Eltrombopag after allogeneic haematopoietic cell transplantation in a case of poor graft function and systematic review of the literature

Eltrombopag can promote platelet implantation after allogeneic hematopoietic stem cell transplantation as safely and similarly to thrombopoietin

Background

Eltrombopag has demonstrated efficacy in treating low platelet (PLT) levels, but it remains unclear whether eltrombopag can promote PLT engraftment after hematopoietic stem cell transplantation (HSCT).

Methods

Forty-one HSCT patients received eltrombopag 50 mg/d from +1 day until PLT >50 × 109/L or 1 month after HSCT. Fifty-one patients in the same period received thrombopoietin (TPO) to promote PLT graft after HSCT and served as a control group.

Results

A total of 51 patients who applied TPO during the same period were treated as a control. In the eltrombopag group, the median time to white blood cells (WBC) graft was 12 days (range, 10-17 days) and the PLT graft was 15 days (range, 10-30 days), whereas for the patients in the TPO group, the median time to WBC and PLT graft was 12 days (range, 9-23 days) and 15.5 days (range, 9-41 days), respectively. In the first month after HSCT, the median WBC count in the eltrombopag group was 4.41 × 109/L (range, 0.87-40.01 × 109/L) and the median PLT was 89x109/L (range, 30-401 × 109/L); the median WBC and PLT \counts in the TPO group were 4.65 × 109/L (range, 0.99-23.63 × 109/L) and 86 × 109/L (range, 5-512 × 109/L), respectively. Patients in the TPO or eltrombopag group did not experience serious side effects after drug administration, and the difference in side effects on liver and kidney function between the two groups was not statistically significant.

Conclusion

Eltrombopag is safe and similarly promotes platelet engraftment to thrombopoietin after allogeneic HSCT.

Management of chemotherapy-induced thrombocytopenia: guidance from the ISTH Subcommittee on Hemostasis and Malignancy

Thrombocytopenia is a common adverse effect of chemotherapy. The development of chemotherapy-induced thrombocytopenia (CIT) is influenced by cancer type and therapy, occurring in approximately one-third of patients with a solid tumor diagnosis and half of all patients with a hematologic malignancy. CIT may complicate the administration of chemotherapy, leading to therapeutic delays or dose reductions. This guidance document, presented by the International Society on Thrombosis and Haemostasis (ISTH) Subcommittee on Hemostasis and Malignancy, provides a comprehensive summary of the evidence and offers direction on the use of thrombopoietin receptor agonists (TPO-RAs) in various settings of CIT, including solid tumors, acute myeloid leukemia, stem cell transplant, and lymphoma. Studies have shown that TPO-RAs can improve platelet counts in CIT, but the clinical benefits of TPO-RA in terms of reducing bleeding, limiting platelet transfusion, avoiding chemotherapy delay, or dose reduction are uncertain. Further research is needed to optimize the selection of appropriate indications and study design to manage thrombocytopenia following chemotherapy.

Oral eltrombopag versus subcutaneous recombinant human thrombopoietin for promoting platelet engraftment after allogeneic stem cell transplantation: A prospective, non-inferiority, randomized controlled trial

Delayed platelet engraftment (DPE) is associated with poor survival and increased transplantation-related mortality after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Therefore, treatments are needed to improve platelet engraftment and prevent DPE. We performed a phase three, non-inferior, randomized controlled study of eltrombopag or recombinant human thrombopoietin (rhTPO) to promot platelet engraftment after allo-HSCT. Candidates for allo-HSCT were randomly assigned to receive oral eltrombopag (50 mg daily) or subcutaneous rhTPO (15000U daily) from the first-day post-transplantation. The primary endpoint was the cumulative numbers of platelet engraftment (platelet recovery ≥20 × 10⁹ /L, without transfusion, for seven consecutive days) on day 60 after transplantation. We performed intention-to-treat analyses with a non-inferior margin of -15%. A total of 92 participants underwent randomization. 44 and 48 patients were randomized to the eltrombopag and rhTPO groups, respectively. The median duration of follow-up was 360 days (range: 12-960 days). The cumulative incidence of platelet engraftment on day 60 after transplantation in eltrombopag group was 86.4% (38/44) compared with 85.4% (41/48) in the rhTPO group (absolute risk difference [ARD] 1%, one-sided lower limit of 95% confidence interval [CI] -13.28%, P_{non-inferirioty}  = 0.014). The rate of DPE in the eltrombopag group was 6.8% (3/44) compared with 12.5% (6/48) in the rhTPO group (ARD -5.7%, one-sided higher limit of 95% CI 6.28%, P_{non-inferirioty}  = 0.063). Approximately, three-fourths of non-hematologic adverse events were not observed in the eltrombopag group but three patients (3/48, 6%) experienecd them in the rhTPO group. In addition, platelet transfusions unite from day 0 to day 21, or from day 22 to day 60, progression-free survival, overall survival were not significantly different between both groups. Eltrombopag was non-inferior to rhTPO in promoting platelet engraftment post allo-HSCT for patients with hematological malignancy. Oral eltrombopag was more convenient for patients than subcutaneous rhTPO (NCT03515096).

Eltrombopag may induce bone marrow fibrosis in allogeneic hematopoietic stem cell transplant recipients with prolonged thrombocytopenia

Poor graft function (PGF) and secondary failure of platelet recovery (SFPR) are significant causes of transplant related morbidity and mortality. Although thrombopoietin receptor agonists (TPO-RA), particularly Eltrombopag (EPAG), have been reported to be efficacious in the treatment of prolonged thrombocytopenia, potential long term adverse effects remain to be elucidated. This retrospective study was performed to determine the efficacy and toxicity profile of TPO-RAs in allogeneic hematopoietic stem cell transplant (alloHCT) recipients. Medical records of 27 patients [median age: 55(21-73) years; male/female: 15/12] who received posttransplant EPAG for SFPR or PGF were analysed. Eltrombopag was started on day 110(33-670) after transplant. Median initial dose was 25(25-50) mg/day which was properly escalated to a maximum dose of 75(50-100) mg/day. Duration of the treatment was median 120(31-377) days. Overall response rate (ORR) was 59.3% in the study population. Time-to-treatment response was 42(3-170) days. Mild-to-moderate bone marrow fibrosis was detected in the posttreatment biopsies of 12/22 patients (54.5%), 9 of whom did not represent any grade of myelofibrosis in their inital biopsies. The grade of posttreatment fibrosis was significantly increased when time-to-treatment response was longer (p = 0.008). Long term use of TPO-RAs may be considered as a potential cause of myelofibrosis in alloHCT recipients.

Exploring the Potential of Eltrombopag: Room for More?

Since its introduction in clinical practice, eltrombopag (ELT) has demonstrated efficacy in heterogeneous clinical contexts, encompassing both benign and malignant diseases, thus leading researchers to make a more in-depth study of its mechanism of action. As a result, a growing body of evidence demonstrates that ELT displays many effects ranging from native thrombopoietin agonism to immunomodulation, anti-inflammatory, and metabolic properties. These features collectively explain ELT effectiveness in a broad spectrum of indications; moreover, they suggest that ELT could be effective in different, challenging clinical scenarios. We reviewed the extended ELT mechanism of action in various diseases, with the aim of further exploring its full potential and hypothesize new, fascinating indications.

Efficacy and Immunomodulating Properties of Eltrombopag in Aplastic Anemia following Autologous Stem Cell Transplant: Case Report and Review of the Literature

Thrombopoietin receptor agonists (TPO-RA) are currently indicated for the treatment of chronic immune thrombocytopenia and relapsed refractory aplastic anemia. However, the off-label use of these drugs is more and more frequent, including in the setting of aplasia secondary to chemotherapy and hemopoietic stem cell transplant (SCT). Growing evidence suggests that mechanisms of action of TPO-RA go beyond the TPO-receptor stimulation and point at the immunomodulating properties of these drugs. Here, we present a case of prolonged bone marrow aplasia secondary to autologous SCT treated with eltrombopag. We describe the clinical efficacy and the immunomodulating effect of this drug on inflammatory cytokine profile and bone marrow histology. Furthermore, we provide a review of the most recent literature highlighting the efficacy and safety of TPO-RA after SCT and chemotherapy for hematologic conditions.

Eltrombopag for Treatment of Thrombocytopenia After Hematopoietic Stem Cell Transplantation

Objective:

This study aimed to evaluate the efficacy and safety of eltrombopag (ELT) in the treatment of thrombocytopenia following hematopoietic stem cell transplantation (HSCT).

Materials and Methods:

Forty-eight patients treated with ELT for thrombocytopenia after allogeneic or autologous transplantation at the Erciyes University Bone Marrow Transplantation Center between July 2017 and July 2021 were evaluated retrospectively.

Results:

Forty-eight HSCT recipients were included in this study. Thirty (62.5%) patients were evaluated as having experienced delayed platelet recovery (DPR) and 18 (37.5%) patients as having experienced secondary failure of platelet recovery (SFPR). The median platelet count before ELT treatment was 13x10⁹/L (range: 3-20x10⁹/L). Twenty-three patients responded to treatment and the cumulative incidence of successful platelet recovery was 48%. Patients with both DPR and SFPR responded, but patients with DPR had a higher response rate (50% vs. 44%). The median platelet count of the 23 responding patients was 12x10⁹/L (5-19x10⁹/L) before treatment and 68x10⁹/L (52-266x10⁹/L) after treatment (p<0.0001). While the number of bone marrow megakaryocytes before treatment was adequate in 22 (46%) cases, it was decreased in 26 (54%) cases. Patients with adequate bone marrow megakaryocytes had a better response rate than those without (77% vs. 23%, p<0.0001). The group with adequate megakaryocytes responded to treatment at a median of 33 days (range: 9-174 days). Patients with decreased megakaryocytes responded at a median of 55 days (30-164 days) (p=0.002). No drug-related side effects were observed in any patients.

Conclusion:

This real-life experience demonstrates that ELT is an effective and safe treatment option for thrombocytopenia after HSCT. The adequacy of bone marrow megakaryocytes before ELT treatment was an important factor affecting response to treatment.

Eltrombopag in the treatment of patients with persistent thrombocytopenia after haploidentical peripheral blood stem cell transplantation: a single-center experience

Persistent thrombocytopenia (PT) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is associated with an increased risk of bleeding and poor survival. The exact pathogenesis underlying PT remains unclear, and its management is difficult. Here we conducted a retrospective study to evaluate the efficacy and safety of eltrombopag (EPAG) in 34 patients with PT after allo-HSCT. Seven patients suffered from prolonged isolated thrombocytopenia (PIT), and 27 had secondary failure of platelet recovery (SFPR). For most patients, the initial dose was 25 mg or 50 mg daily, then adjusted to the maximum dose of 50-100 mg per day according to the response of platelet recovery and toleration of patients. The cumulative incidence (CI) of platelet recovery to at least 20 × 10⁹/L and 50 × 10⁹/L without transfusion support for at least 7 days was 72.1% and 60.7%, respectively. Nineteen (86.4%) of 22 responders were able to taper off the medication; furthermore, the platelet counts remained stable 1 month after withdrawal of EPAG. Although two patients discontinued EPAG during treatment due to headache and nausea, no patients developed grade 3 or 4 toxicities. Hypoplasia of bone marrow and decreased megakaryocytes (MKs) were found to be risk factors for overall response (OR) and complete response (CR) in multivariate analysis, respectively. Overall, our results indicated that EPAG can be used in the treatment of PT and that continuous exposure to EPAG may not be necessary.

Haploidentical donor transplant is associated with secondary poor graft function after allogeneic stem cell transplantation: A single-center retrospective study

Background

Secondary poor graft function (sPGF) is a serious complication after allogeneic hematopoietic stem cell transplantation (allo‐HSCT) related to poor outcome. We aimed to retrospectively evaluate the morbidity and hazard elements of sPGF after allo‐HSCT.

Methods

Eight hundred and sixty‐three patients who achieved initial engraftment of both neutrophils and platelets were retrospectively reviewed in this study.

Results

Fifty‐two patients developed sPGF within 180 days post‐transplants, with the median onset time was 62 days (range, 34–121 days) post‐transplants. The overall cumulative incidence of sPGF within 180 days post‐transplantation was 6.0%, with 3.4%, 3.4%, and 10.1%, respectively, in matched sibling donor (MSD), matched unrelated donor (MUD), and haploidentical donor (HID) transplant (p < 0.0001). Multivariable analysis showed that HID (HID vs. MSD: hazard ratio [HR] 2.525, p = 0.004; HID vs. MUD: [HR] 3.531, p = 0.017), acute graft versus host disease (aGVHD) within +30 days ([HR] 2.323, p = 0.003), and cytomegalovirus (CMV) reactivation ([HR] 8.915, p < 0.0001) within +30 days post‐transplants were hazard elements of sPGF. The patients with sPGF had poorer survival than good graft function (51.7±8.1% vs. 62.9±1.9%, p < 0.0001). Our results also showed that only CMV reactivation was the hazard element for the development of PGF in HID transplant ([HR] 12.521 p < 0.0001).

Conclusion

HID transplant is also an independent hazard element of sPGF except for aGVHD and CMV reactivation.

Eltrombopag for treatment of thrombocytopenia after allogeneic hematopoietic cell transplantation in children: Single-centre experience

Delayed recovery of thrombocytopenia is a well-known complication after allogeneic HSCT. Eltrombopag (ELT), a thrombopoietin receptor agonist (TRAs), induces platelet maturation and release. Mostly conducted in adults, some of the previous studies have shown that ELT seems to enhance platelet recovery for post-allogeneic HSCT thrombocytopenia, appears efficacious, and offers transfusion independence. To evaluate the safety and efficacy of ELT in pediatric patients with prolonged isolated thrombocytopenia (PIT) or secondary failure of platelet recovery (SFPR) after alloHSCT. Retrospective analysis of childhood patients who received treatment with ELT for persistent thrombocytopenia after alloHSCT between May 2016 and August 2019. We evaluated the safety and efficacy of ELT in 18 childhood patients with PIT or SFPR after alloHSCT. Eltrombopag (50 mg/d) treatment was started in all patients, above 6 years of age and 20 kg weight, who had thrombocytopenia despite neutrophil engraftment on the 30th day of HSCT. Our objective was to decrease the need for platelet transfusion and have a platelet count of more than 50 000/µL. The overall response rate was 77.7%. The median time to achieve a platelet level above 30 000/µL and 50 000/µL was 21 and 44 days, respectively. In four patients, platelet count never reached 30 000/mm³ . In two patients, the treatment was discontinued due to grade 3 hepatotoxicity. Our study supports the efficacy and relative safety of ELT use for the treatment of PIT and SFPR seen after alloHSCT in children.

Thrombopoietin Receptor Agonists (TPO-RAs): Drug Class Considerations for Pharmacists

The thrombopoietin receptor agonists (TPO-RAs) romiplostim, eltrombopag, avatrombopag, and lusutrombopag carry unique US Food and Drug Administration (US FDA)- and European Medicines Agency (EMA)-approved indications and may be used to increase platelet counts in a variety of conditions. Current indications for available TPO-RAs include treatment of chronic immune thrombocytopenia (ITP) in cases of insufficient response to prior treatment (avatrombopag, eltrombopag, romiplostim), management of thrombocytopenia in adult patients with chronic liver disease who are scheduled to undergo a procedure (avatrombopag, lusutrombopag), management of severe aplastic anemia (eltrombopag), and management of thrombocytopenia associated with interferon-based therapy for hepatitis C (eltrombopag). Across current indications, pharmacists can assist in stabilizing platelet counts and help to reduce large undulations commonly seen when starting, stopping, or transitioning between these agents. If therapy modifications may benefit the patient, pharmacists should discuss possible changes with the patient's treatment team or treating physician. When used for ITP, romiplostim, eltrombopag, and avatrombopag stimulate TPO receptors on hematopoietic stem cells (also known as c-Mpl, or CD110) to promote platelet production; however, romiplostim is the only TPO-RA that binds at the same site as endogenous TPO. These subtle mechanistic differences may explain why switching TPO-RA may be clinically advantageous in some situations. As pharmacists are called to counsel patients on TPO-RA use, a deep understanding of potential adverse events and management strategies, as well as appropriate monitoring, will increase the likelihood that patients meet their goals of therapy in the shortest timeframe. Other uses of TPO-RAs are also discussed in this review, including use following hematopoietic stem cell transplant, use in myelodysplastic syndrome, and use in chemotherapy-induced thrombocytopenia.

Efficacy and cost analysis of eltrombopag in thrombocytopenia and poor graft function post allogeneic hematopoietic cell transplantation

Eltrombopag has shown efficacy in the treatment of thrombocytopenia and poor graft function (PGF) after allogeneic hematopoietic cell transplantation (HCT) in retrospective observational studies, but is not approved for this indication. The cost of this drug is also a major concern in publicly funded health care systems. We collected data about patients who received eltrombopag for thrombocytopenia or PGF after HCT. Post-HCT thrombocytopenia, PGF, and eltrombopag response were defined as per previously published criteria. Primary outcome was treatment efficacy and secondary outcome was cost comparison between estimated treatment cost prior to and after initiation of eltrombopag. Seventeen patients (males 70.6%; median age = 58) received eltrombopag. Isolated thrombocytopenia was present in 11.8% (n = 2) patients while PGF was present in 88.2% (n = 15) of patients. After 8 weeks of treatment at the maximum dose of 150 mg orally daily, overall response rate (ORR) was seen in 76.5% (13/17) of patients: complete response (CR) in 10/13 patients and partial response (PR) in 3/13 patients. The use of eltrombopag was associated with an overall decrease in the total weekly care costs (5021 vs 2,524 CA$; P = 0.04). Thus, Eltrombopag is an efficacious and possibly cost-effective therapy for thrombocytopenia and PGF after allogeneic HCT.

Use of eltrombopag for the treatment of poor graft function after hematopoietic stem cell transplantation in children

The main objective of this study was to determine whether Eltrombopag, a synthetic thrombopoietin receptor agonist, could improve peripheral blood counts in the three hematopoietic lineages and achieve transfusion independence in children with poor graft function (PGF) after allogenic hematopoietic stem cell transplantation (HSCT). Retrospective study of patients under 18 years who developed PGF post-HSCT in a large tertiary institution between January 2013 and March 2019. Out of 198 allogeneic HSCT, five patients met PGF criteria and were treated with eltrombopag. Median time from HSCT to eltrombopag initiation was 120 days. The median starting dose was 50 mg/day and the maximum dose reached was 75 mg/day. Median treatment duration was 9 months. Three patients achieved complete response and one partial response. The median dose among responders was 75 mg/day and the median time to response 8 weeks. Responses were sustained in three patients and two required a booster dose of CD34⁺ -selected cells from the original donor. None of the patients had to stop treatment due to adverse effects. The use of eltrombopag in children with PGF achieved responses in 80% of cases and demonstrated to be an effective and safe therapeutic option in pediatric patients with PGF.

Eltrombopag for the treatment of poor graft function following allogeneic stem cell transplant: a retrospective multicenter study

This retrospective study assessed the effectiveness of eltrombopag (EPAG), a thrombopoietin receptor agonist, in the treatment of poor graft function (PGF) following an allogeneic haemopoietic stem cell transplantation (HSCT). Complete response was defined as normalization of blood counts, whereas partial response was defined as transfusion independence. A total of 48 patients with full donor chimerism after HSCT, received EPAG for a median of 120 days (range 10-591). Patients with uni- bi- or tri-lineage cytopenia started treatment at a median of 95 days (range 17-877) after HSCT. The overall response rate was 75%: 24 patients had a complete response and 12 had a partial response. Positive predictors of response were an HLA-matched donor, a CD34⁺ dose at transplant > 4 × 10⁶/kg, and starting EPAG treatment at least 90 days after HSCT. Patients with more than one positive predictor had a response rate of 92% for the overall patient cohort and 94% for patients with tri-lineage cytopenia. One-year survival was 89% for complete responders, 60% for partial responders and 20% for non-responders (p = 0.0004). EPAG improves peripheral blood counts in patients with poor graft function following HSCT. Response to EPAG can be predicted and has a significant impact on survival.

The Successful Sequential Use of Plerixafor and Eltrombopag For Hematopoietic Cell Transplantation in a Child With High-risk Neuroblastoma

High-dose chemotherapy with autologous hematopoietic stem cell transplantation improves event-free survival in patients with high-risk neuroblastoma. However, in heavily pretreated patients, poor marrow function can be an obstacle in the successful proceeding of therapy. Priming with plerixafor plus filgrastim is an option for effective mobilization and collection of stem cells. In addition, thrombopoietin agonist eltrombopag can improve the outcome of posttransplantation thrombocytopenia and poor graft function in the posttransplant setting. We describe a case of a child with high-risk neuroblastoma, for whom plerixafor and eltrombopag were used as an effective and safe supportive therapy.

Advances in the understanding of poor graft function following allogeneic hematopoietic stem-cell transplantation

Poor graft function (PGF) following allogeneic hematopoietic stem-cell transplantation (allo-HSCT) is a life-threatening complication and is characterized by bilineage or trilineage blood cell deficiency and hypoplastic marrow with full chimerism. With the rapid development of allo-HSCT, especially haploidentical-HSCT, PGF has become a growing concern. The most common risk factors illustrated by recent studies include low dose of infused CD34+ cells, donor-specific antibody, cytomegalovirus infection, graft versus host disease (GVHD), iron overload and splenomegaly, among others. Because of the poor prognosis of PGF, it is crucial to uncover the underlying mechanism, which remains elusive. Recent studies have suggested that the bone marrow microenvironment may play an important role in the pathogenesis of PGF. Deficiency and dysfunction of endothelial cells and mesenchymal stem cells, elevated reactive oxygen species (ROS) levels, and immune abnormalities are believed to contribute to PGF. In this review, we also discuss recent clinical trials that evaluate the safety and efficacy of new strategies in patients with PGF. CD34+-selected stem-cell boost (SCB) is effective with an acceptable incidence of GVHD, despite the need for a second donation. Alternative strategies including the applications of mesenchymal stem cells, N-acetyl-l-cysteine (NAC), and eltrombopag have shown favorable outcomes, but further large-scale studies are needed due to the small sample sizes of the recent clinical trials.

Evaluation of eltrombopag in thrombocytopenia post Hematopoietic cell transplantation: Rertrospective observational trial

BACKGROUND

Thrombocytopenia remains a life-threatening late complication of HCT with an incidence of 5-20%. Currently, there is no approved drug for the treatment of persistent thrombocytopenia post HCT and platelet transfusion is the maintain stay of treatment. Eltrombopag is approved for the treatment of thrombocytopenia associated with different diseases, however; data on eltrombopag treatment post HCT are limited.

METHODS

This is a retrospective cohort study evaluating the effect of eltrombopag on platelet recovery in patients with persistent thrombocytopenia post HCT. The primary endpoint was platelet recovery to ≥ 20,000/μL for 7 consecutive days without transfusion support after starting eltrombopag. Secondary endpoint was platelet recovery to ≥ 50,000/μL for 7 consecutive days.

RESULTS

Twenty-one patients were included. Twelve (75%) of 16 patients became independent from platelet transfusions. Median time from starting eltrombopag to last transfusion was 60 days (range, 9-226 days). Ten (63%) of 16 transfusion dependent patients with platelet count < 20,000/μL achieved the primary endpoint. Seven (33%) patients of 21 included had successful platelet recovery (ie, ≥50,000/μL without transfusion support) and the median time to platelet recovery in patients who achieved it was 32 days (range, 13-265 days). Ten patients (48%) were able to successfully discontinue eltrombopag without recurrence of thrombocytopenia.

CONCLUSION

Our findings demonstrated that eltrombopag appears to have a clinically significant impact on platelet recovery in persistent thrombocytopenic patients post HCT.

Eltrombopag: Role in Cytopenias Following Hematopoietic Stem Cell Transplantation

Eltrombopag is a small molecule oral agonist of the thrombopoietin receptor. Initially used for improving thrombocytopenia in chronic immune thrombocytopenia (ITP), it was later found to be efficacious in various other etiologies of thrombocytopenia as well as inherited marrow failure syndromes. Lately, it has been used for thrombocytopenia and poor graft function after allogeneic hematopoietic stem cell transplantation (HSCT) without any severe adverse events. Although prospective evidence of the efficacy is limited, there are increasing reports on the safety and efficacy with Eltrombopag in post HSCT thrombocytopenia and poor graft function. This provides an exciting opportunity for further research to evaluate both efficacy and cost-effectiveness of the use of Eltrombopag in this scenario. Here we review the current evidence on the indications for the use of Eltrombopag in the post allogeneic hematopoietic stem cell transplant setting.

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 Treating Thrombocytopenia after Allogeneic Stem Cell Transplantation

Thrombocytopenia after allogeneic hematopoietic stem cell transplantation (allo-SCT) can pose significant problems in management of patients. Eltrombopag is a small-molecule thrombopoietin receptor agonist that has been approved for use in immune thrombocytopenic purpura and aplastic anemia; but its use after allo-SCT is limited. Between 2014 and 2017, we treated 13 patients with eltrombopag for poor platelet engraftment without evidence of relapse at the time of initiation, including 6 patients with primary platelet engraftment failure and 7 with secondary platelet engraftment failure. Eltrombopag was started at an initial dose of 25 or 50 mg per day, and dose adjustments were made in accordance with the manufacturer's recommendation. The cumulative incidence of platelet recovery to ≥50,000/μL without the need for transfusion for at least 7 days was defined as response. The overall response rate was 62% (n = 8). Of the 6 patients with primary isolated platelet failure, 3 (50%) responded, and of the 7 patients with secondary platelet failure, 5 (71%) responded. The median time to response was 33 days (range, 11 to 68 days). In addition, no significant differences in platelet recovery were noted in patients with adequate and decreased bone marrow megakaryocytic reserve (60% and 67%, respectively). Although eltrombopag was well tolerated, and no patient discontinued treatment because of adverse events, only 3 patients were alive at the end of the observation period, with relapse and graft-versus-host disease accounting for majority of the deaths. This suggested that despite the relatively good overall response rate to eltrombopag, inadequate platelet engraftment is a harbinger of poor outcome in allo-SCT.

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.

Eltrombopag is an effective and safe therapy for refractory thrombocytopenia after haploidentical hematopoietic stem cell transplantation

Refractory thrombocytopenia is a frequent and severe complication after haploidentical allogeneic hematopoietic stem cell transplantation (haplo-HSCT) and lacks effective treatment strategies. Eltrombopag has shown promising results in several thrombocytopenia disorders. We report 38 patients treated with eltrombopag for refractory thrombocytopenia after haplo-HSCT. Eight patients had delayed platelet engraftment, 15 patients had secondary failure of platelet recovery, and 15 patients had poor graft function (PGF). Eltrombopag was initiated at 25 or 50 mg daily, and the dosage was adjusted to a maximum of 50-100 mg daily to maintain platelet between 50 × 10⁹/L and 100 × 10⁹/L. The cumulative incidence of platelet recovery to transfusion independence was 63.2% and to ≥50 × 10⁹/L without transfusion support was 52.3%. Furthermore, neutrophil counts and hemoglobin were also increased in the nine responders with PGF. Nineteen (79.2%) of the 24 responders were able to taper off eltrombopag, and the remaining 5 patients were able to begin a taper. The median duration of treatment was 64 (range 14-195) days. The presence of megakaryocyte before initiation was the only independent factor influencing the efficacy of eltrombopag (P = 0.044). Eltrombopag was well tolerated in all patients. In summary, eltrombopag was a safe and effective therapy for refractory thrombocytopenia after haplo-HSCT.

Use of Eltrombopag in Improving Poor Graft Function after Allogeneic Hematopoietic Stem Cell Transplantation

Eltrombopag is a thrombopoietin agonist and has been used in aplastic anemia and post-transplantation thrombocytopenia. The c-MPL receptor is present on hematopoietic stem cells. There are no reports of eltrombopag utilization for improving poor graft function in the post-transplant setting. Here were report a case of a young female with post-transplant poor graft function as evident from the low absolute neutrophil count, anemia, and thrombocytopenia on day 60. Eltrombopag was started on day 72 and resulted in improvement in all 3 cell lines. The counts continued to be stable even after eltrombopag was discontinued. The patient tolerated the drug without significant side effects for 1 year.

Eltrombopag for secondary failure of platelet recovery post-allogeneic hematopoietic stem cell transplant in children

Secondary failure of platelet engraftment occurs in 20% of patients undergoing allogeneic HSCT and is associated with poor outcome. Currently, there are no guidelines for treatment of late thrombocytopenia and platelet transfusion is the mainstay of treatment. Here, we describe the use of Eltrombopag to treat secondary failure of platelet recovery following HSCT in a child with severe aplastic anemia. Eltrombopag resulted in recovery of platelet count with no need for platelet transfusion support with no reported side effects. Eltrombopag may be used successfully in children with secondary failure of platelet recovery post-HSCT for SAA.