Primary immune thrombocytopenia: understanding pathogenesis is the key to better treatments

Lipoprotein lipids and apolipoproteins in primary immune thrombocytopenia: Results from a clinical characteristics and causal relationship verification, potential drug target identification by Mendelian randomization analyses

Primary immune thrombocytopenia (ITP) is an acquired autoimmune disease. Cellular and systemic lipid metabolism plays a significant role in the regulation of immune cell activities. However, the role of lipoprotein lipids and apolipoproteins in ITP remains elusive. The automatic biochemistry analyser was used to measure the levels of serum total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), apolipoprotein A-I (apoA-I), apoB, apoE and lipoprotein a [LP(a)]. Genetic variants strongly associated with circulating lipoprotein lipids and apolipoproteins (LDL-C, apoB, TG, HDL-C and apoA-I) were extracted to perform Mendelian randomization (MR) analyses. Finally, drug-target MR and passive ITP mice model was used to investigate the potential druggable targets of ITP. Levels of HDL-C, apoA-I, decreased and LP(a) increased in ITP patients compared with healthy controls. Low HDL-C was causally associated with ITP susceptibility. Through drug-target MR and animal modelling, ABCA1 was identified as a potential target to design drugs for ITP. Our study found that lipid metabolism is related to ITP. The causative association between HDL-C and the risk of ITP was also established. The study provided new evidence of the aetiology of ITP. ABCA1 might be a potential drug target for ITP.

Treatment of immune thrombocytopenia in Australian adults: A multicenter retrospective observational study

Background

In Australia, prescribing restrictions limit access to internationally recommended second‐line therapies such as rituximab and thrombopoietin agonists (TPO‐A) (eltrombopag and romiplostim). Subsequent lines of therapy include an array of immunosuppressive and immune‐modulating agents directed by drug availability and physician and patient preference.

Objectives

The objective of the study was to describe the use of first and subsequent lines of treatment for adult immune thrombocytopenia (ITP) in Australia and to assess their effectiveness and tolerability.

Patients/Methods

A retrospective review of medical records was conducted of 322 patients treated for ITP at eight participating centers in Australia between 2013 and 2020. Data were analyzed by descriptive statistics and frequency distribution using pivot tables, and comparisons between centers were assessed using paired t tests.

Results

Mean age at diagnosis of ITP was 48.8 years (standard deviation [SD], 22.6) and 58.3% were women. Primary ITP was observed in 72% and secondary ITP in 28% of the patients; 95% of patients received first‐line treatment with prednisolone (76%), dexamethasone (15%), or intravenous immunoglobulin (48%) alone or in combination. Individuals with secondary ITP were less steroid dependent (72% vs. 76%) and required less treatment with a second‐line agent (47% vs. 58%) in the study sample. Over half (56%) of the cohort received treatment with one or more second‐line agents. The mean number of second‐line agents used for each patient was 1.9 (SD, 1.2). The most used second‐line therapy was rituximab, followed by etrombopag and splenectomy. These also generated the highest rates of complete response (60.3%, 72.1%, and 71.8% respectively). The most unfavorable side effect profiles were seen in long‐term corticosteroids and splenectomy.

Conclusion

A wide range of “second‐line” agents were used across centers with variable response rates and side effect profiles. Findings suggest greater effectiveness of rituximab and TPO‐A, supporting their use earlier in the treatment course of patients with ITP across Australia.

Fc receptors gone wrong: A comprehensive review of their roles in autoimmune and inflammatory diseases

Systemic autoimmune and inflammatory diseases have a complex and only partially known pathophysiology with various abnormalities involving all the components of the immune system. Among these components, antibodies, and especially autoantibodies are key elements contributing to autoimmunity. The interaction of antibody fragment crystallisable (Fc) and several distinct receptors, namely Fc receptors (FcRs), have gained much attention during the recent years, with possible major therapeutic perspectives for the future. The aim of this review is to comprehensively describe the known roles for FcRs (activating and inhibitory FcγRs, neonatal FcR [FcRn], FcαRI, FcεRs, Ro52/tripartite motif containing 21 [Ro52/TRIM21], FcδR, and the novel Fc receptor-like [FcRL] family) in systemic autoimmune and inflammatory disorders, namely rheumatoid arthritis, Sjögren's syndrome, systemic lupus erythematosus, systemic sclerosis, idiopathic inflammatory myopathies, mixed connective tissue disease, Crohn's disease, ulcerative colitis, immunoglobulin (Ig) A vasculitis, Behçet's disease, Kawasaki disease, IgG4-related disease, immune thrombocytopenia, autoimmune hemolytic anemia, antiphospholipid syndrome and heparin-induced thrombocytopenia.

Isoniazid-induced Immune Thrombocytopenia

Drug-induced thrombocytopenia occurs through immune-mediated platelet destruction, and its management is challenging during tuberculosis treatment. Although rifampicin is the most common drug causing thrombocytopenia, isoniazid can also cause thrombocytopenia. We herein report a 75-year-old man who developed thrombocytopenia during tuberculosis treatment. Platelet-associated immunoglobulin G and a drug-induced lymphocyte stimulation test for isoniazid were positive; no other causes of thrombocytopenia were identified. The patient was diagnosed with isoniazid-induced immune thrombocytopenia, and the platelet count normalized after isoniazid discontinuation. We describe the immunological mechanism of thrombocytosis due to isoniazid, an uncommon cause of thrombocytopenia that physicians should be aware exists.

Use of bioinformatic analyses in identifying characteristic genes and mechanisms active in the progression of idiopathic thrombocytopenic purpura in individuals with different phenotypes

OBJECTIVE

To explore the mechanism underlying the progression of newly diagnosed idiopathic thrombocytopenic purpura (ITP) to its chronic or remission state using bioinformatic methods.

METHODS

GSE56232 and GSE46922 gene expression profile datasets were downloaded from Gene Expression Omnibus (GEO). Differentially expressed genes were identified and characteristic genes were screened by weighted gene co-expression network analysis. These genes were used for function enrichment analysis and construction of a protein-protein interaction network. Finally, characteristic genes were verified to determine potential molecular mechanisms underlying ITP progression.

RESULTS

We found that characteristic genes in the chronic ITP group were mainly involved in intracellular processes and ion binding, while characteristic genes in the remission ITP group were involved in intracellular processes and nuclear physiological activities. We identified a sub-network of characteristic genes, LMNA, JUN, PRKACG, SMC3, which may indicate the mechanism by which newly diagnosed ITP progresses to chronic. Although no meaningful signaling pathways were found, the expression of NR3C1, TPR, SMC4, PANBP2, CHD1, and U2SURP may affect ITP progression from newly diagnosed to remission.

CONCLUSION

Our findings improve the understanding of the pathogenesis and progression of ITP, and may provide new directions for the development of treatment strategies.

Fostamatinib for the treatment of chronic immune thrombocytopenia

Fostamatinib is a spleen tyrosine kinase inhibitor recently approved for the treatment of chronic immune thrombocytopenia (ITP) in patients without adequate response to at least 1 prior line of therapy. This article reviews fostmatinib's mechanism of action and its clinical safety and efficacy in 2 industry-sponsored multicenter phase 3 randomized controlled trials in North America, Australia, and Europe (FIT1 and FIT2). Cost comparisons are discussed as well as the role of fostamatinib in relation to other options for chronic ITP.

Recent progress in understanding the pathogenesis of immune thrombocytopenia

PURPOSE OF REVIEW

Immune thrombocytopenia (ITP) is a bleeding disorder in which both antibody and cell-mediated autoimmune responses are directed against an individual's own platelets and/or megakaryocytes, leading to either enhanced platelet destruction and/or reduced platelet production, respectively. The cause of this platelet-specific autoimmunity remains unknown, but there has been a constant stream of recent publications that suggest ITP is the result of T-cell dysregulation.

RECENT FINDINGS

In the last 18 months, a rich tapestry of studies has emerged that seems to clarify some immunopathologic issues in ITP while raising new questions related to ITP pathogenesis. The current view on the immunopathogenic mechanisms associated with ITP appears to particularly concentrate on how incompetent CD4+ T-regulatory cells (Tregs) allow autoimmune effector mechanisms to proceed and cause thrombocytopenia. There is a parallel body of recent literature focusing on molecular mimicry mechanisms, B-cell abnormalities, abnormal cytokine patterns and genetic studies in ITP. Of interest, one can recognize inter-relationships between these immune dysregulations.

SUMMARY

This article will discuss the literature from the past 18 months pertaining to these observations and will show that whereas many of the T-cell defects have been clarified, new questions have also come to light and more immunopathological research is warranted.

ITP: Tregs come to the rescue

In this issue of Blood, Bao et al report an increase in regulatory T-cell activity in patients with ITP treated with thrombopoietin receptor (TPO-R) agonists.1 This finding implies that TPO-R agonists may have an unexpected immune-regulatory activity. If this is indeed the case, the mechanism by which TPO-R agonists could perform such a function is currently unclear.