mutation of the X-chromosome gene PIGA accounts for deficiency of glycosyl phosphatidylinositol-anchored proteins (GPI-AP) on affected hematopoietic stem cells and their progeny. However, neither mutant PIGA nor the consequent deficiency of GPI-AP provides a direct explanation for the clonal outgrowth of the mutant stem cells. Therefore, PNH differs from malignant myelopathies in which clonal expansion is directly attributable to a specific, monogenetic event (e.g., t(9;22) in CML) that bestows a growth/survival advantage upon the affected cell. Multiple, discrete PIGA mutant clones are present in many patients, suggesting that a selection pressure that favors the PNH phenotype (i.e., GPI-AP deficiency) was applied to the bone marrow. The nature of this putative selection pressure, however, is speculative, as is the basis of clonal expansion. In many patients, the majority of hematopoiesis is derived from PIGA mutant stem cells. Yet clonal expansion is limited (nonmalignant), and the contribution of the mutant clones to hematopoiesis may remain stable for decades. Understanding the basis of clonal selection and expansion will not only delineate further the pathophysiology of PNH but also provide new insights into stem cell biology and suggest novel therapeutic strategies for enhancing marrow function.

Highly homologous T-cell receptor beta sequences support a common target for autoreactive T cells in most patients with paroxysmal nocturnal hemoglobinuria

Deficiency of glycosylphosphatidylinositol (GPI)-anchored molecules on blood cells accounts for most features of paroxysmal nocturnal hemoglobinuria (PNH) but not for the expansion of PNH (GPI(-)) clone(s). A plausible model is that PNH clones expand by escaping negative selection exerted by autoreactive T cells against normal (GPI(+)) hematopoiesis. By a systematic analysis of T-cell receptor beta (TCR-beta) clonotypes of the CD8+ CD57+ T-cell population, frequently deranged in PNH, we show recurrent clonotypes in PNH patients but not in healthy controls: 11 of 16 patients shared at least 1 of 5 clonotypes, and a set of closely related clonotypes was present in 9 patients. The presence of T-cell clones bearing a set of highly homologous TCR-beta molecules in most patients with hemolytic PNH is consistent with an immune process driven by the same (or similar) antigen(s)-probably a nonpeptide antigen, because patients sharing clonotypes do not all share identical HLA alleles. These data confirm that CD8+ CD57+ T cells play a role in PNH pathogenesis and provide strong new support to the hypothesis that the expansion of the GPI(-) blood cell population in PNH is due to selective damage to normal hematopoiesis mediated by an autoimmune attack against a nonpeptide antigen(s) that could be the GPI anchor itself.

Glycosyl-phosphatidyl-inositol-defective granulocytes from paroxysmal nocturnal haemoglobinuria patients show increased bacterial ingestion but reduced respiratory burst induction

Paroxysmal nocturnal hemoglobinuria (PNH) is characterized by the emergence of a GPI-defective clonal hematopoiesis. Its clinical features are hemolytic anemia, cytopenia, and thrombosis. Circulating monocytes and granulocytes are largely GPI-defective in PNH patients. This study aims to investigate the granulocyte functional properties in PNH. We analyzed bacterial-dependent intracellular ingestion and the consequent activation of oxidative burst in GPI-defective granulocytes from four neutropenic PNH patients. Our data show a significant increase in the ability of GPI-defective granulocytes to ingest opsonized bacteria. In addition, an impaired respiratory burst effectiveness in response to two independent bacterial stimuli, the N-formyl-MetLeuPhe (fMLP) synthetic bacterial peptide and E. coli, was revealed. The occurrence of neutropenia and the severe impairment of oxidative burst, occurring in chronic granulomatosis disease, were unable to significantly affect phagocytosis. Thus, additional mechanisms, able to differentially affect ingestion ability and respiratory burst effectiveness, have to be hypothesized. The reduced burst effectiveness of GPI-defective granulocytes was maintained after treatment with phorbol 12-myristate 13-acetate, a pharmacological stimulus able to extensively recruit and to trigger intracellular protein kinase C (PKC). Moreover, blocking of PKC has been observed to severely affect granulocyte respiratory burst with a mild effect on the phagocytosis. These data suggest a role for a modulation of intracellular PKC in the pathogenesis of the impaired granulocyte oxidative burst.

A patient with paroxysmal nocturnal hemoglobinuria, T cell large granular lymphocyte clonal expansion, and monoclonal gammopathy of undetermined significance

Paroxysmal nocturnal hemoglobinuria (PNH) has been described in association separately with T cell large granular lymphocyte (LGL) clonal expansions and plasma cell dyscrasias. We describe a patient with anemia related to hemolytic PNH, with concurrent T cell LGL oligoclonal expansion and IgG lambda monoclonal gammopathy of undetermined significance. Peripheral blood flow cytometry revealed decreased expression of CD55 and CD59 on erythrocytes and decreased expression of CD55 and CD66 on neutrophils. An LGL population was present in the peripheral blood and was characterized as oligoclonal by polymerase chain reaction-based analysis of the T cell receptor gamma-chain variable region. Serum protein electrophoresis with immunofixation showed a low level IgG lambda monoclonal protein. We describe the diagnostic evaluation of this patient and provide a brief review of the reported associations among PNH, LGL clonal expansion, and monoclonal gammopathy.

Statistical analysis of CDR3 length distributions for the assessment of T and B cell repertoire biases

Complementarity-determining region 3 (CDR3) length distribution analysis explores the diversity of the T cell receptor (TCR) and immunoglobulin (Ig) repertoire at the transcriptome level. Studies of the CDR3, the most hypervariable part of these molecules, have been frequently used to identify recruitment of T and B cell clones involved in immunological responses. CDR3 length distribution analysis gives a clear perception of repertoire variations between individuals and over time. However, the complexity of CDR3 length distribution patterns and the high number of possible repertoire alterations per individual called for the development of robust data analysis methods. The goal of these methods is to identify, quantify and statistically assess differences between repertoires so as to offer a better diagnostic or predictive tool for pathologies involving the immune system. In this review we will explain the benefit of analyzing CDR3 length distribution for the study of immune cell diversity. We will start by describing this technology and its associated data processing, and will subsequently focus on the statistical methods used to compare CDR3 length distribution patterns. Finally, we will address the various methods for assessing CDR3 length distribution gene signatures in pathological states.

Telomere length dynamics in normal hematopoiesis and in disease states characterized by increased stem cell turnover

Telomeres both reflect and limit the replicative lifespan of normal somatic cells. Immature sub-populations of human CD34+38- hematopoietic stem cell (HSC) can be identified in vitro based on their growth kinetics and telomere length. Fluorescence in situ hybridization and flow cytometry (flow-FISH) has been used to characterize telomere length dynamics as a surrogate marker for HSC turnover in vivo. Investigations in normal steady-state hematopoiesis provided the basis for follow-up studies in model scenarios characterized by increased HSC turnover. Disorders with underlying malignant transformation of HSC (e.g., chronic myeloid leukemia (CML)) can be discriminated from disease states with increased HSC turnover rates secondary to depletion of the stem cell compartment, for example, as in defined bone marrow failure syndromes. In some of these model scenarios, the degree of telomere shortening can be correlated with disease duration, disease stage and severity as well as with response to disease-modifying treatment strategies. Whether increased telomere shortening represents a causal link between HSC turnover, replicative senescence and/or the induction of genetic instability in acquired HSC disorders remains to be shown. However, data from congenital disorders, like dyskeratosis congenita (DKC), suggest that disturbed telomere maintenance may play a role for replicative exhaustion of the HSC pool in vivo.

The mutation rate in PIG-A is normal in patients with paroxysmal nocturnal hemoglobinuria (PNH)

Paroxysmal nocturnal hemoglobinuria (PNH) is characterized by the presence in the patient's hematopoietic system of a large cell population with a mutation in the X-linked PIG-A gene. Although this abnormal cell population is often found to be monoclonal, it is not unusual that 2 or even several PIG-A mutant clones coexist in the same patient. Therefore, it has been suggested that the PIG-A gene may be hypermutable in PNH. By a method we have recently developed for measuring the intrinsic rate of somatic mutations (mu) in humans, in which PIG-A itself is used as a sentinel gene, we have found that in 5 patients with PNH, mu ranged from 1.24 x 10(-7) to 11.2 x 10(-7), against a normal range of 2.4 x 10(-7) to 29.6 x 10(-7) mutations per cell division. We conclude that genetic instability of the PIG-A gene is not a factor in the pathogenesis of PNH.