Impact of ruxolitinib pretreatment on outcomes after allogeneic stem cell transplantation in patients with myelofibrosis

Are transplant indications changing for myelofibrosis?

Myelofibrosis is a devastating myeloid malignancy characterized by dysregulation of the JAK-STAT pathway, resulting in splenomegaly, constitutional symptoms, anemia, thrombocytopenia, leukocytosis, and an increased likelihood of progression to acute leukemia. The only curative option is allogeneic stem cell transplantation. The numbers of transplants have been increasing every year, and although there have been improvements in survival, there remain many unanswered questions. In this review, we will evaluate patient selection and appropriate timing for transplantation. We will cover the current prognostic scoring systems, which can aid in the decision of when to move forward with transplant. We will also review the different donor options, as well as the conditioning regimens. The peritransplant management of splenomegaly will be reviewed. We will discuss management of posttransplant complications such as loss of donor chimerism or disease relapse. Finally, we will review what is known about the outlook of patients who have undergone allogeneic stem cell transplant with regards to quality of life and long-term survival.

How I treat transplant-eligible patients with myelofibrosis

Despite the approval of Janus kinase inhibitors and novel agents for patients with myelofibrosis (MF), disease-modifying responses remain limited, and hematopoietic stem cell transplantation (HSCT) remains the only potentially curative treatment option. The number of HSCTs for MF continues to increase worldwide, but its inherent therapy-related morbidity and mortality limit its use for many patients. Furthermore, patients with MF often present at an older age, with cytopenia, splenomegaly, and severe bone marrow fibrosis, posing challenges in managing them throughout the HSCT procedure. Although implementation of molecular analyses enabled improved understanding of disease mechanisms and subsequently sparked development of novel drugs with promising activity, prospective trials in the HSCT setting are often lacking, making an evidence-based decision process particularly difficult. To illustrate how we approach patients with MF with respect to HSCT, we present 3 different clinical scenarios to capture relevant aspects that influence our decision making regarding indication for, or against, HSCT. We describe how we perform HSCT according to different risk categories and, furthermore, discuss our up-to-date approach to reduce transplant-related complications. Last, we show how to harness graft-versus-MF effects, particularly in the posttransplant period to achieve the best possible outcomes for patients.

Definitions, incidence and outcome of poor graft function after hematopoietic cell transplantation: A systematic review and meta-analysis

Poor graft function (PGF) after allogeneic hematopoietic stem cell transplantation (HCT) is a serious complication with high morbidity and mortality. The reported incidence of PGF, its risk factors and outcome vary substantially between studies. This variability may be explained by heterogeneity in patient cohorts and HCT strategies, differences in the underlying causes of cytopenia, as well as by differences in PGF definition. In this systematic review and meta-analysis, we provide an overview of the various PGF definitions used and determined the impact of this variability on the reported incidence and outcome. We searched MEDLINE, EMBASE and Web of Science up to July 2022, for any study on PGF in HCT recipients. We performed random-effect meta-analyses for incidence and outcome and subgroup analyses based on different PGF criteria. Among 69 included studies (14.265 HCT recipients), we found 63 different PGF definitions, using various combinations of 11 common criteria. The median incidence of PGF was 7% (IQR: 5-11%, 22 cohorts). The pooled survival of PGF patients was 53% (95% CI: 45-61%, 23 cohorts). The most commonly reported risk factors associated with PGF were history of cytomegalovirus infection and prior graft-versus-host disease. Incidence was lower in studies with strict cytopenic cutoffs, while survival was lower for primary compared to secondary PGF. This work indicates that a standardized, quantitative definition of PGF is needed to facilitate clinical guideline development and to advance scientific progress.

Spleen volume and length determined by computed tomography impact outcome after allogeneic stem cell transplantation for myelofibrosis

Splenomegaly is a hallmark of myelofibrosis (MF), and reports on the impact of spleen size on the outcome of allo-HSCT have been conflicting, possibly due to differences in methods of assessment. We retrospectively analysed the impact of spleen volume and length measured by computed tomography on allo-HSCT outcome in 93 patients, 74% of whom had prior ruxolitinib treatment. Median spleen volume and length were 1.58 dm3 and 20 cm, respectively. We found a strong correlation between spleen volume and length (Pearson's r = 0.95, p < 0.001), Spearman (rho = 0.96, p < 0.001). After a median follow-up of 41.7 months, 5-year overall and disease-free survival were 66% and 59%, respectively. Spleen size did not impact overall survival or non-relapse mortality. Larger spleen volume and length as continuous variables were associated with slower platelet and leucocyte engraftment and a higher risk of disease relapse in univariate and multivariate analyses. Spleen length measured precisely by imaging is a good surrogate for spleen volume. In the era of JAK inhibitors, larger spleen size reflects advanced disease in MF and is associated with an increased risk of relapse but has no impact on non-relapse mortality and overall survival after allo-HSCT.

CD34+ -selected hematopoietic stem cell transplant conditioned with a myeloablative regimen in patients with advanced myelofibrosis

Allogeneic hematopoietic stem cell transplantation (Allo-HCT) remains the only curative treatment for myelofibrosis (MF). Transplantation in patients with MF is mostly done using a reduced intensity conditioning regimen with calcineurin inhibitors for graft versus host disease (GVHD) prophylaxis. Here we sought to evaluate outcomes of patients who underwent an ex vivo CD34+ -selected allo-HCT using myeloablative conditioning (MAC). Twenty-seven patients were included in this retrospective analysis. All patients were conditioned with busulfan, melphalan and fludarabine and antithymocyte globulin to prevent graft rejection. G-CSF mobilized peripheral blood stem cell grafts were depleted of T-cells using immunomagnetic CD34+ selection by CliniMACS device. Median follow-up among survivors was 50.6 months. The estimated 3-year overall survival, relapse free survival and the combined endpoint of GVHD/relapse free survival were 88% (95% CI, 75-100%), 80% (95% CI, 66-98%) and 74% (95% CI, 59-93%), respectively. The cumulative incidence of grade II-IV acute GVHD at day 100 was 33.3% (95% CI 16.4-51.3%), and two patients suffered chronic GVHD. There were no cases of primary graft failure. However, delayed graft failure occurred in two patients. We conclude that CD34+ selected allo-HCT with a MAC resulted in high survival rates in this cohort of patients with MF.

The Use of Allogeneic Hematopoietic Stem Cell Transplantation in Primary Myelofibrosis

Primary myelofibrosis (PMF) is a BCR-ABL1 negative myeloproliferative neoplasm characterized by clonal proliferation of myeloid cells. This leads to reactive bone marrow fibrosis, ultimately resulting in progressive marrow failure, hepatosplenomegaly, and extramedullary hematopoiesis. PMF is considered the most aggressive of the BCR-ABL1 negative myeloproliferative neoplasms with the least favorable prognosis. Constitutional symptoms are common, which can impact an individual’s quality of life and leukemic transformation remains an important cause of death in PMF patients. The development of the Janus kinase 2 (JAK2) inhibitors have provided a good option for management of PMF-related symptoms. Unfortunately, these agents have not been shown to improve overall survival or significantly alter the course of disease. Allogenic hematopoietic stem cell transplantation (allo-HSCT) remains the only curative treatment option in PMF. However, allo-HSCT is associated with significant treatment-related morbidity and mortality and has historically been reserved for younger, high-risk patients. This review examines patient, disease, and transplant-specific factors which may impact transplant-related outcomes in PMF. Through the vast improvements in donor selection, conditioning regimens, and post-transplant care, allo-HSCT may provide a safe and effective curative option for a broader range of PMF patients in the future.

Myelofibrosis: Genetic Characteristics and the Emerging Therapeutic Landscape

Primary myelofibrosis (PMF) is one of three myeloproliferative neoplasms (MPN) that are morphologically and molecularly inter-related, the other two being polycythemia vera (PV) and essential thrombocythemia (ET). MPNs are characterized by JAK-STAT-activating JAK2, CALR, or MPL mutations that give rise to stem cell-derived clonal myeloproliferation, which is prone to leukemic and, in case of PV and ET, fibrotic transformation. Abnormal megakaryocyte proliferation is accompanied by bone marrow fibrosis and characterizes PMF, while the clinical phenotype is pathogenetically linked to ineffective hematopoiesis and aberrant cytokine expression. Among MPN-associated driver mutations, type 1-like CALR mutation has been associated with favorable prognosis in PMF, while ASXL1, SRSF2, U2AF1-Q157, EZH2, CBL, and K/NRAS mutations have been shown to be prognostically detrimental. Such information has enabled development of exclusively genetic (GIPSS) and clinically integrated (MIPSSv2) prognostic models that facilitate individualized treatment decisions. Allogeneic stem cell transplantation remains the only treatment modality in MF with the potential to prolong survival, whereas drug therapy, including JAK2 inhibitors, is directed mostly at the inflammatory component of the disease and is therefore palliative in nature. Similarly, disease-modifying activity remains elusive for currently available investigational drugs, while their additional value in symptom management awaits controlled confirmation. There is a need for genetic characterization of clinical observations followed by in vitro and in vivo preclinical studies that will hopefully identify therapies that target the malignant clone in MF to improve patient outcomes.

How We Manage Myelofibrosis Candidates for Allogeneic Stem Cell Transplantation

Moving from indication to transplantation is a critical process in myelofibrosis. Most of guidelines specifically focus on either myelofibrosis disease or transplant procedure, and, currently, no distinct indication for the management of MF candidates to transplant is available. Nevertheless, this period of time is crucial for the transplant outcome because engraftment, non-relapse mortality, and relapse incidence are greatly dependent upon the pre-transplant management. Based on these premises, in this review, we will go through the path of identification of the MF patients suitable for a transplant, by using disease-specific prognostic scores, and the evaluation of eligibility for a transplant, based on performance, comorbidity, and other combined tools. Then, we will focus on the process of donor and conditioning regimens’ choice. The pre-transplant management of splenomegaly and constitutional symptoms, cytopenias, iron overload and transplant timing will be comprehensively discussed. The principal aim of this review is, therefore, to give a practical guidance for managing MF patients who are potential candidates for allo-HCT.

Novel therapies vs hematopoietic cell transplantation in myelofibrosis: who, when, how?

Myelofibrosis is one of the classical Philadelphia chromosome-negative myeloproliferative neoplasms characterized by progressive marrow failure and chronic inflammation. Discovery of the JAK2 mutation paved the way for development of small molecular inhibitors and further facilitated the research in understanding of molecular biology of the disease. Development of novel medications and synergistic combinations with standard JAK inhibitor (JAKi) therapy may have the potential to improve depth and duration of disease control and symptomatic benefit, whereas advancements in allogeneic hematopoietic stem cell transplantation (HCT) have improved tolerability and donor availability, allowing for more patients to pursue this potentially curative therapy. The increase in options for medical therapy and changing risk profile of HCT is leading to increased complexity in counseling patients on choice of management strategy. In this case-based review, we summarize our approach to symptom-directed medical therapy, including the use of novel drugs and combination therapies currently under study in advanced clinical trials. We outline our recommendations for optimal timing of HCT, including risk-adapted selection for early HCT as opposed to delayed HCT after upfront JAKi therapy, as well as the use of pretransplant JAKi and alternative donor sources.

Impact of prior JAK-inhibitor therapy with ruxolitinib on outcome after allogeneic hematopoietic stem cell transplantation for myelofibrosis: a study of the CMWP of EBMT

JAK1/2 inhibitor ruxolitinib (RUX) is approved in patients with myelofibrosis but the impact of pretreatment with RUX on outcome after allogeneic hematopoietic stem cell transplantation (HSCT) remains to be determined. We evaluated the impact of RUX on outcome in 551 myelofibrosis patients who received HSCT without (n = 274) or with (n = 277) RUX pretreatment. The overall leukocyte engraftment on day 45 was 92% and significantly higher in RUX responsive patients than those who had no or lost response to RUX (94% vs. 85%, p = 0.05). The 1-year non-relapse mortality was 22% without significant difference between the arms. In a multivariate analysis (MVA) RUX pretreated patients with ongoing spleen response at transplant had a significantly lower risk of relapse (8.1% vs. 19.1%; p = 0.04)] and better 2-year event-free survival (68.9% vs. 53.7%; p = 0.02) in comparison to patients without RUX pretreatment. For overall survival the only significant factors were age > 58 years (p = 0.03) and HLA mismatch donor (p = 0.001). RUX prior to HSCT did not negatively impact outcome after transplantation and patients with ongoing spleen response at time of transplantation had best outcome.

Outcomes of Allogeneic Hematopoietic Cell Transplantation in Patients With Myelofibrosis-A Systematic Review and Meta-Analysis

Allogeneic hematopoietic cell transplant (allo-HCT) remains the only potentially curative therapeutic modality for patients with primary or secondary myelofibrosis (MF). However, many patients are considered ineligible for allo-HCT, and transplant-related mortality can be substantial. Data on the efficacy and safety of allo-HCT are mixed and largely derived from retrospective studies. We aimed to synthesize the available evidence on the safety and efficacy of allo-HCT in MF and to identify patient, disease, and transplant characteristics with prognostic impact on outcomes of patients with MF undergoing allo-HCT. For this systematic review and meta-analysis, Cochrane Library, Google Scholar, Ovid Medline, Ovid Embase, PubMed, Scopus, and Web of Science Core Collection were searched from inception to October 11, 2020, for studies on allo-HCT in MF. Random-effects models were used to pool response rates for the co-primary outcomes of 1-year, 2-year, and 5-year overall survival (OS). Rates of non-relapse mortality and acute and chronic graft-versus-host-disease (GVHD) were studied as secondary endpoints. Subgroup analyses on the effect of conditioning regimen intensity, baseline dynamic international prognostic scoring system (DIPSS) score, and patient age were performed. The study protocol has been registered on PROSPERO (CRD42020188706). Forty-three studies with 8739 patients were identified and included in this meta-analysis. Rates of 1-year, 2-year, and 5-year OS were 66.7% (95% confidence interval [CI], 63.5%-69.8%), 64.4% (95% CI, 57.6%-70.6%), and 55.0% (95% CI, 51.8%-58.3%), respectively. Rates of 1-year, 2-year, and 5-year nonrelapse mortality were 25.9% (95% CI, 23.3%-28.7%), 29.7% (95% CI, 24.5%-35.4%), and 30.5% (95% CI, 25.9%-35.5%), respectively. The combined rate of graft failure was 10.6% (95% CI, 8.9%-12.5%) with primary and secondary graft failure occurring in 7.3% (95% CI, 5.7%-9.4%) and 5.9% (95% CI, 4.3%-8.0%) of patients, respectively. Rates of acute and chronic graft-versus-host disease were 44.0% (95% CI, 39.6%-48.4%; grade III/IV: 15.2%) and 46.5% (95% CI, 42.2%-50.8%; extensive or moderate/severe: 26.1%), respectively. Subgroup analyses did not show any significant difference between conditioning regimen intensity (myeloablative versus reduced-intensity), median patient age, and proportion of DIPSS-intermediate-2/high patients. The quality of the evidence is limited by the absence of randomized clinical trials in the field and the heterogeneity of patient and transplant characteristics across included studies. Given the poor prognosis of patients not receiving transplants and in the absence of curative nontransplantation therapies, our results support consideration of allo-HCT for eligible patients with MF.

Allogeneic Stem Cell Transplantation Platforms With Ex Vivo and In Vivo Immune Manipulations: Count and Adjust

Various allogeneic (allo) stem cell transplantation platforms have been developed over the last 2 decades. In this review we focus on the impact of in vivo and ex vivo graft manipulation on immune reconstitution and clinical outcome. Strategies include anti-thymocyte globulin- and post-transplantation cyclophosphamide-based regimens, as well as graft engineering, such as CD34 selection and CD19/αβT cell depletion. Differences in duration of immune suppression, reconstituting immune repertoires, and associated graft-versus-leukemia effects and toxicities mediated through viral reactivations are highlighted. In addition, we discuss the impact of different reconstituting repertoires on donor lymphocyte infusions and post allo pharmacological interventions to enhance tumor control. We advocate for precisely counting all graft ingredients and therapeutic drug monitoring during conditioning in the peripheral blood, and for adjusting dosing accordingly on an individual basis. In addition, we propose novel trial designs to better assess the impact of variations in transplantation platforms in order to better learn from our diversity of “counts” and potential “adjustments.” This will, in the future, allow daily clinical practice, strategic choices, and future trial designs to be based on data guided decisions, rather than relying on dogma and habits.

Allogeneic Hemopoietic Stem Cell Transplantation for Myelofibrosis: 2021

The aim of this review is to update the current status of allogeneic hemopoietic stem cell transplants (HSCT) for patients with myelofibrosis (MF). We have first summarized the issue of an indication for allogeneic HSCT, discussing several prognostic scoring systems, developed to predict the outcome of MF, and therefore to identify patients who will benefit of an allogeneic HSCT. Patients with low risk MF are usually not selected for a transplant, whereas patients with intermediate or high risk MF are eligible. A separate issue, is how to predict the outcome of HSCT: we will outline a clinical molecular myelofibrosis transplant scoring system (MTSS), which predicts overall survival, ranging from 90% for low risk patients, to 20% for very high risk patients. We will also discuss transfusion burden and spleen size, as predictors of transplant outcome. The choice of a transplant platform including the conditioning regimen, the stem cell source and GvHD prophylaxis, are crucial for a successful program in MF, and will be outlined. Complications such as poor graft function, graft failure, GvHD and relapse of the disease, will also be reviewed. Finally we discuss monitoring the disease after HSCT with donor chimerism, driver mutations and hematologic data. We have made an effort to make this review as comprehensive and up to date as possible, and we hope it will provide some useful data for the clinicians.

Ruxolitinib early administration reduces acute GVHD after alternative donor hematopoietic stem cell transplantation in acute leukemia

This study aimed to observe the safety and clinical efficacy of early application of ruxolitinib to prevent acute graft-versus-host disease (aGVHD) after alternative donor transplantation in acute leukemia. There were 57 patients undergoing allo-HSCT at the Affiliated Cancer Hospital of Zhengzhou University from July 2017 to October 2019. They were divided into control(16 patients) and ruxolitinib (41 patients) groups. For aGVHD prophylaxis, the control group received post-transplantation cyclophosphamide, antithymocyte globulin-Fresenius, cyclosporine A, and mycophenolate mofetil, while in the ruxolitinib group, ruxolitinib 5 mg/d in adults or 0.07–0.1 mg/(kg d) in children was administered from the day of neutrophil engraftment to 100 days post-transplantation based on control group. We found 55 patients had successful reconstitution of hematopoiesis; No significant difference was found in cGVHD, hemorrhagic cystitis, pulmonary infection, intestinal infection, Epstein-Barr virus infection, cytomegalovirus infection, relapse, death, and nonrelapse mortality. The incidences of aGVHD (50 vs. 22%, P = 0.046) and grade II–IV aGVHD (42.9 vs. 12.2%, P = 0.013) were significantly higher in the control group than in the ruxolitinib group. No significant differences were observed in overall survival (P = 0.514), disease-free survival (P = 0.691), and cumulative platelet transfusion within 100 days post-transplantation between two groups. This suggests early application of ruxolitinib can reduce the incidence and severity of aGVHD and patients are well tolerated.

Application of Stem Cell Therapy in Myelofibrosis

Myelofibrosis (MF) belongs to a group of clonal stem cell disorders known as the BCR-ABL-negative myeloproliferative neoplasms. Allogeneic hematopoietic stem cell transplantation (HCT) is currently the only curative treatment option for MF. Because HCT can be associated with significant morbidity and mortality, patients need to be carefully selected based on disease-risk, fitness, and transplant factors. Furthermore, in the era of JAK inhibitors, the timing of transplantation has become a challenging question. Here the authors review recent developments in HCT for MF, focusing on risk stratification and optimal timing.

Primary myelofibrosis: 2021 update on diagnosis, risk-stratification and management

DISEASE OVERVIEW

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm (MPN) characterized by stem cell-derived clonal myeloproliferation that is often but not always accompanied by JAK2, CALR, or MPL mutations. Additional disease features include bone marrow reticulin/collagen fibrosis, aberrant inflammatory cytokine expression, anemia, hepatosplenomegaly, extramedullary hematopoiesis (EMH), constitutional symptoms, cachexia, leukemic progression, and shortened survival.

DIAGNOSIS

Bone marrow morphology is the primary basis for diagnosis. Presence of JAK2, CALR, or MPL mutation, expected in around 90% of the patients, is supportive but not essential for diagnosis; these mutations are also prevalent in the closely related MPNs, namely polycythemia vera (PV) and essential thrombocythemia (ET). The 2016 World Health Organization classification system distinguishes "prefibrotic" from "overtly fibrotic" PMF; the former might mimic ET in its presentation. Furthermore, approximately 15% of patients with ET or PV might progress into a PMF-like phenotype (post-ET/PV MF) during their clinical course.

ADVERSE MUTATIONS

SRSF2, ASXL1, and U2AF1-Q157 mutations predict inferior survival in PMF, independent of each other and other risk factors. RAS/CBL mutations predicted resistance to ruxolitinib therapy.

ADVERSE KARYOTYPE

Very high risk abnormalities include -7, inv (3), i(17q), +21, +19, 12p-, and 11q-.

RISK STRATIFICATION

Two new prognostic systems for PMF have recently been introduced: GIPSS (genetically-inspired prognostic scoring system) and MIPSS70+ version 2.0 (MIPSSv2; mutation- and karyotype-enhanced international prognostic scoring system). GIPSS is based exclusively on mutations and karyotype. MIPSSv2 includes, in addition, clinical risk factors. GIPSS features four and MIPSSv2 five risk categories.

RISK-ADAPTED THERAPY

Observation alone is advised for MIPSSv2 "low" and "very low" risk disease (estimated 10-year survival 56%-92%); allogeneic hematopoietic stem cell transplant (AHSCT) is the preferred treatment for "very high" and "high" risk disease (estimated 10-year survival 0%-13%); treatment-requiring patients with intermediate-risk disease (estimated 10-year survival 30%) are best served by participating in clinical trials. In non-transplant candidates, conventional treatment for anemia includes androgens, prednisone, thalidomide, and danazol; for symptomatic splenomegaly, hydroxyurea and ruxolitinib; and for constitutional symptoms, ruxolitinib. Fedratinib, another JAK2 inhibitor, has now been FDA-approved for use in ruxolitinib failures. Splenectomy is considered for drug-refractory splenomegaly and involved field radiotherapy for non-hepatosplenic EMH and extremity bone pain.

NEW DIRECTIONS

A number of new agents, alone or in combination with ruxolitinib, are currently under investigation for MF treatment (ClinicalTrials.gov); preliminary results from some of these clinical trials were presented at the 2020 ASH annual meeting and highlighted in the current document.

The safety of JAK kinase inhibitors for the treatment of myelofibrosis

INTRODUCTION

During the last decade, the development of small molecule inhibitors of Janus kinases (JAKi) contributed to revolutionize the therapeutic landscape of myelofibrosis (MF). JAKi proved to be effective in controlling disease-related symptoms and splenomegaly with remarkable inter-drug variability. However, in some cases the border between clinical efficacy of JAKi and dose-dependent toxicities is narrow leading to sub-optimal dose modifications and/or treatment discontinuation.

AREAS COVERED

In the current review, the authors aimed at providing a comprehensive review of the safety profile of JAKi that are currently approved or in advanced clinical development. Also, a short discussion of promising JAKi in early clinical evaluation and molecules 'lost' early in clinical development is provided. Finally, we discuss the possible strategies aimed at strengthening the safety of JAKi while improving the therapeutic efficacy.

EXPERT OPINION

Overall, JAKi display a satisfactory risk-benefit ratio, with main toxicities being gastrointestinal or related to the myelo/immunosuppressive effects, generally mild and easily manageable. However, JAKi may be associated with potentially life-threatening toxicities, such as neurological and infectious events. Thus, many efforts are needed in order to optimize JAKi-based therapeutic strategies without burdening patient safety. This could be attempted through drug combinations or the development of more selective molecules.

Atypical Chronic Myeloid Leukemia: Where Are We Now?

Atypical chronic myeloid leukemia, BCR-ABL1 negative (aCML) is a rare myelodysplastic syndrome (MDS)/myeloproliferative neoplasm (MPN) with a high rate of transformation to acute myeloid leukemia, and poor survival. Until now, the diagnosis has been based on morphological grounds only, possibly making the real frequency of the disease underestimated. Only recently, new insights in the molecular biology of MDS/MPN syndromes have deepened our knowledge of aCML, enabling us to have a better molecular profile of the disease. The knowledge gleaned from next generation sequencing has complemented morphologic and laboratory WHO criteria for myeloid neoplasms and can provide greater specificity in distinguishing aCML from alternative MDS/MPN or MPNs. The most commonly mutated genes (>20%) in aCML are SETBP1, ASXL1, N/K-RAS, SRSF2, and TET2, and less frequently (< 10%) CBL, CSFR3, JAK2, EZH2, and ETNK1. Several of these mutations affect the JAK-STAT, MAPK, and ROCK signaling pathways, which are targetable by inhibitors that are already in clinical use and may lead to a personalized treatment of aCML patients unfit for allogeneic transplant, which is currently the only curative option for fit patients. In this review, we present two emblematic clinical cases and address the new molecular findings in aCML and the available treatment options.

Peritransplantation Use of Ruxolitinib in Myelofibrosis

Ruxolitinib is an oral JAK1/2 inhibitor that is approved for use in patients with intermediate and high-risk myelofibrosis (MF) based on its proven spleen and symptom burden reduction. Its impact on hematopoietic stem cell transplantation (HSCT) outcomes is largely unknown, however. A significant number of patients proceeding to HSCT have been treated with ruxolitinib, and the specifics of its peritransplantation use vary widely in the published literature. Here we review the currently published data and experience to guide management of patients with MF on ruxolitinib proceeding to HSCT.

Current and future therapies for myelofibrosis

Myelofibrosis is classified as a 'Philadelphia-chromosome negative' clonal myeloproliferative disorder. The heterogeneity of this condition and patient population and array of often challenging clinical manifestations can frequently make therapeutic decisions challenging. Despite many advances in therapy with targeted and combination approaches, following an enhanced understanding of underlying disease pathogenesis, cure only remains achievable with allogeneic stem cell transplant. This option is often limited to a small group of younger transplant-eligible patients with more advanced disease who have both a suitable donor and no or few co-morbidities. In this article, we will discuss up-to-date disease prognostication, common clinical challenges associated with myelofibrosis and both standard and novel therapeutic approaches. Increasingly complex prognostic modelling utilises patient-specific, haematological and genomic parameters to improve the accuracy of risk assessment and predict disease progression. We will also focus on difficult clinical scenarios such as disease-associated anaemia, thrombocytopenia and extremes of age. Future and evolving therapies within this field are highly anticipated and novel JAK inhibitor and non-JAK inhibitor-based therapy will also be discussed, including the new challenge of how to switch from one JAK inhibitor therapy to another.

A Prospective Pilot Study of Graft-versus-Host Disease Prophylaxis with Post-Transplantation Cyclophosphamide and Ruxolitinib in Patients with Myelofibrosis

INTRODUCTION

This prospective study evaluated a calcineurin inhibitor-free graft-versus-host disease (GVHD) prophylaxis regimen of ruxolitinib in combination with post-transplant cyclophosphamide (PTCy). Patents and Methods: Twenty patients with primary or secondary myelofibrosis were prospectively enrolled. Reduced intensity conditioning was performed, followed by allogeneic stem cell transplantation from related (n = 7) or unrelated (n = 13) donors. GVHD prophylaxis included only PTCy and ruxolitinib (45 mg) from day-7 to day-2, and 15 mg from day+5 to day+100. This trial was registered at www.clinicaltrials.gov as #NCT02806375.

RESULTS

Primary engraftment was documented in 17 patients. One patient experienced primary graft failure and 2 died before engraftment. Eleven patients demonstrated severe poor graft function (SPGF), which required ruxolitinib dose reduction. The regimen was well tolerated, with grade 3-4 non-haematological toxicity in 30%, viral reactivation in 45%, and severe sepsis in 15% of patients. The incidence of acute GVHD grade II-IV was 25%, grade III-IV GVHD was 15%, and moderate chronic GVHD was 20%, with no severe cases. Only 2 patients required systemic steroids. Haematological relapse was documented in 1 patient. Two-year non-relapse mortality was 15%, 2-year overall survival was 85%, and 2-year event-free survival was 72%.

CONCLUSION

GVHD prophylaxis with PTCy and ruxolitinib is associated with low toxicity, good acute and chronic GVHD control, and low relapse incidence. However, the relatively high rate of SPGF should be taken into account. SPGF could possibly be mitigated by ruxolitinib dose reduction.

Allogeneic hematopoietic stem-cell transplantation for myelofibrosis

Myelofibrosis is one of the Philadelphia chromosome (Ph)-negative myeloproliferative neoplasms with heterogeneous clinical course. Though many treatment options, including Janus kinase (JAK) inhibitors, have provided clinical benefits and improved survival, allogeneic hematopoietic stem-cell transplantation (AHSCT) remains the only potentially curative therapy. Considering the significant transplant-related morbidity and mortality, it is crucial to decide who to proceed to AHSCT, and when. In this review, we discuss recent updates in patient selection, prior splenectomy, conditioning regimen, donor type, molecular mutation, and other factors affecting AHSCT outcomes. Relapse is a major cause of treatment failure; we also describe recent data on minimal residual disease monitoring and management of relapse. In addition, emerging studies have reported pretransplant therapy with ruxolitinib for myelofibrosis showing favorable results, and further research is needed to explore its use in the post-transplant setting.

Janus Kinase Inhibition for Graft-Versus-Host Disease: Current Status and Future Prospects

Allogeneic hematopoietic stem cell transplantation (Allo-HSCT) is a curative treatment for many hematological malignant and non-malignant diseases. A major complication of the procedure is the donor T-cell-mediated graft-versus-host disease (GvHD). GvHD accounts for about 10% of early mortality after transplantation. GVHD is also the major cause of morbidity and disability in the late follow-up phase of transplanted patients, mainly because of the low response to first-line steroids, and the lack of efficient second-line standard treatments. The increasing knowledge regarding GVHD pathogenesis provides new pharmacological targets, potentially exploitable in clinical practice, in order to prevent and treat this complication. This review provides a description of GVHD pathogenesis, with a focus on the central role of the Janus kinase-related mechanisms. The first inflammatory innate-immunity response is triggered by a JAK/STAT dependent pathway, and JAK inhibition impairs antigen-presenting cell differentiation and activation and downregulates the expression of signals for T-cell triggering. The chronic evolution of alloreactivity, characterized by the long-term maintenance of inflammation and fibrosis, is also dependent on JAK/STAT activation. Based on preclinical data, we reviewed the rationale behind the clinical use of JAK-inhibitors in GVHD, presenting available results of clinical trials and reports, and looked at future implementation of this new promising treatment approach.

Fludarabine/Busulfan Conditioning-Based Allogeneic Hematopoietic Cell Transplantation for Myelofibrosis: Role of Ruxolitinib in Improving Survival Outcomes

Allogeneic hematopoietic cell transplantation (allo-HCT) is the only curative treatment modality for primary myelofibrosis (MF) and related myeloproliferative neoplasms. Older age at diagnosis and age-related comorbidities make most patients ineligible for allo-HCT, given concerns for nonrelapse mortality (NRM). Here we report the outcomes of 37 consecutive recipients of allo-HCT for MF performed at a single center between 2009 and 2018 with a standardized institutional protocol. Most patients received ruxolitinib before HCT (n = 32), and those with splenomegaly >22 cm received pretransplantation splenic irradiation. The median age at HCT was 60 years (range, 40 to 74 years), and 68% of the cohort carried a JAK2 driver mutation. All patients received fludarabine/busulfan-based conditioning; 22 patients (59%) received a reduced-intensity conditioning regimen. All patients received peripheral blood grafts, from a matched sibling donor in 16 patients (43%), an unrelated donor in 20 patients, and a haploidentical-related donor in 1 patient. Sixty-one percent had a Hematopoietic Cell Transplantation Comorbidity Index ≥3, 40% had a Karnofsky Performance Status score <90, and 24% had a high-risk DIPSS Plus score. With a median follow-up of 40.2 months (range, 16.9 to 115 months), the 3-year overall survival and relapse-free survival were 81.1% (95% confidence interval [CI], 64.4% to 90.5%) and 78.4% (95% CI, 61.4% to 88.5%), respectively. Only 2 patients relapsed/progressed after transplant. NRM at 2 years was 16.2% (95% CI, 6.5% to 29.9%). All patients engrafted. Sixteen patients were treated with ruxolitinib post-transplantation for graft-versus-host disease, graft rejection/relapse, or persistent MF. These results suggest that pretransplantation ruxolitinib, fludarabine/busulfan-based conditioning, and splenic management are keys to improved transplantation outcomes in patients undergoing allo-HCT for MF.

Allogeneic Hematopoietic Stem Cell Transplantation for Post-essential Thrombocythemia and Post-polycythemia Vera Myelofibrosis

Objective Little information is available about the outcome of allogeneic hematopoietic stem cell transplantation (HSCT) for patients with secondary myelofibrosis from essential thrombocythemia (ET) and polycythemia vera (PV). A nationwide retrospective study of the outcome of HSCT for post-ET and post-PV myelofibrosis was conducted in Japan. Patients and Methods Clinical data for patients with post-ET (n=29) and post-PV (n=9) myelofibrosis who had received first allogeneic HSCT were extracted from the Transplant Registry Unified Management Program, which is a registry of the outcomes of HSCT in Japan. Results Five patients died without neutrophil recovery within 60 days after transplantation. The incidence of neutrophil recovery was significantly lower in umbilical cord blood (UCB) transplantation than in related donor transplantation (40% vs. 92%, p=0.010). The 1-year non-relapse mortality for post-ET and post-PV myelofibrosis was 35% and 27%, respectively (p=0.972). No patient or transplantation characteristics were associated with non-relapse mortality. The 4-year overall survival for post-ET and post-PV myelofibrosis was 46% and 65%, respectively (p=0.362). A univariate analysis identified UCB transplantation (vs. related donor, p=0.017) and ≥10 times red blood cell transfusions before transplantation (vs. <10 times, p=0.037) as predictive of a lower overall survival. Conclusion Allogeneic HSCT provides a long-term survival for at least some patients with post-ET and post-PV myelofibrosis. Further studies with more patients are required to determine the best alternative donor.

Reduced-intensity conditioning allogeneic transplant with dual T-cell depletion in myelofibrosis

BACKGROUND

There remains a significant mortality in recipients with MF who undergo allogeneic stem cell transplant (allo-HSCT). The combination of antithymocyte globulin (ATG) and post-transplant cyclophosphamide (PTCy) provides good control of graft-versus-host disease (GVHD) when peripheral blood stem cell grafts are used.

METHODS

We report the outcome of 37 recipients with myelofibrosis who underwent reduced-intensity conditioning (RIC) allo-HSCT with ATG and PTCy. Median follow-up was 16.4 months.

RESULTS

Nine (24.3%) recipients received 10/10 MRD grafts, 17 (45.9%) 10/10 MUD grafts, 4 (10.8%) 9/10 MUD grafts, and 7 (18.9%) haploidentical donor grafts. Six (16.3%) patients had graft failure. The cumulative incidence of grade II-IV and grade III-IV aGVHD at day +100 and moderate/severe chronic GVHD at 1 year was as follows: 13.5%, 5.4%, and 17%. There were no deaths secondary to GVHD. One-year overall survival (OS), relapse-free survival (RFS), non-relapse mortality (NRM), and GVHD-free/RFS (GRFS) were respectively 74.4%, 71.3%, 23%, and 43.3%. Those recipients who had worse KPS ≤ 80% had worse OS and RFS.

CONCLUSION

RIC allo-HSCT with ATG and PTCy results in high OS and RFS in patients with myelofibrosis and absence of mortality secondary to GVHD. Further investigations are required to reduce NRM and graft failure rates.

The role of allogeneic stem-cell transplant in myelofibrosis in the era of JAK inhibitors: a case-based review

Allogeneic hematopoietic stem-cell transplantation (HSCT) is, at present, the only potentially curative therapy for myelofibrosis (MF). Despite many improvements, outcomes of HSCT are still burdened by substantial morbidity and high transplant-related mortality. Allogeneic transplant is generally considered in intermediate-2 and high-risk patients aged <70 years, but the optimal selection of patients and timing of the procedure remains under debate, as does as the role of JAK inhibitors in candidates for HSCT. Starting from a real-life clinical case scenario, herein we examine some of the crucial issues of HSCT for MF in light of recent refinements on MF risk stratification, data on the use of ruxolitinib before and after transplant and findings on the impact of different conditioning regimens and donor selection.

State-of-the-art review: allogeneic stem cell transplantation for myelofibrosis in 2019

Advances in understanding the pathogenesis and molecular landscape of myelofibrosis have occurred over the last decade. Treating physicians now have access to an ever-evolving armamentarium of novel agents to treat patients, although allogeneic hematopoietic stem cell transplantation remains the only curative approach. Improvements in donor selection, conditioning regimens, disease monitoring and supportive care have led to augmented survival after transplantation. Nowadays, there are comprehensive guidelines concerning allogeneic hematopoietic stem cell transplantation for patients with myelofibrosis. However, it commonly remains difficult for both physicians and patients alike to weigh up the risk-benefit ratio of transplantation given the inherent heterogeneity regarding both clinical course and therapeutic response. In this timely review, we provide an up-to-date synopsis of current transplantation recommendations, discuss usage of JAK inhibitors before and after transplantation, examine donor selection and compare conditioning platforms. Moreover, we discuss emerging data concerning the impact of the myelofibrosis mutational landscape on transplantation outcome, peritransplant management of splenomegaly, poor graft function and prevention/management of relapse.

Comparison of Outcomes of Allogeneic Transplantation for Primary Myelofibrosis among Hematopoietic Stem Cell Source Groups

The choice of alternative donor is a major issue in allogeneic hematopoietic stem cell transplantation (HSCT) for patients with primary myelofibrosis (PMF) without an HLA-matched related donor. We conducted this retrospective study using the Japanese national registry data for 224 PMF patients to compare the outcomes of first allogeneic HSCT from HLA-matched related donor bone marrow (Rtd-BM), HLA-matched related donor peripheral blood stem cells (Rtd-PB), HLA-matched unrelated donor bone marrow (UR-BM), unrelated umbilical cord blood (UR-UCB), and other hematopoietic stem cell grafts. Nonrelapse mortality (NRM) rates at 1 year after Rtd-BM, Rtd-PB, UR-BM, UR-UCB, and other transplantations were 16%, 36%, 30%, 41%, and 48%, respectively. Multivariate analysis identified UR-UCB transplantation, other transplantation, frequent RBC transfusion before transplantation, and frequent platelet (PLT) transfusion before transplantation as predictive of higher NRM. Relapse rates at 1 year after Rtd-BM, Rtd-PB, UR-BM, UR-UCB, and other transplantation were 14%, 17%, 11%, 14%, and 15%, respectively. No specific factor was associated with the incidence of relapse. Overall survival (OS) at 1 and 4 years after Rtd-BM, Rtd-PB, UR-BM, UR-UCB, and other transplantation were 81% and 71%, 58% and 52%, 61% and 46%, 48% and 27%, and 48% and 41%, respectively. Multivariate analysis identified older patient age, frequent RBC transfusion before transplantation, and frequent PLT transfusion before transplantation as predictive of lower OS. In conclusion, UR-UCB transplantation, as well as UR-BM transplantation, can be selected for PMF patients without an HLA-identical related donor. However, careful management is required for patients after UR-UCB transplantation because of the high NRM. Further studies including more patients after HLA-haploidentical related donor and HLA-mismatched unrelated donor transplantation would provide more valuable information for patients with PMF when making decisions regarding the choice of alternative donor.

Classical Philadelphia-negative myeloproliferative neoplasms: focus on mutations and JAK2 inhibitors

Classical Philadelphia- negative myeloproliferative neoplasms (MPNs) encompass three main myeloid malignancies: polycythemia vera (PV), essential thrombocythemia (ET), and myelofibrosis (MF). Phenotype-driver mutations in Janus kinase 2 (JAK2), calreticulin (CALR), and myeloproliferative leukemia virus oncogene (MPL) genes are mutually exclusive and occur with a variable frequency. Driver mutations influence disease phenotype and prognosis. PV patients with JAK2 exon 14 mutation do not differ in number of thrombotic events, risk of leukemic and fibrotic transformation, and overall survival to those with JAK2 exon 12 mutation. Type 2-like CALR-mutated ET patients have lower risk of thrombosis if compared with those carrying JAK2 or type 1-like CALR mutation. For ET, overall survival is comparable between patients with JAK2 and either type 1-like and type 2-like CALR mutations. For MF, better OS is demonstrated for patients harboring a type 1-like CALR mutation than those with type 2-like CALR or JAK2. The discovery of driver mutations in MPNs has prompted the development of molecularly targeted therapy. Among JAK2 inhibitors, ruxolitinib (RUX) has been approved for (1) treatment of intermediate-2 and high-risk MF and (2) PV patients who are resistant to or intolerant to hydroxyurea. RUX reduces spleen size and alleviates disease symptoms in a proportion of MF patients. RUX in MF leads to prolonged survival and reduces risk of death. RUX controls hematocrit, reduces spleen size and alleviates symptoms in PV. Adverse events of RUX are moderate, however, its long-term use may be associated with opportunistic infections. Trials with other JAK2 inhibitors are ongoing.