Transient and chronic childhood immune thrombocytopenia are distinctly affected by Fc-γ receptor polymorphisms

Genetic Predisposition to Vaccine-Induced Immune Thrombotic Thrombocytopenia: is there a Family Link?

Background

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a rare life-threatening thrombotic reaction to COVID-19 vaccines.

Case description

Two young male first cousins, with a family history of idiopathic thrombocytopenic purpura, developed VITT after the Ad26.COV2.S vaccine. Both had a favourable clinical and analytical outcome. We investigated the genetic factors that could be associated with a genetic predisposition to VITT.

Conclusions

There are no published cases where the VITT patients were relatives. The genetic study did not reveal any likely pathogenic variants, although the prevalent polymorphism c.497A>G (p.(His166Arg)) in the FCGR2A gene was found in a homozygous state. More studies are required to better understand VITT's pathophysiology and any underlying genetic predispositions.

LEARNING POINTS

Vaccine-induced immune thrombotic thrombocytopenia (VITT), a rare but life-threatening disease, emerged with COVID-19 vaccines.The genetic analyses revealed the FCGR2A gene in a homozygous state.These cases may raise new questions about a family predisposition to VITT.

Intravenous immunoglobulin in chronic inflammatory demyelinating polyradiculoneuropathy (CIDP): mechanisms of action and clinical and genetic considerations

INTRODUCTION

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is an autoimmune peripheral nerve disorder that is characterized by subacute onset, progressive or relapsing weakness, and sensory deficits. Proven treatments include intravenous immunoglobulin (IVIg), corticosteroids, and plasma exchange. This review focuses on the mechanisms of action, pharmacodynamics, genetic variations, and disease characteristics that can affect the efficacy of IVIg.

AREAS COVERED

The proposed mechanisms of action of IVIg that can mediate its therapeutic effects are reviewed. These include anti-idiotypic interactions, inhibition of neonatal Fc receptors (FcRn), anti-complement activity, upregulation of inhibitory FcγRIIB receptors, and downregulation of macrophage activation or co-stimulatory and adhesion molecules. Clinical and genetic factors that can affect the therapeutic response include misdiagnosis, degree of axonal damage, pharmacokinetic variability, and genetic variations.

EXPERT OPINION

The mechanisms of action of IVIg in CIDP and their relative contribution to its efficacy are subject of ongoing investigation. Studies in other autoimmune neurological conditions, in addition, highlight the role of key immunopathological pathways and factors that are likely to be affected. Further investigation into the pathogenesis of CIDP and the mechanisms of action of IVIg may lead to the development of improved diagnostics, better utilization of IVIg, and more targeted and effective therapies.

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.

An update on the pathophysiology of immune thrombocytopenia

: Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder mediated by antiplatelet autoantibodies and antigen-specific T cells that either destroy platelets peripherally in the spleen or impair platelet production in the bone marrow. There have been a plethora of publications relating to the pathophysiology of ITP and since January of 2019, at least 50 papers have been published on ITP pathophysiology.

PURPOSE OF REVIEW

To summarize the literature relating to the pathophysiology of ITP including the working mechanisms of therapies, T-cell and B-cell physiology, protein/RNA/DNA biochemistry, and animal models in an attempt to unify the perceived abnormal immune processes.

RECENT FINDINGS

The most recent pathophysiologic irregularities associated with ITP relate to abnormal T-cell responses, particularly, defective T regulatory cell activity and how therapeutics can restore these responses. The robust literature on T cells in ITP points to the notion that ITP is a disease initiated by faulty self-tolerance mechanisms very much like that of other organ-specific autoimmune diseases. There is also a large literature on new and existing animal models of ITP and these will be discussed. It appears that understanding how to specifically modulate T cells in patients with ITP will undoubtedly lead to effective antigen-specific therapeutics.

CONCLUSIONS

ITP is predominately a T cell disorder which leads to a breakdown in self tolerance mechanisms and allows for the generation of anti-platelet autoantibodies and T cells. Novel therapeutics that target T cells may be the most effective way to perhaps cure this disorder.

A Novel Intraoperative Transient Variant of Immune Thrombocytopenia

Immune thrombocytopenia, also known as immune thrombocytopenic purpura (ITP) is an autoimmune disorder characterized by a very low number of platelets and associated excessive bleeding. Primary ITP is a diagnosis of exclusion and secondary causes of ITP including lymphoproliferative disorders, medications, and certain infections must be ruled out during workup. This is the first report to highlight intraoperative ITP or an ITP-like novel variant in the perioperative setting leading to increased bleeding. The patient's extensive workup failed to reveal any secondary causative factors. The clinical presentation of ITP was transient. She received tranexamic acid (TXA), intravenous steroids, and intravenous immunoglobulins (IVIG) and recovered without complication. This case report explores a potentially underreported cause for intraoperative and postoperative hemorrhage in surgical patients.

Efficacy and safety of rituximab for minors with immune thrombocytopenia: a systematic review and meta-analysis

Objective

We reviewed relevant research on rituximab (RTX) treatment for pediatric immune thrombocytopenia (ITP) to elucidate the efficacy and safety of RTX.

Methods

Prospective clinical trials of RTX for the treatment of pediatric ITP were collected by searching the PubMed, Cochrane Library, Web of Science, and OVID: EMBASE databases and ClinicalTrials.gov. We examined rates of overall response (OR), complete response (CR), partial response (PR), sustained response (SR), relapse (R), and adverse drug reaction (ADR). The Methodological Index for Nonrandomized Studies scale was used, and sensitivity analyses were performed.

Results

For five studies, including 100 patients, the pooled OR, CR, PR, SR, R, and ADR rates were 52% (95% CI: 0.36–0.77, I² = 78%), 52% (95% CI: 0.41–0.67, I² = 45%), 18% (95% CI: 0.10–0.33, I² = 33%), 43% (95% CI: 0.29–0.63, I² = 0%), 25% (95% CI: 0.06–0.96, I² = 52%), and 30% (95% CI: 0.15–0.58, I² = 64%), respectively.

Conclusion

There is evidence, albeit low quality, that RTX may be a better second-line therapy than splenectomy for children with ITP; however, its efficacy and safety need to be validated by further high-quality clinical trials, such as randomized controlled trials.

Platelet FcγRIIA in immunity and thrombosis: Adaptive immunothrombosis

Sepsis and autoimmune diseases remain major causes of morbidity and mortality. The last decade has seen a new appreciation of platelets in host defense, in both immunity and thrombosis. Platelets are first responders in the blood to microbes or non-microbial antigens. The role of platelets in physiologic immunity is counterbalanced by their role in pathology, for example, microvascular thrombosis. Platelets encounter microbes and antigens via both innate and adaptive immune processes; platelets also help to shape the subsequent adaptive response. FcγRIIA is a receptor for immune complexes opsonized by IgG or pentraxins, and expressed in humans by platelets, granulocytes, monocytes and macrophages. With consideration of the roles of IgG and Fc receptors, the host response to microbes and autoantigens can be called adaptive immunothrombosis. Here we review newer developments involving platelet FcγRIIA in humans and humanized mice in immunity and thrombosis, with special attention to heparin-induced thrombocytopenia, systemic lupus erythematosus, and bacterial sepsis. Human genetic diversity in platelet receptors and the utility of humanized mouse models are highlighted.

Immune thrombocytopenia: A review of upfront treatment strategies

Immune thrombocytopenia (ITP), resulting from antibody-mediated platelet destruction combined with impaired platelet production, is a rare cause of thrombocytopenia in both children and adults. The decision to treat newly diagnosed patients is based on several factors, including the desire to increase platelet count to prevent bleeding, induce remission, and improve health-related quality of life (HRQoL). At present, standard first-line therapy is corticosteroids. While this treatment does increase the platelet count in many patients, a high percentage still relapse after discontinuation of therapy. For this reason, alteration or intensification of first-line therapy that results in superior long-term remission rates is desirable. The objective of this review is to outline different upfront strategies for newly diagnosed patients with ITP in an effort to potentially enhance remission rates and prevent relapse, taking into account an assessment of the risks and benefits of each approach. We primarily focus on adults with ITP, highlighting pediatric data and practice when applicable.

Immune Thrombocytopenia (ITP): Current Limitations in Patient Management

Primary immune thrombocytopenia (ITP) is an acquired autoimmune disorder characterized by isolated thrombocytopenia caused by increased platelet destruction and impaired platelet production. First-line therapies include corticosteroids, intravenous immunoglobulin, and anti-D immunoglobulin. For patients who are refractory to these therapies, those who become corticosteroid dependent, or relapse following treatment with corticosteroid, options include splenectomy, rituximab, and thrombopoietin-receptor agonists, alongside a variety of additional immunosuppressive and experimental therapies. Despite recent advances in the management of ITP, many areas need further research. Although it is recognized that an assessment of patient-reported outcomes in ITP is valuable to understand and guide treatment, these measures are not routinely measured in the clinical setting. Consequently, although corticosteroids are first-line therapies for both children and adults, there are no data to suggest that corticosteroids improve health-related quality of life or other patient-related outcomes in either children or adults. In fact, long courses of corticosteroids, in either children or adults, may have a negative impact on a patient's health-related quality of life, secondary to the impact on sleep disturbance, weight gain, and mental health. In adults, additional therapies may be needed to treat overt hemorrhage, but unfortunately the results are transient for the majority of patients. Therefore, there is a need to recognize the limitations of current existing therapies and evaluate new approaches, such as individualized treatment based on the probability of response and the size of effect on the patient's most bothersome symptoms and risk of adverse effects or complications. Finally, a validated screening tool that identifies clinically significant patient-reported outcomes in routine clinical practice would help both patients and physicians to effectively follow a patient's health beyond simply treating the laboratory findings and physical symptoms of ITP. The goal of this narrative review is to discuss management of newly diagnosed and refractory patients with ITP, with a focus on the limitations of current therapies from the patient's perspective.

Outcomes of Eltrombopag Treatment and Development of Iron Deficiency in Children with Immune Thrombocytopenia in Turkey

Objective

Immune thrombocytopenia (ITP) is a rare autoimmune disease and hematologic disorder characterized by reduced platelet counts that can result in significant symptoms, such as bleeding, bruising, epistaxis, or petechiae. The thrombopoietin receptor agonist eltrombopag (EPAG) is a second-line agent used to treat chronic ITP purpura in adults and children.

Materials and Methods

The present retrospective study evaluated the efficacy, safety, and side effects of EPAG treatment in pediatric patients with acute refractory and chronic immune thrombocytopenia, particularly focusing on iron-deficiency anemia.

Results

The diagnosis was chronic ITP in 89 patients and acute refractory ITP in 16 patients. The mean age of patients was 9.5±4.5 years (minimum-maximum: 1.2-18 years) at the beginning of EPAG treatment. The overall response rate was 74.3% (n=78). The mean time for platelet count of ≥50x109/L was 11.6±8 weeks (range: 1-34 weeks). The treatment was stopped for 27 patients (25.7%) at an average of 6.8±9 months (range: 1-38 months). The reason for discontinuation was lack of response in 18 patients, nonadherence in 4 patients, and hepatotoxicity in 2 patients. Response to treatment continued for an average of 4 months after cessation of EPAG in 3 patients.

Conclusion

Results of the current study imply that EPAG is an effective therapeutic option in pediatric patients with acute refractory and chronic ITP. However, patients must be closely monitored for response and side effects during treatment, and especially for iron deficiency.

The association and functional relevance of genetic variation in low-to-medium-affinity Fc-gamma receptors with clinical platelet transfusion refractoriness

BACKGROUND

Inadequate responses to platelet transfusions (i.e., platelet transfusion refractoriness [PLT refractoriness]) are a serious problem. Multiple factors contribute to low yields upon platelet transfusion, among which are platelet-reactive allo-antibodies. Platelet-reactive allo-antibodies occur in up to 30% of patients receiving multiple transfusions, and presumably lead to rapid destruction of the transfused platelets via receptors for IgG, the Fc-gamma receptors (FcγRs). Genetic variation in FcγRs is associated with susceptibility to immune thrombocytopenia, in which autoantibodies against platelets cause thrombocytopenia.

OBJECTIVES

We hypothesized that genetic variation in FcγRs may also influence PLT refractoriness in allo-immunized patients and could help in identifying the patients at risk.

PATIENTS/METHODS

Patients with severe PLT refractoriness for whom diagnostic testing for allo-immunization was requested in the period of 2005 to 2013 were retrospectively included. A case-control study was performed comparing patients in whom platelet-reactive antibodies were detected (n = 181) with ethnically matched healthy controls (n = 180) to determine differences in all known functional copy number variations and single nucleotide polymorphisms in FcγRs.

RESULTS AND CONCLUSIONS

None of the tested FcγR genetic variations seemed associated with the development of severe PLT refractoriness. In contrast to observations in immune thrombocytopenia, genetic variation in FcγRs does not seem to influence the chance to develop PLT refractoriness. Our results do not support determination of FcγR genetic background as a means to identify patients most at risk for PLT refractoriness.

Anti-platelet antibodies in childhood immune thrombocytopenia: Prevalence and prognostic implications

BACKGROUND

Anti-platelet antibody testing may be useful for the diagnosis and management of childhood immune thrombocytopenia (ITP).

OBJECTIVES

Here we aimed to assess the prevalence and prognostic significance of anti-platelet glycoprotein-specific IgM and IgG antibodies.

METHODS

Children with newly diagnosed ITP were included at diagnosis and randomized to an intravenous immunoglobulins (IVIg) or careful observation group (TIKI trial). In this well-defined and longitudinally followed cohort (N = 179), anti-platelet glycoprotein-specific IgM and IgG antibodies were determined by monoclonal antibody-immobilization of platelet antigens.

RESULTS

The dominant circulating anti-platelet antibody class in childhood ITP was IgM (62% of patients); but IgG antibodies were also found (10%). Children without IgM platelet antibodies were older and more often female. There was weak evidence for an association between IgM anti-GP IIb/IIIa antibodies and an increased bleeding severity (P = .03). The IgM and IgG anti-platelet responses partially overlapped, and reactivity was frequently directed against multiple glycoproteins. During 1-year follow-up, children with IgM antibodies in the observation group displayed a faster platelet recovery compared to children without, also after adjustment for age and preceding infections (P = 7.1 × 10-5 ). The small group of patients with detectable IgG anti-platelet antibodies exhibited an almost complete response to IVIg treatment (N = 12; P = .02), suggesting that IVIg was particularly efficacious in these children.

CONCLUSIONS

Testing for circulating anti-platelet antibodies may be helpful for the clinical prognostication and the guidance of treatment decisions in newly diagnosed childhood ITP. Our data suggest that the development of even more sensitive tests may further improve the clinical value of antibody testing.

Genetic Variation in Low-To-Medium-Affinity Fcγ Receptors: Functional Consequences, Disease Associations, and Opportunities for Personalized Medicine

Fc-gamma receptors (FcγR) are the cellular receptors for Immunoglobulin G (IgG). Upon binding of complexed IgG, FcγRs can trigger various cellular immune effector functions, thereby linking the adaptive and innate immune systems. In humans, six classic FcγRs are known: one high-affinity receptor (FcγRI) and five low-to-medium-affinity FcγRs (FcγRIIA, -B and -C, FcγRIIIA and -B). In this review we describe the five genes encoding the low-to-medium -affinity FcγRs (FCGR2A, FCGR2B, FCGR2C, FCGR3A, and FCGR3B), including well-characterized functionally relevant single nucleotide polymorphisms (SNPs), haplotypes as well as copy number variants (CNVs), which occur in distinct copy number regions across the locus. The evolution of the locus is also discussed. Importantly, we recommend a consistent nomenclature of genetic variants in the FCGR2/3 locus. Next, we focus on the relevance of genetic variation in the FCGR2/3 locus in auto-immune and auto-inflammatory diseases, highlighting pathophysiological insights that are informed by genetic association studies. Finally, we illustrate how specific FcγR variants relate to variation in treatment responses and prognosis amongst autoimmune diseases, cancer and transplant immunology, suggesting novel opportunities for personalized medicine.