Pathophysiology and management of thrombocytopenia in bone marrow failure: possible clinical applications of TPO receptor agonists in aplastic anemia and myelodysplastic syndromes

Treatment of newly diagnosed severe aplastic anemia in children: Evidence-based recommendations

Severe aplastic anemia (SAA) is a rare potentially fatal hematologic disorder. Although overall outcomes with treatment are excellent, there are variations in management approach, including differences in treatment between adult and pediatric patients. Certain aspects of treatment are under active investigation in clinical trials. Because of the rarity of the disease, some pediatric hematologists may have relatively limited experience with the complex management of SAA. The following recommendations reflect an up-to-date evidence-based approach to the treatment of children with newly diagnosed SAA.

Efficacy and safety of high dose recombinant human thrombopoietin in the treatment of immune thrombocytopenia

The conventional dose of recombinant human thrombopoietin (rhTPO) in the treatment of immune thrombocytopenia (ITP) is 300 U/kg per day, but the clinical reaction rate is not satisfactory. Accordingly, we explored the efficacy and safety of increasing rhTPO dose in the treatment of ITP. A retrospective study was conducted to collect the clinical data of 105 ITP patients who were divided into two groups, a low-dose group (15 000 U/day) and a high-dose group (30 000 U/day) according to the dose of rhTPO. The total effective rate of the low-dose group and the high-dose group was 31/44 (70.45%) vs. 56/61 (91.80%) (P = .049), and the average time of using rhTPO in the high-dose group was shorter than that in the low-dose group (7 days vs. 10 days, P = .001). On the 7th and 14th day of treatment, the efficacy of the high-dose group was better than that of the low-dose group [45/61 (73.77%) vs. 17/44 (38.64%), P < .001; 55/60 (91.67%) vs. 30/44 (68.18%), P < .05)]. The incidence of treatment related adverse events in the low-dose group and the high-dose group was 6/44 (13.64%) vs. 6/61 (9.84%) (P > .05), which were mild and transient in nature. In our study, high-dose rhTPO had good efficacy and high safety in the treatment of ITP with the efficacy better than low-dose rhTPO especially at day 7.

Congenital Neutropenia with Specific Granulocyte Deficiency Caused by Novel Double Heterozygous SMARCD2 Mutations

SMARCD2 (SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily D, member 2) is critical for myelopoiesis. Recently, bi-allelic SMARCD2 mutations have been reported in five children, causing autosomal recessive congenital neutropenia with specific granulocytes deficiency (CN-SGD); a syndrome resulting in G-CSF resistant neutropenia, recurrent infections, and dysplastic myelopoiesis. We report a new case with CN-SGD caused by two novel heterozygous pathogenic variants in the SMARCD2 gene (c.1081del (p.Gln361Argfs*15)), and (c.217C>T (p.Arg73*)). Treatment with the weekly dosing of thrombopoietin receptor agonist, Romiplostim, along with daily G-CSF transformed her clinical course, implying potential synergism. This report advances the understanding of CN-SGD caused by SMARCD2 mutations.

Dysmegakaryopoiesis and Transient Mild Increase in Bone Marrow Blasts in Patients With Aplastic Anemia Treated With Eltrombopag May Be Signs of Hematologic Improvement and Not Portend Clonal Evolution

Objectives

Eltrombopag, a thrombopoietin-receptor agonist, stimulates hematopoiesis in patients with acquired aplastic anemia (AA). Cytomorphologic changes in bone marrow after eltrombopag administration are still unclear. This study examined the effect of eltrombopag on cytomorphologic findings using data from prior phase 2 studies (E1201 and E1202).

Methods

Microscopic examinations were performed in 31 patients with AA (E1201 [n = 21], E1202 [n = 10]). The relationship between hematologic improvement and morphologic findings was also investigated.

Results

In 5 patients (E1201 [n = 3], E1202 [n = 2]), the bone marrow blast count increased after initiation of eltrombopag treatment compared with screening values. The blast count was less than 5%, and the increase in bone marrow blasts was transient in all 4 patients who had bone marrow examinations at follow-up. In 8 patients (E1201 [n = 5], E1202 [n = 3]), dysplastic forms of megakaryocytes were found in the bone marrow following treatment initiation. Dysmegakaryopoiesis of 10% or more was found in 3 patients. None of the patients revealed micromegakaryocytes. Ten patients showed an increase in bone marrow blasts and/or dysmegakaryopoiesis following treatment initiation. Nine of 10 patients showed hematologic improvement in 1 or more lineages.

Conclusions

Dysmegakaryopoiesis without micromegakaryocytes and a transient increase of less than 5% in bone marrow blast count may be signs of hematologic improvement with eltrombopag for patients with AA.

Recombinant human thrombopoietin improved platelet engraftment after autologous hematopoietic stem cell transplantation in patients with newly diagnosed multiple myeloma

Background

To evaluate the efficacy and safety of recombinant human thrombopoietin (rhTPO) for hematopoietic reconstitution after autologous stem cell transplant (ASCT) in patients with newly diagnosed multiple myeloma (NDMM).

Method

Thirty‐five cases with NDMM had been enrolled into a prospective clinical trial from March 2014. The hematopoietic reconstitution was compared between these 35 cases (rhTPO group) and 98 historic cases not receiving rhTPO (control group) after stem cell reinfusion.

Results

Thirty‐five (100%) cases receiving rhTPO achieved both neutrophil and platelet engraftment within 30 days post‐transplant. The median time to neutrophil and platelet engraftment was the 10^th day and 11^th day after stem cell reinfusion, respectively. Multivariate analysis showed that rhTPO administration was an independent factor for accelerating platelet engraftment (HR 2.013, 95% CI 1.336–3.034, p = 0.001). Subgroup analysis showed that rhTPO improved platelet engraftment and alleviated platelet transfusion needs in patients with inadequate re‐infused CD34⁺ cell counts of <2 × 10⁹/L. All the 35 patients tolerated rhTPO well. Survival analysis showed no decrease in time to progression (TTP) or overall survival (OS) by rhTPO administration.

Conclusion

rhTPO accelerated the platelet engraftment after ASCT in patients with NDMM with good tolerability and long‐term safety, especially for those patients with poor CD34⁺ cell reinfusion. rhTPO might be recommended to be used early after ASCT for patients with NDMM.

Eltrombopag in Combination with Rabbit Anti-thymocyte Globulin/Cyclosporine A in Immunosuppressive Therapy-naïve Patients with Aplastic Anemia in Japan

Objective In Japan, immunosuppressive therapy (IST) with anti-thymocyte globulin (ATG), and cyclosporine A (CsA) is the standard of care in patients with aplastic anemia (AA) who are not indicated for stem-cell transplantation, although some patients may experience relapse. This study assessed the efficacy and safety of eltrombopag in combination with rabbit-ATG/CsA in IST-naïve patients with non-severe or severe AA in Japan. Methods In this non-randomized, open-label, single-arm, phase II study, rabbit-ATG/CsA and eltrombopag were initiated on Days 1 and 15 (±3 days), respectively, and continued for ≥26 weeks; rabbit-ATG was given for 5 days (Days 1 to 5). The primary endpoint was the overall response rate (ORR) at Week 26. Patients Patients with AA who were IST-naïve and ≤70 years old or between 71 and 75 years old based on the recommendation of the investigator were enrolled in Japan. Results Of the 11 enrolled patients, 10 started treatment with eltrombopag. The ORRs at Weeks 26 and 52 were 70.0% and 60.0%, respectively. The ORR at Week 26 was 100% (all 3 patients) in patients with non-severe AA and 57.1% (4/7) in patients with severe AA. Among transfusion-dependent patients, 66.7% (4/6) and 62.5% (5/8) became red blood cell- and platelet-transfusion independent, respectively. The most common adverse events were nausea and headache. No deaths or hematologic malignancies were reported. A cytogenetic abnormality was reported in one patient. Conclusion This study confirmed the clinical benefit of eltrombopag plus rabbit-ATG/CsA in IST-naïve patients with non-severe or severe AA in Japan.

Up-front Treatment With Romiplostim in Children With Acquired Bone Marrow Failure: A Single Institutional Pediatric Case Series

BACKGROUND

Thrombopoietin receptor agonists are emerging as a therapeutic option for patients with aplastic anemia (AA) and myelodysplastic syndrome (MDS). We report our experience of treating children with AA/MDS with romiplostim, thrombopoietin receptor agonist.

OBSERVATIONS

Three children (AA, 2; MDS, 1) received romiplostim treatment at a median dose of 10 μg/kg/week (starting dose: 5 μg/kg/wk; 2.5 μg/kg/wk increment). Trilineage hematopoietic recovery occurred at a median of 13 weeks (range: 13 to 16 wk) without adverse events. Hematopoiesis continued to improve after therapy discontinuation (median follow-up: 2.8 y; range: 0.5 to 3.0).

CONCLUSION

Our experience supports the short-term safety and efficacy of romiplostim in children with AA/MDS.

Healthcare resource use and direct costs in severe aplastic anemia (SAA) patients before and after treatment with eltrombopag

Purpose: This study evaluated healthcare resource utilization (HCRU), and direct costs among severe aplastic anemia (SAA) patients treated with eltrombopag (EPAG) using US claims data.Methods: This retrospective, real-world claims database study identified SAA patients aged ≥2 years treated with EPAG who initiated any SAA treatment between 1 July 2014 and 31 December 2017 (identification period) using the Truven MarketScan databases. A subset of 82 patients treated with EPAG during the identification period were evaluated for all-cause and SAA-related HCRU and direct costs as well as blood transfusion 1 month before EPAG initiation (baseline) and at Month 6 after EPAG initiation (follow-up period).Results: The average patient age was 50.8 (SD = 20.6) years old, predominantly female (n = 43, 52.4%), and had a mean CCI at baseline of 1.1 (SD = 1.7). Hospitalizations, and ER, office, and outpatient visits were significantly lower at Month 6 after EPAG initiation compared with 1 month before EPAG initiation (p < .05 for all four all-cause HCRU and SAA-related hospitalizations). An almost two-fold decrease in reliance on biweekly blood transfusions was observed: 1.0 at weeks 1-2 to 0.5 at Month 6 after EPAG initiation. Although prescription costs (mean [SD]) were significantly higher at Month 6 after EPAG initiation compared with 1 month before EPAG initiation (difference of $11,045 USD [SD = $18,801]), these increases were offset by savings in direct costs. Overall, a mean reduction in total all-cause costs of $29,391 USD [SD = $137,770] was reported at Month 6 after EPAG initiation due to substantial reductions in hospitalization ($40,060 USD [SD = $123,198]) and outpatient visits ($2,043 USD [SD = $25,264]).Conclusion: All-cause and SAA-related HCRU were reduced following EPAG treatment. Prescription costs were higher following treatment; however, these costs were generally offset by reductions in direct costs. These results provide real-world evidence around the role of EPAG in SAA treatment.

Hematologic recovery induced by eltrombopag in Japanese patients with aplastic anemia refractory or intolerant to immunosuppressive therapy

Eltrombopag, an oral thrombopoietin-receptor agonist, stimulates hematopoiesis in patients with acquired aplastic anemia (AA) and has higher exposure in patients of East Asian origin. We evaluated the pharmacokinetics, efficacy, and safety of eltrombopag in Japanese patients with AA refractory or intolerant to immunosuppressive therapy (IST). Twenty-one patients (15 with non-severe AA, six with severe AA) with platelet counts < 30,000/µL received eltrombopag in a dose-escalation fashion (25, 50, 75, or 100 mg once daily) depending on individual platelet responses; the responders continued eltrombopag treatment beyond 6 months. The primary endpoint was hematologic response at 6 months, defined as improvements in blood counts or transfusion requirements. Ten (48%) patients achieved hematologic responses in at least one lineage at 6 months. Six patients achieved tri- and/or bi-lineage responses with continuation of eltrombopag treatment, with two patients no longer requiring eltrombopag treatment. The most common adverse events were nasopharyngitis and abnormal hepatic function, with the majority being grade 1 or 2. Cytogenetic abnormalities were observed in three patients; however, no progression to myelodysplastic syndrome/other malignancy was observed. Eltrombopag can safely restore multi-lineage hematopoiesis in Japanese patients with AA refractory or intolerant to IST.Clinical Trial registration NCT02148133.

Endothelial protein C receptor supports hematopoietic stem cell engraftment and expansion in Mpl-deficient mice

Thrombopoietin (Thpo)/myeloproliferative leukemia virus oncogene (Mpl) signaling controls hematopoietic stem cell (HSC) self-renewal and quiescence; however, how these 2 seemingly opposing functions are controlled is not well understood. By transplantation of lentiviral-transduced hematopoietic cells in the Mpl-deficient mouse model, we addressed whether known or predicted Thpo target genes were able to rescue the Mpl-deficient phenotype of the mice. Among the tested genes, we identified endothelial protein C receptor (Epcr) to expand HSCs with the long-term (LT)-HSC surface phenotype in Mpl−/− mice and to enable secondary transplantation of Mpl-deficient bone marrow (BM). Epcr-transduced Mpl−/− HSCs enter quiescence earlier after transplantation than control-transduced Mpl−/− cells, and upregulated expression of the anti-apoptotic gene Bcl-xL. Also, in the wild-type background, Epcr expression marked the engrafting population in the BM. Furthermore, Epcr expression in Mpl−/− hematopoiesis increased the number of megakaryocytes in the BM. In vitro Thpo supported the surface expression of Epcr on primary murine hematopoietic stem and progenitor cells. With these data, we add new insights into Thpo-dependent influence on HSC engraftment after transplantation. This may be of use for the in vitro manipulation of HSCs, also in the context of gene therapy.

Hematopoietic stem cell loss and hematopoietic failure in severe aplastic anemia is driven by macrophages and aberrant podoplanin expression

Severe aplastic anemia (SAA) results from profound hematopoietic stem cell loss. T cells and interferon gamma (IFNγ) have long been associated with SAA, yet the underlying mechanisms driving hematopoietic stem cell loss remain unknown. Using a mouse model of SAA, we demonstrate that IFNγ-dependent hematopoietic stem cell loss required macrophages. IFNγ was necessary for bone marrow macrophage persistence, despite loss of other myeloid cells and hematopoietic stem cells. Depleting macrophages or abrogating IFNγ signaling specifically in macrophages did not impair T-cell activation or IFNγ production in the bone marrow but rescued hematopoietic stem cells and reduced mortality. Thus, macrophages are not required for induction of IFNγ in SAA and rather act as sensors of IFNγ. Macrophage depletion rescued thrombocytopenia, increased bone marrow megakaryocytes, preserved platelet-primed stem cells, and increased the platelet-repopulating capacity of transplanted hematopoietic stem cells. In addition to the hematopoietic effects, SAA induced loss of non-hematopoietic stromal populations, including podoplanin-positive stromal cells. However, a subset of podoplanin-positive macrophages was increased during disease, and blockade of podoplanin in mice was sufficient to rescue disease. Our data further our understanding of disease pathogenesis, demonstrating a novel role for macrophages as sensors of IFNγ, thus illustrating an important role for the microenvironment in the pathogenesis of SAA.

Value of transfusion independence in severe aplastic anemia from patients' perspectives - a discrete choice experiment

Background

Aplastic anemia is a rare, serious blood disorder due to bone marrow failure to produce blood cells. Transfusions are used to reduce risk of bleeding, infection and relieve anemia symptoms. In severe patients, transfusions may be required more than once/week. It is unclear from the patient perspective the impact that transfusions have on quality of life. This study aimed to elicit patient preferences for attributes associated with severe aplastic anemia (SAA) treatment, including transfusion independence.

Methods

An online discrete choice experiment (DCE) was conducted among patients with SAA who experienced insufficient response to immunosuppressive therapy and transfusion dependence for ≥3 months in the past 2 years. Recruitment occurred through the Aplastic Anemia and Myelodysplastic Syndromes International Foundation and referrals from clinical sites in the US and France. Respondents chose between hypothetical treatment pairs characterized by a common set of attributes: transfusions frequency, fatigue, risk of infection, and risk of serious bleeding. Conditional logit model with effects coding was used to estimate part-worth utilities for different attribute levels and the relative importance of each attribute. Predicted utility scores for transfusion frequency levels were reported.

Results

Thirty patients completed the survey. Most were age ≥ 40 years (73.3%), female (70.0%), and from the US (86.7%). 33.3% underwent bone marrow transplant; 36.7% received iron chelation therapy. Patients largely agreed that transfusion independence would result in less burden on time and costs, greater control and quality of life, less fatigue (86.7% noted each) and less scheduling around medical appointments (83.3%). The DCE found highest relative importance for risk of bleeding (0.30), followed by risk of infection (0.28), fatigue (0.23), and frequency of transfusions (0.20). More frequent transfusions resulted in lower utility, particularly when increasing monthly transfusions frequency from 4 (0.57) to 8 (0.35).

Conclusions

Our study showed that higher utility was associated with fewer transfusions in SAA patients with insufficient response to immunosuppressive therapy. While risk of bleeding, risk of infection, and fatigue were more important for patient treatment preferences, frequency of transfusions was also important.

Bone marrow morphology and disease progression in congenital thrombocytopenia: a detailed clinicopathologic and genetic study of eight cases

Patients with congenital thrombocytopenia have an increased risk of developing myeloid neoplasms. In these cases, the morphologic distinction between disease at baseline and at progression is challenging. This report analyzes clinicopathologic features of congenital thrombocytopenia with long-term follow-up at one referral center. Records from the last 20 years were searched for cases of congenital thrombocytopenia with bone marrow biopsies and peripheral blood smears. The clinical, morphologic, immunophenotypic, and molecular features were analyzed. Six adult and two pediatric patients were identified (six male, two female). Age range at first biopsy was 1-47 (median, 31) years. Underlying diseases included thrombocytopenia-absent radius syndrome, congenital thrombocytopenia with radial-ulnar synostosis, MYH9-related disorder, shortened telomere syndrome, congenital thrombocytopenia with ANKRD26 mutation, and familial platelet disorder with predisposition to acute myeloid leukemia. Four patients had myelodysplastic/myeloproliferative neoplasm-like marrow changes such as hypercellularity, increased myeloid to erythroid ratio, numerous micromegakaryocytes (highlighted by CD42b), and marrow fibrosis. Two patients had marrow hypoplasia and two had unremarkable marrow morphology. Three patients-all in the myelodysplastic/myeloproliferative neoplasm-like group-developed disease progression characterized by erythroid and myeloid dysplasia, elevated bone marrow blasts, and new cytogenetic abnormalities. Unlike non-familial myeloid neoplasms, congenital thrombocytopenia patients in the myelodysplastic/myeloproliferative neoplasm-like group had a long and indolent clinical course (average age at disease progression, 47 years). In summary, three distinct morphologic types of congenital thrombocytopenia were identified: a hyperplastic myelodysplastic/myeloproliferative neoplasm-like group, a hypoplastic bone marrow failure-like group, and a group with relatively normal marrow morphology. Emergence of cytogenetic abnormalities and dysplasia in non-megakaryocyte lineages correlated with disease progression.

[Comparison of efficacy and safety of two different dose of recombinant human thrombopoietin regimens in severe aplastic anemia patients with immunosuppressive therapy]

目的

比较不同重组人TPO（rhTPO）方案联合免疫抑制剂治疗重型再生障碍性贫血（SAA）的近期疗效。

方法

回顾性分析接受一线免疫抑制治疗（IST）的61例成人SAA初诊患者资料，对比分析18例IST联合rhTPO每日1次（连续组）与43例IST联合rhTPO隔日1次（间日组）患者的疗效差异。

结果

两组患者在IST前基础临床特征差异无统计学意义。IST后3个月和6个月进行疗效评估，连续组与间日组患者总体血液学反应率比较差异无统计学意义（3个月：50.0%对51.2%，P= 0.934；6个月：77.8%对69.8%，P=0.525）。连续组IST后3个月良好血液学反应率明显高于间日组（38.9%对9.3%，P=0.011）。rhTPO应用后4周和8周两组脱离红细胞输注率差异无统计学意义（4周：22.2%对18.6%，P=0.736; 8周：55.6%对46.5%，P=0.519），而治疗后8周脱离血小板输注率连续组明显高于间日组（88.9%对48.8%，P=0.003）。每日连续应用rhTPO治疗并不增加不良反应事件的发生。

结论

每日1次较隔日1次应用rhTPO促进SAA造血恢复和减少血小板输注依赖更为有效。

Assessing the Risk of Hemorrhagic Complication following Transjugular Liver Biopsy in Bone Marrow Transplantation Recipients

PURPOSE

To determine if recipients of bone marrow transplants (BMTs) are at increased risk of hemorrhagic complications following transjugular liver biopsy (TJLB).

MATERIALS AND METHODS

TJLBs in BMT and non-BMT patients between January 2007 and July 2014 were reviewed. Patient demographic and pre- and postprocedural laboratory data were reviewed. Mean platelet count and International Normalized Ratio were 174,300 × 10(3)/µL ± 107.3 (standard deviation) and 1.2 ± 0.4, respectively, for BMT recipients, compared with 88,100 × 10(3)/µL ± 70.9 and 1.2 ± 0.5, respectively, for non-BMT. Patients in whom hemoglobin level decreased by > 1 g/dL and/or required transfusion within 15 days of TJLB were reviewed to determine the presence of a biopsy-related hemorrhagic complication.

RESULTS

A total of 1,600 TJLBs in 1,120 patients were analyzed. Of these, 183 TJLBs in 159 BMT recipients and 1,417 TJLBs in 961 patients non-BMT patients were performed. Thirteen TJLBs were complicated by hemorrhage: five in BMT (2.9%) and eight in the non-BMT cohorts (0.6%; P < .01). Preprocedural platelet counts were within normal range (57-268 × 10(3)/µL) in all but one patient (8 × 10(3)/µL). BMT recipients had an odds ratio of 4.9 (95% confidence interval, 1.25-17.3) for post-TJLB bleeding/hemorrhage compared with those without BMTs (P < .01).

CONCLUSIONS

TJLB continues to be a safe procedure in the vast majority of patients. However, hemorrhagic complications occurred at a rate of 2.9% in BMT recipients, compared with 0.6% in patients without BMTs, and therefore caution should be exercised when performing TJLB in this group.

Eltrombopag interference in routine chemistry testing

BACKGROUND

High doses of Eltrombopag have been previously reported to cause bilirubin interference. Following receipt of a sample from a patient receiving high-dose Eltrombopag therapy, the laboratory decided to investigate the effect of this drug on routine chemistry testing.

METHODS

Interference studies were performed by spiking Eltrombopag into aliquots of a serum pool to give concentrations ranging from 0 to 500 µg/mL. The following analytes, namely albumin, alkaline phosphatase, alanine transaminase, aspartate transaminase, Urea, total calcium, cholesterol, triglycerides, glucose, high-density lipoprotein cholesterol, iron, magnesium, inorganic phosphate, creatinine, bicarbonate, transferrin, ferritin, electrolytes, total and direct bilirubin and serum indices (hemolysis, icterus and lipaemia) were then measured on the Roche Cobas 6000 chemistry analyzer (Roche, Indianapolis, USA).

RESULTS

Eltrombopag interference (>10% change of the baseline value) was observed for total cholesterol, triglycerides, inorganic phosphate and high-density lipoprotein cholesterol. Clinical significant interference was observed for total cholesterol, inorganic phosphate and high-density lipoprotein cholesterol

CONCLUSIONS

Presence of high Eltrombopag concentrations in blood samples has been demonstrated to cause interference in the measurement of certain spectrophotometric-based assays on the Roche Cobas 6000 analyzer.

Inhibition of Thrombopoietin/Mpl Signaling in Adult Hematopoiesis Identifies New Candidates for Hematopoietic Stem Cell Maintenance

Thrombopoietin (Thpo) signals via its receptor Mpl and regulates megakaryopoiesis, hematopoietic stem cell (HSC) maintenance and post-transplant expansion. Mpl expression is tightly controlled and deregulation of Thpo/Mpl-signaling is linked to hematological disorders. Here, we constructed an intracellular-truncated, signaling-deficient Mpl protein which is presented on the cell surface (dnMpl). The transplantation of bone marrow cells retrovirally transduced to express dnMpl into wildtype mice induced thrombocytopenia, and a progressive loss of HSC. The aplastic BM allowed the engraftment of a second BM transplant without further conditioning. Functional analysis of the truncated Mpl in vitro and in vivo demonstrated no internalization after Thpo binding and the inhibition of Thpo/Mpl-signaling in wildtype cells due to dominant-negative (dn) effects by receptor competition with wildtype Mpl for Thpo binding. Intracellular inhibition of Mpl could be excluded as the major mechanism by the use of a constitutive-dimerized dnMpl. To further elucidate the molecular changes induced by Thpo/Mpl-inhibition on the HSC-enriched cell population in the BM, we performed gene expression analysis of Lin-Sca1+cKit+ (LSK) cells isolated from mice transplanted with dnMpl transduced BM cells. The gene expression profile supported the exhaustion of HSC due to increased cell cycle progression and identified new and known downstream effectors of Thpo/Mpl-signaling in HSC (namely TIE2, ESAM1 and EPCR detected on the HSC-enriched LSK cell population). We further compared gene expression profiles in LSK cells of dnMpl mice with human CD34+ cells of aplastic anemia patients and identified similar deregulations of important stemness genes in both cell populations. In summary, we established a novel way of Thpo/Mpl inhibition in the adult mouse and performed in depth analysis of the phenotype including gene expression profiling.

Recombinant human thrombopoietin treatment promotes hematopoiesis recovery in patients with severe aplastic anemia receiving immunosuppressive therapy

Objective. To assess the effectiveness of recombinant human thrombopoietin (rhTPO) in severe aplastic anemia (SAA) patients receiving immunosuppressive therapy (IST). Methods. Eighty-eight SAA patients receiving IST from January 2007 to December 2012 were included in this retrospective analysis. Of these, 40 subjects received rhTPO treatment (15000 U, subcutaneously, three times a week). rhTPO treatment was discontinued when the platelet count returned to normal range. Hematologic response, bone marrow megakaryocyte recovery, and time to transfusion independence were compared. Results. Hematologic response was achieved in 42.5%, 62.5%, and 67.5% of patients receiving rhTPO and 22.9%, 41.6%, and 47.9% of patients not receiving rhTPO at 3, 6, and 9 months after treatment, respectively (P = 0.0665, P = 0.0579, and P = 0.0847, resp.). Subjects receiving rhTPO presented an elevated number of megakaryocytes at 3, 6, and 9 months when compared with those without treatment (P = 0.025, P = 0.021, and P = 0.011, resp.). The time to platelet and red blood cell transfusion independence was shorter in patients who received rhTPO than in those without rhTPO treatment. Overall survival rate presented no differences between the two groups. Conclusion. rhTPO could improve hematologic response and promote bone marrow recovery in SAA patients receiving IST.

Clinical indications for thrombopoietin and thrombopoietin-receptor agonists

Thrombocytopenia is a common hematologic disorder. Stimulation of thrombopoiesis may reduce the risk for thrombocytopenia-induced bleeding, prevent severe thrombocytopenia, and reduce the need for platelet transfusion. The key cytokine is thrombopoietin (TPO). It regulates proliferation and maturation of megakaryocytes as well as platelet production. TPO is synthesized in the liver. Development of TPO from the laboratory into a therapeutic tool has turned out to be an unexpected challenge. Clinical trials on first-generation thrombopoietic growth factors were stopped in 2001. At present, second-generation thrombopoiesis-stimulating agents have only been approved as orphan drugs for third-line therapy of patients with chronic immune thrombocytopenia. Larger groups in need are patients with myelodysplastic syndrome, chemotherapy-induced thrombocytopenia, other forms of hereditary and acquired bone marrow failure, hepatitis C infections, or liver cirrhosis.