T-Cell Receptor Sequences Identify Combined Coxsackievirus-Streptococci Infections as Triggers for Autoimmune Myocarditis and Coxsackievirus-Clostridia Infections for Type 1 Diabetes

Recent research suggests that T-cell receptor (TCR) sequences expanded during human immunodeficiency virus and SARS-CoV-2 infections unexpectedly mimic these viruses. The hypothesis tested here is that TCR sequences expanded in patients with type 1 diabetes mellitus (T1DM) and autoimmune myocarditis (AM) mimic the infectious triggers of these diseases. Indeed, TCR sequences mimicking coxsackieviruses, which are implicated as triggers of both diseases, are statistically significantly increased in both T1DM and AM patients. However, TCRs mimicking Clostridia antigens are significantly expanded in T1DM, whereas TCRs mimicking Streptococcal antigens are expanded in AM. Notably, Clostridia antigens mimic T1DM autoantigens, such as insulin and glutamic acid decarboxylase, whereas Streptococcal antigens mimic cardiac autoantigens, such as myosin and laminins. Thus, T1DM may be triggered by combined infections of coxsackieviruses with Clostridia bacteria, while AM may be triggered by coxsackieviruses with Streptococci. These TCR results are consistent with both epidemiological and clinical data and recent experimental studies of cross-reactivities of coxsackievirus, Clostridial, and Streptococcal antibodies with T1DM and AM antigens. These data provide the basis for developing novel animal models of AM and T1DM and may provide a generalizable method for revealing the etiologies of other autoimmune diseases. Theories to explain these results are explored.

Familial immune-mediated aplastic anaemia in six different families

We studied the pathophysiology of aplastic anaemia (AA) in six different pairs of relatives without a family history of hematologic disorders or congenital AA. Five and four of the six pairs shared the HLA-DRB1*15:01 and B*40:02 alleles, respectively. Glycosylphosphatidylinositol-anchored protein-deficient blood cells were detected in eight of the 10 patients evaluated. In a mother-daughter pair from one family, flow cytometry detected leukocytes lacking HLA-A2 due to loss of heterogeneity in chromosome 6p. Whole-exome sequencing of the family pair revealed a missense mutation in MYSM1. These results suggest that genetic inheritance of immune traits might underlie familial AA in some patients.

Clonal evolution in aplastic anemia: failed tumor surveillance or maladaptive recovery?

Clonal evolution to secondary paroxysmal nocturnal hemoglobinuria (PNH) or myeloid neoplasia (MN) represents one of the long-term complications of patients with aplastic anemia (AA). The recent evidence in the field of immunology and the application of next-generation sequencing have shed light on the molecular underpinnings of these clonal complications, revealing clinical and molecular risk factors as well as potential immunological players. Particularly, whether MN evolution represents a failed tumor surveillance or a maladaptive recovery is still a matter of controversy in the field of bone marrow failure syndromes. However, recent studies have explored the precise dynamics of the immune-molecular forces governing such processes over time, generating knowledge useful for potential early therapeutic strategies. In this review, we will discuss the immune pathophysiology of AA and the emergence of clonal hematopoiesis with regard to the adaptive and maladaptive mechanisms at the basis of secondary evolution trajectories operating under the immune pressure.

The similarity of class II HLA genotypes defines patterns of autoreactivity in idiopathic bone marrow failure disorders

Idiopathic aplastic anemia (IAA) is a rare autoimmune bone marrow failure (BMF) disorder initiated by a human leukocyte antigen (HLA)-restricted T-cell response to unknown antigens. As in other autoimmune disorders, the predilection for certain HLA profiles seems to represent an etiologic factor; however, the structure-function patterns involved in the self-presentation in this disease remain unclear. Herein, we analyzed the molecular landscape of HLA complexes of a cohort of 300 IAA patients and almost 3000 healthy and disease controls by deeply dissecting their genotypic configurations, functional divergence, self-antigen binding capabilities, and T-cell receptor (TCR) repertoire specificities. Specifically, analysis of the evolutionary divergence of HLA genotypes (HED) showed that IAA patients carried class II HLA molecules whose antigen-binding sites were characterized by a high level of structural homology, only partially explained by specific risk allele profiles. This pattern implies reduced HLA binding capabilities, confirmed by binding analysis of hematopoietic stem cell (HSC)-derived self-peptides. IAA phenotype was associated with the enrichment in a few amino acids at specific positions within the peptide-binding groove of DRB1 molecules, affecting the interface HLA-antigen-TCR β and potentially constituting the basis of T-cell dysfunction and autoreactivity. When analyzing associations with clinical outcomes, low HED was associated with risk of malignant progression and worse survival, underlying reduced tumor surveillance in clearing potential neoantigens derived from mechanisms of clonal hematopoiesis. Our data shed light on the immunogenetic risk associated with IAA etiology and clonal evolution and on general pathophysiological mechanisms potentially involved in other autoimmune disorders.

Coptidis alkaloids extracted from Coptis chinensis Franch attenuate IFN-γ-induced destruction of bone marrow cells

Coptidis alkaloids are the primary active components of Coptis chinensis Franch. Clinical and pharmacodynamic studies have confirmed that Coptidis alkaloids have multiple therapeutic effects including anti-inflammatory, antioxidant and antitumor effects, and they are usually used to treat various inflammatory disorders and related diseases. Mouse bone marrow cells (BMCs) were isolated from BALB/c mice. Immune-mediated destruction of BMCs was induced by interferon (IFN) -γ. High-performance liquid chromatography-electrospray ionization/ mass spectrometry was used to analyze the ingredients of the aqueous extract from Coptis chinensis Franch. The results confirmed that Coptidis alkaloids were the predominant ingredients in the aqueous extract from Coptis chinensis. The functional mechanism of Coptidis alkaloids in inhibiting immune-mediated destruction of BMCs was studied in vitro. After Coptidis alkaloid treatment, the percentages of apoptotic BMCs and the proliferation and differentiation of helper T (Th) cells and regulatory T (Treg) cells were measured by flow cytometry. The expression and distribution of T-bet in BMCs were observed by immunofluorescence. Western blotting analysis was used to assay the expression of key molecules in the Fas apoptosis and Jak/Stats signaling pathways in BMCs. We identified five alkaloids in the aqueous extract of Coptis chinensis. The apoptotic ratios of BMCs induced by IFN-γ were decreased significantly after Coptidis alkaloid treatment. The levels of key molecules (Fas, Caspase-3, cleaved Caspase-3, Caspase-8 and Caspase-8) in Fas apoptosis signaling pathways also decreased significantly after treatment with low concentrations of Coptidis alkaloids. Coptidis alkaloids were also found to inhibit the proliferation of Th1 and Th17 cells and induce the differentiation of Th2 and Treg cells; further, the distribution of T-bet in BMCs was decreased significantly. In addition, the levels of Stat-1, phospho-Stat-1 and phospho-Stat-3 were also reduced after Coptidis alkaloid treatment. These results indicate that Coptidis alkaloids extracted by water decoction from Coptis chinensis Franch could inhibit the proliferation and differentiation of T lymphocytes, attenuate the apoptosis of BMCs, and suppress the immune-mediated destruction of the BMCs induced by pro-inflammatory cytokines.

The Pathophysiology of Acquired Aplastic Anemia: Current Concepts Revisited

Idiopathic acquired aplastic anemia is a rare, life-threatening bone marrow failure syndrome characterized by cytopenias and hypocellular bone marrow. The pathophysiology is unknown; the most favored model is of a dysregulated immune system leading to autoreactive T-cell destruction of hematopoietic stem and progenitor cells in a genetically susceptible host. The authors review the literature and propose that the major driver of acquired aplastic anemia is a combination of hematopoietic stem and progenitor cells intrinsic defects and an inappropriately activated immune response in the setting of a viral infection. Alterations in bone marrow microenvironment may also contribute to the disease process.

IL-11 promotes the treatment efficacy of hematopoietic stem cell transplant therapy in aplastic anemia model mice through a NF-κB/microRNA-204/thrombopoietin regulatory axis

Hematopoietic stem cell (HSC) transplantation could be of therapeutic value for aplastic anemia (AA) patients, and immunosuppressants may facilitate the efficiency of the procedure. As anti-inflammatory cytokine interleukin-11 (IL-11) has a thrombopoietic effect, its use in cases of chronic bone marrow failure, such as AA, has been proposed to induce HSC function. However, the putative mechanisms that may support this process remain poorly defined. We found that decreased miR-204-5p levels were coincident with increased proliferation in mouse HSCs following exposure to IL-11 in vitro. Through inhibiting NF-кB activity, miR-204-5p repression was demonstrated to be a downstream effect of IL-11 signaling. miR-204-5p was shown to directly target thrombopoietin (TPO) via sequence-dependent 3′-UTR repression, indicating that this microRNA-dependent pathway could serve an essential role in supporting IL-11 functions in HSCs. Increased TPO expression in HSCs following IL-11 exposure could be mimicked or blocked by inhibiting or overexpressing miR-204-5p, respectively. Consistent with these in vitro findings, IL-11 promoted HSC engraftment in a mouse model of AA, an effect that was attenuated in cells overexpressing miR-204-5p. The reduction in miR-204-5p levels is an integral component of IL-11 signaling that may play an essential role in treating AA.

The herbal decoction modified Danggui Buxue Tang attenuates immune-mediated bone marrow failure by regulating the differentiation of T lymphocytes in an immune-induced aplastic anemia mouse model

Angelicae Sinensis, Radix Astragali and Rhizoma Coptidis are all herbs of modified Danggui Buxue Tang (DGBX) and are extensively applied herbs in traditional Chinese medicine for the treatment of anemia and inflammation. In this study, immune-induced AA mice were used as an animal model, and the immunosuppressive agent, Ciclosporin A (CsA), was used as a positive control. Multiple pro-inflammatory cytokines were examined by bead-based multiplex flow cytometry. The T-cell subsets were assessed using a fluorescence-activated cell sorter (FACS). Western blot analysis was used to estimate the protein expression levels of specific transcription factors for T helper cells (Th1, Th2 and Th17) and key molecules of the Janus-activated kinase (Jak)/signal transducer and activator of transcription (Stat3) signaling pathway. DGBX treatment could significantly increase the production of whole blood cells in peripheral blood (PB); inhibit the expansion of Th1 and Th17 cells; increase the differentiation of Th2 and Tregs cells; regulate the expression levels of T-bet, GATA-3, RORγ and proinflammatory cytokines; and decrease the expression levels of key molecules in the Jak/Stat signaling pathway. These results indicate that DGBX can regulate the differentiation of T lymphocytes, resulting in immunosuppressive and hematogenic functions on AA mice. DGBX might be a good candidate for inclusion in a randomized study for AA with more data on the possible side effects and doses used in humans. Ultimately, it may be used for applications of traditional medicine against AA in modern complementary and alternative immunosuppressive therapeutics.

Amifostine Protects Bone Marrow from Benzene-Induced Hematotoxicity in Mice

Benzene is one of the most widely used industrial chemical agents. Long-term benzene exposure causes bone marrow aplasia and leads to a wide range of hematopoietic disorders including aplastic anaemia (AA). There are currently no effective approaches to protect people from benzene-induced hematotoxicity and AA. In addition, current treatments for AA have limitations with short- and long-term risks. Protective agents and new therapeutic approaches, therefore, are needed to prevent and treat the disease. Amifostine is a well-known cytoprotective agent and has been widely used in clinical for protecting normal tissues from the toxic effects of chemotherapy and radiotherapy. The authors utilized an established mouse model to determine the protective effect of amifostine on benzene-induced bone marrow hematotoxicity. Whole-blood cell count, morphological and histopathological alterations in the bone marrow and spleen, as well as the production of inducible toxic oxidative species were examined and compared among the mouse groups. Amifostine treatment in benzene-exposed mice significantly improved blood cell counts, and morphological and histopathological signs of hematotoxicity in the bone marrow as well as in the spleen. Moreover, amifostine prevented benzene-induced bone marrow and spleen cell apoptosis and rescinded the inhibition of cell proliferation induced by benzene exposure. Finally, amifostine significantly inhibited the levels of reactive oxidative species and lipid peroxidation induced by benzene exposure. These data suggest that amifostine appears to have substantial protective effect on benzene-induced bone marrow hematotoxicity.

Autoimmunity and the microbiome: T-cell receptor mimicry of "self" and microbial antigens mediates self tolerance in holobionts: The concepts of "holoimmunity" (TcR-mediated tolerance for the holobiont) and "holoautoimmunity" (loss of tolerance for the holobiont) are introduced

I propose a T-cell receptor (TcR)-based mechanism by which immunity mediates both "genetic self" and "microbial self" thereby, connecting microbiome disease with autoimmunity. The hypothesis is based on simple principles. First, TcR are selected to avoid strong cross-reactivity with "self," resulting in selection for a TcR repertoire mimicking "genetic self." Second, evolution has selected for a "microbial self" that mimics "genetic self" so as to share tolerance. In consequence, our TcR repertoire also mimics microbiome antigenicity, providing a novel mechanism for modulating tolerance to it. Also, the microbiome mimics the TcR repertoire, acting as a secondary immune system. I call this TcR-microbiome mimicry "holoimmunity" to denote immune tolerance to the "holobiont self." Logically, microbiome-host mimicry means that autoimmunity directed at host antigens will also attack components of the microbiome, and conversely, an immunological attack on the microbiome may cross-react with host antigens producing "holoautoimmunity."

Clonal hematopoiesis in acquired aplastic anemia

Clonal hematopoiesis (CH) in aplastic anemia (AA) has been closely linked to the evolution of late clonal disorders, including paroxysmal nocturnal hemoglobinuria and myelodysplastic syndromes (MDS)/acute myeloid leukemia (AML), which are common complications after successful immunosuppressive therapy (IST). With the advent of high-throughput sequencing of recent years, the molecular aspect of CH in AA has been clarified by comprehensive detection of somatic mutations that drive clonal evolution. Genetic abnormalities are found in ∼50% of patients with AA and, except for PIGA mutations and copy-neutral loss-of-heterozygosity, or uniparental disomy (UPD) in 6p (6pUPD), are most frequently represented by mutations involving genes commonly mutated in myeloid malignancies, including DNMT3A, ASXL1, and BCOR/BCORL1 Mutations exhibit distinct chronological profiles and clinical impacts. BCOR/BCORL1 and PIGA mutations tend to disappear or show stable clone size and predict a better response to IST and a significantly better clinical outcome compared with mutations in DNMT3A, ASXL1, and other genes, which are likely to increase their clone size, are associated with a faster progression to MDS/AML, and predict an unfavorable survival. High frequency of 6pUPD and overrepresentation of PIGA and BCOR/BCORL1 mutations are unique to AA, suggesting the role of autoimmunity in clonal selection. By contrast, DNMT3A and ASXL1 mutations, also commonly seen in CH in the general population, indicate a close link to CH in the aged bone marrow, in terms of the mechanism for selection. Detection and close monitoring of somatic mutations/evolution may help with prediction and diagnosis of clonal evolution of MDS/AML and better management of patients with AA.

The complex pathophysiology of acquired aplastic anaemia

Immune-mediated destruction of haematopoietic stem/progenitor cells (HSPCs) plays a central role in the pathophysiology of acquired aplastic anaemia (aAA). Dysregulated CD8(+) cytotoxic T cells, CD4(+) T cells including T helper type 1 (Th1), Th2, regulatory T cells and Th17 cells, natural killer (NK) cells and NK T cells, along with the abnormal production of cytokines including interferon (IFN)-γ, tumour necrosis factor (TNF)-α and transforming growth factor (TGF)-β, induce apoptosis of HSPCs, constituting a consistent and defining feature of severe aAA. Alterations in the polymorphisms of TGF-β, IFN-γ and TNF-α genes, as well as certain human leucocyte antigen (HLA) alleles, may account for the propensity to immune-mediated killing of HSPCs and/or ineffective haematopoiesis. Although the inciting autoantigens remain elusive, autoantibodies are often detected in the serum. In addition, recent studies provide genetic and molecular evidence that intrinsic and/or secondary deficits in HSPCs and bone marrow mesenchymal stem cells may underlie the development of bone marrow failure.

Immune-mediated bone marrow failure in C57BL/6 mice

We established a model of immune-mediated bone marrow (BM) failure in C57BL/6 (B6) mice with 6.5 G total-body irradiation followed by the infusion of 4-10 × 10(6) lymph node (LN) cells/recipient from Friend leukemia virus B/N (FVB) donors. Forty-three percent of animals succumbed, with surviving animals showing marked declines in blood neutrophils, red blood cells, platelets and total BM cells at 8 to 14 days following LN cell infusion. Lowering the total-body irradiation dose to 5 G or altering the LN source from FVB to BALB/cBy donors failed to produce BM destruction. Affected animals showed significant expansion and activation of CD8 T lymphocytes in both the blood and BM; cytotoxic T cells had elevated Fas ligand expression and were oligoclonal, mainly displaying Vβ7 and Vβ17 T cell receptors. There were significant increases in blood plasma interferon γ and tissue necrosis factor α in affected animals. Chemokine ligands CCL3, CCL4, CCL5, CCL20, CXCL2, and CXCL5 and hematopoietic growth factors G-CSF, M-CSF, GM-CSF, VEGF were also elevated. In B6 mice carrying a Fas gene mutation, BM failure was attenuated when they were infused with FVB LN cells. Our model establishes a useful platform to define the roles of individual genes and their products in immune-mediated BM failure.

Increased bone marrow (BM) plasma level of soluble CD30 and correlations with BM plasma level of interferon (IFN)-γ, CD4/CD8 T-cell ratio and disease severity in aplastic anemia

Idiopathic aplastic anemia (AA) is an immune-mediated bone marrow failure syndrome. Immune abnormalities such as decreased lymphocyte counts, inverted CD4/CD8 T-cell ratio and increased IFN-γ-producing T cells have been found in AA. CD30, a surface protein belonging to the tumor necrosis factor receptor family and releasing from cell surface as a soluble form (sCD30) after activation, marks a subset of activated T cells secreting IFN-γ when exposed to allogeneic antigens. Our study found elevated BM plasma levels of sCD30 in patients with SAA, which were closely correlated with disease severity, including absolute lymphocyte count (ALC) and absolute netrophil count (ANC). We also noted that sCD30 levels were positively correlated with plasma IFN-γ levels and CD4/CD8 T-cell ratio in patients with SAA. In order to explain these phenomena, we stimulated T cells with alloantigen in vitro and found that CD30⁺ T cells were the major source of IFN-γ, and induced CD30⁺ T cells from patients with SAA produced significantly more IFN-γ than that from healthy individuals. In addition, increased proportion of CD8⁺ T cells in AA showed enhanced allogeneic response by the fact that they expressed more CD30 during allogeneic stimulation. sCD30 levels decreased in patients responded to immunosuppressive therapy. In conclusion, elevated BM plasma levels of sCD30 reflected the enhanced CD30⁺ T cell-mediated immune response in SAA. CD30 as a molecular marker that transiently expresses on IFN-γ-producing T cells, may participate in mediating bone marrow failure in AA, which also can facilitate our understanding of AA pathogenesis to identify new therapeutic targets.

Expression of Shelterin component POT1 is associated with decreased telomere length and immunity condition in humans with severe aplastic anemia

Abnormal telomere attrition has been found to be closely related to patients with SAA in recent years. To identify the incidence of telomere attrition in SAA patients and investigate the relationship of telomere length with clinical parameters, SAA patients (n=27) and healthy controls (n=15) were enrolled in this study. Telomere length of PWBCs was significantly shorter in SAA patients than in controls. Analysis of gene expression of Shelterin complex revealed markedly low levels of POT1 expression in SAA groups relative to controls. No differences in the gene expression of the other Shelterin components-TRF1, TRF2, TIN2, TPP1, and RAP1-were identified. Addition of IFN-γ to culture media induced a similar fall in POT1 expression in bone marrow cells to that observed in cells cultured in the presence of SAA serum, suggesting IFN-γ is the agent responsible for this effect of SAA serum. Furthermore, ATR, phosphorylated ATR, and phosphorylated ATM/ATR substrate were all found similarly increased in bone marrow cells exposed to SAA serum, TNF-α, or IFN-γ. In summary, SAA patients have short telomeres and decreased POT1 expression. TNF-α and IFN-γ are found at high concentrations in SAA patients and may be the effectors that trigger apoptosis through POT1 and ATR.

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

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

Low expression of basic fibroblastic growth factor in mesenchymal stem cells and bone marrow of children with aplastic anemia

BACKGROUND

Our previous experiments with gene chip suggested that basic fibroblastic growth factor (FGF2) levels were lower in mesenchymal stem cell (MSC) from aplastic anemia patients. The purpose of this study was to determine the expression of FGF2 in MSC and in bone marrow of children with aplastic anemia to better understand the role of low FGF2 expression in the pathogenesis of aplastic anemia.

PROCEDURE

MSCs from the bone marrow of aplastic anemia children and control group were cultured in vitro. Growth curves of primary and passage MSC were plotted. FGF2 gene expression in MSCs was detected using quantitative real-time polymerase chain reaction (RT-PCR). FGF2 protein expression in mononuclear cells and FGF2 protein level in extracellular fluid of bone marrow were also investigated.

RESULT

Decreased growth of MSCs from aplastic anemia children was observed after passage 8 in serial subcultivation, and FGF2 gene expression was downregulated. Within the patients' bone marrow, low FGF2 expression was validated both in mononuclear cells and in the extracellular fluid.

CONCLUSION

Low FGF2 gene expression in MSCs and low FGF2 protein level in bone marrow of aplastic anemia may involve to pathogenesis of aplastic anemia.

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.

STAT3 mutations indicate the presence of subclinical T-cell clones in a subset of aplastic anemia and myelodysplastic syndrome patients

Large granular lymphocyte leukemia (LGL) is often associated with immune cytopenias and can cooccur in the context of aplastic anemia (AA) and myelodysplastic syndromes (MDS). We took advantage of the recent description of signal transducer and activator of transcription 3 (STAT3) mutations in LGL clonal expansions to test, using sensitive methods, for the presence of these mutations in a large cohort of 367 MDS and 140 AA cases. STAT3 clones can be found not only in known LGL concomitant cases, but in a small proportion of unsuspected ones (7% AA and 2.5% MDS). In STAT3-mutated AA patients, an interesting trend toward better responses of immunosuppressive therapy and an association with the presence of human leukocyte antigen-DR15 were found. MDSs harboring a STAT3 mutant clone showed a lower degree of bone marrow cellularity and a higher frequency of developing chromosome 7 abnormalities. STAT3-mutant LGL clones may facilitate a persistently dysregulated autoimmune activation, responsible for the primary induction of bone marrow failure in a subset of AA and MDS patients.

Genetic associations in acquired immune-mediated bone marrow failure syndromes: insights in aplastic anemia and chronic idiopathic neutropenia

Increasing interest on the field of autoimmune diseases has unveiled a plethora of genetic factors that predispose to these diseases. However, in immune-mediated bone marrow failure syndromes, such as acquired aplastic anemia and chronic idiopathic neutropenia, in which the pathophysiology results from a myelosuppressive bone marrow microenvironment mainly due to the presence of activated T lymphocytes, leading to the accelerated apoptotic death of the hematopoietic stem and progenitor cells, such genetic associations have been very limited. Various alleles and haplotypes of human leucocyte antigen (HLA) molecules have been implicated in the predisposition of developing the above diseases, as well as polymorphisms of inhibitory cytokines such as interferon-γ, tumor necrosis factor-α, and transforming growth factor-β1 along with polymorphisms on molecules of the immune system including the T-bet transcription factor and signal transducers and activators of transcription. In some cases, specific polymorphisms have been implicated in the outcome of treatment on those patients.

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

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

Determinants of public T cell responses

Historically, sharing T cell receptors (TCRs) between individuals has been speculated to be impossible, considering the dramatic discrepancy between the potential enormity of the TCR repertoire and the limited number of T cells generated in each individual. However, public T cell response, in which multiple individuals share identical TCRs in responding to a same antigenic epitope, has been extensively observed in a variety of immune responses across many species. Public T cell responses enable individuals within a population to generate similar antigen-specific TCRs against certain ubiquitous pathogens, leading to favorable biological outcomes. However, the relatively concentrated feature of TCR repertoire may limit T cell response in a population to some other pathogens. It could be a great benefit for human health if public T cell responses can be manipulated. Therefore, the mechanistic insight of public TCR generation is important to know. Recently, high-throughput DNA sequencing has revolutionized the study of immune receptor repertoires, which allows a much better understanding of the factors that determine the overlap of TCR repertoire among individuals. Here, we summarize the current knowledge on public T-cell response and discuss future challenges in this field.

MHC class II upregulation and colocalization with Fas in experimental models of immune-mediated bone marrow failure

OBJECTIVE

To test the hypothesis that γ-interferon (IFN-γ) promotes major histocompatibility complex (MHC) class II expression on bone marrow (BM) cell targets that facilitate T-cell-mediated BM destruction in immune-mediated BM failure.

MATERIALS AND METHODS

Allogeneic lymph node (LN) cells were infused into MHC- or minor histocompatibility antigen-mismatched hosts to induce BM failure. MHC class II and Fas expression and cell apoptosis were analyzed by flow cytometry. MHC class II-Fas colocalization was detected by ImageStream Imaging Flow Cytometry and other cell-to-cell associations were visualized by confocal microscopy. T-cell-mediated BM cell apoptosis and effects of IFN-γ on MHC class II-Fas colocalization on normal BM cells were studied using cell culture in vitro followed by conventional and imaging flow cytometry.

RESULTS

BM failure animals had significantly upregulated MHC class II expression on CD4(-)CD8(-)CD11b(-)CD45R(-) residual BM cells and significantly increased MHC class II-Fas colocalization on BM CD150(+) and CD34(+) hematopoietic cells. MHC class II(+)Fas(+) BM cells were closely associated with CD4(+) T cells in the BM of affected animals, and they were significantly more responsive to T-cell-mediated cell apoptosis relative to MHC class II(-)Fas(-) BM cells. Infusion of IFN-γ-deficient LN cells into minor histocompatibility antigen-mismatched recipients resulted in no MHC class II-Fas upregulation and no clinically overt BM failure. Treatment with recombinant IFN-γ significantly increased both MHC class II-Fas coexpression and colocalization on normal BM cells.

CONCLUSIONS

Elevation of the inflammatory cytokine IFN-γ-stimulated MHC class II expression and MHC class II-Fas colocalization, which may facilitate T-cell-mediated cell destruction.

Highly skewed T-cell receptor V-beta chain repertoire in the bone marrow is associated with response to immunosuppressive drug therapy in children with very severe aplastic anemia

One of the major obstacles of immunosuppressive therapy (IST) in children with severe aplastic anemia (SAA) comes from the often months-long unpredictability of bone-marrow (BM) recovery. In this prospective study in children with newly diagnosed very severe AA (n=10), who were enrolled in the therapy study SAA-BFM 94, we found a dramatically reduced diversity of both CD4+ and CD8+ BM cells, as scored by comprehensive V-beta chain T-cell receptor (TCR) analysis. Strongly skewed TCR V-beta pattern was highly predictive for good or at least partial treatment response (n=6, CD8+ complexity scoring median 35.5, range 24–73). In contrast, IST in patients with rather moderate reduction of TCR V-beta diversity (n=4, CD8+ complexity scoring median 109.5, range 82–124) always failed (P=0.0095). If confirmed in a larger series of patients, TCR V-beta repertoire in BM may help to assign children with SAA up-front either to IST or to allogeneic stem-cell transplantation.

Bias in the αβ T-cell repertoire: implications for disease pathogenesis and vaccination

The naïve T-cell repertoire is vast, containing millions of unique T-cell receptor (TCR) structures. Faced with such diversity, the mobilization of TCR structures from this enormous pool was once thought to be a stochastic, even chaotic, process. However, steady and systematic dissection over the last 20 years has revealed that this is not the case. Instead, the TCR repertoire deployed against individual antigens is routinely ordered and biased. Often, identical and near-identical TCR repertoires can be observed across different individuals, suggesting that the system encompasses an element of predictability. This review provides a catalog of αβ TCR bias by disease and by species, and discusses the mechanisms that govern this inherent and widespread phenomenon.

Incidence and etiology of overt gastrointestinal bleeding in adult patients with aplastic anemia

Patients with thrombocytopenia caused by various neoplastic and primary bone marrow diseases are susceptible to major hemorrhage. There are few reports addressing the incidence and outcome of gastrointestinal (GI) bleeding in patients with aplastic anemia characterized by long-standing thrombocytopenia. We sought to retrospectively determine the incidence, etiology, clinical outcomes, and risk factors associated with overt GI bleeding in patients with aplastic anemia. We analyzed the medical records of 508 patients with aplastic anemia after excluding patients below 15 years of age or those who underwent stem cell transplantation between January 1, 2002, and December 31, 2007. A total of 32 patients developed overt GI bleeding during this period. We evaluated the site, etiology, outcomes, and major risk factors in these patients who developed GI bleeding episodes. The incidence of GI bleeding was 6.3% (32 of 508 patients) in adult patients with aplastic anemia. The incidence increased to 12.6% (28 of 222 patients) in patients with severe disease. One patient died from massive GI bleeding. Bleeding sites included the esophagus (two patients, 6.3%), stomach (five, 16.3%), duodenum (two, 6.3%), small intestine (five, 15.6%), large intestine (seven, 21.6%), and unknown site (11, 34.4%). Lower GI bleeds mainly caused by neutropenic enterocolitis (NEC) and solitary ulcer developed more frequently than upper GI bleeds. The major risk factors for GI bleeding included old age (P = 0.004, odds ratio (OR) = 1.039), severe aplastic anemia (P < 0.001, OR = 11.934), non-response to therapy (P = 0.001, OR = 5.652), and major bleeding history in another organ (P < 0.001, OR = 6.677). Overt GI bleeding in patients with aplastic anemia more frequently develops in the lower tract than in the upper tract. The risk of GI bleeding is higher in patients with the following risk factors: older age, severe disease, poor response to treatment, and major bleeding history in another organ.

A hospital-based case control study of aplastic anemia in Shanghai, China

We report results of a hospital-based case control study of 137 consecutive patients diagnosed with aplastic anemia (AA) in participating hospitals over a 4-year period. Diagnoses were made by a single laboratory, subjects were age- and gender-matched to two controls and interviewed concerning previous disease, work histories and exposures to potential etiologic agents. Analysis was conducted on two distinct subgroups: severe aplastic anemia (SAA) and moderate aplastic anemia (MAA). In univariate regression models, the strongest associations were observed for exposure to benzene and SAA (OR=3.12, 95% CI=1.12-8.65) and life on a farm and MAA (OR=3.08, 95% CI=1.44-6.56). Benzene exposure did not show a strong dose-response relationship with either subtype. When accounting for all of the potential confounders we considered in conditional regression models, the previous relationships persisted. Other explanatory variables included hair-dye use for MAA and farm exposures, such as livestock for SAA, although most of these additional variables fell just short of statistical significance. Adjusted R-squared values were only 10% for each subtype, leaving 90% of AA occurrence unexplained. Our results suggest that: (a) benzene exposure is more strongly related to SAA than MAA, (b) farm and livestock exposures are related to both forms of AA, confirming some previous results, and (c) a large percentage of AA remains unexplained, which may indicate that individual susceptibility has a major influence on AA occurrence.

Integrating WHO 2001-2008 criteria for the diagnosis of Myelodysplastic Syndrome (MDS): a case-case analysis of benzene exposure

We characterized the prevalence of hematopoietic and lymphoid disease for 2923 consecutive patients presenting at 29 hospitals from August 2003 to June 2007. Diagnoses were made in our laboratory using WHO criteria based on morphologic, immunophenotypic, cytogenetic, FISH and molecular data. A total of 611 subjects (322 males/289 females) were prospectively diagnosed with MDS using WHO (2001) criteria. Update and re-evaluation of cases using MDS (2008) criteria resulted in 649 MDS cases. Using WHO (2008) criteria, refractory cytopenia with multilineage dysplasia (RCMD) accounted for 68% of total cases, refractory anemia with excess blasts (RAEB), 16.3%; refractory anemia (RA), 6.5%; refractory cytopenia with unilineage dysplasia (RCUD), 4%; and MDS-unclassifiable (MDS-U), 4.5%. Subjects were administered questionnaires and information on previous disease, work histories and exposures to potential etiologic agents such as benzene (BZ) was obtained. A total of 80/649 (13.2%) were determined to have some BZ exposure. The frequency of clonal cytogenetic abnormalities in all MDS was 30%, the most common being +8>del(20)q>del(7q)>del(5q), while the analogous frequency in BZ-exposed cases was only 24%. To further investigate the characteristics of MDS associated with BZ, we identified a subset of cases with high BZ exposure. These BZ signal cases were each matched by age and gender to two cases with no known BZ exposure. When contrasting BZ signal cases vs matched cases with no BZ exposure, we found a high odds ratio (OR) for the WHO subtype MDS-U (OR=11.1), followed by RAEB and RCUD (OR=1), RA (OR=0.7) and RCMD (OR=0.6). Multilineage dysplasia with abnormal eosinophils (MDS-Eo) was strongly associated with BZ exposure, whereas the relative risk of clonal cytogenetic abnormalities was reduced for high BZ-exposed cases (OR=0.5). These findings are strongly indicative that MDS subtypes are influenced by BZ exposure, and taken together with previous studies, the features of MDS-Eo suggest that altered immune regulation plays a major role in the pathogenesis of MDS following chronic exposure to BZ.

Clonal predominance of CD8(+) T cells in patients with unexplained neutropenia

OBJECTIVE

T-cell-mediated autoimmunity may be involved in some cases of idiopathic neutropenia. We hypothesized that a precise T-cell receptor repertoire analysis may uncover cytotoxic T-cell (CTL) expansions that are less pronounced than those seen in T large granular lymphocyte leukemia (T-LGL), but are pathophysiologically analogous and thus can serve as markers of a T-cell-mediated process.

MATERIALS AND METHODS

Using rational algorithms for T-cell receptor analysis and in vivo tracking of CTL responses previously established in our laboratory, we studied patients with unexplained chronic neutropenia (n = 20), T-LGL (n = 15), and healthy controls (n = 12). We further investigated the involvement of soluble inhibitory factors by coculture assays. To determine the level of immune activation, we studied interferon-gamma expression in CD8(+)cells using Taqman polymerase chain reaction.

RESULTS

Fifteen expanded (immunodominant) CTL clones were detected in 12 of 20 patients. In comparison to LGL leukemia, these clones were less immunodominant, but clearly discernible from subclinical lymphoproliferations in controls. As a surrogate of cytotoxic activity, we found markedly increased production of interferon-gamma in most of the neutropenia patients, irrespective of the presence of immunodominant CTL clones.

CONCLUSIONS

These results suggest that, while immunodominant CTL clones are detectable in a proportion of patients only, CTL-mediated pathophysiology may be a general mechanism operating in idiopathic neutropenia. Oligogoclonal CTL expansions in chronic neutropenia may indicate an ongoing autoimmune process, while highly polarized monoclonalities in a subset of neutropenic LGL patients may represent the "extreme" end of the clonal continuum.

The role of production frequency in the sharing of simian immunodeficiency virus-specific CD8+ TCRs between macaques

In some epitope-specific responses, T cells bearing identical TCRs occur in many MHC-matched individuals. The sharing of public TCRs is unexpected, given the enormous potential diversity of the TCR repertoire. We have previously studied the sharing of TCR beta-chains in the CD8(+) T cell responses to two influenza epitopes in mice. Analysis of these TCRbeta repertoires suggests that, even with unbiased V(D)J recombination mechanisms, some TCRbetas can be produced more frequently than others, by a process of convergent recombination. The TCRbeta production frequency was shown to be a good predictor of the observed sharing of epitope-specific TCRbetas between mice. However, this study was limited to immune responses in an inbred population. In this study, we investigated TCRbeta sharing in CD8(+) T cell responses specific for the immunodominant Mamu-A*01-restricted Tat-SL8/TL8 and Gag-CM9 epitopes of SIV in rhesus macaques. Multiple data sets were used, comprising a total of approximately 6000 TCRbetas sampled from 20 macaques. We observed a spectrum in the number of macaques sharing epitope-specific TCRbetas in this outbred population. This spectrum of TCRbeta sharing was negatively correlated with the minimum number of nucleotide additions required to produce the sequences and strongly positively correlated with the number of observed nucleotide sequences encoding the amino acid sequences. We also found that TCRbeta sharing was correlated with the number of times, and the variety of different ways, the sequences were produced in silico via random gene recombination. Thus, convergent recombination is a major determinant of the extent of TCRbeta sharing.

The molecular basis for public T-cell responses?

Public T-cell responses, in which T cells bearing identical T-cell receptors (TCRs) are observed to dominate the response to the same antigenic epitope in multiple individuals, have long been a focus of immune T-cell repertoire studies. However, the mechanism that enables the survival of a specific TCR from the diverse repertoire produced in the thymus through to its involvement in a public immune response remains unclear. In this Opinion article, we propose that the frequency of production of T cells bearing different TCRs during recombination has an important role in the sharing of TCRs in an immune response, with variable levels of 'convergent recombination' driving production frequencies.

Autoimmunity and malignancy in hematology—More than an association

Several associations between hematological malignancies and autoimmunity directed against hematopoietic cells exist. Antibody mediated elimination of mature blood cells such as autoimmune hemolytic anemia (AIHA) and immune thrombocytopenia (ITP) are frequent complications of non-Hodgkin lymphomas, most prominently chronic lymphocytic leukemia. Autoimmunity directed against hematopoietic precursor cells is the hallmark of aplastic anemia, but many features of this disease are shared by two related disorders, paroxysmal nocturnal hemoglobinuria (PNH) and myelodysplastic syndrome (MDS). While the clinical associations between hematological malignancy and autoimmunity have been described many decades ago, only in the last several years have the common pathogenetic mechanisms been elucidated. We summarize the recent progress made in understanding how hematological malignancy gives rise to autoimmunity directed against blood cells and vice versa, and illustrate parallels in the etiology of malignant and autoimmune hematological disorders. Specifically, recent progress in the recognition of the association of lymphoproliferative disorders and autoimmunity against mature blood cells, and common pathogenetic background of aplastic anemia, paroxysmal nocturnal hemoglobinuria, and myelodysplastic syndrome are discussed.

Minor antigen h60-mediated aplastic anemia is ameliorated by immunosuppression and the infusion of regulatory T cells

Human bone marrow (BM) failure mediated by the immune system can be modeled in mice. In the present study, infusion of lymph node (LN) cells from C57BL/6 mice into C.B10-H2(b)/LilMcd (C.B10) recipients that are mismatched at multiple minor histocompatibility Ags, including the immunodominant Ag H60, produced fatal aplastic anemia. Declining blood counts correlated with marked expansion and activation of CD8 T cells specific for the immunodominant minor histocompatibility Ag H60. Infusion of LN cells from H60-matched donors did not produce BM failure in C.B10 mice, whereas isolated H60-specific CTL were cytotoxic for normal C.B10 BM cells in vitro. Treatment with the immunosuppressive drug cyclosporine abolished H60-specific T cell expansion and rescued animals from fatal pancytopenia. The development of BM failure was associated with a significant increase in activated CD4+CD25+ T cells that did not express intracellular FoxP3, whereas inclusion of normal CD4+CD25+ regulatory T cells in combination with C57BL/6 LN cells aborted H60-specific T cell expansion and prevented BM destruction. Thus, a single minor histocompatibility Ag H60 mismatch can trigger an immune response leading to massive BM destruction. Immunosuppressive drug treatment or enhancement of regulatory T cell function abrogated this pathophysiology and protected animals from the development of BM failure.

The role of Wilms' tumor gene peptide-specific cytotoxic T lymphocytes in immunologic selection of a paroxysmal nocturnal hemoglobinuria clone

OBJECTIVE

To clarify an expansion mechanism of a paroxysmal nocturnal hemoglobinuria (PNH) clone with the Wilms' tumor gene (WT1).

MATERIALS AND METHODS

In PNH patients with the HLA-A*2402 allele, frequencies of peripheral blood (PB) WT1 peptide-specific and HLA-A*2402-restricted CD8+ cells and WT1 peptide-stimulated interferon-gamma-producing mononuclear cells (MNCs), cytotoxicity of WT1 peptide-specific and HLA-A*2402-restricted cytotoxic T lymphocyte (CTL) clone (TAK-1) cells on bone marrow (BM) MNCs, and after co-incubation with TAK-1 cells, changes in colony-forming unit granulocyte-macrophage colony formation of CD34+ cells and in CD59 expression in viable CD34+ cells were investigated.

RESULTS

The frequencies of PB WT1 peptide-specific and HLA-A*2402-restricted CD8+ cells (p < 0.005) and WT1 peptide-stimulated interferon-gamma-producing MNCs (p < 0.02) were significantly higher in 5 PNH patients than 8 healthy volunteers (HV). In 5 PNH patients or 3 HV, TAK-1 cells significantly killed BMMNCs and suppressed colony formations of CD34+CD59+ and/or CD34+CD59- cells in the absence and presence of a WT1 peptide or only in the presence of the peptide, respectively, in an HLA-restricted manner. After co-incubation with TAK-1 cells, reduction rates of colony formation of CD34+CD59- cells were significantly less than those of CD34+CD59+ cells in 5 PNH patients (p < 0.002) and proportions of viable CD34+CD59- cells from 5 PNH patients significantly increased in the absence (p < 0.01) and presence (p < 0.01) of a WT1 peptide in an HLA-restricted manner.

CONCLUSION

WT1 peptide-specific and HLA-restricted CTLs may play an important role in expansion of a PNH clone during immunologic selection and/or in the occurrence of BM failure via interferon-gamma in PNH.

Identification of novel regulators in T-cell differentiation of aplastic anemia patients

BACKGROUND

Aplastic anemia (AA) is a bone marrow failure syndrome mostly characterized by an immune-mediated destruction of marrow hematopoietic progenitor/stem cells. The resulting hypocellularity limits a detailed analysis of the cellular immune response. To overcome this technical problem we performed a microarray analysis of CD3+ T-cells derived from bone marrow aspirates and peripheral blood samples of newly diagnosed AA patients and healthy volunteers. Two AA patients were additionally analyzed after achieving a partial remission following immunosuppression. The regulation of selected candidate genes was confirmed by real-time RT-PCR.

RESULTS

Among more than 22,200 transcripts, 583 genes were differentially expressed in the bone marrow of AA patients compared to healthy controls. Dysregulated genes are involved in T-cell mediated cytotoxicity, immune response of Th1 differentiated T-cells, and major regulators of immune function. In hematological remission the expression levels of several candidate genes tend to normalize, such as immune regulators and genes involved in proinflammatory immune response.

CONCLUSION

Our study suggests a pivotal role of Th1/Tc1 differentiated T-cells in immune-mediated marrow destruction of AA patients. Most importantly, immune regulatory genes could be identified, which are likely involved in the recovery of hematopoiesis and may help to design new therapeutic strategies in bone marrow failure syndromes.

Molecular strategies for detection and quantitation of clonal cytotoxic T-cell responses in aplastic anemia and myelodysplastic syndrome

Immune mechanisms are involved in the pathophysiology of aplastic anemia (AA) and myelodysplastic syndrome (MDS). Immune inhibition can result from cytotoxic T cell (CTL) attack against normal hematopoiesis or reflect immune surveillance. We used clonally unique T-cell receptor (TCR) variable beta-chain (VB) CDR3 regions as markers of pathogenic CTL responses and show that while marrow failure syndromes are characterized by polyclonal expansions, overexpanded clones exist in these diseases and can serve as investigative tools. To test the applicability of clonotypic assays, we developed rational molecular methods for the detection of immunodominant clonotypes in blood and in historic marrow biopsies of 35 AA, 37 MDS, and 21 paroxysmal nocturnal hemoglobinuria (PNH) patients, in whom specific CDR3 sequences and clonal sizes were determined. CTL expansions were detected in 81% and 97% of AA and MDS patients, respectively. In total, 81 immunodominant signature clonotypes were identified. Based on the sequence of immunodominant CDR3 clonotypes, we designed quantitative assays for monitoring corresponding clones, including clonotypic Taqman polymerase chain reaction (PCR) and clonotype-specific sequencing. No correlation was found between clonality and disease severity but in patients treated with immunosuppression, truly pathogenic clones were identified based on the decline that paralleled hematologic response. We conclude that immunodominant clonotypes associated with marrow failure may be used to monitor immunosuppressive therapy.

Pathologic clonal cytotoxic T-cell responses: nonrandom nature of the T-cell–receptor restriction in large granular lymphocyte leukemia

T-cell large granular lymphocyte (T-LGL) leukemia is a clonal lymphoproliferation of cytotoxic T cells (CTLs) associated with cytopenias. T-LGL proliferation seems to be triggered/sustained by antigenic drive; it is likely that hematopoietic progenitors are the targets in this process. The antigen-specific portion of the T-cell receptor (TCR), the variable beta (VB)–chain complementarity-determining region 3 (CDR3), can serve as a molecular signature (clonotype) of a T-cell clone. We hypothesized that clonal CTL proliferation develops not randomly but in the context of an autoimmune response. We identified the clonotypic sequence of T-LGL clones in 60 patients, including 56 with known T-LGL and 4 with unspecified neutropenia. Our method also allowed for the measurement of clonal frequencies; a decrease in or loss of the pathogenic clonotype and restoration of the TCR repertoire was found after hematologic remission. We identified 2 patients with identical immunodominant CDR3 sequence. Moreover, we found similarity between multiple immunodominant clonotypes and codominant as well as a nonexpanded, “supporting” clonotypes. The data suggest a nonrandom clonal selection in T-LGL, possibly driven by a common antigen. In contrast, the physiologic clonal CTL repertoire is highly diverse and we were not able to detect any significant clonal sharing in 26 healthy controls.

Immune Pathophysiology of Aplastic Anemia

Acquired aplastic anemia (AA) is considered an immune-mediated disease because approximately 70% of AA patients improve with immunosuppressive therapy. However, little is known about the inciting antigens or the mechanisms responsible for the destruction of hematopoietic stem cells by immune system attack. Recent advances in immunologic techniques have promoted our understanding of the pathogenesis of AA and have provided evidence that AA is an organ-specific T-cell-mediated disease localized in the bone marrow. Moreover, antibody screening of patients' serum with a complementary DNA library derived from hematopoietic cells has identified several proteins as candidate autoantigens in AA.

Defective stromal cell function in a mouse model of infusion-induced bone marrow failure

OBJECTIVE

To study bone marrow (BM) stromal damage in a mouse model of infusion-induced BM failure.

MATERIALS AND METHODS

Sublethally irradiated CByB6F1 mice were infused with 5 x 10(6) C57BL/6 (B6) lymph node (LN) cells. Recipient BM cells were taken at 3, 7, 10, and 14 days following LN infusion and were cultured in vitro in alpha-modified Eagle media for 2-3 weeks. Peripheral blood and was analyzed by complete blood counts while BM lymphocyte infiltration/expansion was analyzed by flow cytometry. Marrow cells from affected and control mice were mixed and cultured in vitro to test nonspecific stromal damage.

RESULTS

Donor lymphocytes infiltrated host BM within 3-7 days and expanded significantly between 7 and 10 days, concurrent with the development of leukopenia, thrombocytopenia, and marrow hypoplasia. BM cells from mice at 7, 10, and 14 days after B6-LN cell infusion were progressively defective in forming stromal feeder layers. A 1:1 mixture of BM cells from affected CByB6F1 mice and normal B6 mice failed to form an effective stromal feeder layer that could support cobblestone colony formation, indicating that lymphocytes in the BM of affected CByB6F1 mice were able to damage stromal cells in the normal B6 BM.

CONCLUSION

Activated lymphocytes destroy both hematopoietic and stromal cells as innocent bystanders in the infusion-induced BM failure model.

Antigen-recognition sites of micromanipulated T cells in patients with acquired aplastic anemia

OBJECTIVE

Acquired aplastic anemia (AA) is a rare disorder characterized by pancytopenia and hypocellular bone marrow. Though experimental and clinical data suggest that AA represents a T cell-mediated disease, neither the immune response nor the nature of inciting antigen(s) have been characterized so far. The identification of a restricted T cell repertoire by PCR techniques in total lymphocyte populations supports an antigen-driven T cell response. In order to investigate the clonal composition, we analyzed the gene rearrangements of the T cell receptor (TCR) variable beta chain (Vbeta) at the single-cell level.

PATIENTS AND METHODS

CD3(+) T lymphocytes were micromanipulated from peripheral blood and bone marrow samples of 8 AA patients and healthy controls. Subsequently amplified VDJ gene segments of the TCRVbeta chain were analyzed for functional rearrangements. More than 500 functionally rearranged TCR loci were studied for Vbeta/Jbeta gene segment usage and molecular composition of the complementary-determining region 3 (CDR3).

RESULTS

In comparison to healthy controls, the Vbeta sequences confirmed a highly restricted T cell repertoire in AA patients at the single-cell level. Both in bone marrow and peripheral blood a predominance of Vbeta13 and Jbeta2S7 was observed. Furthermore, individual clonal T-cell expansion was identified in the majority of patients. However, deduced CDR3 amino acid sequences revealed a high variability without common motifs among the 8 patients.

CONCLUSION

Individual clonal T-cell expansion with high diversity of the antigen-binding sites among the analyzed patients argues for the predominance of private inciting epitopes in AA.

Interferon-gamma-induced gene expression in CD34 cells: identification of pathologic cytokine-specific signature profiles

Hematopoietic effects of interferon-gamma (IFN-gamma) may be responsible for certain aspects of the pathology seen in bone marrow failure syndromes, including aplastic anemia (AA), paroxysmal nocturnal hemoglobinuria (PNH), and some forms of myelodysplasia (MDS). Overexpression of and hematopoietic inhibition by IFN-gamma has been observed in all of these conditions. In vitro, IFN-gamma exhibits strong inhibitory effects on hematopoietic progenitor and stem cells. Previously, we have studied the transcriptome of CD34 cells derived from patients with bone marrow failure syndromes and identified characteristic molecular signatures common to some of these conditions. In this report, we have investigated genome-wide expression patterns after exposure of CD34 and bone marrow stroma cells derived from normal bone marrow to IFN-gamma in vitro and have detected profound changes in the transcription profile. Some of these changes were concordant in both stroma and CD34 cells, whereas others were specific to CD34 cells. In general, our results were in agreement with the previously described function of IFN-gamma in CD34 cells involving activation of apoptotic pathways and immune response genes. Comparison between the IFN-gamma transcriptome in normal CD34 cells and changes previously detected in CD34 cells from AA and PNH patients reveals the presence of many similarities that may reflect molecular signature of in vivo IFN-gamma exposure.

Aplastic anaemia

Aplastic anaemia is a rare haemopoietic stem-cell disorder that results in pancytopenia and hypocellular bone marrow. Although most cases are acquired, there are unusual inherited forms. The pathophysiology of acquired aplastic anaemia is immune mediated in most cases; autoreactive lymphocytes mediate the destruction of haemopoietic stem cells. Environmental exposures, such as to drugs, viruses, and toxins, are thought to trigger the aberrant immune response in some patients, but most cases are classified as idiopathic. Similarly to other autoimmune diseases, aplastic anaemia has a varied clinical course; some patients have mild symptoms that necessitate little or no therapy, whereas others present with life-threatening pancytopenia representing a medical emergency. Paroxysmal nocturnal haemoglobinuria and myelodysplastic syndrome commonly arise in patients with aplastic anaemia, showing a pathophysiological link between these disorders. Acquired aplastic anaemia can be effectively treated by allogeneic bone-marrow transplantation, immunosuppression (generally antithymocyte globulin and ciclosporin), and high-dose cyclophosphamide.

Large granular lymphocyte (LGL)-like clonal expansions in paroxysmal nocturnal hemoglobinuria (PNH) patients

In paroxysmal nocturnal hemoglobinuria (PNH), clonal expansion of glycosylphosphatidylinositol-anchored proteins (GPI-AP)-deficient cells leads to a syndrome characterized by hemolytic anemia, marrow failure, and venous thrombosis. PNH is closely related to aplastic anemia and may share its immune pathophysiology. In vivo expansion of dominant T-cell clones can reflect an antigen-driven immune response but may also represent autonomous proliferation, such as in large granular lymphocytic (LGL)-leukemia. T-cell clonality can be assessed by a combination of T-cell receptor (TCR) flow cytometry and complementarity-determining-region-3 (CDR3) molecular analysis. We studied 24 PNH patients for evidence of in vivo dominant T-cell responses by flow cytometry; TCR-Vbeta-specific expansions were identified in all patients. In four cases, extreme expansions of one Vbeta-subset of CD8+/CD28-/CD56+ (effector) phenotype mimicked subclinical LGL-disease. The monoclonality of these expansions was inferred from unique CDR3-size peak distributions and sequencing of dominant clonotypes. We conclude that the molecular analysis of TCR-beta chain may demonstrate clonal LGL-like expansions at unexpected frequency in PNH patients. Our observations blur the classical boundaries between different bone marrow failure syndromes such as AA, PNH, and LGL, and support the hypothesis that in PNH, the mutant clone may expand as a result of an immune-escape from antigen-driven lymphocyte attack on hematopoietic progenitors.

Stem cells in paroxysmal nocturnal haemoglobinuria and aplastic anaemia: increasing evidence for overlap of haemopoietic defect

The clinical association between paroxysmal nocturnal haemoglobinuria (PNH) and aplastic anaemia (AA) has long been recognized. Haemolytic PNH, as confirmed by a positive Ham's test, can occur in the setting of AA, and conversely AA can be a late complication of PNH. With the development of sensitive flow cytometry to quantify the expression of phosphatidylinositolglycan (PIG)-anchored proteins on blood cells, a small PNH clone can now be detected in a large number of patients with AA at diagnosis. PIG-A gene mutations can also be demonstrated in some AA patients. In haemolytic PNH, there is always marrow suppression despite a morphologically cellular marrow. In vitro cultures show markedly diminished proliferative capacity in both short-term and long-term marrow cultures, similar to that seen in AA. A similar autoimmune process, through the T-cell cytotoxic repertoire, is probably responsible for the pathogenesis of both AA and PNH. PIG-deficient cells may be resistant to immunological attack by autoreactive cytotoxic T cells, because they lack PIG. They are also more resistant to apoptosis than the PIG-normal cell population. This results in the selection of the PIG-deficient clone, in contrast to the PIG-normal stem cells which possess the PIG anchor and hence are targeted and depleted by the autoreactive T cells.

Transcript profile of CD4+ and CD8+ T cells from the bone marrow of acquired aplastic anemia patients

OBJECTIVE

Immune-mediated destruction of hematopoietic stem and progenitor cells is pathophysiologic in most cases of aplastic anemia (AA). We have successfully determined the gene expression profile of the marrow CD34+ target cells in AA. T cells producing IFN-gamma and TNF-alpha have been implicated in hematopoietic destruction in AA. We sought to characterize T cells as immune mediators using the microarray approach.

MATERIALS AND METHODS

We applied Affymetrix GeneChip techniques to determine the detailed profile of mRNA expression of CD4+ and CD8+ cells from the BM of newly diagnosed AA patients and healthy volunteers. For validation, we confirmed our microarray results using quantitative real-time PCR.

RESULTS

Compared to healthy controls, there were 178 and 183 differentially expressed genes in patients' CD4+ cells and CD8+ T cells, respectively; activities of 22 selected genes were confirmed using real-time PCR. Dysregulated genes included those encoding cytokines/chemokines, and involved in transcription regulation, calcium and ion channel formation, and cell adhesion. Unexpected findings were overexpression of toll-like receptor genes in marrow CD4+ cells of patients and of genes for killer-cell immunoglobulin-like receptors (KIR) in AA marrow CD8+ cells.

CONCLUSIONS

Our detailed results at the mRNA level provide insights into the mechanism of AA. Both innate and adaptive immune responses of CD4+ and CD8+ T cells appear to be active in immune-mediated marrow destruction. A variety of cytokines and chemokines active in pathophysiologic cells likely play important roles in the recruitment and activation of lymphocytes to cytotoxic effectors for marrow hematopoietic target cells in AA.