Unrelated Donor Transplantation in Children with Thalassemia using Reduced-Intensity Conditioning: The URTH Trial

Finding a balance in reduced toxicity hematopoietic stem cell transplantation for thalassemia: role of infused CD3+ cell count and immunosuppression

We performed a retrospective analysis on 124 patients with transfusion-dependent thalassemia who were registered in the German pediatric registry for stem cell transplantation. All patients underwent first allogeneic hematopoietic stem cell transplantation (HSCT) between 2011 and 2020 and belonged mainly to Pesaro risk class 1-2. Four-year overall (OS) and thalassemia-free survival (TFS) were 94.5% ± 2.9% and 88.0% ± 3.4% after treosulfan-fludarabine-thiotepa- and 96.9% ± 3.1% (P = 0.763) and 96.9% ± 3.1% (P = 0.155) after busulfan-fludarabine-based conditioning. Mixed chimerism below 75% occurred predominantly in treosulfan-based regimens (27.5% versus 6.2%). OS and TFS did not differ significantly between matched sibling, other matched family and matched unrelated donor (UD) HSCTs (OS: 100.0%, 100.0%, 96.3% ± 3.6%; TFS: 96.5% ± 2.4%, 90.0% ± 9.5%, 88.9% ± 6.0%). However, mismatched UD-HSCTs performed less favorable (OS: 84.7% ± 7.3% (P = 0.029); TFS: 79.9% ± 7.4% (P = 0.082)). We generated a scoring system reflecting the risk to develop mixed chimerism in our cohort. The main risk-reducing factors were a high CD3+ cell count (≥6 × 107/kg) in the graft, busulfan-conditioning, pre-conditioning therapy and low-targeted ciclosporin A trough levels. Acute GvHD grade III-IV in treosulfan-based concepts predominantly occurred in patients with UD and reduced GvHD prophylaxis but not in the context of high CD3+ cell doses. Taken together, this information might be used to develop more risk-adapted HSCT regimens for thalassemia patients.

Defining curative endpoints for transfusion-dependent β-thalassemia in the era of gene therapy and gene editing

β-thalassemia is a monogenic disease that results in varying degrees of anemia. In the most severe form, known as transfusion-dependent β-thalassemia (TDT), the clinical hallmarks are ineffective erythropoiesis and a requirement of regular, life-long red blood cell transfusions, with the development of secondary clinical complications such as iron overload, end-organ damage, and a risk of early mortality. With the exception of allogeneic hematopoietic cell transplantation, current treatments for TDT address disease symptoms and not the underlying cause of disease. Recently, a growing number of gene addition and gene editing-based treatments for patients with TDT with the potential to provide a one-time functional cure have entered clinical trials. A key challenge in the design and evaluation of these trials is selecting endpoints to evaluate if these novel genetic therapies have a curative versus an ameliorative effect. Here, we present an overview of the pathophysiology of TDT, review emerging gene addition or gene editing therapeutic approaches for TDT currently in clinical trials, and identify a series of endpoints that can quantify therapeutic effects, including a curative outcome.

Incidence, management and outcome of Hepatic Veno-Occlusive disease /Sinusoidal Obstruction Syndrome after hematopoietic stem cell transplant in Thalassemia major patients: A prospective study of Pakistani BMT

Objectives

Hepatic Veno occlusive disease (VOD), also known as sinusoidal obstruction syndrome (VOD/SOS), is a post-transplant life threatening complication. In this study, we aimed to discuss the incidence, management and outcome of VOD in post allogenic transplant patients of beta thalassemia major (BTM).

Methods

A prospective study was conducted in Armed Forces Bone Marrow Transplant Center, between 2001-2022. A total of 385 fully Human Leucocyte Antigen (HLA) matched BTM patients, with Ursodeoxycholic acid for prophylaxis, were included in the study. Incidence of VOD was calculated through cumulative incidence estimates. Chi square test and Mann Whitney test were used to compare discrete and continuous variables respectively. VOD was diagnosed and graded according to European Society for Blood and Marrow Transplantation EBMT Pediatric diagnostic criteria. Risk factors for VOD were grouped as recipient, transplant and donor related. Univariate analysis was performed by log-rank test. All patients who developed VOD were managed primarily with fluid restriction and strict input output monitoring. Statistical analyses were performed using SPSS v 25.0.

Results

Out of 385 transplant patients, forty developed VOD. Median time from date of transplant till onset of VOD was 14 days (range 6-30). Cumulative incidence of all grade VOD was 10.39% (95% CI, 7-14). Eleven out of 40 patients who developed VOD died. Cumulative incidence of Transplant related mortality (TRM) for patients with and VOD was 20.5% (95% CI, 16.6-25.1) vs 27.5% (95% CI, 16.1-42) (p value 0.318) respectively. Among risk factors, age of recipient and fibrosis (p value of 0.04 and 0.000 respectively) were found to be significantly associated with VOD.

Conclusions

Careful selection of transplant candidates before transplant can help reduce the incidence of VOD.

Age Impacts Risk of Mixed Chimerism Following Reduced-Intensity Conditioning Hematopoietic Cell Transplantation for Non-Severe Combined Immune Deficiency Inborn Errors of Immunity

Alemtuzumab, fludarabine, and melphalan containing-reduced intensity conditioning (RIC) is commonly used in patients undergoing allogeneic hematopoietic cell transplantation (HCT) for definitive treatment of high-risk inborn errors of immunity (IEI). Although survival is favorable, there is an increased risk of mixed chimerism leading to secondary graft failure. This study evaluated factors associated with the risk of developing mixed chimerism, particularly the influence of age in patients undergoing allogeneic HCT for non-severe combined immune deficiency (SCID) IEI who received a uniform RIC regimen that included intermediate schedule alemtuzumab, fludarabine, and melphalan. We hypothesized that age would impact the incidence of mixed chimerism. We retrospectively reviewed records of patients who underwent HCT for non-SCID IEI with a uniform RIC regimen that included intermediate schedule alemtuzumab (1 mg/kg divided over days -14 to -10), fludarabine (150 mg/m2 or 5 mg/kg if weight <10 kg divided over days -9 to -4), and melphalan (140 mg/m2 or 4.7 mg/kg if weight <10 kg on day -3) between 2010 and 2020 at our institution. Mixed chimerism was defined as <95% donor chimerism on 2 or more consecutive occasions in whole blood. Ninety-three patients who underwent RIC-HCT for non-SCID IEI using intermediate schedule alemtuzumab, fludarabine, and melphalan were categorized into 3 groups: age <1 year, age 1 to 5 years, and age >5 years. Forty-nine patients (52.7%) developed mixed chimerism, at a median of 34 days post-HCT (range, 10 to 1396 days). Mixed chimerism developed in 88.9% (n = 16/18) of the age <1 year group, in 57.1% (n = 20/35) of the age 1 to 5 years group, and in 35% (n =14/40) of the age >5 years group. Patients age <5 years were significantly more likely to develop mixed chimerism (χ2 (3, N = 93) = 14.8; P = .001). We observed a significantly increased cumulative incidence of developing mixed chimerism associated with age <1 year (P = .0002). Competing risk regression analysis showed a 3-fold higher risk of developing mixed chimerism for age <1 year (subdistribution hazard ratio (HR), 3.05; 95% confidence interval [CI], 1.11 to 8.38; P = .031,) compared to age >5 years and a significantly decreased risk of mixed chimerism in patients who developed acute GVHD prior to any intervention (OR, .24; 95% CI, .09 to .65; P = .005) There were no significant associations between mixed chimerism and graft source, graft type, CD34+ or CD3+ cell dose, HLA match, or underlying disease (hemophagocytic lymphohistiocytosis [HLH] versus non-HLH). Additionally, the need for secondary intervention was evaluated; 27 patients (29.0%) required 1 or more secondary interventions (donor lymphocyte infusion, CD34 boost, or second HCT). Patients age <1 year with mixed chimerism were significantly more likely than patients age >5 years to require secondary intervention for mixed chimerism (P = .004). Our study demonstrates that age <5 years, especially age <1 year, is associated with an increased risk of developing mixed chimerism in patients undergoing RIC-HCT for non-SCID IEI using intermediate-schedule alemtuzumab, fludarabine, and melphalan. Our data suggest tailoring regimen intensity based on age to reduce the incidence of mixed chimerism. Children age <5 years, particularly those age <1 year, require a higher-intensity regimen. Possible strategies include adding thiotepa or using a busulfan-based reduced toxicity regimen.

Hematopoietic Stem Cell Transplantation in Thalassemia

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the only consolidated, potentially curative treatment for patients with transfusion-dependent thalassemia major. In the past few decades, several new approaches have reduced the toxicity of conditioning regimens and decreased the incidence of graft-versus-host disease, improving patients' outcomes and quality of life. In addition, the progressive availability of alternative stem cell sources from unrelated or haploidentical donors or umbilical cord blood has made HSCT a feasible option for an increasing number of subjects lacking an human leukocyte antigen (HLA)-identical sibling. This review provides an overview of allogeneic hematopoietic stem cell transplantation in thalassemia, reassesses current clinical results, and discusses future perspectives.

Haploidentical transplant for paediatric patients with severe thalassaemia using post-transplant cyclophosphamide and methotrexate: A prospectively registered multicentre trial from the Bone Marrow Failure Working Group of Hunan Province, China

Haploidentical transplantation strategies for patients with transfusion-dependent thalassaemia (TD-TM) remain to be investigated. In this study, 54 paediatric patients with TD-TM were treated with a novel approach using post-transplant cyclophosphamide (PTCy) and low-dose methotrexate (LD-MTX), following a myeloablative regimen. The incidence of neutrophil and platelet engraftment was 96.3% ± 2.6% and 94.4% ± 3.1% respectively. The cumulative incidence of grades II-III acute graft-versus-host disease (GVHD) was 13.8% ± 4.8% at 100 days. At three years, the cumulative incidence of chronic GVHD was 28.5% ± 8.5%. With a median follow-up of 520 days (132-1325 days), the overall survival (OS) and event-free survival (EFS) were 98.1% ± 1.8% and 90.7% ± 3.9% respectively. Compared with the low-dose cyclophosphamide (CTX) conditioning regimen (120 mg/kg), the high-CTX regimen (200 mg/kg) achieved a higher incidence of stable engraftment (100% vs 66.7% ± 15.7%, p = 0.003), a comparable incidence of grades II-III acute GVHD, a lower incidence of chronic GVHD (20.2% ± 8.3% vs 66.6% ± 19.2%, p = 0.011), and better overall survival (100% vs 88.9% ± 10.5%, p = 0.025) as well as EFS (95.6% ± 3.1% vs 66.7% ± 15.7%, p = 0.008). Our results using unmanipulated haploidentical grafts and PTCy with LD-MTX in TD-TM are encouraging. (chictr.org.cn ChiCTR1800017969).

Gene Editing for Sickle Cell Disease and Transfusion Dependent Thalassemias- A cure within reach

Sickle cell disease (SCD) is associated with significant morbidity and shortened life expectancy. Similarly, patients with transfusion dependent beta thalassemia (TdT) require life-long transfusion therapy, chelation therapy and significant organ dysfunction. Allogeneic transplantation from a matched family donor provided the only curative option for patients with SCD and TdT. Unfortunately, less than 20% of patients have a fully matched related donor and results using unrelated donor transplant were associated with high rate of complications. Ex vivo gene therapy through globin gene addition has been investigated extensively and recent encouraging preliminary data resulted in regulatory approval in patients with TdT. Recent improvements in our understanding of the molecular pathways controlling erythropoiesis and globin switching from fetal hemoglobin to adult hemoglobin offer a new and exciting therapeutic options. Rapid and substantial advances in genome editing tools using CRISPR/Cas9, have raised the possibility of genetic editing and correction in patient derived hematopoietic stem and progenitor cells. We will review results of gene editing approach that can induce fetal hemoglobin production in patients with SCD and TdT.

Decision-making about gene therapy in transfusion dependent thalassemia

BACKGROUND

Hematopoietic stem cell transplantation (HSCT) is a treatment option with curative intent for patients with transfusion dependent thalassemia (TDT) but its application is limited by the lack of suitable donors and acceptability due to the related morbidity/mortality. Transplantation of autologous genetically modified hematopoietic cells, gene therapy (GT) is emerging as a promising treatment option for TDT as it eliminates graft versus host disease (GVHD) and need for immunosuppression. Early results of GT suggest that many, but not all patients achieve transfusion independence after the procedure. There is little information about the acceptability of GT in patients with TDT. We sought to examine patient/family knowledge about GT in TDT and to examine factors that influence decision-making about this therapy.

METHODS

Parents of children with TDT and adults with TDT were who provided informed consent underwent semi-structured interviews to understand patient/family knowledge and decision-making regarding GT in TDT. Transcribed interviews were coded and the data was examined for emerging themes using a combination of thematic and content analysis.

RESULTS

Twenty-five study participants with mean age of 38Y (17-52Y) including eight adults living with TDT, and 17 parents of children with TDT underwent semi-structured qualitative interviews. Participant responses coalesced around broad themes related to knowledge of GT, motivating/deterring factors and outcomes. Study participants expressed a desire for 'cure' from thalassemia including transfusion independence, chelation reduction and improved quality of life as motivators for considering GT. Insufficient knowledge about the process, long-term outcomes, safety, and side effects as well as the potential for death/failure of the procedure were deterrents for the consideration GT. Reduction in frequency of transfusions, even without elimination of transfusions was an acceptable outcome of GT for most participants. Participant choice for preferred treatment modality was split between indefinitely continuing transfusions which was familiar to them versus GT which was unfamiliar, and with an uncertain outcome. None of the participants had a matched sibling donor; alternate donor HSCT was the least preferred option in this group.

CONCLUSION

There is tempered excitement about GT in patients/families with TDT with a general willingness to accept transfusions reduction as the outcome.

Hematopoietic cell transplant for reversal of liver fibrosis in a pediatric patient with erythropoietic protoporphyria

BACKGROUND

EPP is a rare disorder of heme biosynthesis in which patients present with disabling photosensitivity. A subset of patients develop severe liver disease with progressive liver failure necessitating an OLT. A HCT can potentially cure EPP by replacing the native bone marrow, which is the primary site of heme synthesis. However, due to concerns for inherent risks of treatment-related toxicities, the use of HCT has been reserved for patients undergoing an OLT to avoid disease recurrence in the hepatic graft. Data for HCT in EPP are lacking, particularly in the pediatric population.

CASE (METHODS/RESULTS)

We present the case of a 12-year-old patient with EPP photosensitivity and cirrhosis, whom we successfully treated with pre-emptive allogeneic HCT, significantly improving the patient's quality of life. We used a matched-unrelated donor bone marrow-derived graft. Our patient achieved full donor peripheral blood chimerism and has not had any evidence of GVHD. In addition to resolution of photosensitivity, our patient had reversal of liver fibrosis which we feel was largely due to intervention at an early stage of compensated cirrhosis.

CONCLUSION

Our case highlights the successful application of a known RIC regimen to this rare disorder that was well tolerated with sustained donor engraftment. It also emphasizes the importance of timing for HCT in patients with EPP and liver fibrosis. HCT should be considered early in pediatric patients with EPP-hepatopathy to prevent progression to liver failure and need for OLT with lifelong immunosuppression.

Pretransplant myeloid and immune suppression, reduced toxicity conditioning with posttransplant cyclophosphamide: Initial outcomes of novel approach for matched unrelated donor hematopoietic stem cell transplant for hemoglobinopathies

Hematopoietic stem cell transplant (HSCT) is currently the only curative option for thalassemia major (TM) and sickle cell disease (SCD). We report our experience of using pretransplant immune suppression (PTIS), augmented Johns Hopkins conditioning, and posttransplant cyclophosphamide (PTCy) as graft-versus-host disease (GvHD) prophylaxis for matched unrelated donor (MUD) transplant in TM/SCD. At a median follow-up of 307.5 days (range 251-395), all patients (three TM, one SCD) are alive and disease free. MUD HSCT with PTIS, augmented Johns Hopkins conditioning, and PTCy as GvHD prophylaxis is a promising way of treating patients with hemoglobinopathies with low regimen-related toxicity (RRT), no risk of graft failure (GF) and minimal GvHD rates.

Hepatic veno-occlusive disease/sinusoidal obstruction syndrome after hematopoietic stem cell transplantation for thalassemia major: incidence, management, and outcome

Hepatic veno-occlusive disease or sinusoidal obstruction syndrome (VOD/SOS) is a potentially life-threatening complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT). In the present prospective study, we aimed to investigate the incidence, management, and outcome of VOD/SOS in patients with thalassemia major (TM) who received allo-HSCT. VOD/SOS was diagnosed and classified based on the modified Seattle criteria. The prophylactic regimen for VOD/SOS was a combination treatment of dalteparin and lipo-PGE1. VOD/SOS was managed through an approach consisting of adequate supportive measures, short-term withdrawal of calcineurin inhibitors (CNIs), and the use of methylprednisolone and basiliximab for graft-versus-host disease prophylaxis. VOD/SOS was found in 54 of 521 patients (10.4%) at a median time of 12 days after allo-HSCT. The cumulative incidence of all-grade and moderate VOD/SOS was 10.4% and 4.2%, respectively. Among the 54 VOD/SOS patients, no patient developed severe grade and died from VOD/SOS. Besides, the cumulative incidence of transplant-related mortality on day 100 for patients with or without VOD/SOS was 0% vs. 4.0% (P = 0.187), respectively, and the 3-year overall survival rates were 94.3% vs. 93.2% (P = 0.707), respectively. Collectively, we concluded that appropriate symptomatic therapy and short-term withdrawal of CNIs safely mitigated the mortality of VOD/SOS in TM patients who underwent allo-HSCT.

Considerations in Preparative Regimen Selection to Minimize Rejection in Pediatric Hematopoietic Transplantation in Non-Malignant Diseases

The variables that influence the selection of a preparative regimen for a pediatric hematopoietic stem cell transplant procedure encompasses many issues. When one considers this procedure for non-malignant diseases, components in a preparative regimen that were historically developed to reduce malignant tumor burden may be unnecessary. The primary goal of the procedure in this instance becomes engraftment with the establishment of normal hematopoiesis and a normal immune system. Overcoming rejection becomes the primary priority, but pursuit of this goal cannot neglect organ toxicity, or post-transplant morbidity such as graft-versus-host disease or life threatening infections. With the improvements in supportive care, newborn screening techniques for early disease detection, and the expansion of viable donor sources, we have reached a stage where hematopoietic stem cell transplantation can be considered for virtually any patient with a hematopoietic based disease. Advancing preparative regiments that minimize rejection and transplant related toxicity will thus dictate to what extent this medical technology is fully utilized. This mini-review will provide an overview of the origins of conditioning regimens for transplantation and how agents and techniques have evolved to make hematopoietic stem cell transplantation a viable option for children with non-malignant diseases of the hematopoietic system. We will summarize the current state of this facet of the transplant procedure and describe the considerations that come into play in selecting a particular preparative regimen. Decisions within this realm must tailor the treatment to the primary disease condition to ideally achieve an optimal outcome. Finally, we will project forward where advances are needed to overcome the persistent engraftment obstacles that currently limit the utilization of transplantation for haematopoietically based diseases in children.

End points for sickle cell disease clinical trials: renal and cardiopulmonary, cure, and low-resource settings

To address the global burden of sickle cell disease and the need for novel therapies, the American Society of Hematology partnered with the US Food and Drug Administration to engage the work of 7 panels of clinicians, investigators, and patients to develop consensus recommendations for clinical trial end points. The panels conducted their work through literature reviews, assessment of available evidence, and expert judgment focusing on end points related to patient-reported outcome, pain (non-patient-reported outcomes), the brain, end-organ considerations, biomarkers, measurement of cure, and low-resource settings. This article presents the findings and recommendations of the end-organ considerations, measurement of cure, and low-resource settings panels as well as relevant findings and recommendations from the biomarkers panel.

Matched Family versus Alternative Donor Hematopoietic Stem Cell Transplantation for Patients with Thalassemia Major: Experience from a Tertiary Referral Center in South India

Hematopoietic stem cell transplantation (HSCT) is the only curative option available for patients with thalassemia major in India with increasing access to alternate donor transplantation for patients with no matched family donor. We aimed to analyze the impact of family and alternate donor HSCT on morbidity and mortality post-HSCT. We conducted a retrospective study in the department between July 2007 and December 2018 where all children who underwent HSCT for thalassemia major were included. A total of 264 children were included with a median age of 6 years (male/female, 1.4:1). The graft source was matched related donor (MRD) (76%; parent 15%, sibling 85%) and matched unrelated donor (MUD) (22%). All children received a myeloablative conditioning regimen with treosulfan/thiotepa/fludarabine in 93% and busulfan/cyclophosphamide in 7%. The source of stem cells was peripheral blood in 61%, bone marrow in 38%, and umbilical cord blood in 3%. The incidence of bacteremia was 14% versus 25% in MRD versus MUD groups. There was a higher incidence of posterior reversible encephalopathy syndrome (PRES) in the MUD group (10% versus 3%). Engraftment occurred in 97% with a higher trend toward mixed chimerism in the MRD group (12% versus 2%). When indicated, whole-blood donor lymphocyte infusion was used to ensure complete chimerism in children in the MRD group. A statistically significant difference was found in the incidence of graft versus host disease (GVHD), both acute and chronic between the MUD versus MRD groups, 60% versus 20% and 41% versus 17%, respectively (P = .001). Similarly, immune cytopenia and cytomegalovirus reactivation were also significantly higher in the MUD group, 27% versus 1.4% and 25% versus 2%, respectively (P = .001). Thalassemia-free survival in our cohort was 96%, 94%, and 84% with a median follow-up of 65 months in the matched sibling donor, matched family donor, and MUD groups, respectively. Overall survival of 95% and 90% with a median follow-up of 65 months was noted in those who underwent transplantation less than and greater than 7 years of age, respectively. MUD transplantation for patients with thalassemia major involves specific challenges such as PRES and unusual manifestations of GVHD such as immune cytopenia. Early interventions to optimize supportive care and measures to reduce GVHD are required to ensure survival rates of over 90%.

Priorities for Improving Outcomes for Nonmalignant Blood Diseases: A Report from the Blood and Marrow Transplant Clinical Trials Network

Nonmalignant blood diseases such as bone marrow failure disorders, immune dysregulation disorders, and hemoglobinopathies often lead to shortened life spans and poor quality of life. Many of these diseases can be cured with allogeneic hematopoietic cell transplantation, but patients are often not offered the procedure because of perceived insufficient efficacy and/or excess toxicity. In 2018, the Blood and Marrow Transplant Clinical Trials Network convened a task force to identify the most urgently needed yet feasible clinical trials with potential to improve the outcomes for patients with nonmalignant diseases. This report summarizes the task force discussions and specifies the network plans for clinical trial development for nonmalignant blood diseases.

Pulmonary Complications in Pediatric and Adolescent Patients Following Allogeneic Hematopoietic Cell Transplantation

Pulmonary complications after hematopoietic cell transplantation (HCT) can lead to significant morbidity and mortality. Limited evaluation of the true incidence of these complications in children and subsequent outcomes of these complications have not been evaluated recently. In April 2018, the National Heart, Lung, and Blood Institute; the Eunice Kennedy Shriver National Institute of Child Health and Human Development; and the National Cancer Institute cosponsored a meeting of experts to describe the status of pulmonary complications in children after HCT, identify critical gaps in knowledge, and explore avenues for research to advance care and optimize outcomes. The Center for International Blood and Marrow Transplant Research was used to evaluate the cumulative incidence of pulmonary complications in children and their respective survival. Of the 5022 children included in this analysis who received allogeneic HCT from 2010 to 2016, 606 developed pulmonary complications within the first year after HCT. Pneumonitis occurred in 388 patients, 125 patients developed pulmonary hemorrhage, and 200 patients had lung graft-versus-host disease (GVHD). For those developing pulmonary complications within 1 year, overall survival 100 days after diagnosis of pulmonary complications was 49% (95% confidence interval [CI], 43% to 54%) for patients with pneumonitis, 23% (95% CI, 16% to 31%) in patients with pulmonary hemorrhage, and 87% (95% CI, 81% to 91%) in patients with pulmonary GVHD. This study demonstrates the approximate incidence of these complications, as well as their significant effects on survival, and can serve as a baseline for future research.

Effect of increased dose of total body irradiation on graft failure associated with HLA-haploidentical transplantation in patients with severe haemoglobinopathies: a prospective clinical trial

BACKGROUND

Although severe haemoglobinopathies can be cured with allogeneic blood or bone marrow transplantation, availability of matched donors and toxic effects can be problematic. We previously found that non-myeloablative haploidentical related bone marrow transplantation with post-transplantation cyclophosphamide expanded the donor pool while limiting graft-versus-host disease (GVHD). However, graft failure-albeit with full host haemopoietic recovery-occurred in 50% of patients. In this study, we investigated whether increasing total body irradiation from 200 cGy to 400 cGy would improve engraftment while maintaining the safety profile.

METHODS

This study was done at Johns Hopkins Hospital (Baltimore, MD, USA). Patients aged 2-70 years receiving their first bone marrow transplant were eligible for inclusion in the study. Patients received rabbit-derived intravenous anti-thymocyte globulin 0·5 mg/kg on day -9 and 2 mg/kg on days -8 and -7, intravenous fludarabine 30 mg/m² on days -6 to -2, intravenous cyclophosphamide 14·5 mg/kg on days -6 and -5, and total body irradiation 400 cGy administered as a single fraction on day -1. We collected unmanipulated bone marrow and infused on day 0. GVHD prophylaxis comprised intravenous cyclophosphamide 50 mg/kg per day on days 3 and 4 after transplantation, oral mycophenolate mofetil 15 mg/kg per dose (maximum 1 g) every 8 h on days 5 to 35, and oral sirolimus to maintain a level of 5-15 ng/dL for at least 1 year starting on day 5. The original planned primary objectives of this phase 2 clinical trial were transplant-related mortality and progression-free survival. However, the coverage decision by the Centers for Medicare and Medicaid Services to only provide payment for allogeneic bone marrow transplantation for patients with sickle cell disease on a clinical trial that had a comparison arm with patients not receiving bone marrow transplantation prompted the closure of this trial to accrual in 2017. Therefore, as we were unable to perform our planned statistical analysis, the primary objective was modified to evaluate engraftment, assessed by chimerism. This trial is registered with ClinicalTrials.gov, number NCT00489281. The study is closed to new participants and this is the primary analysis.

FINDINGS

Between Sept 24, 2014, and Aug 1, 2017, we enrolled 17 consecutive patients: 12 (71%) with sickle cell disease and 5 (29%) with β-thalassaemia major. The median patient age was 16 years (range 6-31, IQR 7·7-27·5). One (6%) of 17 patients had primary graft failure with recovery of host haemopoiesis. 13 (76%) of 17 patients achieved full donor chimerism and three (18%) had mixed donor-host chimerism. Five (29%) of 17 patients developed grade 2-4 acute GVHD, including four (24%) with maximal grade 2 GVHD and one (6%) with grade 3 GVHD. Chronic GVHD developed in three (18%) patients. As of their last follow-up visit, GVHD had resolved in all patients and no patients were receiving systemic GVHD therapy. All patients remained alive as of Aug 4, 2019, and the median follow-up duration was 705 days (range 355-1294; IQR 398-943). Only one (6%) of the 16 engrafted patients remained transfusion dependent, and 14 (88%) discontinued immunosuppression.

INTERPRETATION

Increasing total body irradiation to 400 cGy substantially reduced graft failure while maintaining the safety of haploidentical bone marrow transplantation with post-transplantation cyclophosphamide. These results suggest that engraftment after haploidentical bone marrow transplantation for haemoglobinopathies is possible, and primary graft failure-the main problem previously reported-might be addressed by this strategy. Therefore, this curative approach should no longer be restricted to patients with HLA-matched donors.

FUNDING

Maryland Stem Cell Research Fund and US National Institutes of Health.

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

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

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.