Genetic analysis of autoantibodies in idiopathic thrombocytopenic purpura reveals evidence of clonal expansion and somatic mutation

The common variable immunodeficiency IgM repertoire narrowly recognizes erythrocyte and platelet glycans

BACKGROUND

Autoimmune cytopenias (AICs) regularly occur in profoundly IgG-deficient patients with common variable immunodeficiency (CVID). The isotypes, antigenic targets, and origin(s) of their disease-causing autoantibodies are unclear.

OBJECTIVE

We sought to determine reactivity, clonality, and provenance of AIC-associated IgM autoantibodies in patients with CVID.

METHODS

We used glycan arrays, patient erythrocytes, and platelets to determine targets of CVID IgM autoantibodies. Glycan-binding profiles were used to identify autoreactive clones across B-cell subsets, specifically circulating marginal zone (MZ) B cells, for sorting and IGH sequencing. The locations, transcriptomes, and responses of tonsillar MZ B cells to different TH- cell subsets were determined by confocal microscopy, RNA-sequencing, and cocultures, respectively.

RESULTS

Autoreactive IgM coated erythrocytes and platelets from many CVID patients with AICs (CVID+AIC). On glycan arrays, CVID+AIC plasma IgM narrowly recognized erythrocytic i antigens and platelet i-related antigens and failed to bind hundreds of pathogen- and tumor-associated carbohydrates. Polyclonal i antigen-recognizing B-cell receptors were highly enriched among CVID+AIC circulating MZ B cells. Within tonsillar tissues, MZ B cells secreted copious IgM when activated by the combination of IL-10 and IL-21 or when cultured with IL-10/IL-21-secreting FOXP3-CD25hi T follicular helper (Tfh) cells. In lymph nodes from immunocompetent controls, MZ B cells, plentiful FOXP3+ regulatory T cells, and rare FOXP3-CD25+ cells that represented likely CD25hi Tfh cells all localized outside of germinal centers. In CVID+AIC lymph nodes, cellular positions were similar but CD25hi Tfh cells greatly outnumbered regulatory cells.

CONCLUSIONS

Our findings indicate that glycan-reactive IgM autoantibodies produced outside of germinal centers may contribute to the autoimmune pathogenesis of CVID.

Current Understanding of Immune Thrombocytopenia: A Review of Pathogenesis and Treatment Options

The management of immune thrombocytopenia (ITP) and the prediction of patient response to therapy still represent a significant and constant challenge in hematology. ITP is a heterogeneous disease with an unpredictable evolution. Although the pathogenesis of ITP is currently better known and its etiology has been extensively studied, up to 75% of adult patients with ITP may develop chronicity, which represents a significant burden on patients' quality of life. A major risk of ITP is bleeding, but knowledge on the exact relationship between the degree of thrombocytopenia and bleeding symptoms, especially at a lower platelet count, is lacking. The actual management of ITP is based on immune suppression (corticosteroids and intravenous immunoglobulins), or the use of thrombopoietin receptor agonists (TPO-RAs), rituximab, or spleen tyrosine kinase (Syk) inhibitors. A better understanding of the underlying pathology has facilitated the development of a number of new targeted therapies (Bruton's tyrosine kinase inhibitors, neonatal Fc receptors, strategies targeting B and plasma cells, strategies targeting T cells, complement inhibitors, and newer TPO-RAs for improving megakaryopoiesis), which seem to be highly effective and well tolerated and result in a significant improvement in patients' quality of life. The disadvantage is that there is a lack of knowledge of the predictive factors of response to treatments, which would help in the development of an optimized treatment algorithm for selected patients.

Pathogenesis of refractory ITP: Overview

A subset of individuals with 'primary' or 'idiopathic' immune thrombocytopenia (ITP) who fail to respond to conventional first- and second-line agents or who lose responsiveness are considered to have 'refractory' disease (rITP), placing them at increased risk of bleeding and complications of intensive treatment. However, the criteria used to define the refractory state vary among studies, which complicates research and clinical investigation. Moreover, it is unclear whether rITP is simply 'more severe' ITP, or if there are specific pathogenic pathways that are more likely to result in refractory disease, and whether the presence or development of rITP can be established or anticipated based on these differences. This paper reviews potential biological features that may be associated with rITP, including genetic and epigenetic risk factors, dysregulation of T cells and cytokine networks, antibody affinity and specificity, activation of complement, impaired platelet production and alterations in platelet viability and clearance. These findings indicate the need for longitudinal studies using novel clinically available methodologies to identify and monitor pathogenic T cells, platelet antibodies and other clues to the development of refractory disease.

The short-term predictive value of CD4+ cells for combination therapy with high-dose dexamethasone and immunoglobulin in newly diagnosed primary immune thrombocytopenia patients

INTRODUCTION

Dexamethasone (DXM) or immunoglobulin (IVIg) are first-line therapies for primary immune thrombocytopenia (ITP), with an effective rate of 80 %. Some patients with both severe bleeding symptoms and platelet counts of <30 × 10⁹/L received a combination of DXM and IVIg. Autoimmune disorders, especially involving CD4⁺ T-cells, play a key role in the pathogenesis of ITP. We assumed that variations in the immune status of CD4⁺ T-cells will lead to different treatment responses. Until now, there have been few relevant clinical studies on CD4⁺ T-cells and the outcome of first-line therapies.

METHODS

A prospective study enrolling 42 newly diagnosed ITP patients and 30 normal control volunteers was performed. The profiles of major CD4⁺ T-cells, including T helper (Th)1, Th2, Th17, and regulatory T (Treg) cells, and the related levels of interleukin (IL)-2, IL-17, and IL-23 were examined. The platelet number was recorded at the time point of day 0, day 14, and day 30.

RESULTS

Greater concentrations of Th1 and Th17 cells and lower relative numbers of Treg cells were found in the ITP group. As for the treatment outcome on day 14, the profiles of Th2 and IL-2 were significantly greater in the NR group, while the expression of IL-17 was elevated in the CR group. As for the treatment outcome on day 30, higher levels of Th2 cells were observed in those patients who needed 2× pulses of HD DXM compared to those who needed only 1× pulse of HD DXM and IVIg, and receiver operating characteristic curve analysis showed that lower Treg cell may predict favorable values. Meanwhile, the higher IL-23 value may predict a poor early response.

CONCLUSIONS

Our results indicate that Th1, Th17, and Treg cells and IL-2 and IL-23 participate in the onset of ITP. Higher profiles of Th2, IL-2 and IL-23 may predict poor treatment outcomes. Higher levels of IL-17 and lower profile of Treg may predict sensitivity to HD DXM and IVIg combination therapy.

T Cell Help in the Autoreactive Germinal Center

The germinal center serves as a site of B cell selection and affinity maturation, critical processes for productive adaptive immunity. In autoimmune disease tolerance is broken in the germinal center reaction, leading to production of autoreactive B cells that may propagate disease. Follicular T cells are crucial regulators of this process, providing signals necessary for B cell survival in the germinal center. Here we review the emerging roles of follicular T cells in the autoreactive germinal center. Recent advances in immunological techniques have allowed study of the gene expression profiles and repertoire of follicular T cells at unprecedented resolution. These studies provide insight into the potential role follicular T cells play in preventing or facilitating germinal center loss of tolerance. Improved understanding of the mechanisms of T cell help in autoreactive germinal centers provides novel therapeutic targets for diseases of germinal center dysfunction.

The Extensive Regulation of MicroRNA in Immune Thrombocytopenia

MicroRNA (miRNA) is a small, single-stranded, non-coding RNA molecule that plays a variety of key roles in different biological processes through post-transcriptional regulation of gene expression. MiRNA has been proved to be a variety of cellular processes involved in development, differentiation, signal transduction, and is an important regulator of immune and autoimmune diseases. Therefore, it may act as potent modulators of the immune system and play an important role in the development of several autoimmune diseases. Immune thrombocytopenia (ITP) is an autoimmune systemic disease characterized by a low platelet count. Several studies suggest that like other autoimmune disorders, miRNAs are deeply involved in the pathogenesis of ITP, interacting with the function of innate and adaptive immune responses. In this review, we discuss emerging knowledge about the function of miRNAs in ITP and describe miRNAs in terms of their role in the immune system and autoimmune response. These findings suggest that miRNA may be a useful therapeutic target for ITP by regulating the immune system. In the future, we need to have a more comprehensive understanding of miRNAs and how they regulate the immune system of patients with ITP.

Immune Thrombocytopenia: Recent Advances in Pathogenesis and Treatments

Immune thrombocytopenia (ITP) is a rare autoimmune disease due to both a peripheral destruction of platelets and an inappropriate bone marrow production. Although the primary triggering factors of ITP remain unknown, a loss of immune tolerance-mostly represented by a regulatory T-cell defect-allows T follicular helper cells to stimulate autoreactive splenic B cells that differentiate into antiplatelet antibody-producing plasma cells. Glycoprotein IIb/IIIa is the main target of antiplatelet antibodies leading to platelet phagocytosis by splenic macrophages, through interactions with Fc gamma receptors (FcγRs) and complement receptors. This allows macrophages to activate autoreactive T cells by their antigen-presenting functions. Moreover, the activation of the classical complement pathway participates to platelet opsonization and also to their destruction by complement-dependent cytotoxicity. Platelet destruction is also mediated by a FcγR-independent pathway, involving platelet desialylation that favors their binding to the Ashwell-Morell receptor and their clearance in the liver. Cytotoxic T cells also contribute to ITP pathogenesis by mediating cytotoxicity against megakaryocytes and peripheral platelets. The deficient megakaryopoiesis resulting from both the humoral and the cytotoxic immune responses is sustained by inappropriate levels of thrombopoietin, the major growth factor of megakaryocytes. The better understanding of ITP pathogenesis has provided important therapeutic advances. B cell-targeting therapies and thrombopoietin-receptor agonists (TPO-RAs) have been used for years. New emerging therapeutic strategies that inhibit FcγR signaling, the neonatal Fc receptor or the classical complement pathway, will deeply modify the management of ITP in the near future.

Evolution and Utility of Antiplatelet Autoantibody Testing in Patients with Immune Thrombocytopenia

To this day, immune thrombocytopenia (ITP) remains a clinical diagnosis made by exclusion of other causes for thrombocytopenia. Reliable detection of platelet autoantibodies would support the clinical diagnosis, but the lack of specificity and sensitivity of the available methods for platelet autoantibody testing limits their value in the diagnostic workup of thrombocytopenia. The introduction of methods for glycoprotein-specific autoantibody detection has improved the specificity of testing and is acceptable for ruling in ITP but not ruling it out as a diagnosis. The sensitivity of these assays varies widely, even between studies using comparable assays. A review of the relevant literature combined with our own laboratory's experience of testing large number of serum and platelet samples makes it clear that this variation can be explained by variations in the characteristics of the tests, including in the glycoprotein-specific monoclonal antibodies, the glycoproteins that are tested, the platelet numbers used in the assay and the cutoff levels for positive and negative results, as well as differences in the tested patient populations. In our opinion, further standardization and optimization of the direct autoantibody detection methods to increase sensitivity without compromising specificity seem possible but will still likely be insufficient to distinguish the often very weak specific autoantibody signals from background signals. Further developments of autoantibody detection methods will therefore be necessary to increase sensitivity to a level acceptable to provide laboratory confirmation of a diagnosis of ITP.

Spleen: Development, anatomy and reactive lymphoid proliferations

The unique architecture of the spleen enables it to play a key role in the interactions between the circulatory, reticuloendothelial and immune systems. Response to circulating antigens in the setting of infection, autoimmune disease or other conditions may result in a range of benign lymphoid proliferations. Moreover, patients with underlying immune deficiency may also show abnormal lymphoid proliferations within the spleen. This review will highlight the histologic, immunophenotypic and clinical features of reactive lymphoid proliferations to aid in their recognition and provide a context for understanding their development in relation to normal splenic structure and function.

Idiopathic thrombocytopenic purpura (ITP) - new era for an old disease

Immune thrombocytopenia is an autoimmune hematological disorder characterized by severely decreased platelet count of peripheral cause: platelet destruction via antiplatelet antibodies which may also affect marrow megakaryocytes. Patients may present in critical situations, with cutaneous and/or mucous bleeding and possibly life-threatening organ hemorrhages (cerebral, digestive, etc.) Therefore, rapid diagnosis and therapeutic intervention are mandatory. Corticotherapy represents the first treatment option, but as in any autoimmune disorder, there is a high risk of relapse. Second line therapy options include: intravenous immunoglobulins, thrombopoietin receptor agonists, rituximab or immunosuppression, but their benefit is usually temporary. Moreover, the disease generally affects young people who need repeated and prolonged treatment and hospitalization and therefore, it is preferred to choose a long term effect therapy. Splenectomy - removal of the site of platelet destruction - represents an effective and stable treatment, with 70-80% response rate and low complications incidence. A challenging situation is the association of ITP with pregnancy, which further increases the risk due to the immunodeficiency of pregnancy, major dangers of bleeding, vital risks for mother and fetus, potential risks of medication, necessity of prompt intervention in the setting of specific obstetrical situations - delivery, pregnancy loss, obstetrical complications, etc. We present an updated review of the current clinical and laboratory data, as well as a detailed analysis of the available therapeutic options with their benefits and risks, and also particular associations (pregnancy, relapsed and refractory disease, emergency treatment).

CD4+ T cell phenotypes in the pathogenesis of immune thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by low platelet counts due to enhanced platelet clearance and compromised production. Traditionally, ITP was regarded a B cell mediated disorder as anti-platelet antibodies are detected in most patients. The very nature of self-antigens, evident processes of isotype switching and the affinity maturation of anti-platelet antibodies indicate that B cells in order to mount anti-platelet immune response require assistance of auto-reactive CD4⁺ T cells. For a long time, ITP pathogenesis has been exclusively reviewed through the prism of the disturbed balance between Th1 and Th2 subsets of CD4⁺ T cells, however, more recently new subsets of these cells have been described including Th17, Th9, Th22, T follicular helper and regulatory T cells. In this paper, we review the current understanding of the role and immunological mechanisms by which CD4⁺ T cells contribute to the pathogenesis of ITP.

Autoimmune Cytopenias in Chronic Lymphocytic Leukemia: Focus on Molecular Aspects

Autoimmune cytopenias, particularly autoimmune hemolytic anemia (AIHA) and immune thrombocytopenia (ITP), complicate up to 25% of chronic lymphocytic leukemia (CLL) cases. Their occurrence correlates with a more aggressive disease with unmutated VHIG status and unfavorable cytogenetics (17p and 11q deletions). CLL lymphocytes are thought to be responsible of a number of pathogenic mechanisms, including aberrant antigen presentation and cytokine production. Moreover, pathogenic B-cell lymphocytes may induce T-cell subsets imbalance that favors the emergence of autoreactive B-cells producing anti-red blood cells and anti-platelets autoantibodies. In the last 15 years, molecular insights into the pathogenesis of both primary and secondary AIHA/ITP has shown that autoreactive B-cells often display stereotyped B-cell receptor and that the autoantibodies themselves have restricted phenotypes. Moreover, a skewed T-cell repertoire and clonal T cells (mainly CD8+) may be present. In addition, an imbalance of T regulatory-/T helper 17-cells ratio has been involved in AIHA and ITP development, and correlates with various cytokine genes polymorphisms. Finally, altered miRNA and lnRNA profiles have been found in autoimmune cytopenias and seem to correlate with disease phase. Genomic studies are limited in these forms, except for recurrent mutations of KMT2D and CARD11 in cold agglutinin disease, which is considered a clonal B-cell lymphoproliferative disorder resulting in AIHA. In this manuscript, we review the most recent literature on AIHA and ITP secondary to CLL, focusing on available molecular evidences of pathogenic, clinical, and prognostic relevance.

High-throughput sequencing of IgG B-cell receptors reveals frequent usage of the rearranged IGHV4-28/IGHJ4 gene in primary immune thrombocytopenia

Primary immune thrombocytopenia (ITP) is an acquired form of thrombocytopenia caused by IgG anti-platelet autoantibodies and represents an organ-specific autoimmune disorder. Although the glycoprotein (GP)IIb/IIIa and GPIb/IX have been shown to be targets for autoantibodies, the antigen specificity of autoantibodies is not fully elucidated. To identify the characteristics of IgG B-cell receptor (BCR) repertoires in ITP, we took advantage of adaptor-ligation PCR and high-throughput DNA sequencing methods for analyzing the clone-based repertoires of IgG-expressing peripheral blood B cells. A total of 2,009,943 in-frame and 315,469 unique reads for IGH (immunoglobulin heavy) were obtained from twenty blood samples. Comparison of the IGHV repertoires between patients and controls revealed an increased usage of IGHV4–28 in ITP patients. One hundred eighty-six distinct IGHV4–28-carrying sequences were identified in ITP patients and the majority of these clones used an IGHJ4 segment. The IGHV4–28/IGHJ4-carrying B-cell clones were found in all ITP patients. Oligoclonal expansions of IGHV4–28/IGHJ4-carrying B cells were accompanied by multiple related clones with single amino substitution in the CDR3 region suggesting somatic hypermutation. Taken together, the expansion of IGHV4–28/IGHJ4-carrying IgG-expressing B cells in ITP may be the result of certain antigenic pressure and may provide a clue for the immune pathophysiology of ITP.

Acquired Glanzmann thrombasthenia: From antibodies to anti-platelet drugs

In contrast to the inherited platelet disorder given by mutations in the ITGA2B and ITGB3 genes, mucocutaneous bleeding from a spontaneous inhibition of normally expressed αIIbβ3 characterizes acquired Glanzmann thrombasthenia (GT). Classically, it is associated with autoantibodies or paraproteins that block platelet aggregation without causing a fall in platelet count. However, inhibitory antibodies to αIIbβ3 are widely associated with primary immune thrombocytopenia (ITP), occur in secondary ITP associated with leukemia and related disorders, solid cancers and myeloma, other autoimmune diseases, following organ transplantation while cytoplasmic dysregulation of αIIbβ3 function features in myeloproliferative and myelodysplastic syndromes. Antibodies to αIIbβ3 occur during viral and bacterial infections, while drug-dependent antibodies reacting with αIIbβ3 are a special case. Direct induction of acquired GT is a feature of therapies that block platelets in coronary artery disease. This review looks at these conditions, emphasizing molecular mechanisms, therapy, patient management and future directions for research.

Emerging Concepts in Immune Thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune disease defined by low platelet counts which presents with an increased bleeding risk. Several genetic risk factors (e.g., polymorphisms in immunity-related genes) predispose to ITP. Autoantibodies and cytotoxic CD8⁺ T cells (Tc) mediate the anti-platelet response leading to thrombocytopenia. Both effector arms enhance platelet clearance through phagocytosis by splenic macrophages or dendritic cells and by induction of apoptosis. Meanwhile, platelet production is inhibited by CD8⁺ Tc targeting megakaryocytes in the bone marrow. CD4⁺ T helper cells are important for B cell differentiation into autoantibody secreting plasma cells. Regulatory Tc are essential to secure immune tolerance, and reduced levels have been implicated in the development of ITP. Both Fcγ-receptor-dependent and -independent pathways are involved in the etiology of ITP. In this review, we present a simplified model for the pathogenesis of ITP, in which exposure of platelet surface antigens and a loss of tolerance are required for development of chronic anti-platelet responses. We also suggest that infections may comprise an important trigger for the development of auto-immunity against platelets in ITP. Post-translational modification of autoantigens has been firmly implicated in the development of autoimmune disorders like rheumatoid arthritis and type 1 diabetes. Based on these findings, we propose that post-translational modifications of platelet antigens may also contribute to the pathogenesis of ITP.

Splenectomy for immune thrombocytopenia: down but not out

Splenectomy is an effective therapy for steroid-refractory or dependent immune thrombocytopenia (ITP). With the advent of medical alternatives such as rituximab and thrombopoietin receptor antagonists, the use of splenectomy has declined and is generally reserved for patients that fail multiple medical therapies. Splenectomy removes the primary site of platelet clearance and autoantibody production and offers the highest rate of durable response (50% to 70%) compared with other ITP therapies. However, there are no reliable predictors of splenectomy response, and long-term risks of infection and cardiovascular complications must be considered. Because the long-term efficacy of different second-line medical therapies for ITP have not been directly compared, treatment decisions must be made without supportive evidence. Splenectomy continues to be a reasonable treatment option for many patients, including those with an active lifestyle who desire freedom from medication and monitoring, and patients with fulminant ITP that does not respond well to medical therapy. We try to avoid splenectomy within the first 12 months after ITP diagnosis for most patients to allow for spontaneous or therapy-induced remissions, particularly in older patients who have increased surgical morbidity and lower rates of response, and in young children. Treatment decisions must be individualized based on patients' comorbidities, lifestyles, and preferences. Future research should focus on comparing long-term outcomes of patients treated with different second-line therapies and on developing personalized medicine approaches to identify subsets of patients most likely to respond to splenectomy or other therapeutic approaches.

Downregulation of hypoxia-inducible factor-1α contributes to impaired megakaryopoiesis in immune thrombocytopenia

Impaired megakaryocyte maturation and exaggerated platelet destruction play a pivotal role in the pathogenesis of immune thrombocytopenia (ITP). Previous studies have shown that HIF-1α promotes the homing and engraftment of haematopoietic stem cells (HSCs), thereby stimulating HSC differentiation. However, whether HIF-1α plays a role in megakaryocytic maturation and platelet destruction in ITP remains elusive. Using enzyme-linked immunosorbent assays (ELISAs), we demonstrated that there were lower HIF-1α levels in the bone marrow (BM) of ITP patients than in that of healthy donors and patients with chemotherapy-related thrombocytopenia. Subjects with lower megakaryocyte (<100/slide) and platelet (<30 × 109/L) counts exhibited significantly decreased BM HIF-1α levels, compared to those with higher megakaryocyte (≥100/slide) and platelet (≥30 × 109/L) counts. To test whether HIF-1α regulates megakaryopoiesis and platelet production, megakaryocytes derived from mouse BM cells were treated with an HIF-1α activator (IOX-2; 50 µM) or inhibitor (PX-478; 50 µM). PX-478 significantly decreased HIF-1α expression, cell size, and the populations of CD41-positive and high-ploidy cells. Importantly, to evaluate the role of HIF-1α as a potential therapeutic target in ITP, mouse BM cells were incubated with plasma from ITP patients in the presence or absence of IOX-2. IOX-2 significantly attenuated the ITP plasma-induced decrease in cell size as well as the proportions of CD41-positive and high-ploidy cells. In addition, IOX-2 increased the number of megakaryocytes from mouse BM cells treated with ITP plasma. Our findings indicate that decreased HIF-1α may contribute to impaired megakaryopoiesis in ITP, and HIF-1α may provide a potential therapy for ITP patients.

Supplementary Material to this article is available online at www.thrombosis-online.com.

Expression of CD markers' in immune thrombocytopenic purpura: prognostic approaches

Immune Thrombocytopenic Purpura (ITP) is a common autoimmune bleeding disorder characterized by a reduction in peripheral blood platelet counts. In this disease, autoantibodies (Auto-Abs) are produced against platelet GPIIb/GPIIIa by B cells, which require interaction with T cells. In this review, the importance of B and T lymphocytes in ITP prognosis has been studied. Relevant literature was identified by a PubMed search (1990-2016) of English-language papers using the terms B and T lymphocyte, platelet, CD markers and immune thrombocytopenic purpura. T and B lymphocytes are the main immune cells in the body. Defective function causes disrupted balance of different subgroups of lymphocytes, and abnormal expression of surface markers of these cells results in self-tolerance dysfunction, as well as induction of Auto-Abs against platelet glycoproteins (PG). Given the role of B and T cells in production of autoantibodies against PG, it can be stated that the detection of changes in CD markers' expression in these cells can be a good approach for assessing prognosis in ITP patients.

Targeted Therapy for Hematologic Malignancies

Background:

The introduction of monoclonal antibodies, either as native molecules or conjugated to radioisotopes or other toxins, has led to new therapeutic options for patients with hematologic malignancies. In addition, the use of small molecules against specific cell surface receptors, enzymes, and proteins has become an important strategy in the treatment of such disorders.

Methods:

The author reviewed the published clinical trials of monoclonal antibody and other targeted therapies in hematologic malignancies.

Results:

Results from several trials demonstrate a therapeutic benefit for the use of monoclonal antibodies (either native or conjugated) and other targeted therapies, used alone or in combination with standard cytotoxic chemotherapy.

Conclusions:

Targeted therapy of hematologic malignancies seems to be an effective and less toxic approach to the treatment of such disorders. Nevertheless, additional studies are needed to determine where and when such management fits into a therapeutic regimen for any given disorder, whether upfront or as salvage therapy, alone or in combination with chemotherapy (concurrent or sequential).

Syk inhibitors in clinical development for hematological malignancies

Spleen tyrosine kinase (Syk) is a cytosolic non-receptor protein tyrosine kinase (PTK) and is mainly expressed in hematopoietic cells. Syk was recognized as a critical element in the B-cell receptor signaling pathway. Syk is also a key component in signal transduction from other immune receptors like Fc receptors and adhesion receptors. Several oral Syk inhibitors including fostamatinib (R788), entospletinib (GS-9973), cerdulatinib (PRT062070), and TAK-659 are being assessed in clinical trials. The second generation compound, entospletinib, showed promising results in clinical trials against B-cell malignancies, mainly chronic lymphoid leukemia. Syk inhibitors are being evaluated in combination regimens in multiple malignancies.

Advances in the pathophysiology of primary immune thrombocytopenia

OBJECTIVES

Classically, immune thrombocytopenia (ITP) was thought to be caused by the destruction and insufficient production of platelets, as mediated by autoantibodies. More recently other immune mechanisms that contribute to the disease have been discovered. This review attempts to address the main unresolved questions in ITP.

METHODS

We review the most current knowledge of the pathophysiology of ITP. Immunological effects of available therapies are also described.

DISCUSSION

The trigger may be a loss of tolerance due to molecular mimicry with cross-reaction of antibodies arising from infectious agents or drugs, genetic factors, and/or platelet Toll receptors. This loss of tolerance activates autoreactive effector B and T lymphocytes, which in turn initiates platelet destruction, mediated by cytotoxic T lymphocytes and the release of pro-inflammatory cytokines (IL-2/IL-17) by T helper (Th) cells (Th1/Th17). Th2 (anti-inflammatory) and regulatory B (Breg) and Treg cells are also inhibited (with decrease in IL-10/TGF-β), which leads to the disease becoming chronic. Some isotypes of autoantibodies may increase the bleeding risk. Corticosteroids, rituximab, and thrombopoietin receptor agonists (A-TPOs) all increase levels of Tregs and TGF-β. The A-TPOs also increase Breg levels, which could explain why complete remission has been seen in some cases.

CONCLUSION

A better understanding of the immunomodulatory effects of each ITP therapy is needed to best manage the disease.

ADAMTS13 autoantibodies cloned from patients with acquired thrombotic thrombocytopenic purpura: 1. Structural and functional characterization in vitro

BACKGROUND

Acquired thrombotic thrombocytopenia purpura (TTP) is a life-threatening illness caused by autoantibodies that decrease the activity of ADAMTS13, the von Willebrand factor-cleaving protease. Despite efficacy of plasma exchange, mortality remains high and relapse is common. Improved therapies may come from understanding the diversity of pathogenic autoantibodies on a molecular or genetic level. Cloning comprehensive repertoires of patient autoantibodies can provide the necessary tools for studying immunobiology of disease and developing animal models.

STUDY DESIGN AND METHODS

Anti-ADAMTS13 antibodies were cloned from four patients with acquired TTP using phage display and characterized with respect to genetic origin, inhibition of ADAMTS13 proteolytic activity, and epitope specificity. Anti-idiotypic antisera raised to a subset of autoantibodies enabled comparison of their relatedness to each other and to polyclonal immunoglobulin (Ig)G in patient plasma.

RESULTS

Fifty-one unique antibodies were isolated comprising epitope specificities resembling the diversity found in circulating patient IgG. Antibodies directed both to the amino terminal domains and to those requiring the ADAMTS13 cysteine-rich/spacer region for binding inhibited proteolytic activity, while those solely targeting carboxy-terminal domains were noninhibitory. Anti-idiotypic antisera raised to a subset of antibody clones crossreacted with and reduced the inhibitory activity of polyclonal IgG from a set of unrelated patients.

CONCLUSIONS

Anti-ADAMTS13 autoantibodies isolated by repertoire cloning display the diversity of epitope specificities found in patient plasma and provide tools for developing animal models of acquired TTP. Shared idiotypes of inhibitory clones with circulating IgG from multiple patients suggest common features of pathogenic autoantibodies that could be exploited for developing more targeted therapies.

The analysis of clonal expansions in normal and autoimmune B cell repertoires

Clones are the fundamental building blocks of immune repertoires. The number of different clones relates to the diversity of the repertoire, whereas their size and sequence diversity are linked to selective pressures. Selective pressures act both between clones and within different sequence variants of a clone. Understanding how clonal selection shapes the immune repertoire is one of the most basic questions in all of immunology. But how are individual clones defined? Here we discuss different approaches for defining clones, starting with how antibodies are diversified during different stages of B cell development. Next, we discuss how clones are defined using different experimental methods. We focus on high-throughput sequencing datasets, and the computational challenges and opportunities that these data have for mining the antibody repertoire landscape. We discuss methods that visualize sequence variants within the same clone and allow us to consider collections of shared mutations to determine which sequences share a common ancestry. Finally, we comment on features of frequently encountered expanded B cell clones that may be of particular interest in the setting of autoimmunity and other chronic conditions.

Imbalanced immune homeostasis in immune thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder resulting from low platelet counts caused by inadequate production as well as increased destruction by autoimmune mechanisms. As with other autoimmune disorders, chronic ITP is characterized by perturbations of immune homeostasis with hyperactivated effector cells as well as defective regulatory arm of the adaptive immune system, which will be reviewed here. Interestingly, some ITP treatments are associated with restoring the regulatory imbalance, although it remains unclear whether the immune system is redirected to a state of tolerance once treatment is discontinued. Understanding the mechanisms that result in breakdown of immune homeostasis in ITP will help to identify novel pathways for restoring tolerance and inhibiting effector cell responses. This information can then be translated into developing therapies for averting autoimmunity not only in ITP but also many autoimmune disorders.

Use of the VH6-1 gene segment to code for anti-interleukin-18 autoantibodies in multiple sclerosis

We investigated whether levels and repertoires of anti-interleukin-18 (IL-18) autoantibodies (auto-Abs) differ in multiple sclerosis (MS) patients and healthy donors (HDs). IL-18 concentration in MS patients' sera was higher than in HD, but the level of anti-IL-18 auto-Abs was lower in MS patients. Correlation patterns of IL-18/anti-IL-18 auto-Abs system differed in HD and MS patients, so we have compared segment composition of the anti-IL-18 single-chain variable fragments (scFvs) selected from MS and naïve phage display libraries. Considerable differences between anti-IL-18 auto-Abs of these libraries were found. MS panel contained auto-Abs displaying both signs of "fetal" and somatically hypermutated repertoires. Naïve panel mainly contained the naïve antibodies. These variations from the norm are possible results of abnormal regulation of the repertoire perhaps determined by remodeling of the molecular mechanisms involved in the V(D)J recombination and/or abnormal selection by antigen in MS pathogenesis.

Helicobacter pylori Eradication in Patients with Immune Thrombocytopenic Purpura: A Review and the Role of Biogeography

Idiopathic thrombocytopenic purpura (ITP) is typically a diagnosis of exclusion, assigned by clinicians after ruling out other identifiable etiologies. Since a report by Gasbarrini et al. in 1998, an accumulating body of evidence has proposed a pathophysiological link between ITP and chronic Helicobacter pylori (H. pylori) infection. Clinical reports have described a spontaneous resolution of ITP symptoms in about 50% of chronic ITP patients following empirical treatment of H. pylori infection, but response appears to be geography dependent. Studies have also documented that ITP patients in East Asian countries are more likely to express positive antibody titers against H. pylori-specific cytotoxic-associated gene A (CagA), a virulence factor that is associated with an increased risk for gastric diseases including carcinoma. While a definitive mechanism by which H. pylori may induce thrombocytopenia remains elusive, proposed pathways include molecular mimicry of CagA by host autoantibodies against platelet surface glycoproteins, as well as perturbations in the phagocytic activity of monocytes. Traditional treatments of ITP have been largely empirical, involving the use of immunosuppressive agents and immunoglobulin therapy. However, based on the findings of clinical reports emerging over the past 20 years, health organizations around the world increasingly suggest the detection and eradication of H. pylori as a treatment for ITP. Elucidating the exact molecular mechanisms of platelet activation in H. pylori-positive ITP patients, while considering biogeographical differences in response rates, could offer insight into how best to use clinical H. pylori eradication to treat ITP, but will require well-designed studies to confirm the suggested causative relationship between bacterial infection and an autoimmune disease state.

Platelet destruction in immune thrombocytopenia. Understanding the mechanisms

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder characterized by isolated thrombocytopenia. A dysfunctional proliferation of autoreactive T cells is suggested to be responsible for the loss of tolerance to self-platelet antigens in ITP patients. Autoreactive T cells induce uncontrolled proliferation of autoantibody producing B cells leading to persistent anti-platelet autoimmunity in some ITP patients. The autoimmune response causes an increased destruction of platelets by antibody-mediated phagocytosis, complement activation but also by T cell mediated cytotoxicity. In addition, abnormalities in thrombopoiesis and insufficient platelet production due to antibody or T cell mediated megakaryocyte inhibition and destruction contribute to the pathophysiology of ITP. These various effector cell responses may account for the heterogeneity in the clinical manifestation of ITP and also, to success or failure of different treatment strategies. A better understanding of the mechanisms behind ITP will hopefully allow for better diagnostic and, particularly, therapeutic strategies in the future.

Next generation sequencing reveals skewing of the T and B cell receptor repertoires in patients with wiskott-Aldrich syndrome

The Wiskott–Aldrich syndrome (WAS) is due to mutations of the WAS gene encoding for the cytoskeletal WAS protein, leading to abnormal downstream signaling from the T cell and B cell antigen receptors (TCR and BCR). We hypothesized that the impaired signaling through the TCR and BCR in WAS would subsequently lead to aberrations in the immune repertoire of WAS patients. Using next generation sequencing (NGS), the T cell receptor β and B cell immunoglobulin heavy chain (IGH) repertoires of eight patients with WAS and six controls were sequenced. Clonal expansions were identified within memory CD4⁺ cells as well as in total, naïve and memory CD8⁺ cells from WAS patients. In the B cell compartment, WAS patient IGH repertoires were also clonally expanded and showed skewed usage of IGHV and IGHJ genes, and increased usage of IGHG constant genes, compared with controls. To our knowledge, this is the first study that demonstrates significant abnormalities of the immune repertoire in WAS patients using NGS.

Immune dysregulation in immune thrombocytopenia

Immune thrombocytopenia (ITP) is a bleeding disorder characterized by low platelet counts due to decreased platelet production as well as increased platelet destruction by autoimmune mechanisms. A shift toward Th1 and possibly Th17 cells together with impaired regulatory compartment, including T-regulatory (Tregs) and B-regulatory (Bregs) cells, have been reported, suggesting a generalized immune dysregulation in ITP. Interestingly, several treatments including the use of thrombopoietic agents appear to be associated with improvement in the regulatory compartment. Understanding how Th1/Th17/Treg differentiation and expansion are controlled is central to uncovering how autoimmunity may be sustained in chronic ITP and reversed following response to therapy. In this review, we will summarize the recent findings on the state of the Breg and Treg compartments in ITP, the role of monocyte subsets in the control of Th/Treg expansion, and our working model of how the regulatory compartment may impact response to treatment and the means by which this information may guide therapy in ITP patients in the future.

Immune thrombocytopenia

Immune thrombocytopenia (ITP) is a common hematologic disorder characterized by isolated thrombocytopenia. ITP presents as a primary or a secondary form. ITP may affect individuals of all ages, with peaks during childhood and in the elderly, in whom the age-specific incidence of ITP is greatest. Bleeding is the most common clinical manifestation of ITP. The pathogenesis of ITP is complex, involving alterations in humoral and cellular immunity. Corticosteroids remain the most common first line therapy for ITP. This article summarizes the classification and diagnosis of primary and secondary ITP, as well as the pathogenesis and options for treatment.

Wiskott-Aldrich Syndrome protein deficiency perturbs the homeostasis of B-cell compartment in humans

Wiskott–Aldrich Syndrome protein (WASp) regulates the cytoskeleton in hematopoietic cells and mutations in its gene cause the Wiskott–Aldrich Syndrome (WAS), a primary immunodeficiency with microthrombocytopenia, eczema and a higher susceptibility to develop tumors. Autoimmune manifestations, frequently observed in WAS patients, are associated with an increased risk of mortality and still represent an unsolved aspect of the disease. B cells play a crucial role both in immune competence and self-tolerance and defects in their development and function result in immunodeficiency and/or autoimmunity. We performed a phenotypical and molecular analysis of central and peripheral B-cell compartments in WAS pediatric patients. We found a decreased proportion of immature B cells in the bone marrow correlating with an increased presence of transitional B cells in the periphery. These results could be explained by the defective migratory response of WAS B cells to SDF-1α, essential for the retention of immature B cells in the BM. In the periphery, we observed an unusual expansion of CD21^low B-cell population and increased plasma BAFF levels that may contribute to the high susceptibility to develop autoimmune manifestations in WAS patients. WAS memory B cells were characterized by a reduced in vivo proliferation, decreased somatic hypermutation and preferential usage of IGHV4-34, an immunoglobulin gene commonly found in autoreactive B cells.

In conclusion, our findings demonstrate that WASp-deficiency perturbs B-cell homeostasis thus adding a new layer of immune dysregulation concurring to the increased susceptibility to develop autoimmunity in WAS patients.

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WASp-deficiency affects both central and peripheral B-cell development.

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An early egress of immature B cells leads to an increase of transitional B cells in periphery.

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Reduced maturation status of WAS memory B cells.

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Altered selection of both protective and autoreactive Ig gene families in WAS patients.

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Potentially autoreactive CD21^low B cells are expanded in WAS patients.

VH1-44 gene usage defines a subset of canine B-cell lymphomas associated with better patient survival

The use of specific immunoglobulin heavy chain variable region (VH) genes has been associated with increased patient survival in human B-cell lymphomas (hBCL). Given the similarity of human and canine BCL (cBCL) in morphology and clinical treatment, we examined the choice of VH in cBCL and determined whether VH gene selection was a distinct feature associated with survival time in dogs. VH gene selection and mutational status in 52 cBCL, including 29 diffuse large B-cell lymphomas (cDLBCL, the most common subtype of cBCL), were analyzed by comparison with the 80 published canine germline VH gene sequences. We further examined the prognostic impact of the subgroups defined by these features on canine survival. We found that VH1-44 was preferentially expressed in the majority of the 52 cBCLs (60%) as well as in the majority of the cDLBCL subset (59%). VH1-44 gene expression was associated with a statistically better overall survival (p=0.039) in cBCL patients, as well as in the cDLBCL subset of patients (p=0.038). These findings suggest that VH gene selection in cBCL is not random and may therefore have functional implications for cBCL lymphomagenesis, in addition to being a useful prognostic biomarker.

Preferential splenic CD8(+) T-cell activation in rituximab-nonresponder patients with immune thrombocytopenia

The pathogenic role of B cells in immune thrombocytopenia (ITP) has justified the therapeutic use of anti-CD20 antibodies such as rituximab (RTX). However, 60% of ITP patients do not respond to RTX. To decipher the mechanisms implicated in the failure of RTX, and because the spleen plays a well-recognized role in ITP pathogenesis, 12 spleens from ITP patients who had been nonresponders to RTX therapy were compared with 11 spleens from RTX-untreated ITP patients and 9 controls. We here demonstrate that in RTX-nonresponder ITP patients, preferential Th1 and Tc1 T lymphocyte polarizations occur, associated with an increase in splenic effector memory CD8(+) T-cell frequency. Moreover, in the RTX- nonresponder patient group, the CD8(+) T-cell repertoire displays a restricted pattern. In the blood, the phenotype of CD8(+) T cells before and after RTX treatment is not modified in responders or nonresponders. Altogether, these results demonstrate for the first time an activation of splenic CD8(+) T cells in ITP patients who did not respond to RTX and suggest their involvement in platelet destruction in these patients.

Update on the Intercontinental Cooperative ITP Study Group (ICIS) and on the Pediatric and Adult Registry on Chronic ITP (PARC ITP)

The Intercontinental Cooperative ITP Study Group (ICIS) was founded in 1997, when the American practice guidelines demonstrated that there is a substantial lack of clinical data. The aim of the group was to promote basic science and clinical research in the field of ITP. Clinical data and more recently DNA is collected to investigate children and adults with ITP. ICIS organizes regular meetings and opened several registries, the most recent being the Pediatric and Adult Registry on Chronic ITP (PARC-ITP), all of which will be briefly discussed. There are many unanswered questions in basic science and clinical research in ITP which need large collaborative studies. The international network of ICIS may be of value in better understanding ITP.

Recognition of highly restricted regions in the β-propeller domain of αIIb by platelet-associated anti-αIIbβ3 autoantibodies in primary immune thrombocytopenia

Platelet-associated (PA) IgG autoantibodies play an essential role in primary immune thrombocytopenia (ITP). However, little is known about the epitopes of these Abs. This study aimed to identify critical binding regions for PA anti-αIIbβ3 Abs. Because PA anti-αIIbβ3 Abs bound poorly to mouse αIIbβ3, we created human-mouse chimera constructs. We first examined 76 platelet eluates obtained from patients with primary ITP. Of these, 26 harbored PA anti-αIIbβ3 Abs (34%). Further analysis of 15 patients who provided sufficient materials showed that the epitopes of these Abs were mainly localized in the N-terminal half of the β-propeller domain in αIIb (L1-W235). We could identify 3 main recognition sites in the region; 2 eluates recognized a conformation formed by the W1:1-2 and W2:3-4 loops, 5 recognized W1:2-3, and 4 recognized W3:4-1. The remaining 4 eluates could not be defined by the binding sites. Within these regions, we identified residues critical for binding, including S29 and R32 in W1:1-2; G44 and P45 in W1:2-3; and P135, E136, and R139 in W2:3-4. Of 11 eluates whose recognition sites were identified, 5 clearly showed restricted κ/λ-chain usage. These results suggested that PA anti-αIIbβ3 Abs in primary ITP tended to recognize highly restricted regions of αIIb with clonality.

Phage display-based strategies for cloning and optimization of monoclonal antibodies directed against human pathogens

In the last two decades, several phage display-selected monoclonal antibodies (mAbs) have been described in the literature and a few of them have managed to reach the clinics. Among these, the anti-respiratory syncytial virus (RSV) Palivizumab, a phage-display optimized mAb, is the only marketed mAb directed against microbial pathogens. Palivizumab is a clear example of the importance of choosing the most appropriate strategy when selecting or optimizing an anti-infectious mAb. From this perspective, the extreme versatility of phage-display technology makes it a useful tool when setting up different strategies for the selection of mAbs directed against human pathogens, especially when their possible clinical use is considered. In this paper, we review the principal phage display strategies used to select anti-infectious mAbs, with particular attention focused on those used against hypervariable pathogens, such as HCV and influenza viruses.

Reduced expression of transforming growth factor-β1 and correlated elevation of interleukin-17 and interferon-γ in pediatric patients with chronic primary immune thrombocytopenia (ITP)

BACKGROUND

Dysregulated T helper (Th) cells are considered important in the pathophysiology of chronic primary immune thrombocytopenia (ITP). The present study investigated whether levels of Th cytokines in pediatric patients with chronic ITP were different compared with healthy controls.

PROCEDURES

Fifty-seven pediatric patients with chronic ITP and 28 healthy controls were enrolled. Patients were divided into three groups based on their platelet counts at the time of the study: (i) active disease <50 × 10(9) /l (n = 23), (ii) stable disease 50-150 × 10(9) /l (n = 23), and (iii) in remission >150 × 10(9) /l (n = 11). Plasma concentration of Th1 [interferon gamma (INF-γ), interleukin 2 (IL-2)], Th2 (IL-4, IL-10), Th3 [transforming growth factor-β1 (TGF-β1)], and Th17 (IL-17) cytokines were investigated by enzyme-linked immunosorbent assay.

RESULTS

IFN-γ was increased in patients with active (P < 0.001) and stable disease (P = 0.026) when compared with controls. The IL-17 level was significantly higher in all of the 3 patient groups. In addition, there was a positive correlation between IL-17 and IFN-γ levels in chronic ITP patients (r = 0.640, P < 0.001). Reduced TGF-β1 expression was observed in patients with active (P < 0.001) and stable disease (P = 0.001) in comparison with controls. Moreover, TGF-β1 level in patients was positively correlated with the platelet count (r = 0.355, P = 0.007).

CONCLUSIONS

Elevation of IL-17 and IFN-γ may be an important dysregulation of cellular immunity in pediatric patients with chronic ITP. The disease activity is associated with reduced production of TGF-β1.

Immunologic effects of rituximab on the human spleen in immune thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune disease with a complex pathogenesis. As in many B cell-related autoimmune diseases, rituximab (RTX) has been shown to increase platelet counts in some ITP patients. From an immunologic standpoint, the mode of action of RTX and the reasons underlying its limited efficacy have yet to be elucidated. Because splenectomy is a cornerstone treatment of ITP, the immune effect of RTX on this major secondary lymphoid organ was investigated in 18 spleens removed from ITP patients who were treated or not with RTX. Spleens from ITP individuals had follicular hyperplasia consistent with secondary follicles. RTX therapy resulted in complete B-cell depletion in the blood and a significant reduction in splenic B cells, but these patients did not achieve remission. Moreover, whereas the percentage of circulating regulatory T cells (Tregs) was similar to that in controls, splenic Tregs were reduced in ITP patients. Interestingly, the ratio of proinflammatory Th1 cells to suppressive Tregs was increased in the spleens of patients who failed RTX therapy. These results indicate that although B cells are involved in ITP pathogenesis, RTX-induced total B-cell depletion is not correlated with its therapeutic effects, which suggests additional immune-mediated mechanisms of action of this drug.

Autoimmunity in common variable immunodeficiency: correlation with lymphocyte phenotype in the French DEFI study

Common variable immunodeficiency (CVID) is the most frequent clinically expressed primary immunodeficiency in adults and is characterized by primary defective immunoglobulin production. Besides recurrent infectious manifestations, up to 20% of CVID patients develop autoimmune complications. In this study, we took advantages of the French DEFI database to investigate possible correlations between peripheral lymphocyte subpopulations and autoimmune clinical expression in CVID adult patients. In order to analyse homogeneous populations of patients with precise clinical phenotypes, we first focused on patients with autoimmune cytopenia because they represent prototypic autoantibody mediated diseases. In a secondary analysis, we have tested our conclusions including all "autoimmune" CVID patients. We describe one of the largest European studies with 311 CVID patients, including 55 patients with autoimmune cytopenia and 61 patients with clinical or serologic autoimmune expression, excluding autoimmune cytopenia. We clarify previous reports and we confirm a very significant correlation between an increased proportion of CD21(low) B cells and CVID associated autoimmune cytopenia, but independently of the presence of other autoimmune disorders or of splenomegaly. Moreover, in CVID associated autoimmune cytopenia, T cells display an activated phenotype with an increase of HLA-DR and CD95 expression and a decrease in the naïve T cell numbers. Patients with other autoimmune manifestations do not harbour this "T and B cells phenotypic picture". In view of recent findings on CD21(low) B cells in CVID and RA, we suggest that both a restricted subset of B cells and a T cell help are required for a breakdown of B cell tolerance against membrane auto antigens in CVID.