Changes in T-cell receptor VB repertoire in aplastic anemia: effects of different immunosuppressive regimens

The Protective Effect of Chronic Intermittent Hypobaric Hypoxia on Preventing the Destruction of CD34+ Haematopoietic Stem Cells in Aplastic Anaemia by Modulating the Th1/Th2 Balance

Aplastic anaemia (AA) is a haematopoietic disorder caused by immune-mediated attack on haematopoietic stem cells (HSCs). Stem cell transplantation and immunosuppressive therapy remain the major treatment choice for AA patients but have limited benefits and undesired side effects. The aim of our study was to clarify the protective role of immunity of chronic intermittent hypobaric hypoxia (CIHH) and the underlying mechanism in AA. Our integrative analysis demonstrated that CIHH pre-treatment significantly improved haematopoiesis and survival in an AA rat model. We further confirmed that CIHH pre-treatment was closely associated with the Th1/Th2 balance and a large number of negative regulatory haematopoietic factors, such as TNF-α and IFN-γ, produced by hyperactive Th1 lymphocytes released in AA rats, which induced the death program in a large number of CD34+ HSCs by activating the Fas/FasL apoptosis pathway, while CIHH pre-treatment effectively downregulated the expression of TNF-α and IFN-γ, resulting in a reduction in Fas antigen expression in CD34+ HSCs. In summary, this study provides evidence that CIHH has good protective effect against AA by modulating immune balance in Th1/Th2 cells and may provide a new therapeutic strategy.

Childhood Myelodysplastic Syndrome

Myelodysplastic syndrome (MDS) in children is rare, accounting for < 5% of all childhood hematologic malignancies. With the advent of next-generation sequencing, the etiology of many childhood MDS (cMDS) cases has been elucidated with the finding of predisposing germline mutations in one-quarter to one-third of cases; somatic mutations have also been identified, indicating that cMDS is different than adult MDS. Herein, cMDS classification schema, clinical presentation, laboratory values, bone marrow histology, differential diagnostic considerations, and the recent molecular findings of cMDS are described.

Single-cell genomics in acquired bone marrow failure syndromes

Mechanistic studies of immune bone marrow failure are difficult because of the scarcity of residual cells, the involvement of multiple cell types, and the inherent complexities of hematopoiesis and immunity. Single-cell genomic technologies and bioinformatics allow extensive, multidimensional analysis of a very limited number of cells. We review emerging applications of single-cell techniques, and early results related to disease pathogenesis: effector and target cell populations and relationships, cell-autonomous and nonautonomous phenotypes in clonal hematopoiesis, transcript splicing, chromosomal abnormalities, and T-cell receptor usage and clonality. Dense and complex data from single-cell techniques provide insights into pathophysiology, natural history, and therapeutic drug effects.

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.

Molecular landscape of immune pressure and escape in aplastic anemia

Idiopathic aplastic anemia (IAA) pathophysiology is dominated by autoreactivity of human leukocyte antigen (HLA)-restricted T-cells against antigens presented by hematopoietic stem and progenitor cells (HSPCs). Expansion of PIGA and HLA class I mutant HSPCs have been linked to immune evasion from T-cell mediated pressures. We hypothesized that in analogy with antitumor immunity, the pathophysiological cascade of immune escape in IAA is initiated by immunoediting pressures and culminates with mechanisms of clonal evolution characterized by hits in immune recognition and response genes. To that end, we studied the genetic and transcriptomic make-up of the antigen presentation complexes in a large cohort of patients with IAA and paroxysmal nocturnal hemoglobinuria (PNH) by using single-cell RNA, high throughput DNA sequencing and single nucleotide polymorphism (SNP)-array platforms. At disease onset, HSPCs displayed activation of selected HLA class I and II-restricted mechanisms, without extensive inhibition of immune checkpoint apparatus. Using a newly implemented bioinformatic framework we found that not only class I but also class II genes were often impaired by acquisition of genetic aberrations. We also demonstrated the presence of novel somatic alterations in immune genes possibly contributing to the evasion from the autoimmune T-cells. In contrast, these hits were absent in myeloid neoplasia. These aberrations were not mutually exclusive with PNH and did not correlate with the accumulation of myeloid-driver hits. Our findings shed light on the mechanisms of immune activation and escape in IAA and define alternative modes of clonal hematopoiesis.

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

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

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

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

Memory Stem T Cells in Autoimmune Disease: High Frequency of Circulating CD8+ Memory Stem Cells in Acquired Aplastic Anemia

Memory stem T cells (TSCMs) constitute a long-lived, self-renewing lymphocyte population essential for the maintenance of functional immunity. Hallmarks of autoimmune disease pathogenesis are abnormal CD4(+) and CD8(+) T cell activation. We investigated the TSCM subset in 55, 34, 43, and 5 patients with acquired aplastic anemia (AA), autoimmune uveitis, systemic lupus erythematosus, and sickle cell disease, respectively, as well as in 41 age-matched healthy controls. CD8(+) TSCM frequency was significantly increased in AA compared with healthy controls. An increased CD8(+) TSCM frequency at diagnosis was associated with responsiveness to immunosuppressive therapy, and an elevated CD8(+) TSCM population after immunosuppressive therapy correlated with treatment failure or relapse in AA patients. IFN-γ and IL-2 production was significantly increased in various CD8(+) and CD4(+) T cell subsets in AA patients, including CD8(+) and CD4(+) TSCMs. CD8(+) TSCM frequency was also increased in patients with autoimmune uveitis or sickle cell disease. A positive correlation between CD4(+) and CD8(+) TSCM frequencies was found in AA, autoimmune uveitis, and systemic lupus erythematosus. Evaluation of PD-1, CD160, and CD244 expression revealed that TSCMs were less exhausted compared with other types of memory T cells. Our results suggest that the CD8(+) TSCM subset is a novel biomarker and a potential therapeutic target for AA.

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.

T-cell receptor Vβ skewing frequently occurs in refractory cytopenia of childhood and is associated with an expansion of effector cytotoxic T cells: a prospective study by EWOG-MDS

Immunosuppressive therapy (IST), consisting of antithymocyte globulin and cyclosporine A, is effective in refractory cytopenia of childhood (RCC), suggesting that, similar to low-grade myelodysplastic syndromes in adult patients, T lymphocytes are involved in suppressing hematopoiesis in a subset of RCC patients. However, the potential role of a T-cell-mediated pathophysiology in RCC remains poorly explored. In a cohort of 92 RCC patients, we prospectively assessed the frequency of T-cell receptor (TCR) β-chain variable (Vβ) domain skewing in bone marrow and peripheral blood by heteroduplex PCR, and analyzed T-cell subsets in peripheral blood by flow cytometry. TCRVβ skewing was present in 40% of RCC patients. TCRVβ skewing did not correlate with bone marrow cellularity, karyotype, transfusion history, HLA-DR15 or the presence of a PNH clone. In 28 patients treated with IST, TCRVβ skewing was not clearly related with treatment response. However, TCRVβ skewing did correlate with a disturbed CD4(+)/CD8(+) T-cell ratio, a reduction in naive CD8(+) T cells, an expansion of effector CD8(+) T cells and an increase in activated CD8(+) T cells (defined as HLA-DR(+), CD57(+) or CD56(+)). These data suggest that T lymphocytes contribute to RCC pathogenesis in a proportion of patients, and provide a rationale for treatment with IST in selected patients with RCC.

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.

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.

Quantification of total T-cell receptor diversity by flow cytometry and spectratyping

BACKGROUND

T-cell receptor diversity correlates with immune competency and is of particular interest in patients undergoing immune reconstitution. Spectratyping generates data about T-cell receptor CDR3 length distribution for each BV gene but is technically complex. Flow cytometry can also be used to generate data about T-cell receptor BV gene usage, but its utility has not been compared to or tested in combination with spectratyping.

RESULTS

Using flow cytometry and spectratype data, we have defined a divergence metric that quantifies the deviation from normal of T-cell receptor repertoire. We have shown that the sample size is a sensitive parameter in the predicted flow divergence values, but not in the spectratype divergence values. We have derived two ways to correct for the measurement bias using mathematical and statistical approaches and have predicted a lower bound in the number of lymphocytes needed when using the divergence as a substitute for diversity.

CONCLUSIONS

Using both flow cytometry and spectratyping of T-cells, we have defined the divergence measure as an indirect measure of T-cell receptor diversity. We have shown the dependence of the divergence measure on the sample size before it can be used to make predictions regarding the diversity of the T-cell receptor repertoire.

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

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

Paroxysmal nocturnal hemoglobinuria: pathophysiology, natural history and treatment options in the era of biological agents

Paroxysmal nocturnal hemoglobinuria (PNH) is a clonal non-malignant hematological disease characterized by the expansion of hematopoietic stem cells (HSCs) and progeny mature cells, whose surfaces lack all the proteins linked through the glycosyl-phosphatidyl inositol anchor. This defect arises from an acquired somatic mutation in the X-linked phosphatidylinositol glycan class A gene, with subsequent clonal expansion of the mutated HSCs as a result of a concomitant, likely immune-mediated, selective pressure. The disease is characterized by complement-mediated chronic intravascular hemolysis, resulting in hemolytic anemia and hemosiderinuria; capricious exacerbations lead to recurrent gross hemoglobinuria. Additional cardinal manifestations of PNH are a variable degree of bone marrow failure and an intrinsic propensity to thromboembolic events. The disease is markedly invalidating, with chronic symptoms requiring supportive therapy – usually including periodical transfusions; possible life-threatening complications may also ensue. The biology of PNH has been progressively elucidated in the past few years, but therapeutic strategies remained unsatisfactory for decades, the only exception being stem cell transplantation, which is restricted to selected patients and retains significant morbidity and mortality. Recently, a biological agent to treat PNH has been developed – the terminal complement inhibitor eculizumab – which has been tested in a number of clinical trials, with exciting results. All the data from worldwide clinical trials confirm that eculizumab radically modifies the symptoms, the biology, and the natural history of PNH, strongly improving the quality of life of PNH patients.

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.

Abnormalities of the alphabeta T-cell receptor repertoire in advanced myelodysplastic syndrome

OBJECTIVE

Analysis of the alphabeta T-cell receptor (TCR) repertoire in patients with myelodysplastic syndrome (MDS) using the technique of TCR beta-chain spectratyping has provided valuable insight into the pathophysiology of cytopenias in a subset of patients with this heterogeneous disorder. TCR beta-chain spectratypes are complex data sets, however, and statistical tools for their comprehensive analysis are limited. The objective of the present work was to develop a method to enable quantitative evaluation and global comparison of spectratype data from different individuals and to study the prevalence of TCR beta repertoire abnormalities in MDS patients.

MATERIALS AND METHODS

We developed a robust statistical method based on k-means clustering analysis, and applied this method to analysis of the alphabeta TCR repertoires in 50 MDS patients and 23 age-matched healthy controls.

RESULTS

Cluster analysis identified a subset of 11 MDS patients with profoundly abnormal alphabeta TCR repertoires. This group of patients was characterized by advanced disease by International Prognostic Scoring System and World Health Organization criteria, increased expression of the Wilms' tumor-1 oncogene, increased bone marrow myeloblast count, and older age.

CONCLUSIONS

We have developed a robust analytic algorithm that enables the comparison of alphabeta TCR repertoires between individuals and have shown that abnormal alphabeta TCR repertoire is a feature of a subset of patients with advanced MDS.

Acquired aplastic anemia in childhood

In comparison to past decades, children who have acquired aplastic anemia (AA) enjoy excellent overall survival that reflects improvements in supportive care, more accurate exclusion of children who have alternate diagnoses, and advances in transplantation and immunosuppressive therapy (IST). Matched sibling-donor hematopoietic stem cell transplants (HSCT) routinely provide long-term survival in the range of 90%, and 75% of patients respond to IST. In this latter group, the barriers to overall and complication-free survival include recurrence of AA, clonal evolution with transformation to myelodysplasia/acute myelogenous leukemia, and therapy-related toxicities. Improvements in predicting responses to IST, in alternative-donor HSCT, and in rationalizing therapy by understanding the pathophysiology in individual patients are likely to improve short- and long-term outcomes for these children.

Immune system derived from homeostatic proliferation generates normal CD8 T-cell memory but altered repertoires and diminished heterologous immune responses

The host responds to lymphopenic environments by acute homeostatic proliferation of T lymphocytes, which acquire phenotypes similar to memory cells. Using T-cell knockout (KO) mice adoptively reconstituted with splenocytes from immunologically naive mice, we examined the immune responses of an immune system derived from homeostatically proliferating (HP) T cells. HP cells mounted relatively normal acute CD8 T-cell responses to lymphocytic choriomeningitis virus (LCMV), but with altered T-cell receptor (TCR) repertoires, and they became functional memory cells capable of recall responses. Although homeostatic proliferation does not normally fully restore T-cell numbers, the CD8(+) T-cell pool was completely restored in T-cell KO mice after LCMV infection. CD4 T-cell responses were lower and not fully restored but seemed sufficient to allow for complete differentiation of CD8 memory T cells. The LCMV-immune HP mouse had an immune repertoire heavily biased with LCMV epitope-specific T cells with oligoclonal expansions. LCMV-immune HP mice had reduced cross-reactive and non-cross-reactive CD8 T-cell responses when challenged with a T cell-cross-reactive virus. Thus, whereas an HP immune system is capable of mounting relatively normal acute and memory CD8 T-cell responses, the narrowing of the T-cell repertoire may reduce immune responses to subsequently encountered pathogens.

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.

HLA association is different in children and adults with severe acquired aplastic anemia

BACKGROUND

Severe aplastic anemia (SAA) is defined as pancytopenia caused by bone marrow failure. The pathogenesis of SAA is thought to involve autoimmune processes. Increased susceptibility to autoimmunity has been shown to be associated with several different HLA alleles. In SAA, few large studies based on data mainly from adults describe a positive HLA correlation with HLA-DR2 (DRB1*15) and HLA-B14.

PROCEDURE

This study explored the HLA constitution of 181 children with SAA who were enrolled in the prospective multi-center study SAA94 between January 1994 and January 2002. The control group consisted of 303 healthy individuals of comparable demographic background. Allelic frequencies between patients and controls are compared using Fisher's exact test.

RESULTS

In our pediatric cohort, we describe a positive association with HLA-B14 (P = 0.0039), but no association of HLA-DR2 with SAA.

CONCLUSION

HLA associations appear to be different in children and adults with SAA. This might point towards a difference in pathophysiology between at least part of the children and adults.

Standardized analysis for the quantification of Vbeta CDR3 T-cell receptor diversity

Assessment of the diversity of the T-cell receptor (TCR) repertoire is often determined by measuring the frequency and distribution of individually rearranged TCRs in a population of T cells. Spectratyping is a common method used to measure TCR repertoire diversity, which examines genetic variation in the third complementarity-determining region (CDR3) region of the TCR Vbeta chain using RT-PCR length-distribution analysis. A variety of methods are currently used to analyze spectratype data including subjective visual measures, qualitative counting measures, and semi-quantitative measures that compare the original data to a standard, control data set. Two major limitations exist for most of these approaches: data files become very wieldy and difficult to manage, and current analytic methods generate data which are difficult to compare between laboratories and across different platforms. Here, we introduce a highly efficient method of analysis that is based upon a normal theoretical Gaussian distribution observed in cord blood and recent thymic emigrants. Using this analysis method, we demonstrate that PBMC obtained from patients with various diseases have skewed TCR repertoire profiles. Upon in vitro activation with anti-CD3 and anti-CD28 coated beads (Xcyte Dynabeads) TCR diversity was restored. Moreover, changes in the TCR repertoire were dynamic in vivo. We demonstrate that use of this streamlined method of analysis in concert with a flexible software package makes quantitative assessment of TCR repertoire diversity straightforward and reproducible, enabling reliable comparisons of diversity values between laboratories and over-time to further collaborative efforts. Analysis of TCR repertoire by such an approach may be valuable in the clinical setting, both for prognostic potential and measuring clinical responses to therapy.

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.

The skewed TCR-BV repertoire displayed at the maternal-fetal interface of women with unexplained pregnancy loss

PROBLEM

The study was undertaken to investigate T-cell receptor (TCR) variable beta (BV)-chain usage at maternal-fetal interface and explore the relationship between the skewed TCR-BV usage and unexplained pregnancy losses.

METHOD OF STUDY

A total of 57 patients with unexplained pregnancy loss including 39 cases with unexplained spontaneous abortion and 18 cases with unexplained recurrent spontaneous abortion (RSA) were chosen in Renji Hospital, Shanghai Second Medical University matched with 41 women with normal pregnancies in first trimester between September 2002 and November 2003. A high-resolution spectratyping analysis of complementarity-determining region 3 (CDR3) was used to detect and compare the degree and pattern of TCR-BV repertoire usage at the maternal-fetal interface between patients with pregnancy loss and normal controls.

RESULTS

There were two comparisons of TCR usage performed between patients and controls, which included the degree (mean value of every TCR-BVn expression) and the pattern (skewed TCR-BVn frequency). The skewed TCR-BVn is defined as an absolute BVn usage of > 5% calculated from the formula or a double increased BVn usage compared with the mean value of normal BVn. According to the degree of TCR-BV usage, BV2 (P = 0.046), BV10 (P = 0.016), and BV11 (P = 0.030) in spontaneous abortion group and BV19 (P = 0.038) in RSA group showed higher usage, while BV5.2 (P = 0.006 and P = 0.046) in both abortion groups showed significantly lower usage when compared with normal controls. About the pattern of skewed TCR-BV distribution, we found that TCR-BV2, -3, -6, and -7 were the four most common BV families in deciduas of patients with both types of abortion and normal controls. Women with spontaneous abortion demonstrated higher frequency of BV10 (P = 0.035) and lower frequencies of BV4 (P = 0.002) and BV5.2 (P = 0.003) in comparison with controls. In RSA, higher frequencies of BV15 (P = 0.018), BV19 (P = 0.049), and BV20 (P = 0.018), in the mean time, lower frequencies of BV4 (P = 0.026) and BV7 (P = 0.018) distributions were verified.

CONCLUSIONS

Our results suggested that a significant skewed TCR-BV repertoire occurred at the maternal-fetal interface with patients undergoing abortion. The specific skewed usages of TCR-BV might be associated with the susceptibility to unexplained pregnancy loss.

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.

Preferential suppression of trisomy 8 compared with normal hematopoietic cell growth by autologous lymphocytes in patients with trisomy 8 myelodysplastic syndrome

Clinical observations and experimental evidence link bone marrow failure in myelodysplastic syndrome (MDS) with a T cell-dominated autoimmune process. Immunosuppressive therapy is effective in improving cytopenias in selected patients. Trisomy 8 is a frequent cytogenetic abnormality in bone marrow cells in patients with MDS, and its presence has been associated anecdotally with good response to immunotherapy. We studied 34 patients with trisomy 8 in bone marrow cells, some of whom were undergoing treatment with antithymocyte globulin (ATG). All had significant CD8+ T-cell expansions of one or more T-cell receptor (TCR) Vbeta subfamilies, as measured by flow cytometry; expanded subfamilies showed CDR3 skewing by spectratyping. Sorted T cells of the expanded Vbeta subfamilies, but not of the remaining subfamilies, inhibited trisomy 8 cell growth in short-term hematopoietic culture. The negative effects of Vbeta-expanded T cells were inhibited by major histocompatibility complex (MHC) class 1 monoclonal antibody (mAb) and Fas antagonist and required direct cell-to-cell contact. Sixty-seven percent of patients who had de novo MDS with trisomy 8 as the sole karyotypic abnormality responded to ATG with durable reversal of cytopenias and restoration of transfusion independence, with stable increase in the proportion of trisomy 8 bone marrow cells and normalization of the T-cell repertoire. An increased number of T cells with apparent specificity for trisomy 8 cells is consistent with an autoimmune pathophysiology in trisomy 8 MDS.

Management of acquired aplastic anaemia

Outcome of patients with aplastic anaemia (AA), whether treated with allogeneic BMT or immunosuppressive therapy has steadily increased over the last three decades. However, there is a difference in quality of outcome between these two therapeutic modalities. There is no plateau for survival after ATG as patients are at later risk of transformation to myelodysplasia (MDS) or acute myeloid leukaemia (AML), paroxysmal nocturnal haemoglobinuria and relapse of their aplasia. In contrast, AA patients are not at risk of these later complications if they have undergone successful bone marrow transplantation. Long term survival after HLA identical sibling BMT is 80-90%, but GVHD and graft rejection remain to be addressed. The results of unrelated donor BMT for AA have shown considerable improvement over the last five years. Difficulties remain for those patients who fail immunosuppressive therapy and in whom BMT is not possible, since alternative immunosuppressive agents have so far proven to be somewhat disappointing.

Aspirin and clopidogrel: efficacy, safety, and the issue of drug resistance

Aspirin and the thienopyridines ticlopidine and clopidogrel are antiplatelet agents that display good antithrombotic activity. In the past few years, the concept of aspirin resistance has been largely emphasized in the medical literature, although its definition is still uncertain. I suggest that "aspirin-resistant" should be considered as a description for those individuals in whom aspirin fails to inhibit thromboxane A2 production, irrespective of the results of unspecific tests of platelet function, such as the bleeding time, platelet aggregation, or the PFA-100 system. Less well known than aspirin resistance, but certainly better characterized, is the issue of "clopidogrel resistance," which is probably mostly caused by inefficient metabolism of the prodrug clopidogrel to its active metabolite. At present, aspirin and clopidogrel resistance should not be looked for in the clinical setting, because there is no definite demonstration of an association with clinical events conditioning cost-effective changes in patient management.

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.

In-vivo dominant immune responses in aplastic anaemia: molecular tracking of putatively pathogenetic T-cell clones by TCR beta-CDR3 sequencing

BACKGROUND

Aplastic anaemia is a bone-marrow-failure syndrome characterised by low blood-cell counts and fatty bone marrow. In most cases, no obvious aetiological factor can be identified. However, clinical responses to immunosuppression strongly suggest an immune pathophysiology.

METHODS

To test the hypothesis that aplastic anaemia results from antigen-specific lymphocyte attack against haemopoietic tissue, we analysed effector immunity, seeking especially dominant specific T-cell responses. Blood samples from 54 patients with aplastic anaemia were subjected to flow cytometry to define T-cell-receptor Vbeta-chain usage and expansion of particular Vbeta subsets. We measured the size distribution of the complementarity-determining region 3 (CDR3) for expanded Vbeta subsets, then cloned and sequenced skewed, oligoclonal, or monoclonal peaks.

FINDINGS

Expanded Vbeta subsets were identified in almost all the patients. Over-represented Vbeta subsets from CD8-positive cells showed oligoclonal or monoclonal CDR3 size patterns. The CDR3 sequence repertoire in aplastic anaemia showed much redundancy compared with healthy donors. We identified patient-specific putative pathogenetic clonotypes that were not detectable in controls. In selected patients who were assessed longitudinally, these clonotypes were quantitatively related to disease activity. Selective killing of autologous haemopoietic progenitors by the Vbeta-specific lymphocyte population was shown in one patient. These apparently pathogenetic CDR3 sequences showed homology between individuals, suggesting a role for a "semi-public" immune response in the pathophysiology of aplastic anaemia.

INTERPRETATION

In-vivo dominant clonal immune response can be identified in many patients with aplastic anaemia, which is evidence for an underlying antigen-driven immune process. Longitudinal tracking by molecular techniques could inform individual clinical decisions and the development of new treatments in autoimmune diseases.

RELEVANCE TO PRACTICE

Although the target of the aberrant immune response is the haemopoietic stem cell, the triggering antigens remain unknown. We combined cell phenotypic, molecular biology, and functional analyses to study the effector arm of immunity in an attempt to establish an immune pathophysiology. Clinical application of such a model could broadly extend to other autoimmune diseases.

Analysis of T-cell repertoire in hepatitis-associated aplastic anemia

Hepatitis-associated aplastic anemia (HAA) is a syndrome of bone marrow failure following an acute attack of seronegative hepatitis. Clinical features and liver histology suggest a central role for an immune-mediated mechanism. To characterize the immune response, we investigated the T-cell repertoire (T-cell receptor [TCR] Vβ chain subfamily) of intrahepatic lymphocytes in HAA patients by TCR spectratyping. In 6 of 7 HAA liver samples, a broad skewing pattern in the 21 Vβ subfamilies tested was observed. In total, 62% ± 18% of HAA spectratypes showed a skewed pattern, similar to 68% ± 18% skewed spectratype patterns in 3 of 4 patients with confirmed viral hepatitis. Additionally, the T-cell repertoire had similarly low levels of complexity. In the peripheral blood lymphocytes (PBLs) of a separate group of HAA patients prior to treatment, 60% ± 15% skewed spectratypes were detected, compared with only 18% ± 8% skewed spectratypes in healthy controls. After successful immunosuppressive treatment, an apparent reversion to a normal T-cell repertoire with a corresponding significant increase in T-cell repertoire complexity was observed in the HAA samples. In conclusion, our data suggest an antigen-driven T-cell expansion in HAA and achievement of a normal T-cell repertoire during recovery from HAA. (Blood. 2004;103:4588-4593)

Incidence and specificity of HLA antibodies in multitransfused patients with acquired aplastic anemia

BACKGROUND

This study aimed to establish the prevalence and characteristics of anti-HLA in antibody acquired aplastic anemia patients following cessation of antithymocyte globulin therapy and to characterize antibody in terms of epitope specificity.

STUDY DESIGN AND METHODS

One hundred and fifty multitransfused, untransplanted patients from eight European centers were investigated by serologic methods.

RESULTS

Sixty-two percent were antibody positive. Eighteen HLA-Class-I-specific antibodies (15 IgG, 3 IgM) were identified in 13 patients; 13 antibodies were specific for HLA-A epitopes and 5 for HLA-B. Epitope analysis identified significant correlation between serum reactivity and amino acid substitutions associated with HLA-Class-I epitopes. An excess of antibodies to HLA-A1-associated cross-reactive groups was identified. There was no significant difference in antibody frequency in patients taking cyclosporine compared to those who were not.

CONCLUSION

Data suggested a contribution from B cell memory of alloantigens introduced during pregnancy. In some cases, antibody production continued many years after the last transfusion, and although the target varied between individual patients, the antibody to HLA was focused on a few specific Class I epitopes, the majority of which mapped to the HLA-A molecule.

Shared and individual specificities of immunodominant cytotoxic T-cell clones in paroxysmal nocturnal hemoglobinuria as determined by molecular analysis

OBJECTIVE

Similar immune mechanisms have been suggested to operate in aplastic anemia (AA) and paroxysmal nocturnal hemoglobinuria (PNH), and the presence of PNH clones in AA may indicate that an immune reaction directed against hematopoietic stem cells may be responsible for the immune selection pressure leading to PNH evolution. We previously described expansions of selective cytotoxic T-lymphocyte (CTL) clones in AA patients.

MATERIALS AND METHODS

We applied a molecular analysis of the T-cell receptor repertoire to study the characteristics of CTL response in patients with various forms of PNH. Immunodominant T-cell clones were detected using combined flow cytometric and molecular analysis of the variable beta (VB) chain and CDR3 representation, followed by determination of the frequency of individual CDR3 clonotypes. Clonotypic polymerase chain reaction (PCR) was performed to establish clonotypic utilization pattern.

RESULTS

In patients with a past history of AA, and when subgrouped by current blood counts as "hypoproliferative" PNH patients (in contrast to purely hemolytic form of PNH), more pronounced skewing of VB family utilization was found, consistent with T-cell responses involving several immunodominant CTL clones. Sequences of the PNH-derived clonotypes were used to design PCR-based assays for the utilization analysis of individual clones in PNH patients. The clonotypic distribution pattern established by this PCR method indicated that immunodominant T-cell specificities were shared between some patients but also may be found at low frequencies in controls.

CONCLUSION

Analysis of the CDR3 sequence pattern as a marker for expanded immunodominant clonotypes may have an application in the study of T-cell responses in PNH.

Gene expression profiling in CD34 cells to identify differences between aplastic anemia patients and healthy volunteers

An immune pathophysiology for acquired aplastic anemia (AA) has been inferred from the responsiveness of the patients to immunosuppressive therapies and experimental laboratory data. To address the transcriptome of hematopoietic cells in AA, we undertook GeneChip analysis of the extremely limited numbers of progenitor and stem cells in the marrow of patients with this disease. We pooled total RNA from highly enriched bone marrow CD34 cells of 36 patients with newly diagnosed AA and 12 healthy volunteers for analysis on oligonucleotide chips. A large number of genes implicated in apoptosis and cell death showed markedly increased expression in AA CD34 cells, and negative proliferation control genes also had increased activity. Conversely, cell cycle progress-enhancing genes showed low expression in AA. Cytokine/chemokine signal transducer genes, stress response genes, and defense/immune response genes were up-regulated, as anticipated from other evidence of the heightened immune activity in AA patients' marrow. In summary, detailed genetic analysis of small numbers of hematopoietic progenitor cells is feasible even in marrow failure states where such cells are present in very small numbers. The gene expression profile of primary human CD34 hematopoietic stem cells from AA was consistent with a stressed, dying, and immunologically activated target cell population. Many of the genes showing differential expression in AA deserve further detailed analysis, including comparison with other marrow failure states and autoimmune disease.

Application of the molecular analysis of the T-cell receptor repertoire in the study of immune-mediated hematologic diseases

The basis for the vast recognition spectrum of the T-cell receptor (TCR) can be determined by the rearrangement and recombination of the variable, diversity and joining regions of the variable portions of beta (B) and alpha (A) chains as well as their recombination and modification. Analysis of the TCR rearrangement has been routinely used to detect clonality for the diagnosis of lymphoid malignancies. However, molecular analysis of the TCR repertoire can be a powerful tool in the study of T-cell responses to pathogens and in autoimmune diseases. The concept of the oligoclonality in the context of cellular immune responses is based on the presence of immunodominant T-cell clones within distinct T-cell subpopulations used for analysis. Under normal circumstances, a limited number of clones undergo periodic expansions in reaction to foreign antigens. Under pathologic conditions, though, the derailment of immune regulation allows expansions of specific and potentially pathogenic T-cell clones. For example, large granular lymphocyte (LGL) leukemia illustrates an extreme expansion of a single T-cell clone associated with a distinct autoimmune pathology, which suggests an exaggerated clonal response to a specific antigenic target. In immune-mediated bone marrow failure syndromes, clonal rearrangement of the TCR cannot be detected in unseparated blood or marrow. Nevertheless, individual T-cell clones can significantly expand and may allow for demonstration of oligoclonality in selected T-cell populations. These subpopulations are defined, for example, by a specific beta (B)-chain usage or other phenotypic markers. Given the diversity of the TCR recognition spectrum, the task of identifying immunodominant clonotypes derived from unique complementarity determining region-3 (CDR3) sequences is very complex. However, expanded T-cell clones likely represent immunodominant responses which can be detected on the molecular level using analysis of the individual TCR VB-chain representation, CDR3 size fragment skewing, and determination of the frequency of individual clonotypic sequences. In the future, TCR VB clonotypes may be applied as a diagnostic tool, analogous to serologic markers. As an investigative tool in hematology, molecular analysis of the TCR utilization pattern and the detection of immunodominant clonotypes represents a novel approach in the study of immune-mediated hematologic diseases, such as aplastic anemia (AA), some forms of myelodysplasia (MDS), anti-leukemic immune surveillance, graft-versus-leukemia effects and graft-versus-host disease (GvHD).

Antigen-driven clonal T cell expansion in disorders of hematopoiesis

Patients with myelodysplastic syndrome, aplastic anemia, and LGL leukemia may have overlapping clinical features. This commentary highlights a possible common pathogenetic mechanism of antigen-driven cytotoxic T lymphocytes mediating hematopoietic failure.

Antithymocyte globulin and cyclosporine for severe aplastic anemia: association between hematologic response and long-term outcome

CONTEXT

In most patients, aplastic anemia results from T-cell-mediated immune destruction of bone marrow. Aplastic anemia can be effectively treated by stem cell transplantation or immunosuppression.

OBJECTIVE

To assess long-term outcomes after immunosuppressive therapy.

DESIGN, SETTING, AND PATIENTS

Cohort of 122 patients (31 were < or =18 years and 91 were >18 years) with severe aplastic anemia, as determined by bone marrow cellularity and blood cell count criteria, were enrolled in a single-arm interventional research protocol from 1991 to 1998 at a federal government research hospital.

INTERVENTIONS

A dose of 40 mg/kg per day of antithymocyte globulin administered for 4 days, 10 to 12 mg/kg per day of cyclosporine for 6 months (adjusted for blood levels), and a short course of corticosteroids (1 mg/d of methylprednisolone for about 2 weeks).

MAIN OUTCOME MEASURES

Survival, improvement of pancytopenia and transfusion-independence, relapse, and evolution to other hematologic diseases.

RESULTS

Response rates were 60% at 3 months after initiation of treatment, 61% at 6 months, and 58% at 1 year. The blood cell counts of patients who responded no longer satisfied severity criteria and they were transfusion-independent. Overall actuarial survival at 7 years was 55%. Survival was associated with early satisfaction of response criteria (86% vs 40% at 5 years; P<.001) and by blood counts at 3 months (reticulocyte count or platelet count of >50 x 10(3)/ microL predicted survival at 5 years of 90% [64/71] vs 42% [12/34] for patients with less robust recovery [P<.001 by log-rank test]). There were no deaths among responders more than 3 years after treatment. Relapse was common, but severe pancytopenia usually did not recur. Relapse did not influence survival. Thirteen patients showed evolution to other hematologic diseases, including monosomy 7.

CONCLUSIONS

Approximately half of patients with severe aplastic anemia treated with antithymocyte globulin and cyclosporine have durable recovery and excellent long-term survival. These outcomes were related to the quality of hematologic recovery.

Immune pathophysiology of aplastic anemia

Aplastic anemia (AA) remains an elusive disease. Its pathophysiology is not only fascinating by the seemingly simple findings of cytopenia and marrow hypoplasia, but may also contain key information to the understanding of other fundamental processes such as stem cell regeneration, evolution, and immune control of clonal diseases. Although measurements of blood counts provide an objective tool to assess the disease activity and response to the therapy, immune pathophysiology of AA, as inferred from the successes of immunosuppression, provides only few other clinical clues. Similarly, the current laboratory evidence remains mostly indirect. In spite of the recognition of immune pathways of hematopoietic inhibition and apoptosis in AA, the fundamental question about the nature of the antigen(s) inciting or maintaining the pathologic immune response that ultimately leads to bone marrow failure, remains open. However, recognition of the immune targets may aid in understanding not only the pathogenesis but also many of clinical associations and the late squelae of AA. For example, abnormal cells in AA and myelodysplastic syndrome (MDS) MDS may harbor inciting antigens but the immune response lacks selectivity. Clonal selection pressure may be a result of this process or alternatively, emergence of tolerance could lead to the establishment of abnormal hematopoiesis. Clonal proliferation of large granular lymphocytosis could represent an example of an exaggerated response to an immunodominant hematopoietic antigen. In addition to the traditional functional or phenotypic analysis, pathologic immune response in AA can be studied on molecular level by identifying and quantitating T cell clones based on the presence of unique variable B-chain CDR3 sequences. Detection of clonal expansion is based on the observation that in infections and autoimmune conditions, the presence of antigenic drive will lead to the expansion and overrepresentation of T cell clones recognizing this antigen. However, simple analysis of clonal representation is not sufficient to resolve the complex nature of the immune repertoire in the context of genetic and clinical heterogeneity. Therefore, we analyzed VB and CDR3 repertoire in CD4 and CD8 cells, activated or effector cell subsets. To distinguish truly expanded and likely immunodominant clones, we first studied VB distribution and cloned CDR3 sequences from expanded VB families. Identified clonotypic sequences can be used to design molecular tests to quantitate the strength of pathologic immune response. Clonotype sharing has been confirmed in patients with similar clinical features indicating presence of common antigens. In addition, quantitative analysis showed correlation with the therapy response. Persistence and patterns of clonotypes may be helpful in the classification of immune-mediated marrow failure based on the immune characteristics and will allow inferences into the inciting pathways.

Oligoclonal and polyclonal CD4 and CD8 lymphocytes in aplastic anemia and paroxysmal nocturnal hemoglobinuria measured by V beta CDR3 spectratyping and flow cytometry

We have hypothesized that in aplastic anemia (AA) the presence of antigen-specific T cells is reflected by their contribution to the expansion of a particular variable beta chain (V beta) subfamily and also by clonal CDR3 skewing. To determine the role of disease-specific "signature" T-cell clones in AA, we studied preferential V beta usage by flow cytometry and analyzed V beta-CDR3 regions for the presence of oligoclonality. We first established the contribution of each V beta family to the total CD4(+) and CD8(+) lymphocyte pool; in AA and paroxysmal nocturnal hemoglobinuria, a seemingly random overrepresentation of different V beta families was observed. On average, we found expansion in 3 (of 22 examined) V beta families per patient. When the contribution of individual V beta families to the effector pool was examined, more striking V beta skewing was found. V beta-CDR3 size distribution was analyzed for the expanded V beta families in isolated CD4(+) and CD8(+) populations; underrepresented V beta families displayed more pronounced CDR3 skewing. Expanded CD4(+)V beta subfamilies showed mostly a polyclonal CDR3 size distribution with only 38% of skewing in expanded V beta families. In contrast, within overrepresented CD8(+)V beta types, marked CDR3 skewing (82%) was seen, consistent with nonrandom expansion of specific CD8(+) T-cell clones. No preferential expansion of particular V beta families was observed, in relation to HLA-type. In patients examined after immunosuppressive therapy, an abnormal V beta-distribution pattern was retained, but the degree of expansion of individual V beta was lower. As V beta skewing may correlate with relative V beta size, oligoclonality in combination with numerical V beta expansion can be applied to recognition of disease-specific T-cell receptors.

Immunosuppressive treatment of acquired aplastic anemia and immune-mediated bone marrow failure syndromes

Modern therapeutic strategies for the treatment of acquired aplastic anemia are based on the current understanding of its pathophysiology as well as empiric observations. Most cases of aplastic anemia appear to be the result of immune-mediated destruction of hematopoietic cells, which can be approached by stem cell transplantation in younger patients with appropriate histocompatible donors or by immunosuppression to reduce T-cell activity. Popular treatment regimens combine antithymocyte globulin with cyclosporine. Although a majority of patients respond with improved blood counts and achieve transfusion-independence, late clonal complications of myelodysplasia and cytogenetic abnormalities occur in a substantial minority of cases. Additionally, there is no clear algorithm for the treatment of refractory disease. Newer methods of treatment, including high-dose cyclophosphamide and the development of potentially tolerizing combinations of drugs. are under study. Effective therapies for aplastic anemia might also be applied to other T-cell mediated, organ-specific human diseases.