Suppression of in vitro megakaryocyte production by antiplatelet autoantibodies from adult patients with chronic ITP

Treatment practices in adults with chronic immune thrombocytopenia - a European perspective

Immune thrombocytopenia (ITP) is characterised by platelet destruction and impaired production leading to isolated thrombocytopenia. The aim of this study, comprising a retrospective longitudinal cohort study complemented by a Delphi panel of 35 physicians, was to describe standard treatment practices and treating physician's perception and preferences for available treatment options in chronic ITP. The medical records of 610 patients were reviewed over 12 months. Mean age at the start of the observational period was 54.6 yr, median platelet count 77 x 10(9)/L with 41% of patients having symptoms of ITP. Treated patients (61%) received an average of 2.7 medications either for ITP or ITP treatment-related side effects. An array of products was used, but the most frequent were corticosteroids. Delphi panel physicians (45%) indicated the main goals for treatment were to increase platelet levels to at least 30 x 10(9)/L to prevent bleeding or haemorrhage. The majority (89%) indicated that personal experience influenced treatment choice. Most (>80%) rated splenectomy and high-dose corticosteroids as the most effective but were concerned about side effects, and many (75%) would like access to interventions with improved efficacy and safety. The study highlights the need for updated evidence-based treatment guidelines to assist physicians in patient treatment decisions and to realise improvements in patient outcomes. It also identified perceived shortcomings of existing therapies and the need to establish an evidence base for newer interventions that could potentially make lasting response to treatment with fewer adverse effects an achievable goal.

Repeated courses of rituximab in chronic ITP: Three different regimens

This study investigated responses to retreatment with rituximab in chronic immune thrombocytopenic purpura (ITP) patients. Treatment with rituximab in chronic ITP patients induces long-lasting responses in approximately 30% of patients but even these patients may relapse. Twenty patients who had achieved a response to rituximab and relapsed were retreated with rituximab (375 mg/m(2)x 4); this data was analyzed retrospectively. Subsequently, 16 patients were prospectively randomized to receive rituximab with cyclophosphamide, vincristine and prednisone (R-CVP) or double dose rituximab (DDR). Retreatment with standard dose rituximab demonstrated responses similar to initial rituximab treatment in 15 of 20 patients. Neither of the two more intensive regimens (R-CVP, DDR) induced responses in any patient who had previously failed to respond to rituximab nor induced substantially longer-lasting responses among previous responders. No additional toxicity was noted with the DDR regimen, whereas R-CVP was not well tolerated. These results suggest that retreatment with standard dose rituximab induces similar responses in 75% of previously responding patients and is well tolerated. Neither combining rituximab with CVP nor doubling the dose of rituximab increased the response rate.

The thrombocytopenia of WAS: a familial form of ITP?

In the first report of the concurrent immunodeficiency, thrombocytopenia, and eczema that we now call the Wiskott-Aldrich Syndrome (WAS), Alfred Wiskott asked whether it could be a familial form of Werlhof's disease (now called ITP). This review summarizes what is known about platelet production, consumption, and function in clinical and murine WAS. Both platelet production and consumption are affected by WASP deficiency. Likely molecular mechanisms have been identified for the former process, but remain problematic for the latter. Recent data in a murine model suggest that WASP deficiency could increase both the incidence of antiplatelet antibodies and susceptibility to their enhancement of platelet consumption. Wiskott's original speculation about the relationship between WAS and ITP may need to be reconsidered.

Treatment of immune thrombocytopenic purpura: focus on eltrombopag

Immune thrombocytopenic purpura (ITP) is a relatively common autoimmune disorder in which antibodies are produced to circulating platelets. Symptoms can be mild, but for most patients the risk of severe bleeding is unacceptable and treatment is required. Glucocorticoids followed by splenectomy had been the mainstays of therapy. High dose intravenous immunoglobulin and anti-RhD therapy are available for patients with severe illness, but produce only temporary benefit. Rituximab may provide more durable responses, danazol may be underutilized, and immunosuppressants and cytotoxic agents are less often required. Recently the pathophysiology of ITP has been more clearly elucidated, particularly the importance of decreased production of platelets in most patients and the very blunted rise that occurs in serum thrombopoietin (TPO). The isolation of TPO and better understanding of its role in thrombopoiesis has led to the development of new highly effective treatments. TPO analogs had some successes in treating highly refractory ITP patients but were taken out of development due to TPO-antibody induction. Two second-generation TPO-mimetics, romiplostim and the orally available eltrombopag, have recently been licensed in some territories for the treatment of ITP. Approval of eltrombopag was based on results from Phase II and III placebo-controlled clinical trials and a long-term extension study. About 80% of patients achieve significant increases in platelet count (11% of placebo patients), with reduced bleeding and reduced use of concomitant medications; responses are often durable with no tachyphylaxis. The side effects of eltrombopag are generally mild and not worse than placebo, although there are concerns about hepatic dysfunction, and the potentials for thromboses, marrow reticulin fibrosis, rebound thrombocytopenia and cataracts. This is an important new option for highly refractory patients, and its niche in earlier treatment (and for other thrombocytopenic disorders) is yet to be defined.

Validity of a procedure to identify patients with chronic idiopathic thrombocytopenic purpura in the Danish National Registry of Patients

BACKGROUND

Administrative data may be useful for epidemiological studies of chronic idiopathic thrombocytopenic purpura (ITP). However, the quality of the recorded diagnoses needs evaluation.

AIM

We evaluated the validity in predicting chronic ITP of the International Classification of Diseases (ICD)-10 diagnoses of ITP in the Danish National Registry of Patients (NRP).

METHODS

We used the NRP to identify patients with ITP, according to code D69.3, from January 1, 1996 to December 31, 2007. We defined chronic ITP as lasting longer than 6 months by including only patients with 2 or more hospital ITP diagnoses over longer than 6 months. We confirmed diagnoses by evaluating each candidate chronic ITP patient's medical chart and estimating the positive predictive value (PPV) and 95% confidence interval (CI) of the recorded NRP diagnostic code.

RESULTS

We identified 513 patients with chronic ITP in the NRP. We were able to retrieve the charts of 439. After evaluation of the charts, 410 patients were deemed to have a valid diagnosis of chronic ITP, yielding a PPV of 0.93 (95% CI: 0.91-0.96).

CONCLUSION

The validity of this procedure to identify chronic ITP patients was high. The NRP is valid for epidemiological studies of patients with chronic ITP.

Development of thrombopoietin receptor agonists for clinical use

Thrombopoietin (TPO) is an essential hematopoietic cytokine for megakaryopoiesis. In 2002, we demonstrated that pegylated-recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF) increased platelet counts in patients with chronic immune thrombocytopenic purpura (ITP) in a Phase I/II clinical trial. After the cessation of clinical trials of PEG-rHuMGDF because of severe thrombocytopenia or pancytopenia due to the development of the neutralizing antibody cross-reacting with endogenous TPO, second generation non-immunogenic TPO receptor agonists have been developed. A small molecule eltrombopag and Romiplostim were approved for clinical use by FDA in 2008 to treat patients with chronic ITP who are refractory to the prior therapy. Although the efficacy of both TPO receptor agonists is convincing for the refractory ITP, further investigation is necessary to assess the potential long-term side effects and clinical applications of these therapies for other thrombocytopenic conditions.

Risk of cataract among idiopathic thrombocytopenic purpura patients in the UK general practice research database

PURPOSE

To estimate the incidence of cataracts in an adult idiopathic thrombocytopenic purpura (ITP) and in a comparable non-ITP population, stratified by age, gender and medication use in order to determine whether the risk of cataracts is greater in ITP patients.

METHODS

Retrospective cohort of 745 newly diagnosed ITP patients and 3725 non-ITP subjects who were 18 years of age or older. The study population included patients registered on the General Practice Research Database (GPRD) during the period 1992-2005. ITP patients, identified using Read/Oxmis codes, were matched to five non-ITP patients. The exposure of interest was oral systemic steroid use and the primary outcome was cataracts.

RESULTS

The overall incidence rate of cataracts in males was 11.8 per 1000 PY (95%CI: 6.3-20.2) and in females 9.0 per 1000 PY (95%CI: 5.2-14.4). In the non-ITP population these rates were 14.0 per 1000 PY (95%CI: 11.0-17.4) and 8.1 per 1000 PY (95%CI: 6.4-10.1), respectively. In the ITP population, users of oral steroids (OS) had a cataract incidence rate of 14.0 per 1000 PY (95%CI: 8.7-21.4) and non-users 6.0 per 1000 PY (95%CI: 2.8-11.4). In the non-ITP population, these rates were 16.9 per 1000 PY (95%CI: 11.9-23.3) and 9.2 per 1000 PY (95%CI: 7.6-11.0), respectively. OS were associated with an increased risk for cataracts.

CONCLUSIONS

The rates of cataract in an adult ITP population are comparable to that in a non-ITP population.

Pathobiology of secondary immune thrombocytopenia

Primary immune thrombocytopenic purpura (ITP) remains a diagnosis of exclusion both from nonimmune causes of thrombocytopenia and immune thrombocytopenia that develops in the context of other disorders (secondary immune thrombocytopenia). The pathobiology, natural history, and response to therapy of the diverse causes of secondary ITP differ from each other and from primary ITP, so accurate diagnosis is essential. Immune thrombocytopenia can be secondary to medications or to a concurrent disease, such as an autoimmune condition (eg, systemic lupus erythematosus [SLE], antiphospholipid antibody syndrome [APS], immune thyroid disease, or Evans syndrome), a lymphoproliferative disease (eg, chronic lymphocytic leukemia or large granular T-lymphocyte lymphocytic leukemia), or chronic infection, eg, with Helicobacter pylori, human immunodeficiency virus (HIV), or hepatitis C virus (HCV). Response to infection may generate antibodies that cross-react with platelet antigens (HIV, H pylori) or immune complexes that bind to platelet Fcγ receptors (HCV), and platelet production may be impaired by infection of megakaryocyte (MK) bone marrow–dependent progenitor cells (HCV and HIV), decreased production of thrombopoietin (TPO), and splenic sequestration of platelets secondary to portal hypertension (HCV). Sudden and severe onset of thrombocytopenia has been observed in children after vaccination for measles, mumps, and rubella or natural viral infections, including Epstein-Barr virus, cytomegalovirus, and varicella zoster virus. This thrombocytopenia may be caused by cross-reacting antibodies and closely mimics acute ITP of childhood. Proper diagnosis and treatment of the underlying disorder, where necessary, play an important role in patient management.

Pathogenesis of chronic immune thrombocytopenia: increased platelet destruction and/or decreased platelet production

Chronic immune thrombocytopenia (ITP) is a haematological disorder in which patients predominantly develop skin and mucosal bleeding. Early studies suggested ITP was primarily due to immune-mediated peripheral platelet destruction. However, increasing evidence indicates that an additional component of this disorder is immune-mediated decreased platelet production that cannot keep pace with platelet destruction. Evidence for increased platelet destruction is thrombocytopenia following ITP plasma infusions in normal subjects, in vitro platelet phagocytosis, and decreased platelet survivals in ITP patients that respond to therapies that prevent in vivo platelet phagocytosis; e.g., intravenous immunoglobulin G, anti-D, corticosteroids, and splenectomy. The cause of platelet destruction in most ITP patients appears to be autoantibody-mediated. However, cytotoxic T lymphocyte-mediated platelet (and possibly megakaryocyte) lysis, may also be important. Studies supporting suppressed platelet production include: reduced platelet turnover in over 80% of ITP patients, morphological evidence of megakaryocyte damage, autoantibody-induced suppression of in vitro megakaryocytopoiesis, and increased platelet counts in most ITP patients following treatment with thrombopoietin receptor agonists. This review summarizes data that indicates that the pathogenesis of chronic ITP may be due to both immune-mediated platelet destruction and/or suppressed platelet production. The relative importance of these two mechanisms undoubtedly varies among patients.

Eltrombopag: A Thrombopoietin Receptor Agonist for Idiopathic Thrombocytopenic Purpura

Objective:

To review the pharmacology, pharmacokinetics, safety, and efficacy of eltrombopag in previously treated patients with chronic idiopathic thrombocytopenic purpura (ITP).

Data Sources:

Articles were identified through a search of the MEDLINE (1950–December 2008) database for English-language articles containing the key words eltrombopag, SB-497115, idiopathic thrombocytopenic purpura, and immune thrombocytopenic purpura. References from publications identified in this search were reviewed for relevant information. Unpublished data received from the manufacturer was also included in this review.

Study Selection and Data Extraction:

All articles identified from the data search were reviewed for relevant information. Applicable information was included in this review.

Data Synthesis:

Eltrombopag is a new oral thrombopoietic receptor agonist approved by the FDA in November 2008 as second-line treatment of chronic ITP. It stimulates human megakaryocyte differentiation and proliferation, leading to increased platelet production. Eltrombopag has been shown in clinical trials to increase platelet counts in a dose-dependent manner regardless of splenectomy status, baseline platelet counts, and concurrent ITP therapy. Available data show a statistically significant decrease in the incidence of any bleeding (World Health Organization Grades 1–4) and clinically significant bleeding (Grades 2–4). Common adverse effects are mild and typically do not lead to treatment discontinuation. Results from clinical studies demonstrated significant increase in platelet counts with minimal adverse effects.

Conclusions:

Eltrombopag treatment provides a potential new resource for clinicians to use in the pharmacotherapy of ITP. Further studies are needed to explore its long-term safety and efficacy in patients with chronic ITP.

ACPE Universal Program Number:

407-000-09-054-H01-P (Pharmacists)

The ITP syndrome: pathogenic and clinical diversity

Immune thrombocytopenia (ITP) is mediated by platelet autoantibodies that accelerate platelet destruction and inhibit their production. Most cases are considered idiopathic, whereas others are secondary to coexisting conditions. Insights from secondary forms suggest that the proclivity to develop platelet-reactive antibodies arises through diverse mechanisms. Variability in natural history and response to therapy suggests that primary ITP is also heterogeneous. Certain cases may be secondary to persistent, sometimes inapparent, infections, accompanied by coexisting antibodies that influence outcome. Alternatively, underlying immune deficiencies may emerge. In addition, environmental and genetic factors may impact platelet turnover, propensity to bleed, and response to ITP-directed therapy. We review the pathophysiology of several common secondary forms of ITP. We suggest that primary ITP is also best thought of as an autoimmune syndrome. Better understanding of pathogenesis and tolerance checkpoint defects leading to autoantibody formation may facilitate patient-specific approaches to diagnosis and management.

Comorbidities of idiopathic thrombocytopenic purpura: a population-based study

A person experiencing more than one medical condition may have ambiguous clinical presentation. ITP is a serious autoimmune disease with little epidemiological evidence on its burden, risk factors, and comorbidities. Using the United Kingdom general practice research database, we conducted a 14 years population-based case control-type study to explore medical conditions more likely to cooccur with ITP and their temporal relationship in association with ITP. ITP patients were matched to non-ITP on practice, age, gender, and follow-up period. Potential comorbidities were represented by patients' medical information at the preferred term level of the MedDRA international classification. As well as death (OR = 60.0; 95% CI [4.47–806.0]) and known clinical signs and symptoms of ITP, ITP is associated with considerable number of medical conditions. The association between ITP and some of these conditions is apparent both before and after ITP diagnosis. Specific targeted studies can now be setup to reexamine observed associations.

Safety and efficacy of long-term treatment with romiplostim in thrombocytopenic patients with chronic ITP

Chronic immune thrombocytopenic purpura (ITP) is characterized by low platelet counts and mucocutaneous bleeding. In previous studies romiplostim (AMG531), a thrombopoiesis-stimulating protein, increased platelet counts in most patients with chronic ITP. This ongoing, long-term open-label, single-arm study investigated safety and efficacy in patients who completed a previous romiplostim study and had platelet counts less than or equal to 50 [corrected] x 10(9)/L. One hundred forty-two patients were treated for up to 156 weeks (mean, 69 weeks). Platelet responses (platelet count > or = 50 x 10(9)/L and double baseline) were observed in 87% of all patients and occurred on average 67% of the time in responding patients. In 77% of patients, the romiplostim dose remained within 2 microg/kg of their most frequent dose at least 90% of the time. Ninety patients (63%) received treatment by self-administration. Treatment-related serious adverse events were reported in 13 patients (9%). Bone marrow reticulin was observed in 8 patients; marrows were not routinely performed in this study, so the true incidence of this event cannot be determined. Severe bleeding events were reported in 12 patients (9%). Thrombotic events occurred in 7 patients (5%). In conclusion, romiplostim increased platelet counts in most patients for up to 156 weeks without tachyphylaxis and had an acceptable safety profile. (ClinicalTrials.gov Identifier NCT00116688).

Decreased DNA methyltransferase 3A and 3B mRNA expression in peripheral blood mononuclear cells and increased plasma SAH concentration in adult patients with idiopathic thrombocytopenic purpura

OBJECTIVE

DNA methylation is known to play an important role in gene transcription and alterations of methylation contribute to the development of certain disorders such as cancer and immunodeficiency. Recent years have found an increasing interest in the role of epigenetic modifications in the etiology of human autoimmune diseases, such as systemic lupus erythromatosus (SLE) and rheumatoid arthritis (RA). DNA methyltransferases (DNMTs) are involved in the epigenetic control of DNA methylation processes. S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH), as the substrate and product of essential cellular methyltransferase reactions, have important indicator action of cellular methylation status. The aim of this study is to explore if DNA methylation plays a role in the pathogenesis of idiopathic thrombocytopenic purpura (ITP).

METHODS

DNMT1, DNMT3A, and DNMT3B mRNA expression in peripheral blood mononuclear cells (PBMCs) of adult ITP patients were analyzed by real-time quantitative polymerase chain reaction. Plasma SAM and SAH levels were assayed with reversed-phase high performance liquid chromatography (HPLC).

RESULTS

DNMT3A and DNMT3B mRNA expressions were significantly lower in ITP patients than in healthy controls (p < 0.001), while DNMT1 mRNA expression was not significantly different between the two groups (p = 0.774). Plasma SAH concentration was significantly elevated in ITP patients than in healthy controls (p < 0.05), while the plasma SAM and SAM/SAH were not significantly different between the two groups (p = 0.133, p = 0.624 respectively).

CONCLUSIONS

Our observations suggest that aberrant DNA methylation status reflected by increased plasma SAH concentration and decreased mRNA expression levels of DNMT3A and 3B are possibly involved in the pathogenesis of ITP although the precise mechanisms need further study.

Platelet production rate predicts the response to prednisone therapy in patients with idiopathic thrombocytopenic purpura

The predictive value of clinical and platelet kinetic parameters for treatment outcome in idiopathic thrombocytopenic purpura (ITP) was investigated in 75 patients with platelets<or=20x10(9)/L. The platelet kinetic studies showed that the platelet production rate (PPR) was decreased (<100x10(9)/day), normal, or increased (>355x10(9)/day) in 33%, 48%, and 19% of patients, respectively. All patients started with prednisone at diagnosis (1 mg/kg/day). Initial complete and partial response (CR/PR) rate was 84% and a durable CR/PR (>or=6 months without treatment) was attained in 44% of the patients. Durable CR/PR was noticed in 64% of the patients with decreased PPR during a median follow-up time without treatment of 81 (range 18-92) months, compared to 34% of the patients with normal or increased PPR during a median follow-up time without treatment of 141 (range 10-284) months (p=0.03). Splenectomy was performed in 32% of patients with decreased PPR and in 62% of patients with normal or increased PPR (p=0.03). In conclusion, ITP patients with suppressed PPR have a significant higher durable CR/PR rate to prednisone therapy and are less frequently exposed to splenectomy than those with a normal or increased PPR.

Compromised ITAM-based platelet receptor function in a patient with immune thrombocytopenic purpura

BACKGROUND

Receptors on platelets that contain immunoreceptor tyrosine-based activation motifs (ITAMs) include collagen receptor glycoprotein (GP) VI, and FcgammaRIIa, a low affinity receptor for immunoglobulin (Ig) G.

OBJECTIVES

We examined the function of GPVI and FcgammaRIIa in a patient diagnosed with immune thrombocytopenic purpura (ITP) who had unexplained pathological bruising despite normalization of the platelet count with treatment.

METHODS AND RESULTS

Patient platelets aggregated normally in response to ADP, arachadonic acid and epinephrine, but not to GPVI agonists, collagen or collagen-related peptide, or to FcgammaRII-activating monoclonal antibody (mAb) 8.26, suggesting ITAM receptor dysfunction. Plasma contained an anti-GPVI antibody by MAIPA and aggregated normal platelets. Aggregating activity was partially (approximately 60%) blocked by FcgammaRIIa-blocking antibody, IV.3, and completely blocked by soluble GPVI ectodomain. Full-length GPVI on the patient platelet surface was reduced to approximately 10% of normal levels, and a approximately 10-kDa GPVI cytoplasmic tail remnant and cleaved FcgammaRIIa were detectable by western blot, indicating platelet receptor proteolysis. Plasma from the patient contained approximately 150 ng mL(-1) soluble GPVI by ELISA (normal plasma, approximately 15 ng mL(-1)) and IgG purified from patient plasma caused FcgammaRIIa-mediated, EDTA-sensitive cleavage of both GPVI and FcgammaRIIa on normal platelets.

CONCLUSIONS

In ITP patients, platelet autoantibodies can curtail platelet receptor function. Platelet ITAM receptor dysfunction may contribute to the increased bleeding phenotype observed in some patients with ITP.

Recruitment of T cells into bone marrow of ITP patients possibly due to elevated expression of VLA-4 and CX3CR1

In idiopathic thrombocytopenic purpura (ITP), platelets are destroyed in the spleen, liver, and bone marrow (BM) by autoantibodies and cytotoxic T cells. In a DNA microarray screen of peripheral blood T cells, we found that VLA-4, CX3CR1, and CXCR4, involved in T-cell homing, had increased expression in ITP patients compared with controls. However, we only found increased protein expression of VLA-4 on T cells from peripheral blood by flow cytometry. To address a possible recruitment of T cells into the organs involved in platelet destruction, we analyzed T cells in BM. In BM, T-cell surface expression of VLA-4 and CX3CR1 was increased in ITP patients compared with controls. Furthermore, the number of CD3(+) T cells in BM, but not in blood, was increased in ITP patients compared with controls. This finding was confirmed by immunohistochemistry of BM biopsies. The number of regulatory T cells (CD4(+)/CD25(bright)) was decreased in the BM of ITP patients, whereas Fas expression was increased. In conclusion, ITP is associated with accumulation and activation of T cells in the BM. Recruitment of T cells into the target organ (eg, BM) is plausible and may be facilitated through increased VLA-4 and CX3CR1 expression. These molecules might serve as new treatment targets in ITP.

Effect of eradication of Helicobacter pylori on platelet recovery in patients with chronic idiopathic thrombocytopenic purpura: a controlled trial

Several recent studies have suggested that an association exists between Helicobacter pylori (HP) eradication and improvement in platelet count in a significant proportion of patients with idiopathic thrombocytopenic purpura (ITP). In this controlled study, we prospectively examined adult patients with chronic ITP for HP infection, and assessed the effect of HP eradication on platelet count. One hundred forty-two consecutive Iranian patients with chronic ITP were assessed. Those who met the criteria and had platelet counts >30 x 10(9)/L within the medication-free screening month were enrolled (n = 129; 66 females; mean age, 29.2 +/- 7.0 years). HP-positive patients received a 2-week course of triple HP eradication therapy (i.e., amoxicillin, clarithromycin, and omeprazole) and were followed for 48 weeks. An ITP response was defined as a platelet count of >100 x 10(9)/L 24 weeks after treatment, together with an increase in the platelet count >30 x 10(9)/L over the baseline value. HP infection was detected in 79 (61%) patients. HP-positive patients were significantly older than HP-negative subjects (P = 0.018). HP eradication was successful in 87% (62/71) of those who completed the eradication therapy. Whereas 48% (30/62) of HP-eradicated patients showed an ITP response, no HP-negative patient had an ITP response. The ITP response persisted for 48 weeks in 93% (28/30) of the responders. The ITP responders had a shorter disease duration than the nonresponders (P = 0.002). The management of mild-to-moderate chronic ITP in Iranian patients, especially those with a recent onset of disease, should include an investigation for and eradication of infection with HP.

Management of immune thrombocytopenic purpura in pregnancy

Chronic immune thrombocytopenic purpura (ITP) is an autoimmune disease characterized by a low platelet count and mucocutaneous bleeding. Pregnancy does not increase the incidence of ITP nor does it exacerbate a preexisting disease. Although pregnant women with ITP may experience several maternal and fetal complications, in most cases even with a very low platelet count, there is neither maternal nor fetal morbidity or mortality. Corticosteroids are the first line of therapy in pregnant women; intravenous immune globulin is commonly used in steroid resistant patients. Other treatments such as intravenously administered anti-D (Rhogam) and splenectomy during pregnancy have been reported. Antiplatelet IgG antibodies can cross the placenta and can induce fetal thrombocytopenia. In most women there is no indication to assess fetal platelet counts during the pregnancy. The mode of delivery is determined by obstetrical considerations.

CD8+ T cells suppress autologous megakaryocyte apoptosis in idiopathic thrombocytopenic purpura

To investigate the effect and mechanism of the CD8+ T cells in bone marrow on autologous megakaryocytopoiesis in idiopathic thrombocytopenic purpura (ITP) patients, we prepared bone marrow mononuclear cells (MNCs) from 15 chronic ITP patients and 13 controls. MNCs were cultured in vitro directly (MNC group) or after depleting CD8+ T cells (CD8+ T-dep group) or adding purified autologous CD8+ T cells to CD8+ T-dep MNCs (Coculture group) or adding dexamethasone to the coculture (DEX group) all in semi-solid and liquid culture systems. The quantity and quality of megakaryocytes were measured. The megakaryocyte count was increased in the presence of autologous CD8+ T cells of patients with chronic ITP, while platelet production was reduced. In addition, lower percentages of polyploidy and apoptotic megakaryocytes, and higher levels of soluble Fas (sFas) in supernatant were observed. Dexamethasone successfully corrected this effect of CD8+ T cells on autologous megakaryocytopoiesis. These studies provide evidence that activated CD8+ T cells in bone marrow of patients with chronic ITP might suppress megakaryocyte apoptosis, leading to impaired platelet production. Megakaryocyte apoptosis would be a novel target for the management of ITP.

The pathogenesis of chronic immune thrombocytopenic purpura

Chronic immune thrombocytopenic purpura (ITP) is an autoimmune disorder in which the patient's immune system reacts with a platelet autoantigen(s) resulting in thrombocytopenia due to immune-mediated platelet destruction and/or suppression of platelet production. Platelet membrane proteins, for reasons that are unclear, become antigenic and stimulate the immune system to produce autoantibodies and cytotoxic T cells. The initial antigenic response probably occurs in the spleen followed by stimulation of other antibody-producing tissues, particularly the bone marrow. Autoantibodies against platelet glycoprotein (GP) IIb-IIIa and/or GPIb-IX are produced by the majority of ITP patients and can be detected using antigen-specific assays. Many patients produce multiple antibodies; this has been attributed to the phenomenon of epitope spreading. Once produced, autoantibody may either bind to platelets, causing their destruction by either phagocytosis or possibly complement activation and lysis, or bind to megakaryocytes, resulting in decreased thrombopoiesis. Evidence for platelet destruction in ITP includes the following: (1) infusion of ITP blood or plasma into normal recipients may result in thrombocytopenia; (2) there is decreased intravascular survival of radiolabeled platelets in most ITP patients; (3) morphologic and in vitro evidence of platelet phagocytosis can be demonstrated; and (4) cytotoxic T cells can induce lysis of autologous platelets. Evidence for suppressed platelet production in ITP includes the following: (1) morphologic studies show megakaryocyte damage in most ITP patients; (2) there is normal or decreased platelet turnover in the majority of patients; (3) in vitro studies show antibody-induced inhibition of megakaryocyte production and maturation; and (4) an increase in the platelet count occurs in many ITP patients receiving treatment with thrombopoietin mimetics. In summary, activation of the immune system by platelet autoantigens in ITP may result in platelet destruction and/or inhibition of platelet production. The importance of each mechanism in the individual patient probably varies.

Efficacy of romiplostim in patients with chronic immune thrombocytopenic purpura: a double-blind randomised controlled trial

BACKGROUND

Chronic immune thrombocytopenic purpura (ITP) is characterised by accelerated platelet destruction and decreased platelet production. Short-term administration of the thrombopoiesis-stimulating protein, romiplostim, has been shown to increase platelet counts in most patients with chronic ITP. We assessed the long-term administration of romiplostim in splenectomised and non-splenectomised patients with ITP.

METHODS

In two parallel trials, 63 splenectomised and 62 non-splenectomised patients with ITP and a mean of three platelet counts 30x10(9)/L or less were randomly assigned 2:1 to subcutaneous injections of romiplostim (n=42 in splenectomised study and n=41 in non-splenectomised study) or placebo (n=21 in both studies) every week for 24 weeks. Doses of study drug were adjusted to maintain platelet counts of 50x10(9)/L to 200x10(9)/L. The primary objectives were to assess the efficacy of romiplostim as measured by a durable platelet response (platelet count > or =50x10(9)/L during 6 or more of the last 8 weeks of treatment) and treatment safety. Analysis was per protocol. These studies are registered with ClinicalTrials.gov, numbers NCT00102323 and NCT00102336.

FINDINGS

A durable platelet response was achieved by 16 of 42 splenectomised patients given romplostim versus none of 21 given placebo (difference in proportion of patients responding 38% [95% CI 23.4-52.8], p=0.0013), and by 25 of 41 non-splenectomised patients given romplostim versus one of 21 given placebo (56% [38.7-73.7], p<0.0001). The overall platelet response rate (either durable or transient platelet response) was noted in 88% (36/41) of non-splenectomised and 79% (33/42) of splenectomised patients given romiplostim compared with 14% (three of 21) of non-splenectomised and no splenectomised patients given placebo (p<0.0001). Patients given romiplostim achieved platelet counts of 50x10(9)/L or more on a mean of 13.8 (SE 0.9) weeks (mean 12.3 [1.2] weeks in splenectomised group vs 15.2 [1.2] weeks in non-splenectomised group) compared with 0.8 (0.4) weeks for those given placebo (0.2 [0.1] weeks vs 1.3 [0.8] weeks). 87% (20/23) of patients given romiplostim (12/12 splenectomised and eight of 11 non-splenectomised patients) reduced or discontinued concurrent therapy compared with 38% (six of 16) of those given placebo (one of six splenectomised and five of ten non-splenectomised patients). Adverse events were much the same in patients given romiplostim and placebo. No antibodies against romiplostim or thrombopoietin were detected.

INTERPRETATION

Romiplostim was well tolerated, and increased and maintained platelet counts in splenectomised and non-splenectomised patients with ITP. Many patients were able to reduce or discontinue other ITP medications. Stimulation of platelet production by romiplostim may provide a new therapeutic option for patients with ITP.

Diagnosis, pathophysiology and management of children with refractory immune thrombocytopenic purpura

PURPOSE OF REVIEW

Refractory immune thrombocytopenic purpura is infrequent in children, but carries substantial morbidity and even mortality. Management of these children is controversial despite the availability of several treatment options as these strategies have not been directly compared and there are many definitions for refractory immune thrombocytopenic purpura. This review will provide an update on the pathogenesis, diagnosis and treatment options for children with severe, acute and chronic refractory immune thrombocytopenic purpura.

RECENT FINDINGS

Recent studies have demonstrated a number of immunologic alterations (dominant proinflammatory state, inadequate thrombopoiesis, and various B and T lymphocyte disturbances) in the pathogenesis of chronic immune thrombocytopenic purpura. New agents that target certain of these mechanisms (e.g. anti-CD20 monoclonal antibody, thrombopoietic agents) have shown promising results in recent clinical trials, primarily but not solely in adults.

SUMMARY

Management of refractory immune thrombocytopenic purpura often requires multiple agents that may provide only short-term benefit. Lack of clear views about the use of these medications, their unwanted side effects and an inability to specifically target a particular patient's disease all lead to frustration among patients, family and the physicians. Better understanding of pathogenesis with the availability of newer therapies with different mechanisms of effect should, however, allow improved management of these patients.

The Pathophysiology of ITP Revisited: Ineffective Thrombopoiesis and the Emerging Role of Thrombopoietin Receptor Agonists in the Management of Chronic Immune Thrombocytopenic Purpura

Autoimmune thrombocytopenia (ITP) is characterized by autoantibody-mediated platelet destruction that can be demonstrated by shortened radiolabeled platelet survival. An additional role of ineffective thrombopoiesis was suggested by autologous platelet kinetic studies performed in the 1980s. Sera of patients with ITP have been demonstrated to inhibit megakaryocyte growth in culture supporting the concept of suboptimal platelet production as a contributing factor to the thrombocytopenia. The relatively modest rise in thrombopoietin (TPO) levels in thrombocytopenic patients with ITP has helped to identify the TPO receptor as a potential target for the treatment of ITP. Initial studies with recombinant TPO in patients with ITP were encouraging, and novel compounds designed to stimulate the TPO receptor and resultant pathways have been shown in randomized trials to be effective in raising the platelet count and sustaining it at safe levels. Adverse effects of these agents have been relatively mild, although rare serious events including increased bone marrow reticulin deposition, increased numbers of circulating blasts and thrombosis have occurred, and theoretic risks of stimulation of megakaryocytopoiesis and platelet activation remain a concern. As these agents become available it will be important to identify those patients who will most benefit from their use. The place of these drugs in the current management algorithms of ITP will evolve over time as results of clinical trials with these agents and experience with their use in the clinic clarify short-term and long-term efficacy and potential toxicities.

Pathogenesis of chronic immune thrombocytopenic purpura

PURPOSE OF REVIEW

This article summarizes recent insights into the pathophysiology of immune thrombocytopenic purpura, a disorder in which autoantibodies against cell-specific glycoproteins (GPIIb-IIIa, GPIb-IX and others) accelerate platelet destruction.

RECENT FINDINGS

Autoantibodies are produced by a limited number of B-cell clones. Platelet antibodies may also impair megakaryocyte development and platelet turnover, thromobopoietin levels are normal or only modestly increased and a compensatory increase in platelet production is not effective in many patients. Patients may show impaired immune regulation manifested by increased proliferation of helper T lymphocytes. Cytotoxic T lymphocytes from patients can lyse platelets in vitro. If cytotoxic T lymphocytes are also capable of perturbing megakaryocyte function, this mechanism may contribute to impaired platelet production. Polymorphisms in the Fcgamma-RIIIa gene may correlate with response to certain forms of therapy and similar genetic approaches may help to identify subsets of patients that differ in their natural history and response to various interventions.

SUMMARY

Better understanding of autoantibody development, inhibition of thrombopoiesis and Fcgamma receptor and other polymorphisms will assume increased importance in elucidating the pathogenesis and targeting treatment of chronic immune thrombocytopenic purpura.

Immune thrombocytopenic purpura

Immune thrombocytopenic purpura (ITP) is an autoantibody-mediated thrombocytopenic disorder in which accelerated destruction of platelets occurs; platelet production may also be impaired by these antibodies. ITP is characterized by mucocutaneous bleeding. Rarely, more severe hemorrhages, such as intracranial hemorrhage, may occur. Traditional therapies, such as steroids, immunoglobulin therapy, and splenectomy, generally reduce peripheral destruction of platelets. More recently, with a better understanding of the immunopathologic mechanisms underlying thrombocytopenia, several new treatments have been developed, including thrombopoietic agents, specific inhibitors of Fcgamma receptor (FcgammaR) signaling, and B-cell depletion therapies. This article outlines current understanding of the epidemiology, etiology, diagnosis, and treatment of ITP. The focus is on recent pathophysiologic insights and areas of potential controversy in which studies are ongoing.

New therapeutic options for adult chronic immune thrombocytopenic purpura: a brief review

BACKGROUND

Patients with chronic immune thrombocytopenic purpura (ITP) only require treatment if they are bleeding, or prior to scheduled operations. Patients are also treated if platelet counts are very low. Some patients become refractory, relapse or do not respond to treatment with steroids. Splenectomy is effective in raising the platelet count in most patients, but as spontaneous remission may occur even after 1 year or more, it is justified to defer splenectomy. Furthermore, splenectomy and/or first-line treatment modalities may not suit all patients. Therefore, alternatives are desirable.

MATERIALS

This review will focus on anti-B cell therapy with rituximab, and two thrombopoietin mimetic agents that have entered clinical trials, AMG 531 and eltrombopag. These therapeutics have been studied in patients who were refractory to first-line treatment and/or splenectomy, and to defer splenectomy.

RESULTS

There are no controlled trials with rituximab, but clinical experience has shown a success rate of 40% to 60%. Encouraging phase 1 and 2 data have been published for both thrombopoietin mimetics; preliminary data from an open-label extension trial with AMG 531 and from phase 3 studies with eltrombopag further confirm their efficacy.

CONCLUSION

Clinical experience will ultimately determine the appropriate indications of these new treatments for ITP.

Idiopathic thrombocytopenic purpura and dysmegakaryocytopoiesis

Idiopathic thrombocytopenic purpura (ITP) is an autoimmune disorder characterized with thrombocytopenia, primarily caused by platelet destruction. However, the studies of platelet kinetics show platelet turn over are normal or decreased, suggesting that reduced platelet production may lead to severity of ITP. We review recent research progress on abnormal cell events involved in megakaryocytopoiesis contributing to thrombocytopenia.