Treosulfan-Based Conditioning Regimen in Sibling and Alternative Donor Hematopoietic Stem Cell Transplantation for Children with Sickle Cell Disease

Effect of allogeneic hematopoietic stem cell transplantation on sickle cell disease-related organ complications: A systematic review and meta-analysis

Sickle cell disease (SCD)-related organ complications are a major cause of morbidity and mortality in patients with SCD. We sought to assess whether hematopoietic stem cell transplantation (HSCT) stabilizes, attenuates, or exacerbates organ decline. We performed a systematic review and meta-analysis of trials investigating organ function before and after HSCT in patients with SCD. We searched MEDLINE/PubMed and EMBASE up to September 21, 2023. Continuous data were expressed as standardized mean difference (SMD) and pooled in a weighted inverse-variance random-effects model; binomial data were expressed as risk ratio (RR) using the Mantel-Haenszel random-effects meta-analyses. Of 823 screened studies, 34 were included in this review. Of these, 17 (774 patients, 23.6% adults, 86.3% HLA-identical sibling donor, 56.7% myeloablative conditioning regimen) were included in the meta-analyses. Pulmonary function remained stable. Mean tricuspid regurgitant jet velocity decreased but did not reach statistical significance. In children, estimated glomerular filtration rate decreased (SMD -0.80, p = .01), and the presence of proteinuria increased (RR 2.00, p = <.01), while splenic uptake and phagocytic function improved (RR 0.31, p = <.01; RR 0.23, p = <.01). Cerebral blood flow improved (SMD -1.39, p = <.01), and a low incidence of stroke after transplantation in high-risk patients was found. Retinopathy and avascular osteonecrosis were investigated in only one study, showing no significant changes. While HSCT can improve some SCD-related organ dysfunctions, transplantation-related toxicity may have an adverse effect on others. Future research should focus on identifying individuals with SCD who might benefit most from HSCT and which forms of organ damage are more likely to exacerbate post-transplantation.

The effectiveness of hematopoietic stem cell transplantation in treating pediatric sickle cell disease: Systematic review and meta-analysis

Background

Patients with sickle cell disease (SCD) have just one recognized curative therapy option: hematopoietic stem cell transplantation (HSCT), which results in a long-lasting improvement in the clinical phenotype. Here, we assessed the effectiveness of HSCT in treating children with SCD by a systematic review and meta-analysis.

Methods

Up until January 2024, a comprehensive search was done using Web of Science, CINAHL, Embase, Google Scholar, Cochrane Library, PubMed/Medline, and Embase. Two reviewers worked separately to extract the data, and Newcastle-Ottawa Quality Assessment tool was used to assess the research's quality. The outcomes analyzed were Overall survival (OS), event-free survival (EFS), graft failure (GF) and mortality.

Results

Nineteen papers satisfied our inclusion requirements and were assessed to be of fair quality. The pooled rate of OS was high (92%; 95% CI: 90.3%-93.5%). Similar finding was detected for EFS (85.8%; 95% CI: 83.7%-87.7%). In the other hand, pooled rates of GF and mortality were 6.9% (95% CI: 5.3%-8.9%) and 7.4% (95% CI: 5%-10.7%), respectively. A significant publication bias was detected for OS, EFS and GF outcomes. Subgroups analysis showed that study design was the major source of heterogeneity.

Conclusion

Our results show that HSCT is effective and safe, with pooled survival rates above 90%. It is important to assess innovative tactics in light of the alarming GF and mortality rates.

Cerebral hemodynamic changes after haploidentical hematopoietic stem cell transplant in adults with sickle cell disease

ABSTRACT

Preliminary evidence from a series of 4 adults with sickle cell disease (SCD) suggests that hematopoietic stem cell transplant (HSCT) improves cerebral hemodynamics. HSCT largely normalizes cerebral hemodynamics in children with SCD. We tested the hypothesis in adults with SCD that cerebral blood flow (CBF), oxygen extraction fraction (OEF), and cerebral metabolic rate of oxygen (CMRO2) measured using magnetic resonance imaging, normalized to healthy values, comparing measurements from ∼1 month before to 12 to 24 months after HSCT (n = 11; age, 33.3 ± 8.9 years; 389 ± 150 days after HSCT) with age-, race- and sex-matched values from healthy adults without sickle trait (n = 28; age, 30.2 ± 5.6 years). Before transplant, 7 patients had neurological indications for transplant (eg, overt stroke) and 4 had nonneurological reasons for haploidentical bone marrow transplant (haplo-BMT). All received haplo-BMT from first-degree relatives (parent, sibling, or child donor) with reduced-intensity preparation and maintained engraftment. Before transplant, CBF was elevated (CBF, 69.11 ± 24.7 mL/100 g/min) compared with that of controls (P = .004). Mean CBF declined significantly after haplo-BMT (posttransplant CBF, 48.2 ± 13.9 mL/100 g/min; P = .003). OEF was not different from that of controls at baseline and did not change significantly after haplo-BMT (pretransplant, 43.1 ± 6.7%; posttransplant, 39.6 ± 7.0%; P = .34). After transplant, CBF and OEF were not significantly different from controls (CBF, 48.2 ± 13.4 mL/100 g/min; P = .78; and OEF, 39.6 ± 7.0%; P > .99). CMRO2 did not change significantly after haplo-BMT (pretransplant, 3.18 ± 0.87 mL O2/100 g/min; posttransplant, 2.95 ± 0.83; P = .56). Major complications of haplo-BMT included 1 infection-related death and 1 severe chronic graft-versus-host disease. Haplo-BMT in adults with SCD reduces CBF to that of control values and maintains OEF and CMRO2 on average at levels observed in healthy adult controls. The trial was registered at www.clinicaltrials.gov as #NCT01850108.

Hematopoietic Stem Cell Transplantation in Sickle Cell Disease: A Multidimentional Review

While exagamglogene autotemcel (Casgevy) and lovotibeglogene autotemcel (Lyfgenia) have been approved by the US Food and Drug Administration (FDA) as the first cell-based gene therapies for the treatment of patients 12 years of age and older with sickle cell disease (SCD), this treatment is not universally accessible. Allogeneic hematopoietic stem cell transplant (HSCT) has the potential to eradicate the symptoms of patients with SCD, but a significant obstacle in HSCT for SCD is the availability of suitable donors, particularly human leukocyte antigen (HLA)-matched related donors. Furthermore, individuals with SCD face an elevated risk of complications during stem cell transplantation due to SCD-related tissue damage, endothelial activation, and inflammation. Therefore, it is imperative to consider optimal conditioning regimens and investigate HSCT from alternative donors. This review encompasses information on the use of HSCT in patients with SCD, including the indications for HSCT, conditioning regimens, alternative donors, and posttransplant outcomes.

A systematic review comparing allogeneic hematopoietic stem cell transplant to gene therapy in sickle cell disease

INTRODUCTION

Allogeneic hematopoietic stem cell transplant (HSCT) and gene therapy (GT) are two potentially curative approaches for sickle cell disease (SCD), but they have never been compared in clinical trials.

OBJECTIVE

To compare the safety and efficacy of HSCT and GT to assist clinicians and patients in making informed treatment decisions.

METHODS

Phase I-III clinical trials and case reports/series were included. Regimens included HSCT from all stem cell sources, lentiviral gene therapy, and gene editing, with any conditioning regimen. We searched Medline and EMBASE databases as of 1st June 2020 for studies reporting HSCT and GT outcomes in SCD. The Newcastle-Ottawa scale was used to assess the risk of bias. Descriptive statistics and post-hoc imputation for standard deviations of mean change in FEV1 and FVC were performed.

RESULTS

In total, 56 studies (HSCT, n = 53; GT, n = 3) representing 1,198 patients met inclusion criteria (HSCT, n = 1,158; GT, n = 40). Length of follow-up was 3,881.5 and 58.7 patient-years for HSCT and GT, respectively. Overall quality of evidence was low, with no randomized controlled trials identified. Two-year overall survival for HSCT was 91%; mortality was 2.5% for GT. Acute chest syndrome and vaso-occlusive episodes were reduced post-HSCT and GT. Meta-analysis was not possible due to lack of comparator and heterogeneity in outcome measures reporting. Very few studies reported post-transplant end-organ function. Six secondary malignancies (5 post-HSCT, 1 post-GT) were reported.

DISCUSSION

Reporting of SCD-related complications and patient-important outcomes is lacking for both strategies. We advocate for standardized reporting to better compare outcomes within and between treatment groups.

A novel mutation in MECOM affects MPL regulation in vitro and results in thrombocytopenia and bone marrow failure

MECOM-associated syndrome (MECOM-AS) is a rare disease characterized by amegakaryocytic thrombocytopenia, progressive bone marrow failure, pancytopenia and radioulnar synostosis with high penetrance. The clinical phenotype may also include finger malformations, cardiac and renal alterations, hearing loss, B-cell deficiency and predisposition to infections. The syndrome, usually diagnosed in the neonatal period because of severe thrombocytopenia, is caused by mutations in the MECOM gene, encoding for the transcription factor EVI1. The mechanism linking the alteration of EVI1 function and thrombocytopenia is poorly understood. In a paediatric patient affected by severe thrombocytopenia, we identified a novel variant of the MECOM gene (p.P634L), whose effect was tested on pAP-1 enhancer element and promoters of targeted genes showing that the mutation impairs the repressive activity of the transcription factor. Moreover, we demonstrated that EVI1 controls the transcriptional regulation of MPL, a gene whose mutations are responsible for congenital amegakaryocytic thrombocytopenia (CAMT), potentially explaining the partial overlap between MECOM-AS and CAMT.

Outcomes and long-term effects of hematopoietic stem cell transplant in sickle cell disease

INTRODUCTION

Hematopoietic stem cell transplant (HSCT) is the only readily available curative option for sickle cell disease (SCD). Cure rates following human leukocyte antigen (HLA)-matched related donor HSCT with myeloablative or non-myeloablative conditioning are >90%. Alternative donor sources, including haploidentical donor and autologous with gene therapy, expand donor options but are limited by inferior outcomes, limited data, and/or shorter follow-up and therefore remain experimental.

AREAS COVERED

Outcomes are improving with time, with donor type and conditioning regimens having the greatest impact on long-term complications. Patients with stable donor engraftment do not experience SCD-related symptoms and have stabilization or improvement of end-organ pathology; however, the long-term effects of curative strategies remain to be fully established and have significant implications in a patient's decision to seek therapy. This review covers currently published literature on HSCT outcomes, including organ-specific outcomes implicated in SCD, as well as long-term effects.

EXPERT OPINION

HSCT, both allogeneic and autologous gene therapy, in the SCD population reverses the sickle phenotype, prevents further organ damage, can resolve prior organ dysfunction in both pediatric and adult patients. Data support greater success with HSCT at a younger age, thus, curative therapies should be discussed early in the patient's life.

Transplant for non-malignant disorders: an International Society for Cell & Gene Therapy Stem Cell Engineering Committee report on the role of alternative donors, stem cell sources and graft engineering

Hematopoietic stem cell transplantation (HSCT) is curative for many non-malignant disorders. As HSCT and supportive care technologies improve, this life-saving treatment may be offered to more and more patients. With the development of new preparative regimens, expanded alternative donor availability, and graft manipulation techniques, there are many options when choosing the best regimen for patients. Herein the authors review transplant considerations, transplant goals, conditioning regimens, donor choice, and graft manipulation strategies for patients with non-malignant disorders undergoing HSCT.

Hypogammaglobulinemia in Children After Hematopoietic Stem Cell Transplantation and Rituximab Treatment: Relevance of B Cell Subsets

Rituximab (RTX) is widely employed to treat Epstein-Barr virus reactivation in children undergoing Hematopoietic Cell Transplantation (HCT). The resulting loss of B cells may cause persistent hypogammaglobulinemia. This retrospective cross-sectional study aims to identify flow cytometry biomarkers associated with persistent hypogammaglobulinemia in patients receiving RTX after HCT. We analyzed 5 patients (cases group) requiring immunoglobulin substitution due to low level of IgG (IgG <5 g/L) detected after RTX treatment and 5 patients (controls group) not requiring long-term immunoglobulin (Ig) substitution. We investigated the B cell reconstitution, and in patients group we observed a significantly lower count in B total, IgD+CD27+ marginal B cells and IgD-CD27+ switched-memory B cells, after a median of 5 years from HCT, compared with the control group. Despite the importance limits of our study and the heterogeneity of our data (age of included patients, time of evaluation, interval between RTX dose and assessment) we conclude that RTX given early after HCT might cause a deranged B cell maturation, contributing to the delation in B cell recovery following HCT, and switched memory and marginal zone B cell counts could be a promising biomarker to identify patients requiring long-term Ig substitution.

Allogeneic Transplant and Gene Therapy: Evolving Toward a Cure

Curative therapies for sickle cell disease (SCD) include allogeneic human leukocyte antigen (HLA)- matched sibling and haploidentical hematopoietic cell transplant (HCT), gene therapy, and gene editing. However, comparative trial data that might facilitate selecting one curative therapy over another are unavailable. New strategies to decrease graft rejection and graft-versus-host disease (GVHD) risks are needed to expand haploidentical HCT. Myeloablative gene therapy and gene editing also has limitations. Herein, we review recent studies on curative therapies for SCD in the past 5 years.

The effect of intensity of conditioning regimen on the outcome of HSCT in children with sickle cell disease

BACKGROUND

Allogeneic hematopoietic stem cell transplantation (HSCT) provides a cure for patients with sickle cell disease (SCD). This study describes the effect of conditioning regimen intensity on HSCT outcomes among children younger than 14 years with SCD.

METHODS

Transplants from HLA-matched related donors (MRD) and unrelated donors (MUD) using either myeloablative conditioning (MAC) regimens or reduced intensity conditioning (RIC) regimens were considered. Event-free survival (EFS) was the primary endpoint. Secondary endpoints included overall survival (OS) and occurrence of GVHD.

RESULTS

48 SCD patients underwent HSCT, 45 (93.8%) patients had MRD, 1 (2.1%) had 9/10 related donor, and 2 (4.1%) had MUD. The median age at transplant was 8.6 years (range, 3.1-13.8). Conditioning regimens were myeloablative (MAC) in 41 (85.4%) patients and of reduced intensity in 7 (14.6%) patients. EFS at 2 years was 100% among MAC group compared to 29% in the RIC group (p < .001). The median follow-up was 43.4 months (range 26.8-134). All events in the RIC group were secondary graft failure. However, OS was 100% in both groups at 2 years. Acute GVHD II-IV was diagnosed in 2 (4.1%) patients. Chronic GVHD occurred in 2 (4.1%) patients. GVHD did not occur in patients who underwent MUD HSCT.

CONCLUSIONS

MAC in children with SCD is well tolerated and associated with an excellent outcome for HLA-matched HSCT in SCD. There was a high rate of secondary graft failure with the use of RIC. Future studies are needed to optimize RIC regimens in HSCT of children with SCD.

Fertility preservation for pediatric patients with hemoglobinopathies: Multidisciplinary counseling needed to optimize outcomes

Hemoglobinopathies are autosomal recessive disorders that occur when genetic mutations negatively impact the function of hemoglobin. Common hemoglobinopathies that are clinically significant include sickle cell disease, alpha thalassemia, and beta thalassemia. Advancements in disease-modifying and curative treatments for the common hemoglobinopathies over the past thirty years have led to improvements in patient quality of life and longevity for those who are affected. However, the diseases, their treatments and cures pose infertility risks, making fertility preservation counseling and treatment an important part of the contemporary comprehensive patient care. Sickle cell disease negatively impacts both male and female infertility, primarily by testicular failure and decreased ovarian reserve, respectively. Fertility in both males and females with beta thalassemia major are negatively impacted by iron deposition due to chronic blood transfusions. Hematopoietic stem cell transplant (HSCT) is currently the only curative treatment for SCD and transfusion dependent beta thalassemia. Many of the conditioning regimens for HSCT contain chemotherapeutic agents with known gonadotoxicity and whole-body radiation. Although most clinical studies on toxicity and impact of HSCT on long-term health do not evaluate fertility, gonadal failure is common. Male fertility preservation modalities that exist prior to gonadotoxic treatment include sperm banking for pubertal males and testicular cryopreservation for pre-pubertal boys. For female patients, fertility preservation options include oocyte cryopreservation and ovarian tissue cryopreservation. Oocyte cryopreservation requires controlled ovarian hyperstimulation (COH) with ten to fourteen days of intensive monitoring and medication administration. This is feasible once the patient has undergone menarche. Follicular growth is monitored via transvaginal or transabdominal ultrasound, and hormone levels are monitored through frequent blood work. Oocytes are then harvested via a minimally invasive approach under anesthesia. Complications of COH are more common in patients with hemoglobinopathies. Ovarian hyperstimulation syndrome creates a greater risk to patients with underlying vascular, pulmonary, and renal injury, as they may be less able to tolerate fluids shifts. Thus, it is critical to monitor patients undergoing COH closely with close collaboration between the hematology team and the reproductive endocrinology team. Counseling patients and families about future fertility must take into consideration the patient's disease, treatment history, and planned treatment, acknowledging current knowledge gaps.

Across the Myeloablative Spectrum: Hematopoietic Cell Transplant Conditioning Regimens for Pediatric Patients with Sickle Cell Disease

One out of every five hundred African American children in the United States has sickle cell disease (SCD). While multiple disease-modifying therapies are available, hematopoietic cell transplantation (HCT) remains the only curative option for children with SCD. HLA-matched sibling HCT has demonstrated excellent efficacy, but its availability remains limited; alternative donor strategies are increasingly explored. While Busulfan-Cyclophosphamide has become the most widespread conditioning regimen employed in HCT for pediatric SCD, many other regimens have been examined. This review explores different conditioning regimens across the intensity spectrum: from myeloablative to non-myeloablative. We describe survival and organ function outcomes in pediatric SCD patients who have received HCT and discuss the strengths and weaknesses of the various conditioning intensities. Finally, we posit novel directions in allogeneic HCT for SCD.

Curative therapy for hemoglobinopathies: an International Society for Cell & Gene Therapy Stem Cell Engineering Committee review comparing outcomes, accessibility and cost of ex vivo stem cell gene therapy versus allogeneic hematopoietic stem cell transplantation

Thalassemia and sickle cell disease (SCD) are the most common monogenic diseases in the world and represent a growing global health burden. Management is limited by a paucity of disease-modifying therapies; however, allogeneic hematopoietic stem cell transplantation (HSCT) and autologous HSCT after genetic modification offer patients a curative option. Allogeneic HSCT is limited by donor selection, morbidity and mortality from transplant conditioning, graft-versus-host disease and graft rejection, whereas significant concerns regarding long-term safety, efficacy and cost limit the broad applicability of gene therapy. Here the authors review current outcomes in allogeneic and autologous HSCT for transfusion-dependent thalassemia and SCD and provide our perspective on issues surrounding accessibility and costs as barriers to offering curative therapy to patients with hereditary hemoglobinopathies.

Stem cell therapies for autoimmune hepatitis

Autoimmune hepatitis is a chronic inflammatory hepatic disorder which may cause liver fibrosis. Appropriate treatment of autoimmune hepatitis is therefore important. Adult stem cells have been investigated as therapies for a variety of disorders in latest years. Hematopoietic stem cells (HSCs) were the first known adult stem cells (ASCs) and can give rise to all of the cell types in the blood and immune system. Originally, HSC transplantation was served as a therapy for hematological malignancies, but more recently researchers have found the treatment to have positive effects in autoimmune diseases such as multiple sclerosis. Mesenchymal stem cells (MSCs) are ASCs which can be extracted from different tissues, such as bone marrow, adipose tissue, umbilical cord, and dental pulp. MSCs interact with several immune response pathways either by direct cell-to-cell interactions or by the secretion of soluble factors. These characteristics make MSCs potentially valuable as a therapy for autoimmune diseases. Both ASC and ASC-derived exosomes have been investigated as a therapy for autoimmune hepatitis. This review aims to summarize studies focused on the effects of ASCs and their products on autoimmune hepatitis.

Allogeneic hematopoietic stem cell transplantation from sibling and unrelated donors in pediatric patients with sickle cell disease-A single center experience

HSCT is curative in SCD. Patients with HLA-identical sibling donor have an excellent outcome ranging from 90%-100% overall and event-free survival. However, due to the lack of matched sibling donors this option is out of reach for 70% of patients with SCD. The pool of potential donors needs to be extended. Transplantations from HLA-matched unrelated donors were reported to be less successful with shorter event-free survival and higher incidences of complications including graft-vs-host disease, especially in patients with advanced stage SCD. Here we report transplantation outcomes for 25 children with SCD transplanted using HLA-matched grafts from related or unrelated donors. Overall survival was 100% with no severe (grade III-IV) graft-vs-host disease and a 12% rejection rate. Mixed donor chimerisms only occurred in transplantations from siblings, while transplantations from unrelated donors resulted in either complete donor chimerism or rejection. Despite the small patient number, overall and disease-free survival for unrelated donor transplantations is excellent in this cohort. The advanced disease state, higher alloreactive effect and stronger immunosuppression in unrelated donor transplantations raises patient risk, for which possible solutions could be found in optimization of transplant preparation, graft manipulation or haploidentical transplantation using T cell receptor α/β-depleted grafts.

Systematic Review/Meta-Analysis on Efficacy of Allogeneic Hematopoietic Cell Transplantation in Sickle Cell Disease: An International Effort on Behalf of the Pediatric Diseases Working Party of European Society for Blood and Marrow Transplantation and the Sickle Cell Transplantation International Consortium

Sickle cell disease (SCD) affects more than 300,000 children annually worldwide. Despite improved supportive care, long-term prognosis remains poor. Allogeneic hematopoietic cell transplantation (allo-HCT) is the sole validated curative option, resulting in sustained resolution of the clinical phenotype. The medical literature on allo-HCT for SCD is largely limited to children. Recent studies have evaluated allo-HCT efficacy in adults. Here, we conducted a systematic review/meta-analysis to assess the totality of evidence on the efficacy, or lack thereof, of allo-HCT in treating SCD. We performed a comprehensive literature search using PubMed/Medline, Embase, and Cochrane library databases on November 13, 2019. Four authors independently extracted data on clinical outcomes related to benefits (overall survival [OS] and disease-free survival [DFS]) and harms (acute graft-versus-host disease [aGVHD], chronic graft-versus-host disease [cGVHD], nonrelapse mortality [NRM], and graft failure [GF]). Our search identified a total of 1906 references. Only 33 studies (n= 2853 patients) met our inclusion criteria. We also performed a subset analysis by age. Analyses of all-age groups showed pooled rates of 96% for OS, 90% for DFS, 20% for aGVHD, 10% for cGVHD, 4% for NRM, and 5% for GF. In the pediatric population, pooled rates for OS, DFS, aGVHD, cGVHD, NRM, and GF were 97%, 91%, 26%, 11%, 5%, and 3%, respectively. In adults, pooled rates for OS, DFS, aGVHD, cGVHD, NRM, and GF were 98%, 90%, 7%, 1%, 0%, and 14%, respectively. Our data show that allo-HCT is safe and effective, yielding pooled OS rates exceeding 90%. The high GF rate of 14% in adults is concerning and emphasizes the need to evaluate new strategies.

Longitudinal Description of Gonadal Function in Sickle-cell Patients Treated With Hematopoietic Stem Cell Transplant Using Alkylator-based Conditioning Regimens

OBJECTIVES

This study describes the hormone profiles for gonadal late effects after alkylator-based hematopoietic stem cell transplant (HSCT) regimens used for sickle-cell disease (SCD).

METHODS

This is a retrospective chart review of subjects followed in the post-HSCT clinic for sickle-cell disease. Patient demographics, pubertal development, characteristics of pre-HSCT disease severity, treatment before HSCT, conditioning regimens, presence of graft versus host disease and follicle-stimulating hormone, anti-Müllerian hormone (AMH), luteinizing hormone and testosterone were abstracted from the medical record.

RESULTS

Forty subjects (24 female individuals) with SCD were 9 (±4.3) years old at HSCT and 7.9 years (±5.6) from HSCT. At the time of transplant, 8% of female individuals and no male individuals were pubertal and 58% of female individuals and 38% of male individuals had been treated with hydroxyurea. Post-HSCT, all of the female individuals had diminished ovarian reserve on the basis of low AMH values and 10 of the pubertal female individuals (71%) had premature ovarian insufficiency defined as follicle-stimulating hormone >40 mIU/mL ×2. There was no ovarian recovery and AMH remained very low or undetectable up to 13 years post-HSCT. In male individuals, luteinizing hormone and testosterone levels were normal for age.

CONCLUSIONS

Post-HSCT for SCD, all female individuals had diminished ovarian reserve and most female individuals had POI, whereas male individuals had normal testosterone hormone production.

Treosulfan-fludarabine-thiotepa-based conditioning treatment before allogeneic hematopoietic stem cell transplantation for pediatric patients with hematological malignancies

Treosulfan-based conditioning prior to allogeneic transplantation has been shown to have myeloablative, immunosuppressive, and antineoplastic effects associated with reduced non-relapse mortality (NRM) in adults. Therefore, we prospectively evaluated the safety and efficacy of treosulfan-based conditioning in children with hematological malignancies in this phase II trial. Overall, 65 children with acute lymphoblastic leukemia (35.4%), acute myeloid leukemia (44.6%), myelodysplastic syndrome (15.4%), or juvenile myelomonocytic leukemia (4.6%) received treosulfan intravenously at a dose of 10 mg/m²/day (7.7%), 12 g/m²/day (35.4%), or 14 g/m²/day (56.9%) according to their individual body surface area in combination with fludarabine and thiotepa. The incidence of complete donor chimerism at day +28 was 98.4% with no primary and only one secondary graft failure. At 36 months, NRM was only 3.1%, while relapse incidence was 21.7%, and overall survival was 83.0%. The cumulative incidence of acute graft-vs.-host disease was 45.3% for grades I–IV and 26.6% for grades II–IV. At 36 months, 25.8% overall and 19.4% moderate/severe chronic graft-vs.-host disease were reported. These data confirm the safe and effective use of treosulfan-based conditioning in pediatric patients with hematological malignancies. Therefore, treosulfan/fludarabine/thiotepa can be recommended for myeloablative conditioning in children with hematological malignancies.

Curative options for sickle cell disease: haploidentical stem cell transplantation or gene therapy?

Haematopoietic stem cell transplantation (HSCT) is curative in sickle cell disease (SCD); however, the lack of available matched donors makes this therapy out of reach for the majority of patients with SCD. Alternative donor sources such as haploidentical HSCT expand the donor pool to nearly all patients with SCD, with recent data showing high overall survival, limited toxicities, and effective reduction in acute and chronic graft-versus-host disease (GVHD). Simultaneously, multiple gene therapy strategies are entering clinical trials with preliminary data showing their success, theoretically offering all patients yet another curative strategy without the morbidity and mortality of GVHD. As improvements are made for alternative donors in the allogeneic setting and as data emerge from gene therapy trials, the optimal curative strategy for any individual patient with SCD will be determined by many critical factors including efficacy, transplant morbidity and mortality, safety, patient disease status and preference, cost and applicability. Haploidentical may be the preferred choice now based mostly on availability of data; however, gene therapy is closing the gap and may ultimately prove to be the better option. Progress in both strategies, however, makes cure more attainable for the individual with SCD.

Choice of Donor Source and Conditioning Regimen for Hematopoietic Stem Cell Transplantation in Sickle Cell Disease

In the United States, one out of every 500 African American children have sickle cell disease (SCD), and SCD affects approximately 100,000 Americans. Significant advances in the treatment of this monogenetic disorder have failed to substantially extend the life expectancy of adults with SCD over the past two decades. Hematopoietic stem cell transplantation (HSCT) remains the only curative option for patients with SCD. While human leukocyte antigen (HLA) matched sibling HSCT has been successful, its availability is extremely limited. This review summarizes various conditioning regimens that are currently available. We explore recent efforts to expand the availability of allogeneic HSCT, including matched unrelated, umbilical cord blood, and haploidentical stem cell sources. We consider the use of nonmyeloablative conditioning and haploidentical donor sources as emerging strategies to expand transplant availability, particularly for SCD patients with complications and comorbidities who can undergo neither matched related transplant nor myeloablative conditioning. Finally, we show that improved conditioning agents have improved success rates not only in the HLA-matched sibling setting but also alternative donor settings.

HLA-haploidentical hematopoietic stem cell transplantation in pediatric patients with hemoglobinopathies: current practice and new approaches

We review current approaches in HLA-haploidentical hematopoietic stem cell transplantation (haplo-HSCT) for pediatric patients with hemoglobinopathies with a focus on recent developments using TCRα/β+/CD19+ depleted grafts in patients with β-thalassemia major (TM) or sickle cell disease (SCD) in two European transplant units. Eleven TM and three SCD patients (Roma cohort) received a preparative regimen consisting of busulfan/thiotepa/cyclophosphamide/ATG preceded by fludarabine/hydroxyurea/azathioprine. The preparative regimen for 5 SCD patients included treosulfan/thiotepa/fludarabine/ATG (Berlin pilot cohort). All grafts were PBSC engineered by TCR-α/β+/CD19+ depletion. In both cohorts, rates for graft failure, treatment related mortality (TRM) and GvHD were encouraging. Overall survival (OS) and disease-free survival (DFS) in the Roma cohort were 84 and 69%, respectively, while OS and DFS are 100% in the Berlin cohort. Immune reconstitution was satisfactory. Although asymptomatic viral reactivation was common, no severe viral infection occured. These data confirm that TCR-α/β+/CD19+ depletion is a well-suited haplo-HSCT strategy for children with hemoglobinopathies. We discuss the results in the context of additional optimization strategies and introduce our concepts for multicenter trial protocols in Germany.

Hemoglobin disorders: lentiviral gene therapy in the starting blocks to enter clinical practice

The β-hemoglobinopathies, transfusion-dependent β-thalassemia and sickle cell disease, are the most prevalent inherited disorders worldwide and affect millions of people. Many of these patients have a shortened life expectancy and suffer from severe morbidity despite supportive therapies, which impose an enormous financial burden to societies. The only available curative therapy is allogeneic hematopoietic stem cell transplantation, although most patients do not have an HLA-matched sibling donor, and those who do still risk life-threatening complications. Therefore, gene therapy by one-time ex vivo modification of hematopoietic stem cells followed by autologous engraftment is an attractive new therapeutic modality. The first proof-of-principle of conversion to transfusion independence by means of a lentiviral vector expressing a marked and anti-sickling β^T87Q-globin gene variant was reported a decade ago in a patient with transfusion-dependent β-thalassemia. In follow-up multicenter Phase II trials with an essentially identical vector (termed LentiGlobin BB305) and protocol, 12 of the 13 patients with a non-β⁰/β⁰ genotype, representing more than half of all transfusion-dependent β-thalassemia cases worldwide, stopped red blood cell transfusions with total hemoglobin levels in blood approaching normal values. Correction of biological markers of dyserythropoiesis was achieved in evaluated patients. In nine patients with β⁰/β⁰ transfusion-dependent β-thalassemia or equivalent severity (β^IVS1-110), median annualized transfusion volume decreased by 73% and red blood cell transfusions were stopped in three patients. Proof-of-principle of therapeutic efficacy in the first patient with sickle cell disease was also reported with LentiGlobin BB305. Encouraging results were presented in children with transfusion-dependent β-thalassemia in another trial with the GLOBE lentiviral vector and several other gene therapy trials are currently open for both transfusion-dependent β-thalassemia and sickle cell disease. Phase III trials are now under way and should help to determine benefit/risk/cost ratios to move gene therapy toward clinical practice.

When there is no match, the game is not over: Alternative donor options for hematopoietic stem cell transplantation in sickle cell disease

Many patients with sickle cell disease experience severe morbidity and early mortality. The only curative option remains hematopoietic stem cell transplantation. Although HLA-matched sibling transplantation has been very successful for adults and children, the vast majority of patients with sickle cell disease do not have an HLA-matched sibling. Alternative donor options include haploidentical, unrelated umbilical cord blood, and matched unrelated donor transplantation. This report summarizes major alternative donor transplantation studies reported to date and ongoing and upcoming clinical trials. We conclude that when there is no HLA-match, all these approaches should be systematically considered before ruling out the option of hematopoietic stem cell transplantation.

Bone Marrow Transplantation after Nonmyeloablative Treosulfan Conditioning Is Curative in a Murine Model of Sickle Cell Disease

Allogeneic hematopoietic stem cell transplantation (HSCT) can be curative for patients with sickle cell disease (SCD). However, morbidity associated with myeloablative conditioning and graft-versus-host disease has limited its utility. To this end, autologous HSCT for SCD using lentiviral gene-modified bone marrow (BM) or peripheral blood stem cells has been undertaken, although toxicities of fully ablative conditioning with busulfan and incomplete engraftment have been encountered. Treosulfan, a busulfan analog with a low extramedullary toxicity profile, has been used successfully as part of a myeloablative conditioning regimen in the allogeneic setting in SCD. To further minimize toxicity of conditioning, noncytotoxic monoclonal antibodies that clear stem cells from the marrow niche, such as anti-c-Kit (ACK2), have been considered. Using a murine model of SCD, we sought to determine whether nonmyeloablative conditioning followed by transplantation with syngeneic BM cells could ameliorate the disease phenotype. Treosulfan and ACK2, in a dose-dependent manner, decreased BM cellularity and induced cytopenia in SCD mice. Conditioning with treosulfan alone at nonmyeloablative dosing (3.6 g/kg), followed by transplantation with syngeneic BM donor cells, permitted long-term mixed-donor chimerism. Level of chimerism correlated with improvement in hematologic parameters, normalization of urine osmolality, and improvement in liver and spleen pathology. Addition of ACK2 to treosulfan conditioning did not enhance engraftment. Our data suggests that pretransplant conditioning with treosulfan alone may allow sufficient erythroid engraftment to reverse manifestations of SCD, with clinical application as a preparative regimen in SCD patients undergoing gene-modified autologous HSCT.