Recruitment of T cells into bone marrow of ITP patients possibly due to elevated expression of VLA-4 and CX3CR1. Blood. 2008;112:1078-1084. [PMID: 18519809 DOI: 10.1182/blood-2008-02-139402]

The many facets of immune-mediated thrombocytopenia: Principles of immunobiology and immunotherapy

Immune thrombocytopenia (ITP) is a rare autoimmune condition, due to peripheral platelet destruction through antibody-dependent cellular phagocytosis, complement-dependent cytotoxicity, cytotoxic T lymphocyte-mediated cytotoxicity, and megakaryopoiesis alteration. This condition may be idiopathic or triggered by drugs, vaccines, infections, cancers, autoimmune disorders and systemic diseases. Recent advances in our understanding of ITP immunobiology support the idea that other forms of thrombocytopenia, for instance, occurring after immunotherapy or cellular therapies, may share a common pathophysiology with possible therapeutic implications. If a decent pipeline of old and new agents is currently deployed for classical ITP, in other more complex immune-mediated thrombocytopenic disorders, clinical management is less harmonized and would deserve further prospective investigations. Here, we seek to provide a fresh overview of pathophysiology and current therapeutical algorithms for adult patients affected by this disorder with specific insights into poorly codified scenarios, including refractory ITP and post-immunotherapy/cellular therapy immune-mediated thrombocytopenia.

Immune attack on megakaryocytes in immune thrombocytopenia

A State of the Art lecture titled "Immune Attack on Megakaryocytes in ITP: The Role of Megakaryocyte Impairment" was presented at the International Society on Thrombosis and Haemostasis Congress in 2023. Immune thrombocytopenia (ITP) is an acquired autoimmune disorder caused by autoantibodies against platelet surface glycoproteins that provoke increased clearance of circulating platelets, leading to reduced platelet number. However, there is also evidence of a direct effect of antiplatelet autoantibodies on bone marrow megakaryocytes. Indeed, immunologic cells responsible for autoantibody production reside in the bone marrow; megakaryocytes progressively express during their maturation the same glycoproteins against which ITP autoantibodies are directed, and platelet autoantibodies have been detected in the bone marrow of patients with ITP. In vitro studies using ITP sera or monoclonal antibodies against platelet and megakaryocyte surface glycoproteins have shown an impairment of many steps of megakaryopoiesis and thrombopoiesis, such as megakaryocyte differentiation and maturation, migration from the osteoblastic to the vascular niche, adhesion to extracellular matrix proteins, and proplatelet formation, resulting in impaired and ectopic platelet production in the bone marrow and diminished platelet release in the bloodstream. Moreover, cytotoxic T cells may target bone marrow megakaryocytes, resulting in megakaryocyte destruction. Altogether, these findings suggest that antiplatelet autoantibodies and cellular immunity against bone marrow megakaryocytes may significantly contribute to thrombocytopenia in some patients with ITP. Finally, we summarize relevant new data on this topic presented during the 2023 International Society on Thrombosis and Haemostasis Congress. The complete unraveling of the mechanisms of immune attack-induced impairment of megakaryopoiesis and thrombopoiesis may open the way to new therapeutic approaches.

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.

A mAb to SIRPα downregulates the priming of naive CD4 + T cell in Primary immune thrombocytopenia

SIRPα is a transmembrane protein that binds the protein tyrosine phosphatases SHP-1 and SHP-2 through its cytoplasmic region and is abundantly expressed on monocytes, dendritic cells, and macrophages. Studies recently showed that SIRPα is essential for priming of CD4 + T cells by DCs and for development of Th17 cell-mediated autoimmune diseases. We have now further evaluated the importance of SIRPα and that of its ligand CD47 in primary immune thrombocytopenia (ITP). In this study, we show that there was a low expression state of SIRPα on the surface of monocytes. Treatment of cells culture from ITP patients with a mAb to SIRPα that blocks the binding of SIRPα to CD47 downregulated the ITP response. The abilities of monocytes from ITP patients to stimulate an allogenic MLR were reduced. The proliferation of, and production of IL-2, by CD4 + T cells from ITP patients were inhibited, the Treg cell numbers and the production of IL-10 pairs were upregulated, and the production of TGF-β not was inhibited, by a mAb to SIRPα. Moreover, a mAb to SIRPα, the expression of HLA-DR and CD86 were markedly inhibited and the expression of CD80 was slightly upregulated, on the surface of CD14 + monocytes from ITP patients as compared with healthy subjects. However, blockade of SIRPα increased the secretion of TLR-dependent cytokines TNF-α, IL-6 and IL-1β by PBMCs, which may be considered as a reserve in response to danger signals. These results suggest that SIRPα on monocytes is essential for the priming of naive T cells and the development of ITP. Therefore, SIRPα is a potential therapeutic target for ITP and other autoimmune diseases.

Prolonged cytopenia following CD19 CAR T cell therapy is linked with bone marrow infiltration of clonally expanded IFNγ-expressing CD8 T cells

Autologous anti-CD19 chimeric antigen receptor T cell (CAR T) therapy is highly effective in relapsed/refractory large B cell lymphoma (rrLBCL) but is associated with toxicities that delay recovery. While the biological mechanisms of cytokine release syndrome and neurotoxicity have been investigated, the pathophysiology is poorly understood for prolonged cytopenia, defined as grade ≥3 cytopenia lasting beyond 30 days after CAR T infusion. We performed single-cell RNA sequencing of bone marrow samples from healthy donors and rrLBCL patients with or without prolonged cytopenia and identified significantly increased frequencies of clonally expanded CX3CR1hi cytotoxic T cells, expressing high interferon (IFN)-γ and cytokine signaling gene sets, associated with prolonged cytopenia. In line with this, we found that hematopoietic stem cells from these patients expressed IFN-γ response signatures. IFN-γ deregulates hematopoietic stem cell self-renewal and differentiation and can be targeted with thrombopoietin agonists or IFN-γ-neutralizing antibodies, highlighting a potential mechanism-based approach for the treatment of CAR T-associated prolonged cytopenia.

Rituximab resistance in ITP and beyond

The pathophysiology of immune thrombocytopenia (ITP) is complex and encompasses innate and adaptive immune responses, as well as megakaryocyte dysfunction. Rituximab is administered in relapsed cases and has the added benefit of inducing treatment-free remission in over 50% of patients. Nevertheless, the responses to this therapy are not long-lasting, and resistance development is frequent. B cells, T cells, and plasma cells play a role in developing resistance. To overcome this resistance, targeting these pathways through splenectomy and novel therapies that target FcγR pathway, FcRn, complement, B cells, plasma cells, and T cells can be useful. This review will summarize the pathogenetic mechanisms implicated in rituximab resistance and examine the potential therapeutic interventions to overcome it. This review will explore the efficacy of established therapies, as well as novel therapeutic approaches and agents currently in development.

Assessment of circulating blood lymphocytes in adult patients on rituximab to treat immune thrombocytopenia: Circulating number of NK cells is associated with the response at 6 months

Immune thrombocytopenia (ITP) is defined by a low platelet count that can trigger potentially life-threatening haemorrhages. Three-quarters of adult patients exhibit persistent or chronic disease and require second-line treatments. Among these, rituximab, an anti-CD20 antibody, has yielded valuable results, with global responses in 60% of patients at 6 months and complete responses in 30% at 5 years. Factors predictive of response to ITP therapy would help physicians choose optimal treatments. We retrospectively analysed clinical courses, biological markers and blood lymphocyte subset numbers of 72 patients on rituximab to treat persistent/chronic ITP followed-up in our department between 2007 and 2021, divided into three groups according to the platelet count at 6 months: complete, partial or no response. Among all studied parameters, a low number of CD3^- CD16⁺ CD56⁺ circulating NK cells was associated with the complete response to rituximab. We also found that, after rituximab therapy, complete responders exhibited increased NK and decreased activated CD8⁺ T cell percentages. These results emphasize that the role played by NK cells in ITP remains incompletely known but that factors predictive of response to rituximab can be easily derived using blood lymphocyte subset data.

Sustained Remission Off-Treatment (SROT) of TPO-RAs: The Burgos Ten-Step Eltrombopag Tapering Scheme

Background and Objectives: TPO-RAs (romiplostim/eltrombopag/avatrombopag) have broadly demonstrated high efficacy rates (59-88%), durable responses (up to three years) and a satisfactory safety profile in clinical trials. The effect of TPO-RAs is classically considered to be transient because platelet numbers usually dropped rapidly to baseline unless therapy was maintained. However, several groups have reported the possibility of successfully discontinuing TPO-RAs in some patients without further need for concomitant treatments. This concept is usually referred as sustained remission off-treatment (SROT). Materials and Methods: Unfortunately, we still lack predictors of the response to discontinuation even after the numerous biological, clinical and in vitro studies performed to study this phenomenon. The frequency of successful discontinuation is matter of controversy, although a percentage in the range of 25-40% may probably be considered a consensus. Here, we describe all major routine clinical practice studies and reviews that report the current position on this topic and compare them with our own results in Burgos. Results: We report our Burgos ten-step eltrombopag tapering scheme with which we have achieved an elevated percentage rate of success (70.3%) in discontinuing treatment. Conclusions: We hope this protocol may help successfully taper and discontinue TPO-RAs in daily clinical practice.

Novel Biomarkers for Diagnosis and Monitoring of Immune Thrombocytopenia

Lower-than-normal platelet counts are a hallmark of the acquired autoimmune illness known as immune thrombocytopenia, which can affect both adults and children. Immune thrombocytopenia patients' care has evolved significantly in recent years, but the disease's diagnosis has not, and it is still only clinically achievable with the elimination of other causes of thrombocytopenia. The lack of a valid biomarker or gold-standard diagnostic test, despite ongoing efforts to find one, adds to the high rate of disease misdiagnosis. However, in recent years, several studies have helped to elucidate a number of features of the disease's etiology, highlighting how the platelet loss is not only caused by an increase in peripheral platelet destruction but also involves a number of humoral and cellular immune system effectors. This made it possible to identify the role of immune-activating substances such cytokines and chemokines, complement, non-coding genetic material, the microbiome, and gene mutations. Furthermore, platelet and megakaryocyte immaturity indices have been emphasized as new disease markers, and prognostic signs and responses to particular types of therapy have been suggested. Our review's goal was to compile information from the literature on novel immune thrombocytopenia biomarkers, markers that will help us improve the management of these patients.

How we treat primary immune thrombocytopenia in adults

Primary immune thrombocytopenia (ITP) is an immune-mediated bleeding disorder characterized by decreased platelet counts and an increased risk of bleeding. Multiple humoral and cellular immune abnormalities result in accelerated platelet destruction and suppressed platelet production in ITP. The diagnosis remains a clinical exclusion of other causes of thrombocytopenia. Treatment is not required except for patients with active bleeding, severe thrombocytopenia, or cases in need of invasive procedures. Corticosteroids, intravenous immunoglobulin, and anti-RhD immunoglobulin are the classical initial treatments for newly diagnosed ITP in adults, but these agents generally cannot induce a long-term response in most patients. Subsequent treatments for patients who fail the initial therapy include thrombopoietic agents, rituximab, fostamatinib, splenectomy, and several older immunosuppressive agents. Other potential therapeutic agents, such as inhibitors of Bruton's tyrosine kinase and neonatal Fc receptor, are currently under clinical evaluation. An optimized treatment strategy should aim at elevating the platelet counts to a safety level with minimal toxicity and improving patient health-related quality of life, and always needs to be tailored to the patients and disease phases. In this review, we address the concepts of adult ITP diagnosis and management and provide a comprehensive overview of current therapeutic strategies under general and specific situations.

Abnormalities of bone marrow B cells and plasma cells in primary immune thrombocytopenia

Primary immune thrombocytopenia (ITP) is an autoantibody-mediated hemorrhagic disorder in which B cells play an essential role. Previous studies have focused on peripheral blood (PB), but B cells in bone marrow (BM) have not been well characterized. We aimed to explore the profile of B-cell subsets and their cytokine environments in the BM of patients with ITP to further clarify the pathogenesis of the disease. B-cell subpopulations and their cytokine/chemokine receptors were detected by using flow cytometry. Plasma concentrations of cytokines/chemokines were measured by using enzyme-linked immunosorbent assay. Messenger RNA levels of B cell-related transcription factors were determined by using quantitative polymerase chain reaction. Regulatory B cell (Breg) function was assessed by quantifying their inhibitory effects on monocytes and T cells in vitro. Decreased proportions of total B cells, naive B cells, and defective Bregs were observed in patients with ITP compared with healthy controls (HCs), whereas an elevated frequency of long-lived plasma cells was found in BM of autoantibody-positive patients. No statistical difference was observed in plasmablasts or in short-lived plasma cells between patients with ITP and HCs. The immunosuppressive capacity of BM Bregs from patients with ITP was considerably weaker than HCs. An in vivo study using an active ITP murine model revealed that Breg transfusion could significantly alleviate thrombocytopenia. Moreover, overactivation of CXCL13-CXCR5 and BAFF/APRIL systems were found in ITP patient BM. Taken together, B-cell subsets in BM were skewed toward a proinflammatory profile in patients with ITP, suggesting the involvement of dysregulated BM B cells in the development of the disease.

T cell-mediated autoimmunity in immune thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by a low platelet count and an increased risk of bleeding. In addition to anti-platelet autoantibodies, CD8⁺ T cells have been implicated as a mechanism of platelet destruction. The current evidence for the existence of platelet-specific CD8⁺ T cells in ITP is inconclusive. The purpose of this review is to summarize the studies that investigated CD8⁺ T cells in ITP and to review the methods that have been used to detect autoreactive CD8⁺ T cells in other autoimmune diseases.

Diversity, localization, and (patho)physiology of mature lymphocyte populations in the bone marrow

The bone marrow (BM) is responsible for generating and maintaining lifelong output of blood and immune cells. In addition to its key hematopoietic function, the BM acts as an important lymphoid organ, hosting a large variety of mature lymphocyte populations, including B cells, T cells, natural killer T cells, and innate lymphoid cells. Many of these cell types are thought to visit the BM only transiently, but for others, like plasma cells and memory T cells, the BM provides supportive niches that promote their long-term survival. Interestingly, accumulating evidence points toward an important role for mature lymphocytes in the regulation of hematopoietic stem cells (HSCs) and hematopoiesis in health and disease. In this review, we describe the diversity, migration, localization, and function of mature lymphocyte populations in murine and human BM, focusing on their role in immunity and hematopoiesis. We also address how various BM lymphocyte subsets contribute to the development of aplastic anemia and immune thrombocytopenia, illustrating the complexity of these BM disorders and the underlying similarities and differences in their disease pathophysiology. Finally, we summarize the interactions between mature lymphocytes and BM resident cells in HSC transplantation and graft-versus-host disease. A better understanding of the mechanisms by which mature lymphocyte populations regulate BM function will likely improve future therapies for patients with benign and malignant hematologic disorders.

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.

Platelet autoantibodies in the bone marrow of patients with immune thrombocytopenia

Autoantibodies cause platelet destruction in patients with immune thrombocytopenia (ITP); yet only 50% to 60% of patients have detectable platelet autoantibodies in peripheral blood. We hypothesized that in some ITP patients, platelet autoantibodies are sequestered in the bone marrow where pathological immune reactions target megakaryocytes or newly formed platelets. In this study, we modified the platelet glycoprotein-specific assay to test bone marrow aspiration samples for free platelet autoantibodies or antibodies bound to bone marrow cells in aspirate fluid from patients with ITP (n = 18), patients with nonimmune thrombocytopenia (n = 3), and healthy donors (n = 6). We found that 10 (56%) of 18 patients with ITP had autoantibodies in the bone marrow, including 5 (50%) of 10 with autoantibodies in bone marrow only, and 5 (50%) of 10 with autoantibodies in bone marrow and peripheral blood. In comparison, 6 (33%) of 18 ITP patients had autoantibodies in peripheral blood, most of whom (5 [83%] of 6) also had autoantibodies in bone marrow. Bone marrow autoantibodies were not detected in patients with nonimmune thrombocytopenia or healthy donors; however, peripheral blood autoantibodies were detectable in 1 (33%) of 3 patients with nonimmune thrombocytopenia. The sensitivity of platelet autoantibodies for the diagnosis of ITP increased from 60% (peripheral blood testing) to 72% (peripheral blood and bone marrow testing). Immune reactions limited to the bone marrow may be characteristic of certain subsets of ITP patients.

Association of FOXP3 gene polymorphisms with chronic immune thrombocytopenia in a Chinese Han population

INTRODUCTION

Forkhead box P3 (Foxp3) is encoded by the human FOXP3, an X-chromosome gene, and is a transcription factor that regulates regulatory T-cell (Treg) development and function. FOXP3 gene polymorphisms have recently been investigated as candidate risk factors in various autoimmune diseases. This study aimed to investigate the possible influence of FOXP3 gene polymorphisms on genetic predisposition to chronic immune thrombocytopenia (ITP).

METHODS

The study cohort comprised 329 chronic ITP patients and 279 healthy controls, who were genotyped for three polymorphisms in the promoter region of FOXP3 gene, -6054 del/ATT, -3279 A/C, and -924 A/G.

RESULTS

Of the three polymorphisms identified, the -3279 AA genotype was more frequent in female patients with chronic ITP than in female controls (P = .035, OR 0.434, 95% CI 0.223-0.846), and the -3279 A carrier was shown to be associated with the risk of chronic ITP in female cohort (P = .003, OR 0.610, 95% CI 0.437-0.851). Furthermore, the female patients with chronic ITP had remarkably more frequent haplotype -6054 del/-3279 A/-924 A (P = .027, OR 3.584, 95% CI 1.148-11.186) and less haplotype -6054 del/-3279 C/-924 G (P = .039, OR 0.445, 95% CI 0.204-0.973) in comparison with female healthy controls. Although there were no significant differences in the male cohort, when the combined alleles and haplotypes of the two genders were analyzed, the results obtained were similar to those of females.

CONCLUSION

According to our data, the -3279 A/C polymorphism of FOXP3 gene may be associated with the susceptibility to chronic ITP in Chinese Han population.

Imbalance of T Lymphocyte Subsets in Adult Immune Thrombocytopenia

BACKGROUND

Primary immune thrombocytopenia (ITP) is defined as an acquired autoimmune disease characterized by isolated thrombocytopenia. This work is to further clarify the relationship between T cell immune dysfunction and the pathogenesis of ITP.

METHODS

37 adult patients with ITP were selected and were classified into newly diagnosed ITP (nITP, n = 13), persistent ITP (pITP, n = 6) and chronic ITP (cITP n = 18). The frequency of cytotoxic T lymphocytes (Tc1, Tc2, and Tc17) and helper T cells (Th1, Th2, and Th17), Tregs, and the expression of chemokine receptors and PD-1 on CD4+ T cells were investigated by flow cytometry. Plasma levels of T cell-related cytokines (IL-2, IL-4, IL-6, IL-10, TNF-α, IFN-γ, IL-17) were measured by cytometric beads array (CBA).

RESULTS

The percentage of Tc1 in cITP was greatly higher than nITP and healthy controls (p < 0.05, p < 0.01). The percentage of Treg in nITP and cITP groups was remarkably lower than those in healthy control group (p < 0.05, p < 0.001); and according to platelet count analysis (PLT<50x109/L or PLT>50x109/L), Treg cells in ITP group were significantly lower than those in healthy control group (p < 0.001, p < 0.05). The percentage of CD4+CXCR3+ of cITP was significantly higher than healthy controls and nITP (p < 0.01, p < 0.05). The percentage of CD4+CCR6+ in cITP was significantly higher than healthy controls and nITP (p < 0.001, p < 0.05). The expression of PD-1 in cITP patients was higher than healthy control (p < 0.05), but there was no significant difference among nITP, pITP and cITP (p = 0.25). The levels of IL-2, IFN-γ and TNFα in nITP group and cITP group were significantly higher than those in healthy control group (p < 0.01, p < 0.05; p < 0.01, p < 0.05; p < 0.05, p < 0.05), and the level of IL-10 in nITP group was significantly higher than that in pITP group (p < 0.05).

CONCLUSION

Our results suggest that T lymphocyte immune dysfunction does exist in adult ITP patients and plays an important role in the pathogenesis of ITP.

Platelet desialylation and TFH cells-the novel pathway of immune thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune disease characterized by immune-mediated destruction of one's own platelets. The progression of thrombocytopenia involves an imbalance of platelet production and clearance. B cells can induce autoantibodies, and T cells contribute to the pathological progression as well. Some patients with ITP have a poor response to common first-line therapies. Recent studies have shown that a novel Fc-independent platelet clearance pathway is associated with poor prognosis in these patients. By this pathway, desialylated platelets can be cleared by Ashwell-Morell receptor (AMR) on hepatocytes. Research has demonstrated that patients with refractory ITP usually have a high level of desialylation, indicating the important role of sialylation on platelet membrane glycoprotein (GP) in patients with primary immune thrombocytopenia, and neuraminidase 1(NEU1) translocation might be involved in this process. Patients with ITP who are positive for anti-GPIbα antibodies have a poor prognosis, which indicates that anti-GPIbα antibodies are associated with this Fc-independent platelet clearance pathway. Experiments have proven that these antibodies could lead to the desialylation of GPs on platelets. The T follicular helper (TFH) cell level is related to the expression of the anti-GPIbα antibody, which indicates its role in the progression of desialylation. This review will discuss platelet clearance and production, especially the role of the anti-GPIbα antibody and desialylation in the pathophysiology of ITP and therapy for this disease.

Crosstalk Between Platelets and Microbial Pathogens

Platelets, small anucleate cells circulating in the blood, are critical mediators in haemostasis and thrombosis. Interestingly, recent studies demonstrated that platelets contain both pro-inflammatory and anti-inflammatory molecules, equipping platelets with immunoregulatory function in both innate and adaptive immunity. In the context of infectious diseases, platelets are involved in early detection of invading microorganisms and are actively recruited to sites of infection. Platelets exert their effects on microbial pathogens either by direct binding to eliminate or restrict dissemination, or by shaping the subsequent host immune response. Reciprocally, many invading microbial pathogens can directly or indirectly target host platelets, altering platelet count or/and function. In addition, microbial pathogens can impact the host auto- and alloimmune responses to platelet antigens in several immune-mediated diseases, such as immune thrombocytopenia, and fetal and neonatal alloimmune thrombocytopenia. In this review, we discuss the mechanisms that contribute to the bidirectional interactions between platelets and various microbial pathogens, and how these interactions hold relevant implications in the pathogenesis of many infectious diseases. The knowledge obtained from "well-studied" microbes may also help us understand the pathogenesis of emerging microbes, such as SARS-CoV-2 coronavirus.

[Immune thrombocytopenia: From pathogenesis to treatment]

Immune thrombocytopenia (ITP) is a rare autoimmune disease due to an immune peripheral destruction of platelets and an inappropriate platelet production. The pathogenesis of ITP is now better understood: it involves a humoral immune response which dependents on the stimulation of B cells by specific T cells called T follicular helper cells, leading to their differentiation into plasma cells that produce antiplatelet antibodies thus promoting the phagocytosis of platelets mainly by splenic macrophages. The deciphering of ITP pathogenesis has led to a better understanding of the inefficiency of treatments such as rituximab, although it has not provided yet the determination of biological predictive factor of response to treatments. Moreover, new therapeutic perspectives have been opened in the last few years with the development of molecules targeting Fcγ receptor signalling such as Syk inhibitor, or molecules increasing the clearance of pathogenic autoantibodies such as inhibitors of the neonatal Fc receptor (FcRn).

[Adult immune thrombocytopenia and thrombopoietin receptor agonist: Ten years later]

Ten years after their licence in France, the use of the two thrombopoietin receptor agonists (TPO-RA), eltrombopag and romiplostim, has deeply modified the landscape of immune thrombocytopenia (ITP) treatment. In this review, we summarise data on efficacy and safety of these treatments during ITP, as well as their use in clinical practice. Their place in therapeutic strategy, the recent description of persistant remission after discontinuation of TPO-RA, and future new thrombopoietic agents are also discussed. Their use has progressively increased and early use at a newly diagnosed stage of the disease is under evaluation. However physician have to keep in mind that thromboembolism rates appear to be higher with TPO-RA treatment in ITP patients at high risk of thrombosis, and that data from "real-life" studies with very long term follow up are not available. Finally, the cost of these treatments should also be evaluated in future therapeutic strategies comparisons.

Rituximab and immune thrombocytopenia in adults: The state of knowledge 20 years later

Rituximab has been used for immune thrombocytopenia (ITP) for almost 20 years and is now considered a valid off-label second-line treatment. About 60% to 70% of patients with ITP show initial response to rituximab, but in half of these patients, the disease will eventually relapse. Therefore, in 30% of patients with persistent or chronic ITP, one course of rituximab at 375 mg/m²/week for 4 weeks or 2 fixed 1000-mg rituximab infusions allows for a sustained response rate at 5 years. Unfortunately, to date, no robust predictor of long-term sustained response has been found to assist the physician in deciding to treat with rituximab on an individual basis, and the choice of rituximab or another second-line treatment must be individualized and shared with the patient. Retreatment with rituximab has been found efficient, with a similar or higher magnitude and duration of response in most patients. Rituximab is usually well tolerated, with mainly mild and easily manageable infusion-related adverse events. Severe infections are uncommon, including in the long-term, and occur in patients with at least another contributing factor in more than two thirds. Several issues remain to be resolved. Indeed, head-to-head comparisons with other and new treatments in ITP and robust predictors of long-term response are urgently needed to better determine the position of rituximab in the therapeutic armamentarium for adult ITP. Additionally, the place of combination therapies, maintenance therapy with rituximab and rituximab in newly-diagnosed ITP deserve additional studies.

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.

Novel scientific approaches and future research directions in understanding ITP

Diagnosis of immune thrombocytopenia (ITP) and prediction of response to therapy remain significant and constant challenges in hematology. In patients who present with ITP, the platelet count is frequently used as a surrogate marker for disease severity, and so often determines the need for therapy. Although there is a clear link between thrombocytopenia and hemostasis, a direct correlation between the extent of thrombocytopenia and bleeding symptoms, especially at lower platelet counts is lacking. Thus, bleeding in ITP is heterogeneous, unpredictable, and nearly always based on a multitude of risk factors, beyond the platelet count. The development of an evidence-based, validated risk stratification model for ITP treatment is a major goal in the ITP community and this review discusses new laboratory approaches to evaluate the various pathobiologies of ITP that may inform such a model.

Disrupted balance of CD4+ T-cell subsets in bone marrow of patients with primary immune thrombocytopenia

Disequilibrium of CD4⁺ T-cell subpopulations in peripheral blood (PB) of patients with primary immune thrombocytopenia (ITP) has been well established, whereas the profile of CD4⁺ T-cell subpopulations in bone marrow (BM) remains elusive. In the present study, the frequencies of T helper 22 (Th22), Th17, Th1, Th2, follicular T helper (Tfh) cells and regulatory T cells (Tregs) as well as their effector cytokines in BM and PB from active ITP patients and healthy controls (HCs) were determined. Results showed that the frequencies of Th22, Th17, Th1, and Tfh cells were significantly higher, but Treg number was remarkably lower in BM from ITP patients than from HCs. In the ITP group, it was notable that the numbers of BM Th22, Th17, Th1, Th2, and Tfh cells were significantly elevated compared with the matched PB counterparts, while Treg number in BM was considerably reduced compared with that in PB. In consistence with the BM Th subset pattern, plasma levels of interleukin (IL)-22, IL-17A, and interferon (INF)-γ in BM from ITP patients were significantly increased compared with that from HCs. Therefore, the balance of CD4⁺ T-cell subsets was disrupted in both BM and PB of ITP patients, suggesting that this might play important roles in the pathophysiological process of ITP.

Management of immune thrombocytopenia in elderly patients

Despite the improvement in understanding its pathogenesis and the introduction of novel treatment options, the management of primary immune thrombocytopenia (ITP) still remains challenging. Considering its increased incidence with aging and prolonged life-expectancy, ITP is often diagnosed in elderly patients, a subset that deserves some special precautions. Ensure the diagnosis is a crucial step, and carefully attention must be given in excluding other causes of thrombocytopenia, especially among older people that frequently suffer from many comorbidities. When it comes to treatment decision, it is worth keeping into account that the elderly have an increased risk of bleeding, thrombosis and infections, that they often require many concomitant therapies, including antiplatelet or anticoagulant agents, and that treatment-related toxicities are often increased and sometimes more dangerous that the disease itself. There are not dedicated guidelines, and only few specific studies. Steroids with or without IVIG remain the first-line treatment. Splenectomy is less effective than in youngers and burdened by an increased thrombotic and infectious risk. Rituximab is a good option in non-immunocompromised patients, but long-term remissions are few. Eltrombopag and romiplostim have a good safety and efficacy profile, and have become a prominent drug in this subset, even if they are associated with a possible increased risk of thrombosis, and long-term toxicity is unknown. Other drugs, such as dapsone and danazol, have a well-known efficacy and safety profile, and still represent a valid option among elderly patients.

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.

Immune dysregulation in primary immune thrombocytopenia patients

OBJECTIVES

To explore the immunological abnormalities in patients with primary immune thrombocytopenia (ITP), and analyze its relationship with treatment.

METHODS

Proportion of different immune cell subsets were detected in the peripheral blood of 124 ITP patients at different time points and 45 normal controls by flow cytometry. The treatments included glucocorticoids, intravenous IgG as first-line treatment and second-line drugs.

RESULTS

Elevated CD4/CD8 ratio and decreased the proportion of NK and CD4 + CD25 + CD127low regulatory T cells (Tregs) were found in pre-treated ITP patients than healthy controls. The newly diagnosed group had a significantly higher CD4/CD8 ratio than the relapsed group, but no differences in the proportion of B cells, NK cells and Tregs. No relationships were found between the curative effect and the pre-treated cell subsets within both the effective and ineffective groups. Furthermore, compared with the ineffective group, the effective group had higher Tregs and lower CD4/CD8 ratio post-treatment, but no significant differences in NK and B cells.

CONCLUSION

ITP patients presented with a high CD4/CD8 ratio and low levels of Tregs and NK cells, suggesting that immune deregulation was involved in the pathogenesis of ITP. The pre-treated immune status of ITP patients may not be related to the curative effect. Tregs significantly increased in the effective group post-treatment, highlighting that the mechanism of restoring Tregs may be involved in the treatment of ITP. However, whether or not the targeted regulation of Tregs is an effective treatment for ITP still requires further studies.

Tissue-specific Role of CX3CR1 Expressing Immune Cells and Their Relationships with Human Disease

Chemokine (C-X3-C motif) ligand 1 (CX₃CL1, also known as fractalkine) and its receptor chemokine (C-X3-C motif) receptor 1 (CX₃CR1) are widely expressed in immune cells and non-immune cells throughout organisms. However, their expression is mostly cell type-specific in each tissue. CX₃CR1 expression can be found in monocytes, macrophages, dendritic cells, T cells, and natural killer (NK) cells. Interaction between CX₃CL1 and CX₃CR1 can mediate chemotaxis of immune cells according to concentration gradient of ligands. CX₃CR1 expressing immune cells have a main role in either pro-inflammatory or anti-inflammatory response depending on environmental condition. In a given tissue such as bone marrow, brain, lung, liver, gut, and cancer, CX₃CR1 expressing cells can maintain tissue homeostasis. Under pathologic conditions, however, CX₃CR1 expressing cells can play a critical role in disease pathogenesis. Here, we discuss recent progresses of CX₃CL1/CX₃CR1 in major tissues and their relationships with human diseases.

Differential expression of T-cell genes in blood and bone marrow between ITP patients and controls

Primary immune thrombocytopenia (ITP) is an autoimmune disease characterised by premature platelet destruction in spleen, liver and bone marrow and a diminished production of platelets. T-cells are important in all forms of autoimmunity including ITP; however, very little is known about T-cells in organs where platelets are destroyed. Our aim was to investigate differences in gene expression in peripheral blood-derived T-cells and bone marrow-derived T-cells between ITP patients and controls. T-cells and subsequent RNA were isolated from blood and bone marrow from chronic ITP patients and healthy controls followed by DNA microarray analysis. There were 1554 differentially expressed genes in peripheral blood-derived T-cells and 976 in bone marrow-derived T-cells between ITP patients and controls and three genes were verified with real-time PCR. Using Gene Ontology functional enrichment analysis we found that genes involved in growth, development, migration, chemotaxis, adhesion and apoptosis were enriched in bone marrow-derived T-cells in ITP. Immune-related genes involved in T-helper cell differentiation, T-cell chemotaxis, migration, immunoglobulin-mediated immune response and classical and alternative pathway complement activation were also enriched in bone marrow-derived T-cells in ITP. Only 213 T-cell genes were differentially expressed in both blood and bone marrow between ITP patients and controls. In conclusion, our findings show that genes involved in major pathophysiologic pathways in ITP such as T-helper cell differentiation, autoantibody response and complement activation are altered in bone marrow-derived T-cells in ITP patients compared with controls. This further supports the concept that bone marrow is an important compartment in ITP.

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.

Clinical updates in adult immune thrombocytopenia

Immune thrombocytopenia (ITP) occurs in 2 to 4/100 000 adults and results in variable bleeding symptoms and thrombocytopenia. In the last decade, changes in our understanding of the pathophysiology of the disorder have led to the publication of new guidelines for the diagnosis and management of ITP and standards for terminology. Current evidence supports alternatives to splenectomy for second-line management of patients with persistently low platelet counts and bleeding. Long-term follow-up data suggest both efficacy and safety, in particular, for the thrombopoietin receptor agonists and the occurrence of late remissions. Follow-up of patients who have undergone splenectomy for ITP reveals significant potential risks that should be discussed with patients and may influence clinician and patient choice of second-line therapy. Novel therapeutics are in development to address ongoing treatment gaps.

Hepatitis B infection is associated with an increased incidence of thrombocytopenia in healthy adults without cirrhosis

The association between HBV infection and incident thrombocytopenia among subjects without cirrhosis or splenomegaly is unknown. Therefore, we sought to elucidate the association between HBV infection and the development of thrombocytopenia in a large cohort of apparently healthy men and women. A cohort study was performed in 122 200 participants without liver cirrhosis or splenomegaly who underwent comprehensive health examinations and were followed until December 2014. HBV infection was defined by the presence of hepatitis B surface antigen (HBsAg) at baseline. Thrombocytopenia was defined as a platelet count <150 000/μL. Cox proportional hazard models were used to estimate adjusted hazard ratios with 95% confidence intervals (CIs) for incident thrombocytopenia. HBsAg was positive in 4857 of 122 200 subjects (4.0%) at baseline. During 883 983 person-years of follow-up, 2037 incident cases of thrombocytopenia were identified (incident rate 2.3 per 1000 person-years). HBsAg-positive subjects had a higher incidence of thrombocytopenia than did healthy controls (11.2 vs 1.9 per 1000 person-years, respectively). The multivariate-adjusted hazard ratio (95% CI) for incident thrombocytopenia comparing HBsAg-positive to HBsAg-negative subjects was 5.71 (5.10-6.38). Strong associations between HBsAg positivity and thrombocytopenia were consistently observed across prespecified subgroups. In this large cohort study of an apparently healthy population, HBsAg positivity was strongly and independently associated with incident thrombocytopenia, indicating that mechanisms of thrombocytopenia other than portal hypertension may exist in healthy HBV carriers.

Pathogenesis and Therapeutic Mechanisms in Immune Thrombocytopenia (ITP)

Immune thrombocytopenia (ITP) is a complex autoimmune disease characterized by low platelet counts. The pathogenesis of ITP remains unclear although both antibody-mediated and/or T cell-mediated platelet destruction are key processes. In addition, impairment of T cells, cytokine imbalances, and the contribution of the bone marrow niche have now been recognized to be important. Treatment strategies are aimed at the restoration of platelet counts compatible with adequate hemostasis rather than achieving physiological platelet counts. The first line treatments focus on the inhibition of autoantibody production and platelet degradation, whereas second-line treatments include immunosuppressive drugs, such as Rituximab, and splenectomy. Finally, third-line treatments aim to stimulate platelet production by megakaryocytes. This review discusses the pathophysiology of ITP and how the different treatment modalities affect the pathogenic mechanisms.

Low dose IL-2 increase regulatory T cells and elevate platelets in a patient with immune thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune disorder in which its immune system destroys platelets and leads to haemorrhage symptom. Recent studies have found that regulatory T cells (Tregs) in peripheral blood, bone marrow, and spleen were reduced in ITP patients and recovered after effective ITP therapy. Low-dose Interleukin-2 (IL-2) has been reported recently to increase Tregs and used to treat autoimmune disease including graft-versus-host disease (GVHD) after organ transplantation and HCV-related autoimmune vasculitis. However, it is unknown whether IL-2 is able to treat ITP. We have used low-dose IL-2 (1.0 million IU/day) on 5 consecutive days per week for 4 weeks in a 36-year-old patient with ITP. The result has shown that low-dose IL-2 induces expansion of Tregs significantly and increase platelet count was gradually from 36 × 10⁹ /L to maximum 85 × 10⁹ /L. No side effects of IL-2 have been found. This result suggested that low-dose of IL-2 may have therapeutic potential for ITP. © 2016 International Clinical Cytometry Society.

Decreased immunosuppressive actions of 1α, 25-dihydroxyvitamin D3 in patients with immune thrombocytopenia

Primary immune thrombocytopenia (ITP) is an acquired autoimmune disease. 1α, 25-dihydroxyvitamin D₃ [1,25(OH)₂D₃] and vitamin D receptor (VDR) play important immune-suppressive roles in immune system. It has been reported that serum 1,25(OH)₂D₃ were lower in ITP patients. In this study, we evaluated local 1,25(OH)₂D₃ level and VDR mRNA expression further, and determined whether 1,25(OH)₂D₃/VDR were correlated with T cell dysfunction in ITP patients. We found that 1,25(OH)₂D₃/VDR levels were decreased in active ITP patients, and 1,25(OH)₂D₃ had significant anti-inflammatory effects on ITP patients, including both anti-proliferation of peripheral blood mononuclear cells (PBMCs) and reversing the abnormal T cells polarization. 1,25(OH)₂D₃ inhibited the differentiation of T helper (Th)1 and Tc1 cells but induced the differentiation of Th2, Tc2 and T regulatory (Treg) cells in ITP patients. However, the percentage of Th17 cells were not affected obviously with 1,25(OH)₂D₃. In addition, 1,25(OH)₂D₃ also suppressed pro-inflammatory cytokines (INF-γ and IL-17A) but promoted anti-inflammatory cytokine (IL-10) secretion in ITP patients. In conclusion, decreased 1,25(OH)₂D₃/VDR might participate in the pathogenesis of ITP, and appropriate supplement of 1,25(OH)₂D₃ may be a promising treatment.

Reduced potency of cytotoxic T lymphocytes from patients with high-risk myelodysplastic syndromes

INTRODUCTION

Myelodysplastic syndromes (MDS) are a group of clonal bone marrow disorders, with dysplasia, cytopenias and increased risk of progression to acute myeloid leukemia. A dysregulated immune system precipitates MDS, and to gain insights into the relevance of cytotoxic T lymphocyte (CTL) in this process, we examined the frequency and function of CX3CR1- and CD57-positive T lymphocytes from MDS patients.

MATERIALS AND METHODS

Peripheral blood and/or bone marrow samples from 31 MDS patients and 12 healthy controls were examined by flow cytometry. Expression of cytotoxic granule constituents, immunological co-receptors, adhesion molecules and markers of activation were quantified on unstimulated lymphocytes. Degranulation, cytotoxicity and conjugate formation with target cells following co-culture of CTL with target cell lines or autologous bone marrow-derived CD34(+) cells were quantified by flow cytometry.

RESULTS

CX3CR1 expression was increased in bone marrow from high-risk MDS patients compared to healthy controls. Expression of CD57 and CX3CR1 was closely correlated, identifying a CTL subset with high cytotoxic capacity. In vitro, TCR-induced redirected cytotoxicity was markedly decreased for high-risk MDS patients compared to controls. CTL from MDS patients with the lowest target cell cytotoxicity had reduced expression of adhesion molecules and formed fewer conjugates with target cells.

DISCUSSION

Although phenotypically defined CTL numbers were increased in the bone marrow of MDS patients, we found that CTL from high-risk MDS patients exhibited a lower TCR-induced redirected cytotoxic capacity. Thus, decreased T cell cytotoxicity seems related to reduced adhesion to target cells and may contribute to impaired anti-leukemic immune surveillance in MDS.

Abnormalities of the bone marrow immune microenvironment in patients with immune thrombocytopenia

Immune thrombocytopenia (ITP) is an acquired autoimmune disease. Although antiplatelet antibodies are considered as the primary immunologic defect in these patients, dysfunctional cellular immunity is also important in the pathophysiology of ITP. Peripheral T cell abnormalities have been demonstrated in patients with ITP; however, whether the impaired bone marrow (BM) microenvironment, specifically the BM immune microenvironment, is involved in the pathogenesis of ITP remains unknown. In this study, the compartments of the BM immune microenvironment and BM vascular microenvironment were analyzed in 26 untreated patients with ITP and 26 healthy donors (HD). Subsets of T cells in the BM immune microenvironment, including Th1, Th2, Tc1, Tc2, Th17, and Treg cells, were analyzed via flow cytometry. BM endothelial cells and perivascular cells, which are key elements of the vascular microenvironment, were analyzed via flow cytometry as well as hematoxylin-eosin (H&E) and immunohistochemical (IHC) staining in situ. Elements of the BM vascular microenvironment were found to be normal in patients with ITP, but abnormal characteristics of the BM immune microenvironment, including excessive polarization in Th1, Tc1, and Th17 cells and a remarkable decrease in Treg cells, were observed in patients with ITP. Therefore, a deregulated T cell response in the BM microenvironment might play an important role in the pathogenesis of ITP.

Is There a Relationship Between CXCR4 Gene Expression and Prognosis of Immune Thrombocytopenia in Children?

Immune thrombocytopenia (ITP) is a common autoimmune disorder characterized by decreased platelet count (thrombocytopenia) and bleeding symptoms due to production of autoantibodies against platelets. Chemokines are molecules inducing chemotaxis and play an important role in megakaryopoiesis, including CXCR4 chemokine receptor. CXCR4 is expressed on cells of megakaryocytic series, especially platelets, and triggers several mechanisms in these cells. The purpose of this study was to evaluate the pattern of CXCR4 gene changes upon diagnosis and after treatment and its comparison with laboratory findings in peripheral blood samples from newly diagnosed ITP patients. 35 newly diagnosed patients with ITP and 35 healthy controls were enrolled in this study. CXCR4 gene expression was investigated before and after treatment using real-time PCR. HPRT gene was used as the reference gene to calculate the expression rate of CXCR4 as CXCR4/HPRT ratio. CXCR4 gene expression upon diagnosis and after treatment in peripheral blood plasma of ITP patients showed a significant decrease in comparison with the control group while its expression did not change before and after treatment. No significant correlation was found between the expression of this gene and laboratory parameters. Due to unpredictable course of ITP in patients and the possibility of its progress to refractory form, accurate choice of a biomarker is essential for evaluating prognosis and detection of resistant forms.

The Centenary of Immune Thrombocytopenia - Part 1: Revising Nomenclature and Pathogenesis

The natural history of the immune thrombocytopenia (ITP) is interesting and intriguing because it traces different steps underlying autoimmune diseases. The review points out the main steps that have accompanied the stages of its history and the consequential changes related to its terminology. ITP is an autoimmune disease resulting from platelet antibody-mediated destruction and impaired megakaryocyte and platelet production. However, research advances highlight that a complex dysregulation of the immune system is involved in the pathogenesis of this condition. The review examines the role of the multiple immune components involved in the autoimmunity process, focusing on the more recent mechanisms, which could be new promising therapeutic targets for ITP patients.

Recruitment of CD8(+) T cells into bone marrow might explain the suppression of megakaryocyte apoptosis through high expression of CX3CR1(+) in prolonged isolated thrombocytopenia after allogeneic hematopoietic stem cell transplantation

Prolonged isolated thrombocytopenia is a common complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT), which is associated with a poor prognosis. This study aimed to investigate the pathogenesis of prolonged isolated thrombocytopenia (PT). We analysed the expression of CX3CR1 on CD4 and CD8 T cells in bone marrow (BM) and peripheral blood (PB) at +90 days from allo-HSCT recipients with or without PT by flow cytometry analyses. We then determined the megakaryocytes ploidy distributions, apoptosis rate and Fas expression of recipients with or without PT in vitro directly or after depleting CD8(+) T cells or adding purified autologous CD8(+) T cells to CD8(+) T-dep MNCs. We found that the percentage of CD8(+) T cells in BM was higher in the patients with PT than in the controls. The elevated expression of the CX3CR1 was associated with PT. There was a marked increase in the percentage of low ploidy megakaryocytes in the recipients with PT. The depletion of CD8(+) T cells increased the apoptosis of megakaryocytes and decreased the expression of Fas, which could be corrected by re-adding purified autologous CD8(+) T cells. The increase of CD8(+) T cells and CD8(+)/CX3CR1(+) T cells in BM at +90 days were independent risk factors for PT according to multivariate analysis. Our data implied that the recruitment of CD8(+) T cells into BM might explain the suppression of megakaryocyte apoptosis through the elevated expression of CX3CR1(+) in PT after allo-HSCT. CX3CR1 might be a novel treatment target in recipients with PT.

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.

Altered cytokine levels in pediatric ITP

Immune thrombocytopenia (ITP) is an autoimmune disease where platelets are destroyed prematurely. In the majority of children, the disease resolves, but in some, it becomes chronic. Cytokines are important mediators of the immune response and are known to be dysregulated in autoimmune diseases. Therefore, our aim was to investigate differences in plasma levels of cytokines between children with ITP and healthy controls. We had two cohorts of children: one Swedish with 18 children with ITP and seven healthy children and a second Chinese one with 58 children with ITP and 30 healthy children. Plasma levels of chemokine (C-X3-C motif) ligand 1 (CX3CL1), transforming growth factor β1 (TGF-β1), and interleukin 22 (IL-22) were analyzed in both cohorts using enzyme-linked immunosorbent assays (ELISAs). We found lower plasma levels of TGF-β1 and elevated levels of CX3CL1 and IL-22 in children with ITP compared with controls in both the Swedish and the Chinese cohort. In conclusion, all three cytokines differ between pediatric ITP and healthy controls and may, therefore, be potential biomarkers for the disease.