Eltrombopag Added to Standard Immunosuppression for Aplastic Anemia

Use of eltrombopag in aplastic anemia in Europe

Eltrombopag (ELT), an oral thrombopoietin receptor agonist, has recently emerged as a promising new drug for the treatment of aplastic anemia (AA). How ELT is used outside of clinical trials in the real-world setting and results of this treatment are not known. We conducted therefore a retrospective survey on the use of ELT in AA among EBMT member centers. We analyzed the 134 patients reported in our survey together with 46 patients recently published by Lengline et al. The median follow-up from start of ELT treatment was 15.3 months, with 85.6% patients alive at last follow-up. Importantly, only 28.9% of our patients received ELT according to the FDA/EMA label as monotherapy in the relapsed/refractory setting, whereas 16.7% received ELT upfront. The overall response rate in our cohort was 62%, very similar to the results of the pivotal ELT trial. In multivariate analysis, combination therapy with ELT/cyclosporine/ATG and response to previous therapy were associated with response. Overall survival was favorable with a 1-year survival from ELT start of 87.4%. We identified age, AA severity before ELT start and response to ELT as variables significantly associated with OS. Two patients transformed to MDS; other adverse events were mostly benign. In sum, ELT is used widely in Europe to treat AA patients, mostly in the relapsed/refractory setting. Response to ELT is similar to the clinical trial data across different age groups, treatment lines, and treatment combinations and results in favorable survival.

Haploidentical donor transplants for severe aplastic anemia

Haploidentical stem cell transplantation (HAPLO) is being increasingly used, and significant progress has been made both with ex vivo T-cell depleted grafts as well as with unmanipulated marrow or peripheral blood grafts. We here review the current status of HAPLO grafts in patients with acquired severe aplastic anemia. Several transplant platforms have been tested, to overcome graft severe rejection and graft vs host disease (GvHD): these include differences in the conditioning regimen, in graft source and graft manipulation, and in GvHD prophylaxis. The latter include ex vivo T-cell depletion and/or antithymocyte globulin and/or high dose post-transplant cyclophosphamide. Some programs also include the use of marrow or cord blood mesenchymal stem cells, infused at the time of transplantation. Extremely encouraging results are being reported especially in the pediatric population, but also in young adults: we will review reports on 375 patients, with an average rejection rate of 6%, grade II-IV GvHD of 23% and 1-year survival of 80%. Finally we will discuss the place of HAPLO transplants in the context of alternative donor grafts for acquired aplastic anemia.

Evaluation of eltrombopag in patients with aplastic anemia in real-world experience

Background

Although eltrombopag has recently been approved for treating AA, the effects of its clinical use remain unknown.

Methods

We retrospectively analyzed 11 patients with AA, who had been treated with eltrombopag from August 2017 to May 2018.

Results

Overall response rate was 55%. There was tri-lineage recovery in four patients and platelet recovery in two. The reactive time was within 8 weeks after treatment initiation. Stage at the initial assessment, the neutrophil-to-lymphocyte ratio and platelet counts were significantly different between the responders and non-responders.

Conclusion

Eltrombopag is a promising agent for treating patients with any degree of AA.

Idiopathic Aplastic Anemia: An Update

"Bone marrow failure" encompass all the conditions and syndromes in which there are qualitative or quantitative disorders of one or more lineages (erythroid, myelomonocytic, and/or megakaryocytic). A few years ago, the pathophysiology of these syndromes was completely unknown. Today we have better knowledge for these diseases, allowing the development of new treatment options and the improvement of patients' outcome. Acquired bone marrow failure syndromes include myelodysplastic syndromes, aplastic anemia, paroxysmal nocturnal hemoglobinuria, idiopathic neutropenia and large granular leukemia. All these syndromes share some common features and pathophysiology. The most important feature is the possibility of clonal evolution and progression into acute myelogenous leukemia, and open questions still remain on how to prevent evolution in these patients.

CD3+/CD19+ Depleted Matched and Mismatched Unrelated Donor Hematopoietic Stem Cell Transplant with Targeted T Cell Addback Is Associated with Excellent Outcomes in Pediatric Patients with Nonmalignant Hematologic Disorders

Unrelated donor hematopoietic stem cell transplantation (HSCT) is increasingly being used to cure nonmalignant hematologic diseases (NMHD) in patients who lack HLA matched related donors. Both graft rejection and graft-versus-host disease (GVHD) remain major barriers to safe and effective transplant for these patients requiring unrelated donors. Partial T cell depletion combined with peripheral stem cell transplantation (pTCD-PSCT) has the potential advantages of providing a high stem cell dose to facilitate rapid engraftment, maintaining cells that may facilitate engraftment, and decreasing GVHD risk compared with T cell-replete HSCT. Here, we report a single-institution, retrospective experience of unrelated donor pTCD-PSCT for pediatric patients with NMHD. From 2014 to 2017, 12 pediatric patients with transfusion-dependent NMHD underwent matched unrelated donor (MUD) or mismatched unrelated donor (MMUD) pTCD HSCT in our center using disease-specific conditioning. Donor PSCs underwent CD3+ T cell and CD19+ B cell depletion using CliniMACS, followed by a targeted addback of 1 × 105 CD3+ T cells/kg to the graft before infusion. All 12 patients demonstrated rapid trilinear engraftment. At a median follow-up of 740days (range, 279 to 1466), all patients were alive with over 92% total peripheral blood donor chimerism and without transfusion dependence or recurrence of their underlying hematologic disease. Immune reconstitution was rapid and comparable with T cell-replete HSCT. No patients developed severe acute GVHD (grades III to IV) or chronic extensive GVHD, and all patients had discontinued systemic immune suppression. Viral reactivations were common, but no patient developed symptoms of life-threatening infectious disease. Our data indicate that MUD and MMUD pTCD-PSCTs are safe and effective approaches that enable rapid engraftment and immune reconstitution, prevent severe GVHD, and expand availability of HSCT to any patients with NMHD who have closely MUDs.

GDF11 is increased in patients with aplastic anemia

OBJECT

To explore the critical role of growth differentiation factor 11 (GDF11) in the pathobiology of aplastic anemia (AA).

METHODS

We have examined the serum GDF11 levels for 79 AA patients and 30 healthy controls. A total of 79 AA patients, which included 29 new diagnosed (untreated) cases, 14 cases with no response, 21 partial remission (PR) cases and 15 complete remission (CR) cases after immunosuppressive therapy (IST). GDF11 serum levels were assessed by an enzyme-linked immunosorbent assay. GDF11 mRNA expression in peripheral blood mononuclear (PBMNC) was detected through real time polymerase chain reaction. The correlation between GDF11 expression and erythropoietic function was evaluated.

RESULTS

The serum GDF11 levels in untreated AA patients were higher than that of the control group. The serum GDF11 levels of PR patients or CR patients after IST was decreased, compared with untreated patients, but did not recover back to the normal levels. GDF11 levels had a negative correlation with hemoglobin (Hb) levels and reticulocyte counts in AA patients. GDF11 levels did not correlate with age, sex and severity of in AA patients.

CONCLUSION

Serum GDF11 levels were increased and negatively correlated with Hb levels and reticulocyte counts in AA patients. This suggests an impaired GDF11 response contributing to anemia in AA patients.

Eltrombopag maintains human hematopoietic stem and progenitor cells under inflammatory conditions mediated by IFN-γ

The proinflammatory cytokine interferon-γ (IFN-γ) has been implicated in human hematopoietic stem and progenitor cell (HSPC) depletion in immune-mediated bone marrow failure syndromes. We show that IFN-γ specifically prevents full engagement of thrombopoietin (TPO), a primary positive regulator of HSPC survival, to its receptor (c-MPL) via steric occlusion of the low-affinity binding site, contributing to perturbation of TPO-induced signaling pathways and decreased survival of human HSPCs. Eltrombopag, a synthetic small molecule mimetic of TPO that interacts with c-MPL at a position distinct from the extracellular binding site of TPO, bypasses this inhibition, providing an explanation for its clinical activity in bone marrow failure, despite already elevated endogenous TPO levels. Thus, IFN-γ-mediated perturbation of TPO:c-MPL complex formation and the resulting inhibition of a critical pathway of growth factor cell signaling may represent a general mechanism by which IFN-γ impairs the function of human HSPCs. This understanding could have broad therapeutic implications for various disorders of chronic inflammation.

Eltrombopag for use in children with immune thrombocytopenia

Eltrombopag is currently the only US Food and Drug Administration-approved thrombopoietin receptor agonist for the treatment of chronic immune thrombocytopenia (ITP) in children. This oral, once-per-day therapy has shown favorable efficacy and adverse effect profiles in children. Two multicenter, double-blind, placebo controlled clinical trials (PETIT [Efficacy and Safety Study of Eltrombopag in Pediatric Patients With Thrombocytopenia From Chronic Idiopathic Thrombocytopenic Purpura (ITP)] and PETIT2 [Study of a New Medication for Childhood Chronic Immune Thrombocytopenia (ITP), a Blood Disorder of Low Platelet Counts That Can Lead to Bruising Easily, Bleeding Gums, and/or Bleeding Inside the Body]) demonstrated efficacy in raising platelet counts, reducing bleeding, and reducing the need for concomitant ITP therapies with relatively few adverse effects. The most commonly reported drug-related adverse effects include headache, nausea, and hepatobiliary laboratory abnormalities. Long-term safety data in children are limited, and studies in adults have not revealed a clinically significant increased incidence of thrombosis, marrow fibrosis, or cataract formation. Eltrombopag has also been approved for treating refractory severe aplastic anemia (AA) and has potential for expanded use in ITP and severe AA as well as in other conditions associated with thrombocytopenia.

Eltrombopag for post-transplant cytopenias due to poor graft function

Persistent cytopenia due to poor graft function (PoGF) is a relatively common complication which may affect up to 20% of patients undergoing allogeneic hematopoietic stem cell transplantation (HSCT). Treatment options for PoGF remain limited, and reinfusion of additional HSC is often the only way to rescue hematopoiesis. Here we describe a retrospective single-center experience with the thrombopoietin-mimetic agent eltrombopag for the treatment of PoGF. Thirteen patients have received eltrombopag for either PoGF (n = 12) or primary graft failure (n = 1). In the 12 PoGF patients eltrombopag was started at the median time of 79 days after HSCT, due to persistent thrombocytopenia, with concomitant anemia and neutropenia in 7 and 3 patients, respectively. The treatment was started at the dose of 50 mg per day, and eventually increased up to 150 mg in case of lack of response. Hematological response was seen in 7 patients, with 6 complete responses. Hematological responses were seen both in patients with evidence of immune-mediated pathophysiology, and with possible infectious/iatrogenic causes. In responding patients, eltrombopag was discontinued in 6/7 patients without further relapse. These results suggest that eltrombopag is safe and possibly effective in the setting of the treatment of PoGF, and pave the way for future prospective studies.

Immunosuppressive therapy versus haploidentical transplantation in adults with acquired severe aplastic anemia

Our study aimed to compare treatment outcomes between hematopoietic stem cell transplantation (HSCT) from haploidentical donors (HID) and immunosuppressive therapy (IST) in adults with acquired severe aplastic anemia (SAA). The medical records of 113 SAA adults who received IST, including rabbit ATG and cyclosporin (N = 37), or HID HSCT (N = 76) within 6 months of diagnosis at two institutions were retrospectively reviewed. Estimated 8-year overall survival (OS) was comparable between the IST and HID HSCT groups (75.6 vs. 83.7%, respectively, P = 0.328), but failure free survival (FFS) was significantly lower in IST group than HID HSCT group (38.5 vs. 83.7%, respectively, P = 0.001). Furthermore, a significant improvement in FFS was observed with HSCT over IST in patients under 40 years old. At the last follow-up, patients in HSCT group achieved better Karnofsky Performance Status (KPS) than those in IST group (100 [20-100] vs. 90 [20-100], P = 0.002). In terms of blood count, 83.1% (54/65) of patients in HSCT group showed complete recovery compared to only 38.2% (13/34) in IST group (P < 0.001). These data suggest that HID HSCT could be an effective alternative treatment option for SAA adults, and additional prospective studies are necessary.

Eltrombopag in long-term management of pediatric thrombocytopenia

Eltrombopag is a thrombopoietin receptor agonist that may be effective in a broad range of thrombocytopenias of distinct etiology. We have observed rapid, robust, and sustained responses to eltrombopag in two young patients with refractory thrombocytopenia, one with primary immune thrombocytopenia and the other with Evans syndrome.

Methimazole-Induced Aplastic Anemia with Concomitant Hepatitis in a Young Filipina with Graves' Disease

A 34-year-old female Filipino with Graves' disease on methimazole came in due to fever, sore throat and jaundice. She was initially diagnosed with methimazole-induced agranulocytosis and drug-induced liver injury. She was treated with intravenous broad-spectrum antibiotic and granulocyte colony stimulating factor. On day 4 of admission, she developed pancytopenia and was managed as methimazole-induced aplastic anemia. She was started on steroid therapy and received 1 unit of packed red blood cell. The jaundice also increased, hence, she was given ursodeoxycholic acid. On day 9 of admission, with the consideration of "lineage steal phenomenon," biopsy was done and eltrombopag was started. Patient was discharged stable at 12th hospital day. This case presents 3 rare life-threatening complications of methimazole namely: agranulocytosis, aplastic anemia and hepatitis.

Haematological immune-related adverse events induced by anti-PD-1 or anti-PD-L1 immunotherapy: a descriptive observational study

BACKGROUND

Anti-programmed cell death 1 (PD-1) and anti-programmed cell death ligand 1 (PD-L1) antibodies are novel immunotherapies for cancer that can induce immune-related adverse events (irAEs). These adverse events can involve all organs, including the haemopoietic system. Thus far, haematological irAEs (haem-irAEs) have not been extensively characterised. This study aims to provide a comprehensive report of the haem-irAEs induced by anti-PD-1 or anti-PD-L1.

METHODS

In this descriptive observational study, we included consecutive patients aged at least 18 years with grade 2 or worse haem-irAEs induced by anti-PD-1 or anti-PD-L1 immunotherapy registered in three French pharmacovigilance databases: the Registre des Effets Indésirables Sévères des Anticorps Monoclonaux Immunomodulateurs en Cancérologie (REISAMIC; a prospective registry of patients treated with anti-PD-1 or anti-PD-L1 at a single centre), the ImmunoTOX committee of Gustave Roussy (a national referral database of suspected irAEs in patients treated with immunotherapy), and the registry of the Centre de Référence des Cytopénies Auto-Immunes de l'Adulte (CeReCAI; a national database of autoimmune cytopenias). Cases were reviewed by a central committee; adverse events had to be classed as certainly or probably related to anti-PD-1 or anti-PD-L1 therapy, and their severity was assessed according to the Common Terminology Criteria for Adverse Events (version 4.03). The primary endpoint was clinical description of haem-irAEs, as reported in all databases, and their frequency, as reported in the prospective REISAMIC registry.

FINDINGS

We screened 948 patients registered in the three databases from June 27, 2014, to June 29, 2018 (745 from REISAMIC, 190 from the ImmunoTOX committee, and 13 from CeReCAI). 35 patients (21 men and 14 women) with haem-irAEs related to anti-PD-1 or anti-PD-L1 were included in the study. Of 745 patients in the REISAMIC registry treated with anti-PD-1 or anti-PD-L1, four had haem-irAEs, giving a frequency of 0·5%. Median age in the 35 patients was 65 years (IQR 51-75), and the most common tumour types were melanoma (15 [43%] patients), non-small-cell lung cancer (12 [34%] patients), and lymphoma (four [11%] patients). 20 (57%) patients received nivolumab, 14 (40%) received pembrolizumab, and one (3%) received atezolizumab. Among the 35 patients, neutropenia, autoimmune haemolytic anaemia, and immune thrombocytopenia were the most common types of haem-irAE (each in nine patients [26%]), followed by pancytopenia or aplastic anaemia (five patients [14%]), bicytopenia (one patients with thrombocytopenia plus anaemia and one patient with neutropenia plus anaemia [6%]), and pure red cell aplasia (one patient [3%]). The maximum grade of severity was grade 2 in three (9%) patients, grade 3 in five (14%) patients, and grade 4 in 25 (71%) patients; two (6%) patients died from febrile neutropenia during haem-irAE related to anti-PD-1. Haem-irAEs resolved in 21 (60%) of the 35 patients.

INTERPRETATION

Haem-irAEs induced by PD-1 or PD-L1 inhibitors are rare but potentially life-threatening events. The most common clinical presentations are neutropenia, autoimmune haemolytic anaemia, immune thrombocytopenia, and aplastic anaemia. Investigations into earlier detection and better management are warranted.

FUNDING

Gustave Roussy and Gustave Roussy Immunotherapy Program.

A brief, but comprehensive, guide to clonal evolution in aplastic anemia

Acquired aplastic anemia (AA) is an immune-mediated bone marrow aplasia that is strongly associated with clonal hematopoiesis upon marrow recovery. More than 70% of AA patients develop somatic mutations in their hematopoietic cells. In contrast to other conditions linked to clonal hematopoiesis, such as myelodysplastic syndrome (MDS) or clonal hematopoiesis of indeterminate potential in the elderly, the top alterations in AA are closely related to its immune pathogenesis. Nearly 40% of AA patients carry somatic mutations in the PIGA gene manifested as clonal populations of cells with the paroxysmal nocturnal hemoglobinuria phenotype, and 17% of AA patients have loss of HLA class I alleles. It is estimated that between 20% and 35% of AA patients have somatic mutations associated with hematologic malignancies, most characteristically in the ASXL1, BCOR, and BCORL1 genes. Risk factors for evolution to MDS in AA include the duration of disease, acquisition of high-risk somatic mutations, and age at AA onset. Emerging data suggest that several HLA class I alleles not only predispose to the development of AA but may also predispose to clonal evolution in AA patients. Long-term prospective studies are needed to determine the true prognostic implications of clonal hematopoiesis in AA. This article provides a brief, but comprehensive, review of our current understanding of clonal evolution in AA and concludes with 3 cases that illustrate a practical approach for integrating results of next-generation molecular studies into the clinical care of AA patients in 2018.

Alternative donor transplants for severe aplastic anemia

Allogeneic hematopoietic stem-cell transplantation remains the only curative treatment for patients with acquired severe aplastic anemia (SAA). When a matched sibling is not available, one can search for a matched unrelated donor or a cord blood unit (CB) in the international registries or, more recently, for an HLA haploidentical (HAPLO) family member. International guidelines call for a course of antithymocyte globulin (ATG) and cyclosporine before a patient with SAA receives a transplant from a donor other than an HLA identical sibling, but whether this is necessary for patients age <20 years is less clear. Here I will examine the rapid increase in HAPLO transplantations for SAA, showing encouraging early results both in children and young adults. Graft-versus-host disease prophylaxis remains of primary importance in patients with SAA, and in vivo T-cell depletion with either ATG or alemtuzumab offers a significant survival advantage. Finally, I will discuss the strong age effect, which is particularly evident at >40 and 50 years of age for reasons not entirely clear and which should be taken into account when designing a treatment strategy for a given patient.

Activity of eltrombopag in severe aplastic anemia

Since the approval of horse antithymocyte globulin (ATG) decades ago, there was a long hiatus in therapies with activity in severe aplastic anemia (SAA). This scenario changed in 2014 when eltrombopag, a thrombopoietin receptor agonist, was approved for SAA after an insufficient response to initial immunosuppressive therapy (IST). The basis for this approval was the observation of single-agent activity of eltrombopag in this patient population, where 40% to 50% recovered blood counts at times involving >1 lineage. The achievement of transfusion independence confirmed the clinical benefit of this approach. Increase in marrow cellularity and CD34+ cells suggested a recovery to a more functioning bone marrow. Further in its development, eltrombopag was associated with standard horse ATG plus cyclosporine in first line, producing increases in overall (at about 90%) and complete response rates (at about 40%) and leading to transfusion independence and excellent survival. Interestingly, best results were observed when all drugs were started simultaneously. The cumulative incidence of clonal cytogenetic abnormalities to date has compared favorably with the vast experience with IST alone in SAA. Longer follow-up will help in define these long-term risks. In this review, the development of eltrombopag in SAA will be discussed.

Efficacy and Safety of Eltrombopag for Aplastic Anemia: A Systematic Review and Meta-analysis

BACKGROUND AND OBJECTIVES

Eltrombopag seems to be effective in treating patients with aplastic anemia in several clinical trials. This paper aims to perform the first meta-analysis analyzing the efficacy and safety of eltrombopag for aplastic anemia.

METHODS

Literatures were retrieved from PubMed, EMBASE, OVID, Web of Science, Cochrane, Wanfang, http://clinicaltrials.gov and World Health Organization International Clinical Trials Registry Platform search portal from establishment to July 2018. Using Stata statistical software version 12.0, subgroup analyses and sensitivity analyses were conducted.

RESULTS

The overall hematologic response rate is 88% (95% CI 83-94%) for patients treated with eltrombopag plus immunosuppressive therapy, and 47% (95% CI 38-56%) for patients with refractory aplastic anemia using eltrombopag alone. Karyotype abnormality rates include an overall rate of 10% (95% CI 7-14%), a subtotal rate of 8% (95% CI 3-13%) for patients who are treated with eltrombopag plus immunosuppressive therapy without using antithymocyte globulin before, and a subtotal rate of 17% (95% CI 10-24%) for patients with refractory aplastic anemia treated with eltrombopag alone.

CONCLUSIONS

With different treatments and in different conditions eltrombopag showed a distinctive effect for aplastic anemia. However, clone evolution and adverse events were associated with treatment.

NK cells suppress CD8+ T cell immunity via NKG2D in severe aplastic anemia

The roles of natural killer (NK) cells in shaping the immune system had raised wide interests. Here we intended to explore the regulatory functions of NK cells on CD8⁺ T cells in severe aplastic anemia (SAA) using human participants and lymphocyte infusion-induced bone marrow failure (BMF) mouse model. In SAA patients, NK cells had over-expressions of NKG2D and NKp46, under-expression of NKG2A and enhanced cytotoxicity. NK cells limited autologous CD8⁺ T cell immunity in an effector/target ratio manner. The suppression was dependent on the existence of NKG2D. We also observed upregulated MICA expression on activated CD8⁺ T cells, which were susceptible to NK cell mediated lysis in SAA. Animal model concurred with the data from patients. Infusion of NK cells suppressed the proliferation of CD8⁺ T cells and decreased IFN-γ production. In conclusion, NK cells served NKG2D-dependent immunoregulatory roles by attenuating autologous CD8⁺ T cell response in SAA.

Addition of eltrombopag to immunosuppressive therapy in patients with newly diagnosed aplastic anemia

BACKGROUND

The immune-mediated destruction of hematopoietic stem cells is implicated in the pathophysiology of aplastic anemia (AA). Immunosuppressive therapy (IST) using antithymocyte globulin and cyclosporine is successful in this setting. Eltrombopag is active in patients with refractory AA, presumably by increasing the bone marrow progenitors.

METHODS

This phase 2 trial initially was designed to evaluate standard IST in newly diagnosed patients with severe AA and later was amended to add eltrombopag to simultaneously address immune destruction and stem cell depletion. The primary outcome was the overall response rate (ORR) at 3 months and 6 months.

RESULTS

A total of 38 patients were enrolled: 17 (45%) received IST alone and 21 (55%) received additional eltrombopag. The ORR was 74%. Patients receiving IST plus eltrombopag had a similar ORR (76% vs 71%; P = .72), complete remission rate (38% vs 29%; P = .73), and median time to response (84 days vs 57 days; P = .30) compared with those receiving IST alone. The 2-year overall survival rate in the IST group was 91% compared with 82% for those patients treated with IST plus eltrombopag (P = .82). No cumulative toxicities were noted after the addition of eltrombopag.

CONCLUSIONS

The addition of eltrombopag to standard IST was well tolerated and resulted in similar responses.

Aplastic anemia: Etiology, molecular pathogenesis, and emerging concepts

Aplastic anemia (AA) is rare disorder of bone marrow failure which if severe and not appropriately treated is highly fatal. AA is characterized by morphologic marrow features, namely hypocellularity, and resultant peripheral cytopenias. The molecular pathogenesis of AA is not fully understood, and a uniform process may not be the culprit across all cases. An antigen-driven and likely autoimmune dysregulated T-cell homeostasis is implicated in the hematopoietic stem cell injury which ultimately founds the pathologic features of the disease. Defective telomerase function and repair may also play a role in some cases as evidenced by recurring mutations in related telomerase complex genes such as TERT and TERC. In addition, recurring mutations in BCOR/BCORL, PIGA, DNMT3A, and ASXL1 as well as cytogenetic abnormalities, namely monosomy 7, trisomy 8, and uniparental disomy of the 6p arm seem to be intimately related to AA pathogenesis. The increased incidence of late clonal disease has also provided clues to accurately describe plausible predispositions to the development of AA. The emergence of newer genomic sequencing and other techniques is incrementally improving the understanding of the pathogenic mechanisms of AA, the detection of the disease, and ultimately offers the potential to improve patient outcomes. In this comprehensive review, we discuss the current understanding of the immunobiology, molecular pathogenesis, and future directions of such for AA.

Diagnosis and management of chronic and refractory immune cytopenias in children, adolescents, and young adults

Children, adolescents, and young adults with chronic refractory autoimmune cytopenias represent a rare but challenging group of patients, who are managed frequently by pediatric hematologists. Novel diagnostic tests and genomic discoveries are refining historical diagnoses of Evans syndrome and common variable immunodeficiency, while also elucidating the cellular and molecular basis for these disorders. Genetic characterization of chronic and refractory autoimmune cytopenias has led to targeted therapies with improved clinical outcomes and fewer off-target toxicities. In this review, we focus on the appropriate diagnostic workup, expanded genetic testing, and novel treatment opportunities that are available for these challenging patients.

THPO gene variants in patients with acquired aplastic anemia

Background

Methods

Results

Conclusion

Upfront eltrombopag monotherapy induces stable hematologic remission in pediatric patients with nonsevere idiopathic aplastic anemia

Aplastic anemia (AA) is characterized by multilineage cytopenias and bone marrow hypocellularity. Severe AA can be treated with immunosuppressive therapy (IST) and/or allogeneic hematopoietic stem cell transplantation. The thrombopoietin agonist eltrombopag has been shown to induce hematopoietic recovery and transfusion independence in adults with refractory and relapsed AA. Recently, upfront eltrombopag therapy in patients with AA in combination with IST has shown efficacy. Data for its use without concurrent IST in pediatric patients with AA remain sparse. Here we report two pediatric patients with AA not meeting severe criteria who achieved hematologic response with upfront eltrombopag monotherapy.

Eltrombopag-based combination treatment for immune thrombocytopenia

Immune thrombocytopenia (ITP) is a bleeding disorder caused by a decrease in platelet count resulting from increased destruction and insufficient production of platelets. Although impaired regulatory T-lymphocyte activity plays a critical role in platelet destruction, many other immunologic abnormalities are also likely to be involved. Importantly, patients with ITP appear to have defects in a thrombopoietin-mediated physiological mechanism that compensates for a decrease in platelet count by increasing platelet production. Thus, simultaneous treatment of multiple pathogenic pathways involved in ITP could potentially result in synergistic efficacy. While conventional treatments for ITP suppress or modulate the immune system to reduce platelet destruction, a unique class of ITP therapy, namely thrombopoietin receptor agonists (TPO-RAs), improves platelet production by activating the thrombopoietin pathway. As hypothesized, preliminary studies show that combinations of eltrombopag, an oral TPO-RA, with conventional treatments improve outcomes in both newly diagnosed and refractory patients. In this review, the clinical experience with eltrombopag-based combinations in patients with ITP is summarized and the implications of the available data are discussed.

Lnk/Sh2b3 deficiency restores hematopoietic stem cell function and genome integrity in Fancd2 deficient Fanconi anemia

Fanconi anemia (FA) is a bone marrow failure (BMF) syndrome that arises from mutations in a network of FA genes essential for DNA interstrand crosslink (ICL) repair and replication stress tolerance. While allogeneic stem cell transplantation can replace defective HSCs, interventions to mitigate HSC defects in FA do not exist. Remarkably, we reveal here that Lnk (Sh2b3) deficiency restores HSC function in Fancd2^−/− mice. Lnk deficiency does not impact ICL repair, but instead stabilizes stalled replication forks in a manner, in part, dependent upon alleviating blocks to cytokine−mediated JAK2 signaling. Lnk deficiency restores proliferation and survival of Fancd2^−/− HSCs, while reducing replication stress and genomic instability. Furthermore, deletion of LNK in human FA-like HSCs promotes clonogenic growth. These findings highlight a new role for cytokine/JAK signaling in promoting replication fork stability, illuminate replication stress as a major underlying origin of BMF in FA, and have strong therapeutic implications.

Loss of Fancd2 leads to replication stress intolerance and Fanconi Anemia, where haematopoietic stem cell (HSC) function is compromised. Here, the authors show that Lnk/Sh2b3 loss restores HSC proliferation and survival in Fancd2 knockout mice and ameliorates replication stress in a cytokine/JAK2 signaling dependent manner.

Thrombopoietin receptor-independent stimulation of hematopoietic stem cells by eltrombopag

Eltrombopag (EP), a small-molecule thrombopoietin receptor (TPO-R) agonist and potent intracellular iron chelator, has shown remarkable efficacy in stimulating sustained multilineage hematopoiesis in patients with bone marrow failure syndromes, suggesting an effect at the most immature hematopoietic stem and multipotent progenitor level. Although the functional and molecular effects of EP on megakaryopoiesis have been studied in the past, mechanistic insights into its effects on the earliest stages of hematopoiesis have been limited. We investigated the effects of EP treatment on hematopoietic stem cell (HSC) function using purified primary HSCs in separation-of-function mouse models, including a TPO-R-deficient strain, and stem cells isolated from patients undergoing TPO-R agonist treatment. Our mechanistic studies showed a stimulatory effect on stem cell self-renewal independently of TPO-R. Human and mouse HSCs responded to acute EP treatment with metabolic and gene expression alterations consistent with a reduction of intracellular labile iron pools that are essential for stem cell maintenance. Iron preloading prevented the stem cell stimulatory effects of EP. Moreover, comparative analysis of stem cells in the bone marrow of patients receiving EP showed a marked increase in the number of functional stem cells compared to patients undergoing therapy with romiplostim, another TPO-R agonist lacking an iron-chelating ability. Together, our study demonstrates that EP stimulates hematopoiesis at the stem cell level through iron chelation-mediated molecular reprogramming and indicates that labile iron pool-regulated pathways can modulate HSC function.

Incidence and treatment outcome of aplastic anemia in Taiwan-real-world data from single-institute experience and a nationwide population-based database

Aplastic anemia (AA) is a rare disease characterized by pancytopenia and bone marrow failure. The incidence of AA tends to be higher in Asia than in the West, but real-world data about AA in Asia remain limited. We aimed to describe the basic data, treatment, and outcome of AA patients from our institute and evaluate the incidence of AA in Taiwan with a nationwide population-based cohort from National Health Insurance Research Database (NHIRD). We identified patients older than 2 years with AA in the Registry of Catastrophic Illness of NHIRD between 2001 and 2010 and excluded patients with any diagnosis suggestive of congenital or secondary bone marrow failure. With a total of 1270 patients, the overall incidence was 5.67 per million people per year, and there was a biphasic age distribution of incidence rate, highest in ≥ 70 years (19.83 per million people per year) and another peak at age 2-9 years (5.26 per million people per year). Overall, the 5-year survival was 60.0%. Hematopoietic stem cell transplantation (HSCT) and anti-thymocyte globulin-based immunosuppressive therapy (IST) were the major first-line treatments in patients younger than 40 years and were linked with good survival. In contrast, the majority of patients older than 60 years were treated with androgen, and the survival was poor. In multivariate analysis, "severe AA," "very severe AA," and "treatment other than HSCT, IST, or androgen" were independent risk factors for inferior survival. In conclusion, the incidence of AA in Taiwan is consistent with nearby Asian countries and is higher than in the West. Advanced age is associated with higher incidence and poorer outcome.

Effect of cyclosporine coadministration on the pharmacokinetics of eltrombopag in healthy volunteers

PURPOSE

Eltrombopag is indicated in patients with severe aplastic anemia (SAA) refractory to prior immunosuppressive therapy. The combination of eltrombopag and immunosuppressive therapy (such as cyclosporine) is currently being evaluated in patients with treatment-naive SAA. Cyclosporine is a human breast cancer resistance protein (BCRP) inhibitor, and can potentially alter plasma exposure to eltrombopag, a BCRP substrate. This phase 1, open-label, randomized, 3-period, crossover study evaluated the effect of cyclosporine on the pharmacokinetics of eltrombopag in healthy adults.

METHODS

Thirty-nine subjects were randomized to either single dose of eltrombopag 50 mg, cyclosporine 200 mg + eltrombopag 50 mg or cyclosporine 600 mg + eltrombopag 50 mg treatment groups. Eltrombopag pharmacokinetic parameters (C_max, t_max, AUC_last, AUC_inf, %AUC_ex, t_1/2, and CL/F) were determined using noncompartmental methods.

RESULTS

Geometric mean AUC_inf, AUC_last, and C_max, were decreased by 18, 20, and 25%, respectively, for cyclosporine 200 mg + eltrombopag and by 24, 22, and 39%, respectively, for cyclosporine 600 mg + eltrombopag groups compared to the eltrombopag alone group. The median t_max was prolonged by ~ 1 h in both coadministration treatments. The geometric mean t_1/2 was ≈ 21, ≈ 24, and ≈ 26 h, respectively, in cyclosporine 200 mg + eltrombopag, cyclosporine 600 mg + eltrombopag and eltrombopag alone groups. All the treatments were safe and well-tolerated. No serious adverse event or death was reported during the study.

CONCLUSION

These changes in exposure were not considered clinically meaningful as the dose of eltrombopag is adjusted using within-patient dose titration based on platelet counts.

Thrombopoietin receptor agonists in hereditary thrombocytopenias

Hereditary thrombocytopenias (HTPs) constitute a heterogeneous group of diseases characterized by a reduction in platelet count and a potential bleeding risk. As a result of advances in diagnostic methods, HTPs are increasingly being identified, and appear to be less rare than previously thought. Most HTPs do not have effective treatments, except for platelet transfusion when bleeding occurs and in preparation for procedures associated with a risk of bleeding. Preliminary clinical evidence suggests that thrombopoietin receptor agonists (TPO-RAs) with an established use in the treatment of certain acquired thrombocytopenias are well tolerated and provide clinical benefits in patients with some forms of HTP. These drugs may therefore be considered for the treatment of HTPs in clinical practice. However, caution and close monitoring are recommended, owing to the absence of long-term safety data and the potential risks posed by prolonged bone marrow stimulation in certain HTPs. In this review, we summarize the available clinical data on TPO-RAs in the treatment of HTPs, and discuss their use in patients with these disorders. We believe that TPO-RAs will play a major role in the treatment of HTPs, particularly myosin heavy chain 9-related disease, Wiskott-Aldrich syndrome, X-linked thrombocytopenia, and thrombocytopenia caused by THPO mutations.

Successful treatment of secondary poor graft function post allogeneic hematopoietic stem cell transplantation with eltrombopag

Poor graft function (PGF) is a life-threatening complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Current treatment strategies include the use of growth factors, CD34⁺-selected stem cell boost, mesenchymal stem cell transfusion, and second allo-HSCT, but these treatments are not effective in all patients. Eltrombopag, an oral thrombopoietin receptor agonist, which showed promising results in severe aplasia anemia, may be an alternative choice for PGF patients. Therefore, we treated 12 patients who responded poorly to standard treatments for secondary PGF after allo-HSCT with eltrombopag. The median duration was 116 (35–1000) days from transplantation to PGF diagnosis and 59 (30–180) days from PGF diagnosis to eltrombopag treatment. Eltrombopag was started at a dose of 25 mg/d for 3 days and then increased to 50 or 75 mg/d. Median treatment duration was 8 (2–23) weeks. Ten patients (83.3%) responded to the treatment: 8 achieved complete response (CR), and the remaining 2 achieved partial response. In the 10 responding subjects, median platelet count was 18 (5–27) × 10⁹/L vs 74 (30–117) × 10⁹/L prior to and after treatment. Neutrophil count was 0.51 (0.28–0.69) × 10⁹/L vs 1.84 (0.78–4.90) × 10⁹/L. Hemoglobin was 88 (63–123) vs 101 (78–134) g/L. In the 8 patients who achieved CR, the time from eltrombopag initiation to achieving CR was 29 (10–49) days; the response lasted until the last follow-up in all 8 CR subjects (10–18 months). The 12-month overall survival rate was 83.3%. There was no treatment-related mortality and no evidence of cataract, thrombosis, or any other grade 3/4 toxicities.

Eltrombopag Improves Refractory Thrombocytopenia in a Patient with Systemic Lupus Erythematosus

A 42-year-old woman with systemic lupus erythematosus (SLE) was admitted to our hospital for evaluation of severe thrombocytopenia. She was treated with steroids, intravenous cyclophosphamide, intravenous immunoglobulin, and plasma exchange, but her thrombocytopenia did not improve. Renal biopsy showed class IV-S(C) + V lupus nephritis, according to the classification of the International Society of Nephrology/Renal Pathology Society. The PA-IgG and serum thrombopoietin (TPO) levels were elevated. Her thrombocytopenia responded to off-label administration of eltrombopag, which was discontinued after 42 months. At 18 months after stopping eltrombopag, the platelet count was 19.3 × 10⁴/μL. Eltrombopag may be a therapeutic option for SLE patients with severe thrombocytopenia refractory to conventional therapy.

Cytokine control of megakaryopoiesis

Platelets are anuclear blood cells required for haemostasis and are implicated in other processes including inflammation and metastasis. Platelets are produced by megakaryocytes, specialized cells that are themselves generated by a process of controlled differentiation and maturation of bone-marrow stem and progenitor cells. This process of megakaryopoiesis involves the coordinated interplay of transcription factor-controlled cellular programming with extra-cellular cues produced locally in supporting niches or as circulating factors. This review focuses on these external cues, the cytokines and chemokines, that drive production of megakaryocytes and support the terminal process of platelet release. Emphasis is given to thrombopoietin (Tpo), the major cytokine regulator of steady-state megakaryopoiesis, and its specific cell surface receptor, the Mpl protein, including normal and pathological roles as well as clinical application. The potential for alternative or supplementary regulatory mechanisms for platelet production, particularly in times of acute need, or in states of infection or inflammation are also discussed.

The Pathophysiology of Acquired Aplastic Anemia: Current Concepts Revisited

Idiopathic acquired aplastic anemia is a rare, life-threatening bone marrow failure syndrome characterized by cytopenias and hypocellular bone marrow. The pathophysiology is unknown; the most favored model is of a dysregulated immune system leading to autoreactive T-cell destruction of hematopoietic stem and progenitor cells in a genetically susceptible host. The authors review the literature and propose that the major driver of acquired aplastic anemia is a combination of hematopoietic stem and progenitor cells intrinsic defects and an inappropriately activated immune response in the setting of a viral infection. Alterations in bone marrow microenvironment may also contribute to the disease process.

Eculizumab Bridging before Bone Marrow Transplant for Marrow Failure Disorders Is Safe and Does Not Limit Engraftment

Paroxysmal nocturnal hemoglobinuria (PNH) often develops secondary to other bone marrow failure (BMF) disorders, especially aplastic anemia (AA). Patients with the AA/PNH syndrome may require treatment with both eculizumab to reduce intravascular hemolysis and the risk of thrombosis and allogeneic stem cell transplant for the severe BMF. There has been concern that eculizumab could adversely affect the outcomes for transplant in these patients. This is a retrospective, single-center study of severe AA (SAA)/PNH patients treated with eculizumab immediately before the start of conditioning for transplant. Metrics of engraftment and infectious outcomes are described. Eight patients with SAA/PNH and PNH-related symptoms were treated with eculizumab and then proceeded to transplant. All were successfully transplanted without adverse events related to C5 blockage before conditioning. All were also cured of their both PNH and SAA. Eculizumab is safe and efficacious in patients with PNH clones who require transplant. This is sometimes required to "bridge" patients before bone marrow transplantation and does not appear to adversely impact outcomes even when using HLA matched unrelated or haploidentical donors.

Rabbit antithymocyte globulin dose does not affect response or survival as first-line therapy for acquired aplastic anemia: a multicenter retrospective study

In a prospective randomized study, treatment for aplastic anemia (AA) with rabbit antithymocyte globulin (r-ATG) and cyclosporine showed inferior hematological response and survival in comparison to horse antithymocyte globulin (h-ATG) and cyclosporine. However, h-ATG was discontinued in most Asian, South American, and European countries, where r-ATG became the only ATG formulation available. We retrospectively evaluated consecutive patients with acquired AA who received either rabbit (n = 170) or horse (n = 85) ATG and cyclosporine for first-line treatment from 1992 to 2014 in seven referral centers in Brazil and Argentina. Overall response at 3 months was 17% (95%CI, 11-23%) for r-ATG and 44% (95%CI, 33-55%) for h-ATG (p < 0.001). At 6 months, it was 31% (95%CI, 34-39%) for r-ATG and 59% (95%CI, 48-69%) for h-ATG (p < 0.001). Overall survival at 5 years was 57% (95%CI, 47-65%) for r-ATG and 80% (95%CI, 69-87%) for h-ATG (log-rank = 0.001). Relapse was significantly higher in patients receiving h-ATG (28%; 95%CI, 17-43%) as compared to r-ATG (9.4%; 95%CI, 4-21%; log-rank, p = 0.01). The type of ATG was the only factor associated with both response and survival. The r-ATG dose varied from 1 to 5 mg/kg/day, but it did not correlate with outcomes. In summary, this is the largest multicenter study comparing the two ATG formulations in AA. Our results indicate that the dose of r-ATG does not influence hematologic response or survival in first-line therapy for acquired AA. Considering the toxicity and costs of r-ATG, our findings challenge its aggregate benefit to cyclosporine therapy and further strengthen that h-ATG should remain standard therapy in AA.