Multirefractory primary immune thrombocytopenia; targeting the decreased sialic acid content

Course of immune thrombocytopenia according to the site of platelet destruction identified by indium-111 platelet scintigraphy

In primary immune thrombocytopenia (ITP), predictors of disease evolution and treatment response are needed. Data based on the site of platelet destruction are scarce. We performed a retrospective single-centre study of adult patients with primary ITP undergoing at least one Indium-111 platelet scintigraphy (IPS) between 2009 and 2018. Thirty-three patients had isolated hepatic platelet destruction (H-group), and 97 isolated splenic destruction (S-group). Median age at diagnosis (p < 0.001), proportion of associated cardiovascular (p < 0.001), organ-specific autoimmune diseases (p = 0.02), dependence on steroids (p = 0.003) and failure to rituximab (p = 0.01) were higher and relapse more frequent (p = 0.03) in H-group compared to non-splenectomized patients in S-group. Splenectomy was only performed in patients from S-group (as patients with hepatic sequestration are not splenectomized in our centre): 79% were in relapse-free remission at the end of a median 3.4-year post-IPS follow-up, 16% relapsed. In multivariate analyses, only a history of organ-specific autoimmune or inflammatory disease was significantly associated with hepatic sequestration (OR = 4.3, 95% CI = 1.2-15, p = 0.02). Patients with isolated hepatic sequestration were older, had more cardiovascular events and organ-specific autoimmune diseases, greater dependence on steroids, more relapses and a decreased response rate to rituximab suggesting an increased refractoriness to immunomodulatory therapies. Patients with isolated splenic sequestration responded well to splenectomy.

Desialylation by neuraminidases in platelets, kiss of death or bittersweet?

PURPOSE OF REVIEW

Loss of surface sialic acid by neuraminidases is known as 'desialylation'. Platelets are desialylated in bacterial or viral infections, during storage, senescence, various mutations, platelet auto antibodies, hemostasis and shear stress. In this review the recent literature on the different sialic acid capped glycan structures will be covered as well as platelet desialylation in inherited glycan disorders and induced by external neuraminidases.

RECENT FINDINGS

Neuraminidases are released from platelet intracellular stores and translocated to the platelet surface. Apart from clearance, loss of surface sialic acid by neuraminidases ('desialylation') affects platelet signaling including ligand binding and their procoagulant function. Platelets are also desialylated in infections, various mutations, presence of platelet auto antibodies.

SUMMARY

Since platelet desialylation occurs in various healthy and pathological conditions, measuring desialylation might be a new diagnostic tool.

Corticosteroids plus metformin versus corticosteroids as front-line treatment for patients with newly diagnosed ITP and pre-existing type 2 diabetes mellitus: A multicentre propensity score-matched study

Corticosteroids are the standard first-line treatment for primary immune thrombocytopenia (ITP), with a high initial response but unsatisfactory sustained response (SR). Additionally, corticosteroids usually lead to hyperglycaemia especially in patients with pre-existing type 2 diabetes mellitus (T2DM). Besides reducing the blood glucose levels, metformin was found to have immunomodulatory effects. We hereby conducted a multicentre propensity score matching analysis of corticosteroids plus metformin versus corticosteroids for newly diagnosed ITP patients with pre-existing T2DM. After matching at a ratio of 1:1, there were 57 patients in each group. Baseline characteristics, comorbidities and other medications including concurrent hypoglycaemic medications were balanced between the two groups. No statistical difference was observed in the initial response rate at day 14. It was notable that patients in the metformin group had a significantly higher SR rate and longer duration of response compared to the non-metformin group. Metformin inclusion was associated with a higher incidence of stomach upset, which were generally tolerable. Our study provided evidence that the addition of metformin to corticosteroids might be a promising front-line treatment for newly diagnosed ITP patients with pre-existing T2DM.

Desialylation and Apoptosis in Immune Thrombocytopenia: Implications for Pathogenesis and Treatment

Immune thrombocytopenia (ITP) is an autoimmune disease in which platelet autoantibodies play a significant role in its pathogenesis. Regulatory T cell dysfunction and T cell-mediated cytotoxicity also contribute to thrombocytopenia. Current therapies are directed towards immune suppression and modulation as well as stimulation of platelet production with thrombopoietin receptor agonists. Additional mechanisms of the pathogenesis of ITP have been suggested by recent experimental data. One of these processes, known as desialylation, involves antibody-induced removal of terminal sialic acid residues on platelet surface glycoproteins, leading to hepatic platelet uptake and thrombocytopenia. Apoptosis, or programmed platelet death, may also contribute to the pathogenesis of ITP. The extent of the impact of desialylation and apoptosis on ITP, the relative proportion of patients affected, and the role of antibody specificity are still the subject of investigation. This review will discuss both historical and new evidence of the influence of desialylation and apoptosis in the pathogenesis of ITP, with an emphasis on the clinical implications of these developments. Further understanding of both platelet desialylation and apoptosis might change current clinical practice and improve patient outcomes.

The role of platelet desialylation as a biomarker in primary immune thrombocytopenia: mechanisms and therapeutic perspectives

Primary immune thrombocytopenia (ITP) is an acquired autoimmune disorder characterized by the destruction of platelets. Although it was long believed that the critical role of autoantibodies in platelet destruction, primarily through the Fc-dependent platelet clearance pathway, recent findings indicate that the significance of the Fc-independent platelet clearance pathway mediated by hepatocytes, thus shedding light on a previously obscure aspect of ITP pathogenesis. Within this context, the desialylation of platelets has emerged as a pivotal biochemical marker. Consequently, targeting platelet desialylation emerges as a novel therapeutic strategy in the pathogenesis of ITP. Notably, prevailing research has largely focused on antiplatelet antibodies and the glycosylation-associated mechanisms of platelet clearance, while comprehensive analysis of platelet desialylation remains scant. In response, we retrospectively discuss the historical progression, inducing factors, generation process, and molecular regulatory mechanisms underlying platelet desialylation in ITP pathogenesis. By systematically evaluating the most recent research findings, we contribute to a comprehensive understanding of the intricate processes involved. Moreover, our manuscript delves into the potential application of desialylation regulatory strategies in ITP therapy, heralding novel therapeutic avenues. In conclusion, this manuscript not only fills a critical void in existing literature but also paves the way for future research by establishing a systematic theoretical framework. By inspiring new research ideas and offering insights into the development of new therapeutic strategies and targeted drugs, our study is poised to significantly advance the clinical management of ITP.

Successful treatment with oseltamivir phosphate in children with ITP who failed first-line therapy: a case series report

Immune thrombocytopenia (ITP) is a common bleeding disorder in children. First-line medicines (glucocorticoids and immunoglobulin) may not be effective for some children, endangering their lives, posing challenges for healthcare facilities, and leading to an unfavorable prognosis. As a sialidase inhibitor, oseltamivir phosphate can reduce the destruction of platelets in liver macrophages by inhibiting the sialylation of platelets, and finally achieve the purpose of increasing platelet count. In this paper, three cases of children with ITP who failed first-line therapy and were cured by oral administration of oseltamivir phosphate granules were reported. The mechanism of action of oseltamivir phosphate granules was clarified.

Improving the chances of response to splenectomy in immune thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder characterized by isolated thrombocytopenia. Its pathogenesis is complex relying in large part on destruction of platelets recognized by autoantibodies within the spleen. However, other mechanisms, such as platelet desialylation, may play a role in platelet reduction by accelerating their clearance in the liver. In their study, Mendoza and colleagues reported on platelet scintigraphy performed in 51 ITP patients, showing a response in 87.5% when the sequestration occurred in the spleen versus 45% in case of non-splenic destruction. Platelet desialylation was also measured after splenectomy and found to be higher in non-responder patients. These latter results, while requiring confirmation prior to splenectomy, support platelet desialylation may also be a potential biomarker of non-response to splenectomy. Commentary on: Mendoza et al. Study of platelet kinetics in immune thrombocytopenia to predict splenectomy response. Br J Haematol 2024;204:315-323.

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.

Study of platelet kinetics in immune thrombocytopenia to predict splenectomy response

Despite the efficacy of splenectomy for chronic immune thrombocytopenia (ITP), its considerable failure rate and its possible related complications prove the need for further research into potential predictors of response. The platelet sequestration site determined by 111 In-labelled autologous platelet scintigraphy has been proposed to predict splenectomy outcome, but without standardisation in clinical practice. Here, we conducted a single-centre study by analysing a cohort of splenectomised patients with ITP in whom 111 In-scintigraphy was performed at La Paz University Hospital in Madrid to evaluate the predictive value of the platelet kinetic studies. We also studied other factors that could impact the splenectomy outcome, such as patient and platelet characteristics. A total of 51 patients were splenectomised, and 82.3% responded. The splenic sequestration pattern predicted a higher rate of complete response up to 12 months after splenectomy (p = 0.005), with 90% sensitivity and 77% specificity. Neither age, comorbidities, therapy lines nor previous response to them showed any association with response. Results from the platelet characteristics analysis revealed a significant loss of sialic acid in platelets from the non-responding patients compared with those who maintained a response (p = 0.0017). Our findings highlight the value of splenic sequestration as an independent predictor of splenectomy response.

New insights into the glycobiology of immune thrombocytopenia

PURPOSE OF REVIEW

The platelet surface harbors a lush forest of glycans (carbohydrate polymers) attached to membrane proteins and lipids. Accumulating evidence suggests that these glycans may be relevant to the pathophysiology of immune thrombocytopenia (ITP). Here, we critically evaluate data that point to a possible role for loss of sialic acid in driving platelet clearance in ITP, comment on the potential use of neuraminidase inhibitors for treatment of ITP, and highlight open questions in this area.

RECENT FINDINGS

Multiple lines of evidence suggest a role for loss of platelet sialic acid in the pathophysiology of thrombocytopenia. Recent work has tested the hypothesis that neuraminidase-mediated cleavage of platelet sialic acid may trigger clearance of platelets in ITP. Some clinical evidence supports efficacy of the viral neuraminidase inhibitor oseltamivir in ITP, which is surprising given its lack of activity against human neuraminidases.

SUMMARY

Further study of platelet glycobiology in ITP is necessary to fill key knowledge gaps. A deeper understanding of the roles of platelet glycans in ITP pathophysiology will help to guide development of novel therapies.

Desialylated Platelet Clearance in the Liver is a Novel Mechanism of Systemic Immunosuppression

Platelets are small, versatile blood cells that are critical for hemostasis/thrombosis. Local platelet accumulation is a known contributor to proinflammation in various disease states. However, the anti-inflammatory/immunosuppressive potential of platelets has been poorly explored. Here, we uncovered, unexpectedly, desialylated platelets (dPLTs) down-regulated immune responses against both platelet-associated and -independent antigen challenges. Utilizing multispectral photoacoustic tomography, we tracked dPLT trafficking to gut vasculature and an exclusive Kupffer cell-mediated dPLT clearance in the liver, a process that we identified to be synergistically dependent on platelet glycoprotein Ibα and hepatic Ashwell-Morell receptor. Mechanistically, Kupffer cell clearance of dPLT potentiated a systemic immunosuppressive state with increased anti-inflammatory cytokines and circulating CD4+ regulatory T cells, abolishable by Kupffer cell depletion. Last, in a clinically relevant model of hemophilia A, presensitization with dPLT attenuated anti-factor VIII antibody production after factor VIII ( infusion. As platelet desialylation commonly occurs in daily-aged and activated platelets, these findings open new avenues toward understanding immune homeostasis and potentiate the therapeutic potential of dPLT and engineered dPLT transfusions in controlling autoimmune and alloimmune diseases.

B cells and antibodies in refractory immune thrombocytopenia

Immune thrombocytopenia (ITP) is an acquired bleeding disorder mediated by pathogenic autoantibodies secreted by plasma cells (PCs) in many patients. In refractory ITP patients, the persistence of splenic and bone marrow autoreactive long-lived PCs (LLPCs) may explain primary failure of rituximab and splenectomy respectively. The reactivation of autoreactive memory B cells generating new autoreactive PCs contributes to relapses after initial response to rituximab. Emerging strategies targeting B cells and PCs aim to prevent the settlement of splenic LLPCs with the combination of anti-BAFF and rituximab, to deplete autoreactive PCs with anti-CD38 antibodies, and to induce deeper B-cell depletion in tissues with novel anti-CD20 monoclonal antibodies and anti-CD19 therapies. Alternative strategies, focused on controlling autoantibody mediated effects, have also been developed, including SYK and BTK inhibitors, complement inhibitors, FcRn blockers and inhibitors of platelet desialylation.

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.

Characterization of the human platelet N- and O-glycome upon storage using tandem mass spectrometry

Changes in surface glycan determinants, specifically sialic acid loss, determine platelet life span. The gradual loss of stored platelet quality is a complex process that fundamentally involves carbohydrate structures. Here, we applied lipophilic extraction and glycan release protocols to sequentially profile N- and O-linked glycans in freshly isolated and 7-day room temperature-stored platelet concentrates. Analytical methods including matrix assisted laser desorption/ionization time-of-flight mass spectrometry, tandem mass spectrometry, and liquid chromatography were used to obtain structural details of selected glycans and terminal epitopes. The fresh platelet repertoire of surface structures revealed diverse N-glycans, including high mannose structures, complex glycans with polylactosamine repeats, and glycans presenting blood group epitopes. The O-glycan repertoire largely comprised sialylated and fucosylated core-1 and core-2 structures. For both N- and O-linked glycans, we observed a loss in sialylated epitopes with a reciprocal increase in neutral structures as well as increased neuraminidase activity after platelet storage at room temperature. The data indicate that loss of sialylated glycans is associated with diminished platelet quality and untimely removal of platelets after storage.

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.

Immune thrombocytopenia: a review on the pathogenetic role of immune cells

INTRODUCTION

Immune thrombocytopenia [ITP] is a common bleeding disorder with an isolated platelet count of less than 100 × 109/L.

AREAS COVERED

Relevant literature from 2003 to 2022 was retrieved and reviewed from the Google Scholar search engine and PubMed database. Antibodies produced by autoreactive B lymphocytes and the phagocytic function of macrophages are considered the most critical factors in platelet destruction. Also, macrophages present the antigen to T lymphocytes and activate them. Follicular helper T-cells [TFH] play a role in stimulating, differentiating, and activating autoreactive B cells, while cluster of differentiation [CD]-8+ T plays a role in platelet destruction through apoptosis. The classical pathway of the complement system also causes platelet destruction. By inhibiting platelet production, low levels of thrombopoietin and an immune response against megakaryocytes in the bone marrow worsen thrombocytopenia.

EXPERT OPINION

T-cell subset changes and an increase in activated autoreactive B cells, in addition to the function of components of the innate immune system [the complement system, dendritic cells, and natural killer cells], play a critical role in the pathogenesis of the ITP. Accurate detection of these changes may lead to developing new therapeutic strategies and identifying better prognostic/diagnostic factors.

Recent progress in ITP treatment

In this review, the recently approved drugs avatrombopag and fostamatinib, which were not extensively covered within 2019 international recommendations for ITP, will be discussed in some detail. Avatrombopag appears more convenient than eltrombopag as it does not require dietary restrictions or subcutaneous administration like romiplostim. However, data on quality of life (QoL) are lacking and the rate of thromboembolic events in exposed patients is not negligible. Efficacy of fostamatinib, an inhibitor of macrophagic activity, is supported by placebo-controlled trials in patients refractory to several therapies, including TPO-RA. While hypertension and diarrhea have been reported, only one minor thrombotic event occurred in 146 exposed patients. In addition, several new treatment combinations and new agents entered clinical investigation in recent years. In a UK trial, combining mycophenolate mofetil with corticosteroids as first line therapy was more effective than corticosteroids alone, but at the cost of worse QoL. No combination, including oseltamivir or all-trans retinoic acid or danazol, resulted in convincing evidence of superior efficacy and safety when used in first or later lines of treatment. Agents targeting specific mechanisms are also discussed: sutimlimab (complement inhibitor); rilzabrutinib (BTK inhibitor) and efgartigimod (modified Fc fragment inhibiting FcRn). Only efgartigimod has completed phase 3 investigation.

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.

Clinical efficacy of recombinant human thrombopoietin combined with glucocorticoids in the treatment of immune thrombocytopenia

OBJECTIVE

Herein, we aimed to determine the clinical efficacy of recombinant human thrombopoietin (rhTPO) combined with glucocorticoids for treating immune thrombocytopenia (ITP).

METHODS

Clinical data of 87 patients with ITP admitted to our hospital were retrospectively analyzed, and patients were divided into two groups according to the treatment employed: 42 patients in the control group (CG) were prescribed glucocorticoids, and 45 patients in the study group (SG) received rhTPO combined with glucocorticoids.

RESULTS

The total effective treatment rate in the SG (95.56%) was higher than that in the CG (76.19%) (P < 0.05). The SG achieved a platelet (PLT) count > 50 × 10⁹/L faster and required fewer PLT transfusions than the CG (P < 0.05). At 1, 7, and 14 days after treatment, the PLT count increased in both groups and was higher in the SG than in the CG (P < 0.05). After treatment, CD3+, CD4+, and CD4+/CD8+ T cells increased, whereas CD8 + decreased in both groups, with the SG exhibiting a superior improvement to the CG (P < 0.05). Considering prothrombin time, activated partial thromboplastin time, and fibrinogen, differences between the two groups were not statistically significant, both before and after treatment (P > 0.05).

CONCLUSION

rhTPO combined with glucocorticoids for treating ITP can effectively enhance the therapeutic effect, regulate the T lymphocyte subpopulation, rapidly increase the PLT level, and induce no significant effect on the coagulation function of patients, with good safety and high clinical promotion value.

Platelet Desialylation Is a Novel Mechanism and Therapeutic Target in Daboia siamensis and Agkistrodon halys Envenomation-Induced Thrombocytopenia

Venom-induced thrombocytopenia (VIT) is one of the most important hemotoxic effects of a snakebite, which is often associated with venom-induced consumptive coagulopathy (VICC). Refractory thrombocytopenia without significant coagulation abnormalities has also been reported after envenomation by some viperid snakes; however, the mechanisms are not well understood and therapeutic strategies are lacking. Here, we found that patients injured by Daboia siamensis or Agkistrodon halys snakes, who were resistant to standard antivenom treatment, had developed coagulopathy-independent thrombocytopenia. Venoms from these viperid snakes, rather than from the elapid snake (Bungarus multicinctus), induced platelet surface expression of neuraminidase-1 (NEU-1), and significantly increased the desialylation of the glycoproteins on human platelets. The desialylated platelets caused by viperid snake venoms were further internalized by macrophages, which resulted in reduced platelet numbers in peripheral blood. Importantly, neuraminidase inhibitor significantly decreased viper venom-induced platelet desialylation, therefore inhibiting platelet phagocytosis by macrophages, and alleviating venom-induced thrombocytopenia. Collectively, these findings support an important role for desialylated platelet clearance in the progression of viper envenomation-induced, coagulopathy-independent thrombocytopenia. Our study demonstrates that the neuraminidase inhibitor may be a potential therapy or adjuvant therapy to treat snakebite-induced thrombocytopenia.

Systemic lupus erythematosus-complicating immune thrombocytopenia: From pathogenesis to treatment

Immune thrombocytopenia (ITP) is a common hematological manifestation of systemic lupus erythematosus (SLE). The heterogeneity of its clinical characteristics and therapeutic responses reflects a complex pathogenesis. A better understanding of its pathophysiological mechanisms and employing an optimal treatment regimen is therefore important to improve the response rate and prognosis, and avoid unwanted outcomes. Besides glucocorticoids, traditional immunosuppressants (i.e. cyclosporine, mycophenolate mofetil) and intravenous immunoglobulins, new therapies are emerging and promising for the treatment of intractable SLE-ITP, such as thrombopoietin receptor agonists (TPO-RAs), platelet desialylation inhibitors(i.e. oseltamivir), B-cell targeting therapy(i.e. rituximab, belimumab), neonatal Fc receptor(FcRn) inhibitor, spleen tyrosine kinase(Syk) inhibitor and Bruton tyrosine kinase(BTK) inhibitor et al., although more rigorous randomized controlled trials are needed to substantiate their efficacy. In this review, we update our current knowledge on the pathogenesis and treatment of SLE-ITP.

Current therapeutic strategies and perspectives in refractory ITP: What have we learned recently?

Immune thrombocytopenia (ITP) is an acquired autoimmune bleeding disorder featured by increased platelet destruction and deficient megakaryocyte maturation. First-line treatments include corticosteroids, intravenous immunoglobulin and intravenous anti-D immunoglobulin. Second-line treatments consist of rituximab, thrombopoietin receptor agonists and splenectomy. Although most patients benefit from these treatments, an individualized treatment approach is warranted due to the large heterogeneity among ITP patients. In addition, ITP patients may relapse and there remains a subset of patients who become refractory to treatments. The management of these refractory patients is still a challenge. This review aims to summarize emerging therapeutic approaches for refractory ITP in several categories according to their different targets, including macrophages, platelets/megakaryocytes, T cells, B cells, and endothelial cells. Moreover, current management strategies and combination regimens of refractory ITP are also discussed.

Clinical impact of glycans in platelet and megakaryocyte biology

Humans produce and remove 1011 platelets daily to maintain a steady-state platelet count. The tight regulation of platelet production and removal from the blood circulation prevents anomalies in both processes from resulting in reduced or increased platelet count, often associated with the risk of bleeding or overt thrombus formation, respectively. This review focuses on the role of glycans, also known as carbohydrates or oligosaccharides, including N- and O-glycans, proteoglycans, and glycosaminoglycans, in human and mouse platelet and megakaryocyte physiology. Based on recent clinical observations and mouse models, we focused on the pathologic aspects of glycan biosynthesis and degradation and their effects on platelet numbers and megakaryocyte function.

Oseltamivir as rescue therapy for persistent, chronic, or refractory immune thrombocytopenia: a case series and review of the literature

Immune thrombocytopenia (ITP) is an autoimmune disease that results from antibody-mediated platelet destruction and impaired platelet production. Novel therapies have emerged in the last decade, but 15-20% of patients will relapse or fail and require further therapy. We performed a prospective, single-arm intervention study on seven patients with chronic, persistent, or refractory ITP from the Hospital Universitario "Dr. José E González", in Monterrey, Mexico between 2015 and 2019. Eligible patients received oral oseltamivir 75 mg twice daily for 5 days and were followed up for six months. Most patients received a median of three distinct therapies (range 2-6). Four patients (57.1%) received combined therapy. The median time for any response was 55.5 days (range = 14-150). All patients responded at some point in time (ORR = 100%, six had a proportion of loss of response [PR], and one achieved [CR]). Six months after oseltamivir administration, three patients (42.9%) maintained a response, and one patient had a CR (14.3%). Oseltamivir was well tolerated with a good overall response rate and was useful for treating chronic ITP. We observed an initial increase in the number of platelets; however, this response was not maintained.

Novel compound heterozygous mutations in a GNE myopathy with congenital thrombocytopenia: A case report and literature review

We reported a GNE myopathy with congenital thrombocytopenia on a young male patient. He presented with a 3-year history of lower distal extremity weakness initially affecting his legs. The weakness slowly progressed to lower proximal legs and upper arms last 6 months. Whole-exome sequencing revealed that the patient harbored two heterozygous gene mutations, including a novel insertion mutation c.*1037_*1038CACACACACACACACACACACA and c.C478T in exome 12 and 3 of the GNE gene (NM_001128227), respectively. The levels of serum sialic acid in this patient were considerably decreased. Muscle MRI imaging showed the anterior and medial parts of his quadriceps were heavily affected by this disease. Hematoxylin and eosin staining showed prominent rimmed vacuoles with a lack of inflammatory response in the atrophied muscle. We also undertook a review of the current literature, searching for reports in which the GNE gene mutation caused the thrombocytopenia with or without muscle weakness. This new gene mutation finding broadens the GNE disease genotype spectrum, and further investigation of the relationship between GNE gene mutations and the heterogeneity of its clinical manifestations is needed.

Sialic acid and platelet count regulation: Implications in immune thrombocytopenia

Platelets are blood components that survive in circulation for 7 to 10 days in humans. Thus, platelet production by bone marrow (BM) megakaryocytes (MKs), and their removal from the blood circulation is precisely orchestrated to maintain an average platelet count. Abnormalities in both processes can result in thrombocytopenia (low platelet count) or thrombocytosis (high platelet count), often associated with the risk of bleeding or overt thrombus formation, respectively. Platelet glycans, particularly sialic acids, are indicators of platelet count. Loss of platelet sialic acids leads to platelet clearance. A State-of-the-Art lecture titled "Platelet and Megakaryocyte Glycobiology" was presented at the ISTH virtual congress 2021 to discuss (i) the loss of O-glycan sialic acid on BM MKs, revealing the Thomsen-Friedenreich (TF) antigen as a new concept of thrombocytopenia; herein, impaired thrombopoiesis is attributed to activation of immune cells with a plasmacytoid dendritic cell signature; and (ii) upregulation of antibodies against the TF antigen in pediatric patients with immune thrombocytopenia (ITP), positing that glycan alterations such as MK asialylation can lead to immune cell responses. Here, we discuss our findings alongside new data presented at the 2020 and 2021 ISTH congresses on the role of sialic acids and glycans in regulating platelet count. Desialylation is a prominent feature in thrombocytopenia, notably in ITP presentation. We compare similarities between ITP mediated with shear-stress and with storage-related asialylation. We also discuss genes involved in sialic acid synthesis leading to thrombocytopenia. Increased awareness in gene-regulating MK and platelet glycans is a giant leap to understanding the underpinning mechanisms of ITP and other forms of thrombocytopenia.

Effect of oseltamivir phosphate versus placebo on platelet recovery and plasma leakage in adults with dengue and thrombocytopenia; a phase 2, multicenter, double-blind, randomized trial

Background

Thrombocytopenia, bleeding and plasma leakage are major complications of dengue. Activation of endogenous sialidases with desialylation of platelets and endothelial cells may underlie these complications. We aimed to assess the effects of the neuraminidase inhibitor oseltamivir on platelet recovery and plasma leakage in dengue.

Methods

We performed a phase 2, double-blind, multicenter, randomized trial in adult dengue patients with thrombocytopenia (<70,000/μl) and a duration of illness ≤ 6 days. Oseltamivir phosphate 75mg BID or placebo were given for a maximum of five days. Primary outcomes were the time to platelet recovery (≥ 100,000/μl) or discharge from hospital and the course of measures of plasma leakage.

Results

A total of 70 patients were enrolled; the primary outcome could be assessed in 64 patients (31 oseltamivir; 33 placebo). Time to platelet count ≥100,000/μl (n = 55) or discharge (n = 9) were similar in the oseltamivir and placebo group (3.0 days [95% confidence interval, 2.7 to 3.3] vs. 2.9 days [2.5 to 3.3], P = 0.055). The kinetics of platelet count and parameters of plasma leakage (gall bladder thickness, hematocrit, plasma albumin, syndecan-1) were also similar between the groups.

Discussion

In this trial, adjunctive therapy with oseltamivir phosphate had no effect on platelet recovery or plasma leakage parameters.

Trial registration

ISRCTN35227717.

Moderate to severe thrombocytopenia is common in the febrile and/or critical phase of dengue virus infection. Platelets are important for preservation of vascular integrity, especially during inflammation, and low platelet counts may contribute to plasma leakage. Currently, no therapeutic intervention that targets the pathogenic pathway is available for DENV infection, including therapies to prevent or reduce thrombocytopenia or plasma leakage. Oseltamivir phosphate is widely used for prevention and treatment of influenza by inhibiting viral neuraminidase. However, oseltamivir may also inhibit human endogenous neuraminidase involved in sialic acid metabolism, and as such extend the lifespan of platelets. In the phase 2 TOTO trial (Treatment Of Thrombocytopenia with Oseltamivir in acute dengue virus infection: a randomized, placebo controlled, multicenter trial) we investigated the potential of oseltamivir phosphate to shorten the time to platelet recovery and reduce plasma leakage in patients with DENV infection. In this trial involving 70 adult thrombocytopenic patients, hospitalized with acute DENV infection, adjunctive therapy with oseltamivir phosphate did not shorten platelet recovery time compared with placebo. The trial also did not show an effect of adjunctive oseltamivir on plasma leakage parameters. The reasons that oseltamivir had no apparent effect on platelet counts, markers of plasma leakage and glycocalyx distortion in this study remain speculative, but may involve one or more of the following; first, dengue-associated thrombocytopenia and plasma leakage are both multifactorial in origin and targeting neuraminidase alone may be insufficient to impact these processes. Second, oseltamivir phosphate was designed to inhibit viral neuraminidase, and data of its inhibitory actions on human neuraminidases are inconclusive. The finding in this study also suggest that while laboratory works may lead to hypotheses for novel treatment, proof of concept studies are essential to test them in a clinical setting.

Severe Congenital Thrombocytopenia Characterized by Decreased Platelet Sialylation and Moderate Complement Activation Caused by Novel Compound Heterozygous Variants in GNE

Background

Hereditary thrombocytopenias constitute a genetically heterogeneous cause of increased bleeding. We report a case of a 17-year-old boy suffering from severe macrothrombocytopenia throughout his life. Whole genome sequencing revealed the presence of two compound heterozygous variants in GNE encoding the enzyme UDP-N-acetyl-glucosamine-2-epimerase/N-acetylmannosamine kinase, crucial for sialic acid biosynthesis. Sialic acid is required for normal platelet life span, and biallelic variants in GNE have previously been associated with isolated macrothrombocytopenia. Furthermore, sialic acid constitutes a key ligand for complement factor H (FH), an important inhibitor of the complement system, protecting host cells from indiscriminate attack.

Methods

Sialic acid expression and FH binding to platelets and leukocytes was evaluated by flow cytometry. The binding of FH to erythrocytes was assessed indirectly by measuring the rate of complement mediated hemolysis. Complement activation was determined by measuring levels of C3bBbP (alternative pathway), C4d (classical/lectin pathway) and soluble terminal complement complex assays.

Results

The proband exhibited markedly decreased expression of sialic acid on platelets and leukocytes. Consequently, the binding of FH was strongly reduced and moderate activation of the alternative and classical/lectin complement pathways was observed, together with an increased rate of erythrocyte lysis.

Conclusion

We report two previously undescribed variants in GNE causing severe congenital macrothrombocytopenia in a compound heterozygous state, as a consequence of decreased platelet sialylation. The decreased sialylation of platelets, leukocytes and erythrocytes affects the binding of FH, leading to moderate complement activation and increased hemolysis.

Early oseltamivir reduces risk for influenza-associated aspergillosis in a double-hit murine model

Invasive pulmonary aspergillosis (IPA) is a life-threatening fungal infection occurring mainly in immunocompromised patients. We recently identified IPA as an emerging co-infection with high mortality in critically ill, but otherwise immunocompetent influenza patients. The neuraminidase inhibitor oseltamivir is the current standard-of-care treatment in hospitalized influenza patients; however, its efficacy in influenza-associated pulmonary aspergillosis (IAPA) is not known. Therefore, we have established an imaging-supported double-hit mouse model to investigate the therapeutic effect of oseltamivir on the development of IAPA. Immunocompetent mice received intranasal instillation influenza A or PBS followed by orotracheal inoculation with Aspergillus fumigatus 4 days later. Oseltamivir treatment or placebo was started at day 0, day 2, or day 4. Daily monitoring included micro-computed tomography and bioluminescence imaging of pneumonia and fungal burden. Non-invasive biomarkers were complemented with imaging, molecular, immunological, and pathological analysis. Influenza virus-infected immunocompetent mice developed proven airway IPA upon co-infection with Aspergillus fumigatus, whereas non-influenza-infected mice fully cleared Aspergillus, confirming influenza as a risk factor for developing IPA. Longitudinal micro-CT showed pulmonary lesions after influenza infection worsening after Aspergillus co-infection, congruent with bioluminescence imaging and histology confirming Aspergillus pneumonia. Early oseltamivir treatment prevented severe influenza pneumonia and mitigated the development of IPA and associated mortality. A time-dependent treatment effect was consistently observed with imaging, molecular, and pathological analyses. Hence, our findings underscore the importance of initiating oseltamivir as soon as possible, to suppress influenza infection and mitigate the risk of potentially lethal IAPA disease.

Circulating platelet count and glycans

PURPOSE OF THE REVIEW

This review highlights recent advancements in understanding the regulation of platelet numbers, focusing on mechanisms by which carbohydrates (glycans) link platelet removal with platelet production in the bone marrow in health and disease.

RECENT FINDINGS

This review is focused on the role of carbohydrates, specifically sialic acid moieties, as a central mediator of platelet clearance. We discuss recently identified novel mechanisms of carbohydrate-mediated platelet removal and carbohydrate-binding receptors that mediate platelet removal.

SUMMARY

The platelet production rate by megakaryocytes and removal kinetics controls the circulating platelet count. Alterations in either process can lead to thrombocytopenia (low platelet count) or thrombocytosis (high platelet count) are associated with the risk of bleeding or overt thrombus formation and serious complications. Thus, regulation of a steady-state platelet count is vital in preventing adverse events. There are few mechanisms delineated that shed light on carbohydrates' role in the complex and massive platelet removal process. This review focuses on carbohydrate-related mechanisms that contribute to the control of platelet numbers.

Viper venoms drive the macrophages and hepatocytes to sequester and clear platelets: novel mechanism and therapeutic strategy for venom-induced thrombocytopenia

Venomous snakebites cause clinical manifestations that range from local to systemic and are considered a significant global health challenge. Persistent or refractory thrombocytopenia has been frequently reported in snakebite patients, especially in cases caused by viperidae snakes. Viper envenomation-induced thrombocytopenia may persist in the absence of significant consumption coagulopathy even after the antivenom treatment, yet the mechanism remains largely unknown. Our study aims to investigate the mechanism and discover novel therapeutic targets for coagulopathy-independent thrombocytopenia caused by viper envenomation. Here we found that patients bitten by Protobothrops mucrosquamatus and Trimeresurus stejnegeri, rather than Naja. atra may develop antivenom-resistant and coagulopathy-independent thrombocytopenia. Crude venoms and the derived C-type lectin-like proteins from these vipers significantly increased platelet surface expression of neuraminidase and platelet desialylation, therefore led to platelet ingestion by both macrophages and hepatocytes in vitro, and drastically decreased peripheral platelet counts in vivo. Our study is the first to demonstrate that desialylation-mediated platelet clearance is a novel mechanism of viper envenomation-induced refractory thrombocytopenia and C-type lectin-like proteins derived from the viper venoms contribute to snake venom-induced thrombocytopenia. The results of this study suggest the inhibition of platelet desialylation as a novel therapeutic strategy against viper venom-induced refractory thrombocytopenia.

New treatments for primary immune thrombocytopenia

Primary immune thrombocytopenia (ITP) is an autoimmune disease leading to a decreased platelet count and an ensuing haemorrhagic risk. First-line treatment against ITP consists in the administration of immunomodulators aimed at decreasing platelet destruction. Up to 70% of individuals with an ITP diagnosis treated with corticosteroids do not achieve a clinical response or demonstrate a high relapse rate, requiring treatment to prevent a haemorrhagic risk. Less than 30% of patients treated with thrombopoietin analogues, 60% of those treated with splenectomy and 20% of those treated with rituximab reach sustained remission in the absence of treatment. Because of these reasons, it is unquestionable that treatment of patients with ITP should be optimized. Through this study, we will review new actual and future options of treatment.

Platelet features allow to differentiate immune thrombocytopenia from inherited thrombocytopenia

Immune thrombocytopenia (ITP) is an acquired bleeding disorder, for which no specific diagnostic test exists. Inherited thrombocytopenia (IT) can mimic ITP and lead to unappropriated management with significant morbidity. Here, in small cohorts of these two disorders, we explored whether platelet sialylation and platelet activation could allow to discriminate the two conditions. We also aimed to confirm the value of immature platelet counts in this discrimination. Platelet sialylation and the expression level of P-selectin were assessed by multiparameter flow cytometry. Immature platelets were estimated on a Sysmex XN 9000 analyzer. No significant difference in platelet sialylation was observed between ITP and IT. Contrarily, platelet activation was significantly higher in ITP patients (p = 0.008). The immature platelet fraction, as previously demonstrated, was significantly lower in the ITP group compared to the IT group (p = 0.014). That statistical significance was achieved in this small pilot study suggests that the two easily available assays of immature platelet count and P-selectin expression could help physicians to reach the proper diagnosis in complex cases of thrombocytopenia.

Potential Diagnostic Approaches for Prediction of Therapeutic Responses in Immune Thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder in which, via unresolved mechanisms, platelets and megakaryocytes (MKs) are targeted by autoantibodies and/or T cells resulting in increased platelet destruction and impairment of MK function. Over the years, several therapeutic modalities have become available for ITP, however, therapeutic management has proven to be very challenging in several cases. Patients refractory to treatment can develop a clinically worsening disease course, treatment-induced toxicities and are predisposed to development of potentially life-endangering bleedings. It is therefore of critical importance to timely identify potential refractory patients, for which novel diagnostic approaches are urgently needed in order to monitor and predict specific therapeutic responses. In this paper, we propose promising diagnostic investigations into immune functions and characteristics in ITP, which may potentially be exploited to help predict platelet count responses and thereby distinguish therapeutic responders from non-responders. This importantly includes analysis of T cell homeostasis, which generally appears to be disturbed in ITP due to decreased and/or dysfunctional T regulatory cells (Tregs) leading to loss of immune tolerance and initiation/perpetuation of ITP, and this may be normalized by several therapeutic modalities. Additional avenues to explore in possible prediction of therapeutic responses include examination of platelet surface sialic acids, platelet apoptosis, monocyte surface markers, B regulatory cells and platelet microparticles. Initial studies have started evaluating these markers in relation to response to various treatments including glucocorticosteroids (GCs), intravenous immunoglobulins (IVIg) and/or thrombopoietin receptor agonists (TPO-RA), however, further studies are highly warranted. The systematic molecular analysis of a broad panel of immune functions may ultimately help guide and improve personalized therapeutic management in 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.

Neuraminidase and SIGLEC15 modulate the host defense against pulmonary aspergillosis

Influenza-associated pulmonary aspergillosis (IAPA) has been reported increasingly since the advent of use of neuraminidase (NA) inhibitors following the 2009 influenza pandemic. We hypothesize that blocking host NA modulates the immune response against Aspergillus fumigatus. We demonstrate that NA influences the host response against A. fumigatus in vitro and that oseltamivir increases the susceptibility of mice to pulmonary aspergillosis. Oseltamivir impairs the mouse splenocyte and human peripheral blood mononuclear cell (PBMC) killing capacity of A. fumigatus, and adding NA restores this defect in PBMCs. Furthermore, the sialic acid-binding receptor SIGLEC15 is upregulated in PBMCs stimulated with A. fumigatus. Silencing of SIGLEC15 decrease PBMC killing of A. fumigatus. We provide evidence that host NA activity and sialic acid recognition are important for anti-Aspergillus defense. NA inhibitors might predispose individuals with severe influenza to invasive aspergillosis. These data shed light on the pathogenesis of invasive fungal infections and may identify potential therapeutic targets.

The Importance of Platelet Glycoside Residues in the Haemostasis of Patients with Immune Thrombocytopaenia

Loss of sialic acid from the carbohydrate side chains of platelet glycoproteins can affect platelet clearance, a proposed mechanism involved in the etiopathogenesis of immune thrombocytopaenia (ITP). We aimed to assess whether changes in platelet glycosylation in patients with ITP affected platelet counts, function, and apoptosis. This observational, prospective, and transversal study included 82 patients with chronic primary ITP and 115 healthy controls. We measured platelet activation markers and assayed platelet glycosylation and caspase activity, analysing samples using flow cytometry. Platelets from patients with ITP with a platelet count <30 × 10³/µL presented less sialic acid. Levels of α1,6-fucose (a glycan residue that can directly regulate antibody-dependent cellular cytotoxicity) and α-mannose (which can be recognised by mannose-binding-lectin and activate the complement pathway) were increased in the platelets from these patients. Platelet surface exposure of other glycoside residues due to sialic acid loss inversely correlated with platelet count and the ability to be activated. Moreover, loss of sialic acid induced the ingestion of platelets by human hepatome HepG2 cells. Changes in glycoside composition of glycoproteins on the platelets’ surface impaired their functional capacity and increased their apoptosis. These changes in platelet glycoside residues appeared to be related to ITP severity.

Dexamethasone plus oseltamivir versus dexamethasone in treatment-naive primary immune thrombocytopenia: a multicentre, randomised, open-label, phase 2 trial

BACKGROUND

Primary immune thrombocytopenia is an autoimmune bleeding disorder. Preclinical reports suggest that the sialidase inhibitor oseltamivir induces a platelet response in the treatment of immune thrombocytopenia. This study investigated the activity and safety of dexamethasone plus oseltamivir versus dexamethasone alone as initial treatment in adult patients with primary immune thrombocytopenia.

METHODS

This multicentre, randomised, open-label, parallel group, phase 2 trial was done in five tertiary medical hospitals in China. Eligible patients were aged 18 years or older with newly diagnosed, treatment-naive primary immune thrombocytopenia. Participants were randomly assigned (1:1), using block randomisation, to receive either dexamethasone (orally at 40 mg per day for 4 days) plus oseltamivir (orally at 75 mg twice a day for 10 days) or dexamethasone monotherapy (orally at 40 mg a day for 4 days). Patients who did not respond to treatment (platelet counts remained <30 × 10⁹ cells per L or showed bleeding symptoms by day 10) were given an additional cycle of dexamethasone for 4 days in each group. Patients in the dexamethasone plus oseltamivir group who relapsed (platelet counts reduced again to <30 × 10⁹ cells per L) after an initial response were allowed a supplemental course of oseltamivir (75 mg twice a day for 10 days). The coprimary endpoints were 14-day initial overall response and 6-month overall response. Complete response was defined as a platelet count at or above 100 × 10⁹ cells per L and an absence of bleeding. Partial response was defined as a platelet count at or above 30 × 10⁹ cells per L but less than 100 × 10⁹ cells per L and at least a doubling of the baseline platelet count and an absence of bleeding. A response lasting for at least 6 months without any additional primary immune thrombocytopenia-specific intervention was defined as sustained response. All patients who were randomly assigned and received the allocated intervention were included in the modified intention-to-treat population analysis. This study has been completed and is registered with ClinicalTrials.gov, number NCT01965626.

FINDINGS

From Feb 1, 2016, to May 1, 2019, 120 patients were screened for eligibility, of whom 24 were ineligible and excluded, 96 were enrolled and randomly assigned to receive dexamethasone plus oseltamivir (n=47) or dexamethasone (n=49), and 90 were included in the modified intention-to-treat analysis. Six patients did not receive the allocated intervention. Patients in the dexamethasone plus oseltamivir group had a significantly higher initial response rate (37 [86%] of 43 patients) than did those in the dexamethasone group (31 [66%] of 47 patients; odds ratio [OR] 3·18; 95 CI% 1·13-9·23; p=0·030) at day 14. The 6-month sustained response rate in the dexamethasone plus oseltamivir group was also significantly higher than that in the dexamethasone group (23 [53%] vs 14 [30%]; OR 2·17; 95 CI% 1·16-6·13; p=0·032). During the median follow-up of 8 months (IQR 5-14), two of 90 patients discontinued treatment due to serious adverse events (grade 3); one (2%) patient with general oedema in the dexamethasone plus oseltamivir group and one (2%) patient with fever in the dexamethasone group. The most frequently observed adverse events of any grade were fatigue (five [12%] of 43 in the dexamethasone plus oseltamivir group vs eight [17%] of 47 in the dexamethasone group), gastrointestinal reactions (eight [19%] vs three [6%]), insomnia (seven [16%] vs four [9%]), and anxiety (five [12%] vs three [6%]). There were no grade 4 or 5 adverse events and no treatment-related deaths.

INTERPRETATION

Dexamethasone plus oseltamivir offers a readily available combination therapy in the management of newly diagnosed primary immune thrombocytopenia. The preliminary activity of this combination warrants further investigation. Multiple cycles of oseltamivir, as a modification of current first-line treatment, might be more effective in maintaining the platelet response.

FUNDING

National Natural Science Foundation of China.

Insights on chronic immune thrombocytopenia pathogenesis: A bench to bedside update

Immune thrombocytopenia (ITP) is a heterogeneous disease with an unpredictable course. Chronicity can develop in up to two-thirds of adults and 20-25% of children, representing a significant burden on patients' quality of life. Despite acceptable responses to treatment, precise etiology and pathophysiology phenomena driving evolution to chronicity remain undefined. We analyzed reported risk factors for chronic ITP and associated them with proposed underlying mechanisms in its pathogenesis, including bone marrow (BM) microenvironment disturbances, clinical features, and immunological markers. Their understanding has diagnostic implications, such as screening for the presence of specific antibodies or BM examination employing molecular tools, which could help predict prognosis and recognize main pathogenic pathways in each patient. Identifying these underlying mechanisms could guide the use of personalized therapies such as all-trans retinoic acid, mTor inhibitors, FcRn inhibitors, oseltamivir, and others. Further research should lead to tailored treatments and chronic course prevention, improving patients' quality of life.

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.

Emerging Therapies in Immune Thrombocytopenia

Immune thrombocytopenia (ITP) is a rare autoimmune disorder caused by peripheral platelet destruction and inappropriate bone marrow production. The management of ITP is based on the utilization of steroids, intravenous immunoglobulins, rituximab, thrombopoietin receptor agonists (TPO-RAs), immunosuppressants and splenectomy. Recent advances in the understanding of its pathogenesis have opened new fields of therapeutic interventions. The phagocytosis of platelets by splenic macrophages could be inhibited by spleen tyrosine kinase (Syk) or Bruton tyrosine kinase (BTK) inhibitors. The clearance of antiplatelet antibodies could be accelerated by blocking the neonatal Fc receptor (FcRn), while new strategies targeting B cells and/or plasma cells could improve the reduction of pathogenic autoantibodies. The inhibition of the classical complement pathway that participates in platelet destruction also represents a new target. Platelet desialylation has emerged as a new mechanism of platelet destruction in ITP, and the inhibition of neuraminidase could dampen this phenomenon. T cells that support the autoimmune B cell response also represent an interesting target. Beyond the inhibition of the autoimmune response, new TPO-RAs that stimulate platelet production have been developed. The upcoming challenges will be the determination of predictive factors of response to treatments at a patient scale to optimize their management.

Autoantibody-mediated desialylation impairs human thrombopoiesis and platelet lifespan

Immune thrombocytopenia is a common bleeding disease caused by autoantibody-mediated accelerated platelet clearance and impaired thrombopoiesis. Accumulating evidence suggests that desialylation affects platelet life span in immune thrombocytopenia. Herein, we report on novel effector functions of autoantibodies from immune thrombocytopenic patients which might interfere with the clinical picture of the disease. Data from our study show that a subgroup of autoantibodies is able to induce cleave of sialic acid residues from the surface of human platelets and megakaryocytes. Moreover, autoantibody-mediated desialylation interferes with the interaction between cells and extracellular matrix proteins leading to impaired platelet adhesion and megakaryocyte differentiation. Using a combination of ex vivo model of thrombopoiesis, a humanized animal model, and a clinical cohort study, we demonstrate that cleavage of sialic acid induces significant impairment in production, survival as well as function of human platelets. These data may indicate that prevention of desialylation should be investigated in the future in clinical studies as a potential therapeutic approach to treat bleeding in immune thrombocytopenia.

[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).

Multifaceted role of glycosylation in transfusion medicine, platelets, and red blood cells

Glycosylation is highly prevalent, and also one of the most complex and varied posttranslational modifications. This large glycan diversity results in a wide range of biological functions. Functional diversity includes protein degradation, protein clearance, cell trafficking, cell signaling, host-pathogen interactions, and immune defense, including both innate and acquired immunity. Glycan-based ABO(H) antigens are critical in providing compatible products in the setting of transfusion and organ transplantation. However, evidence also suggests that ABO expression may influence cardiovascular disease, thrombosis, and hemostasis disorders, including alterations in platelet function and von Willebrand factor blood levels. Glycans also regulate immune and hemostasis function beyond ABO(H) antigens. Mutations in glycogenes (PIGA, COSMC) lead to serious blood disorders, including Tn syndrome associated with hyperagglutination, hemolysis, and thrombocytopenia. Alterations in genes responsible for sialic acids (Sia) synthesis (GNE) and UDP-galactose (GALE) and lactosamine (LacNAc) (B4GALT1) profoundly affect circulating platelet counts. Desialylation (removal of Sia) is affected by human and pathogenic neuraminidases. This review addresses the role of glycans in transfusion medicine, hemostasis and thrombosis, and red blood cell and platelet survival.

Measuring beta-galactose exposure on platelets: Standardization and healthy reference values

BACKGROUND

Correct diagnosis of the cause of thrombocytopenia is crucial for the appropriate management of patients. Hyposialylation/desialylation (characterized by abnormally high β-galactose exposure) accelerates platelet clearance and can lead to thrombocytopenia. However, the reference range for β-galactose exposure in healthy individuals has not been defined previously.

OBJECTIVE

The objective of the present study was to develop a standardized assay of platelet β-galactose exposure for implementation in a clinical laboratory.

METHODS

β-Galactose exposure was measured in platelet-rich plasma by using flow cytometry and Ricinus communis agglutinin (RCA). A population of 120 healthy adults was recruited to study variability.

RESULTS

We determined an optimal RCA concentration of 12.5 μg/mL. The measure was stable for up to 4 hours (mean fluorescence intensity [MFI]-RCA: 1233 ± 329 at 0 hour and 1480 ± 410 at 4 hours). The platelet count did not induce a variation of RCA and the measure of RCA was stable when tested up to 24 hours after blood collection (MFI-RCA: 1252 ± 434 at day 0 and 1140 ± 297 24 hours after blood sampling). To take into account the platelet size, results should be expressed as RCA/forward scatter ratio. We used the assay to study variability in 120 healthy adults, and we found that the ratio is independent of sex and blood group.

CONCLUSION

We defined a normal range in a healthy population and several preanalytical and analytical variables were evaluated, together with positive and negative controls. This assay may assist in the diagnosis of thrombocytopenic diseases linked to changes in β-galactose exposure.

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.

Platelet and immune characteristics of immune thrombocytopaenia patients non-responsive to therapy reveal severe immune dysregulation

Multifactorial mechanisms leading to diminished platelet counts in immune thrombocytopaenia (ITP) might condition the ability of patients with ITP to respond to treatments. Examining their platelet and immune features, we aimed to detect singular characteristics of patients with ITP who do not respond to any treatment. We studied patients with chronic primary ITP who had been without treatment, or untreated (UT-ITP), for at least six months; included were responders to agonists of thrombopoietin receptors (TPO-RA), patients who showed no response to first- and second-line treatments (NR-ITP), and healthy controls. Platelets from NR-ITP patients exposed a reduced amount of sialic acid residues. Increased loss of platelet surface sialic acid residues was associated with increased platelet apoptosis. NR-ITP patients had an increased fraction of naive lymphocyte (L) B cells and a reduced LTreg (Lymphocyte T-regulator) subset. They also presented an anomalous monocyte and NK (Natural Killer) cells distribution. TPO-RA-treated patients seemed to recover an immune homeostasis similar to healthy controls. In conclusion, our results indicate a severe deregulation of the immune system of NR-ITP. The inverse correlation between loss of sialic acid and LTreg count suggests a potential relationship between glycan composition on the platelet surface and immune response, positing terminal sugar moieties of the glycan chains as aetiopathogenic agents in ITP.

Current and emerging treatments for immune thrombocytopenia

Introduction: Immune thrombocytopenia (ITP) is an autoimmune disease. Even though there are many treatments available, some patients remain resistant to multiple treatments. Therefore, it is very important to develop new treatment options. Areas covered: Here, the authors summarize several current and emerging treatments developed for ITP in recent years. They include a summary of their mechanisms of action and clinical trial results. Expert opinion: At present, the first-line treatment of ITP is glucocorticoid and intravenous immunoglobulin (IVIg). Other traditional therapies include splenectomy, thrombopoietin (TPO), rituximab and other immunosuppressive agents. The several emerging treatments developed recently for ITP may change the treatment pattern in the future.