Unrelated donor cord blood transplantation for children with severe sickle cell disease: results of one cohort from the phase II study from the Blood and Marrow Transplant Clinical Trials Network (BMT CTN)

Stem cell research and regenerative medicine at King Abdullah International Medical Research Center

Translation of stem cell research from bench to bedside opens up exciting new therapeutic options for patients. Although stem cell research has progressed rapidly, its clinical applications have not kept pace. We report on the establishment of a stem cell research and regenerative medicine program at King Abdullah International Medical Research Center (KAIMRC). The purpose of this unit is to coordinate advanced stem cell research and translational outcomes with the goal of treating chronic human diseases, such as cancer, diabetes, cardiovascular, neurological, immunological, and liver diseases. Our first step in achieving this goal was to integrate the stem cells and regenerative medicine unit with our umbilical cord blood bank and bone marrow registry. This organizational structure will provide different sources for stem cells for research and clinical purposes, and facilitate our stem cell research and stem cell transplantation program. We are at an early and exciting stage in our program, but we believe that our progress to the international stage will be rapid and have a significant impact.

Hematopoietic stem cell transplantation in sickle cell disease: patient selection and special considerations

Hematopoietic stem cell transplantation remains the only curative treatment currently in use for patients with sickle cell disease (SCD). The first successful hematopoietic stem cell transplantation was performed in 1984. To date, approximately 1,200 transplants have been reported. Given the high prevalence of this disorder in Africa, and its emergence in the developed world through immigration, this number is relatively small. There are many reasons for this; primary among them are the availability of a donor, the risks associated with this complex procedure, and the cost and availability of resources in the developing world. Of these, it is fair to say that the risks associated with the procedure have steadily decreased to the point where, if currently performed in a center with experience using a matched sibling donor, overall survival is close to 100% and event-free survival is over 90%. While there is little controversy around offering hematopoietic stem cell transplantation to symptomatic SCD patients with a matched sibling donor, there is much debate surrounding the use of this modality in “less severe” patients. An overview of the current state of our understanding of the pathology and treatment of SCD is important to show that our current strategy is not having the desired impact on survival of homozygous SCD patients, and should be changed to significantly impact the small proportion of these patients who have matched siblings and could be cured, especially those without overt clinical manifestations. Both patient families and providers must be made to understand the progressive nature of SCD, and should be encouraged to screen full siblings of patients with homozygous SCD for their potential to be donors. Matched siblings should be referred to an experienced transplant center for evaluation and counseling. In this review, we will discuss the rationale for these opinions and make recommendations for patient selection.

Allogeneic Hematopoietic Cell Transplantation for Children with Sickle Cell Disease Is Beneficial and Cost-Effective: A Single-Center Analysis

Limited data exist regarding health care utilization (HCU) in patients receiving allogeneic hematopoietic cell transplantation (alloHCT) for sickle cell disease. Financial data from 2002 to 2011 were analyzed for 26 alloHCT patients and 48 control subjects (referred but without alloHCT). HCU of alloHCT was determined over 3 time periods: pre-alloHCT, during alloHCT (day 0 to day +365), and post-alloHCT. The median total cost per patient during the alloHCT year was $413,000 inpatient and $18,000 outpatient. Post-alloHCT HCU decreased when compared with pre-alloHCT and control subjects. The median cost of post-alloHCT outpatient visits per patient was significantly less when compared with pre-alloHCT (P = .044). The median cost of post-alloHCT inpatient visits per patient approached significance when compared with those pre-alloHCT (P = .079). Sixteen post-alloHCT patients, 19 control subjects, and 14 unaffected siblings were surveyed using Pediatric Quality of Life Inventory and EuroQOL questionnaires; however, the questionnaire scores across all 3 patient groups were not statistically significant (P = .2638). When adjusted for health-related quality of life, the analysis suggested alloHCT has a positive impact on health-related quality of life over control subjects. These pilot data support our hypothesis that alloHCT in children with sickle cell disease reduces HCU compared with control subjects without alloHCT.

Alemtuzumab based reduced intensity transplantation for pediatric severe aplastic anemia

BACKGROUND

Hematopoietic cell transplantation (HCT) is curative in patients with severe aplastic anemia (SAA). HCT is considered at presentation when a HLA-matched related donor (MRD) is available and has a high success rate. Unrelated donor (URD) transplants are typically undertaken if immunosuppressive therapy fails. Increased toxicity and graft rejection are often encountered in this setting.

PROCEDURE

We report a prospective multi-center trial of HCT in 17 children with SAA following novel reduced intensity conditioning with alemtuzumab, fludarabine and melphalan, and the best available donor. Nine were URD transplants matched at 7-8/8 loci, and performed following failure of immune suppression. Median follow up was 61 months (range 6-128).

RESULTS

All patients engrafted. Estimated 5 year event-free and overall-survival was 88% (95%CI 65.7-96.7). Five year overall survival for MRD and URD transplants was 100% and 78% (95%CI 45-93.6) respectively. Median times to neutrophil and platelet engraftment was 14 (range 10-27) and 23.5 (range 11-65) days respectively. Treatment related mortality was 12%. The incidence of grade II-IV and III-IV acute graft-versus-host disease was 29% and 18% respectively. At two years, all but one patient discontinued immunosuppression successfully. Laboratory measures of immune reconstitution normalized at one year and infection rates were low in the latter part of the first year.

CONCLUSIONS

HCT using this RIC approach was well tolerated and successful in achieving donor engraftment and early immune reconstitution with good quality of life free of immune suppression. Children with SAA can be successfully transplanted using alemtuzumab based conditioning.

Current attitudes of parents and patients toward hematopoietic stem cell transplantation for sickle cell anemia

BACKGROUND

Allogeneic hematopoietic stem cell transplantation (HSCT) is the only available cure for sickle cell anemia (SCA). HSCT-associated risks are one of many barriers to its widespread use for SCA. The study objective was to assess parent and patient perceptions of HSCT in the era of more widespread knowledge about HSCT for SCA.

PROCEDURE

We surveyed parents of children with SCA and adolescents with SCA using the standard reference gamble paradigm. Survey responses between Africans (A) and African Americans (AA) and between parents and adolescents were compared.

RESULTS

Seventy-two percent (64/89) of the respondents were willing to accept ≥ 5% risk of mortality, while 57% said they would accept a risk of ≥ 10% of graft versus host disease (GVHD). Twenty-two percent were unwilling to accept any risk of mortality or GVHD. Risk averseness did not differ between A or AA respondents. Fifty-six percent of respondents were willing to accept infertility post-HSCT.

CONCLUSIONS

These data suggest that the majority of parents and adolescents are willing to accept the current risks associated with matched sibling HSCT for SCA. However, there continue to be significant numbers of parents and adolescents who are unwilling to accept any risk of HSCT-associated mortality or GVHD.

Use of Alefacept for Preconditioning in Multiply Transfused Pediatric Patients with Nonmalignant Diseases

Transfusion-related alloimmunization is a potent barrier to the engraftment of allogeneic hematopoietic stem cells in patients with nonmalignant diseases (NMDs). Memory T cells, which drive alloimmunization, are relatively resistant to commonly used conditioning agents. Alefacept, a recombinant leukocyte function antigen-3/IgG1 fusion protein, targets CD2 and selectively depletes memory versus naive T cells. Three multiply transfused pediatric patients with NMD received a short course of high-dose i.v. alefacept (.25 mg/kg/dose on days -40 and -9 and .5 mg/kg/dose on days -33, -26, -19, and -12) before undergoing unrelated allogeneic transplant in the setting of reduced-intensity pretransplant conditioning and calcineurin inhibitor-based post-transplant graft-versus-host disease (GVHD) prophylaxis. Alefacept infusions were well tolerated in all patients. Peripheral blood flow cytometry was performed at baseline and during and after alefacept treatment. As expected, after the 5 weekly alefacept doses, each patient demonstrated selective loss of CD2(hi)/CCR7(-)/CD45RA(-) effector memory (Tem) and CD2(hi)/CCR7(+)/CD45RA(-) central memory (Tcm) CD4(+) and CD8(+) T cells with relative preservation of the CD2(lo) Tem and Tcm subpopulations. In addition, depletion of CD2(+) natural killer (NK) cells also occurred. Neutrophil recovery was rapid, and all 3 patients had 100% sorted (CD3/CD33) peripheral blood donor chimerism by day +100. Immune reconstitution (by absolute neutrophil, monocyte, and lymphocyte counts) was comparable with a cohort of historical control patients. All 3 patients developed GVHD but are all now off immune suppression and >2 years post-transplant with stable full-donor engraftment. These results suggest that alefacept at higher dosing can deplete both memory T cells and NK cells and that incorporating CD2-targeted depletion into a reduced-intensity transplant regimen is feasible and safe in heavily transfused patients.

How I treat and manage strokes in sickle cell disease

Neurologic complications are a major cause of morbidity and mortality in sickle cell disease (SCD). In children with sickle cell anemia, routine use of transcranial Doppler screening, coupled with regular blood transfusion therapy, has decreased the prevalence of overt stroke from ∼11% to 1%. Limited evidence is available to guide acute and chronic management of individuals with SCD and strokes. Current management strategies are based primarily on single arm clinical trials and observational studies, coupled with principles of neurology and hematology. Initial management of a focal neurologic deficit includes evaluation by a multidisciplinary team (a hematologist, neurologist, neuroradiologist, and transfusion medicine specialist); prompt neuro-imaging and an initial blood transfusion (simple followed immediately by an exchange transfusion or only exchange transfusion) is recommended if the hemoglobin is >4 gm/dL and <10 gm/dL. Standard therapy for secondary prevention of strokes and silent cerebral infarcts includes regular blood transfusion therapy and in selected cases, hematopoietic stem cell transplantation. A critical component of the medical care following an infarct is cognitive and physical rehabilitation. We will discuss our strategy of acute and long-term management of strokes in SCD.

Single Daily Busulfan Dosing for Infants with Nonmalignant Diseases Undergoing Reduced-Intensity Conditioning for Allogeneic Hematopoietic Progenitor Cell Transplantation

Busulfan (Bu) is widely used in conditioning regimens for infants undergoing allogeneic hematopoietic progenitor cell transplantation (HPCT), but the best approach to administer Bu in this population is still unknown. Here, we report a single-center experience of the use of a test dose to guide dose adjustment of intravenous (i.v.) Bu therapy in infants. Between 2004 and 2013, 33 infants younger than 1 year with nonmalignant conditions received allogeneic peripheral blood or cord blood HPCT after a reduced-intensity conditioning (RIC) regimen consisting of fludarabine, antithymocyte globulin, and 2 single daily doses of i.v. Bu. Pharmacokinetic results of a test dose of i.v. Bu (.8 mg/kg) were used to determine the dose of 2 single daily i.v. Bu regimen doses, adjusted to target an area under the curve (AUC) of 4000 μMol*minute per day in a first cohort (n = 12) and 5000 μMol*minute in a second cohort (n = 21). The mean Bu clearance in our infant patients was found to be 3.67 ± 1.03 mL/minute/kg, and the test dose clearance was highly predictive of the regimen dose clearance. The mean AUC achieved after the first single daily regimen dose was 3951 ± 1239 in the AUC 4000 cohort and 4884 ± 766 for the AUC 5000 cohort. No patient in either cohort developed hepatic sinusoidal obstructive syndrome or seizures attributable to Bu. Primary graft failure occurred in 4 patients and secondary graft failure occurred in 3, predominantly in the AUC 4000 cohort (6 of 7). Among the engrafted patients (n = 28), 16 achieved full donor chimerism and 9 patients attained stable mixed chimerism. Overall survival of patients at 6 years after transplantation was 59.5% for the AUC 4000 cohort and 85.4% for the AUC 5000 cohort, with primary graft failure in the first cohort being a major contributor to morbidity. Logistic regression analysis showed that the risk of graft failure increased significantly if cord blood hematopoietic progenitor cells were used or if total Bu exposure was below 4000 μMol*minute per day for 2 days. The difference in clinical outcomes between the 2 cohorts supports the conclusion that targeting a higher Bu AUC of 5000 μMol*minute per day for 2 days improves donor engraftment in infants with nonmalignant conditions undergoing RIC HPCT without increasing toxicity. Measuring i.v. Bu pharmokinetics using a test dose allows timely adjustment of single daily regimen doses and optimization of total Bu exposure, resulting in an effective and safe regimen for these infants.

Hematopoietic stem cell transplantation in thalassemia major and sickle cell disease: indications and management recommendations from an international expert panel

Thalassemia major and sickle cell disease are the two most widely disseminated hereditary hemoglobinopathies in the world. The outlook for affected individuals has improved in recent years due to advances in medical management in the prevention and treatment of complications. However, hematopoietic stem cell transplantation is still the only available curative option. The use of hematopoietic stem cell transplantation has been increasing, and outcomes today have substantially improved compared with the past three decades. Current experience world-wide is that more than 90% of patients now survive hematopoietic stem cell transplantation and disease-free survival is around 80%. However, only a few controlled trials have been reported, and decisions on patient selection for hematopoietic stem cell transplantation and transplant management remain principally dependent on data from retrospective analyses and on the clinical experience of the transplant centers. This consensus document from the European Blood and Marrow Transplantation Inborn Error Working Party and the Paediatric Diseases Working Party aims to report new data and provide consensus-based recommendations on indications for hematopoietic stem cell transplantation and transplant management.

Experience with Alemtuzumab, Fludarabine, and Melphalan Reduced-Intensity Conditioning Hematopoietic Cell Transplantation in Patients with Nonmalignant Diseases Reveals Good Outcomes and That the Risk of Mixed Chimerism Depends on Underlying Disease, Stem Cell Source, and Alemtuzumab Regimen

Alemtuzumab, fludarabine, and melphalan reduced-intensity conditioning (RIC) regimens are increasingly used for the hematopoietic cell transplantation (HCT) of pediatric and young adult patients with nonmalignant diseases. Early experience suggests that these regimens are associated with good survival but a high incidence of mixed chimerism, which we have previously shown to be influenced by the alemtuzumab schedule. We hypothesized that the underlying diagnosis and donor graft source would also affect the development of mixed chimerism and that the majority of patients would survive RIC HCT without graft loss. To examine this, we conducted a retrospective study of 206 patients with metabolic diseases, non-Fanconi anemia marrow failure disorders, and primary immune deficiencies who underwent 210 consecutive RIC HCT procedures at Cincinnati Children's Hospital. Ninety-seven percent of the patients engrafted. Mixed donor and recipient chimerism developed in 46% of patients. Patients with marrow failure had a low risk of mixed chimerism (hazard ratio [HR], .208; 95% confidence interval [CI], .061 to .709; P = .012). The risk of mixed chimerism was high in patients who received a cord blood graft (HR, 3.122; 95% CI, 1.236 to 7.888; P = .016). As expected, patients who received a proximal or higher dose per kilogram of alemtuzumab schedule also experienced higher rates of mixed chimerism (all HR > 2, all P < .05). At the time of last follow-up (median, 654 days; range, 13 to 3337), over 75% of patients had greater than 90% whole blood donor chimerism. A second transplantation was performed in 5% of patients. Three-year survival without retransplantation was 84% (95% CI, 71% to 98%) for patients who underwent transplantation with an HLA-matched sibling donor. Survival without retransplantation was negatively affected by lack of a matched related donor, increasing age, and development of grades III and IV acute graft-versus-host disease. We conclude that alemtuzumab, fludarabine, and melphalan RIC HCT offers good results for many patients and that the risk of developing mixed chimerism is influenced by underlying diagnosis, graft source, and alemtuzumab dosing.

Hematopoietic Cell Transplantation Using Reduced-Intensity Conditioning Is Successful in Children with Hematologic Cytopenias of Genetic Origin

Genetically derived hematologic cytopenias are a rare heterogeneous group of disorders. Allogeneic hematopoietic cell transplantation (HCT) is curative but offset by organ toxicities from the preparative regimen, graft rejection, graft-versus-host disease (GVHD), or mortality. Because of these possibilities, consideration of HCT can be delayed, especially in the unrelated donor setting. We report a prospective multicenter trial of reduced-intensity conditioning (RIC) with alemtuzumab, fludarabine, and melphalan and HCT in 11 children with marrow failure of genetic origin (excluding Fanconi anemia) using the best available donor source (82% from unrelated donors). The median age at transplantation was 23 months (range, 2 months to 14 years). The median times to neutrophil (>500 × 10(6)/L) and platelet (>50 × 10(9)/L) engraftment were 13 (range, 12 to 24) and 30 (range, 7 to 55) days, respectively. The day +100 probability of grade II to IV acute GVHD and the 1-year probability of limited and extensive GVHD were 9% and 27%, respectively. The probability of 5-year overall and event-free survival was 82%; 9 patients were alive with normal blood counts at last follow-up and all were successfully off systemic immunosuppression. In patients with genetically derived severe hematologic cytopenias, allogeneic HCT with this RIC regimen was successful in achieving a cure. This experience supports consideration of HCT early in such patients even in the absence of suitable related donors.

Treosulfan-based conditioning regimen for allogeneic haematopoietic stem cell transplantation in children with sickle cell disease

Although allogeneic haematopoietic stem cell transplantation (HSCT) still represents the only consolidated possibility of cure for sickle cell disease (SCD) patients, its use has been limited by the risk of morbidity and mortality associated with conventional myeloablative therapy. The introduction of treosulfan to replace busulfan in conditioning regimens has recently been explored by virtue of its lower toxicity profile. We report our experience with a treosulfan/thiotepa/fludarabine conditioning for human leucocyte antigen (HLA)-matched sibling or unrelated donor-HSCT in 15 children with SCD, and compare patient outcomes with those of a historical cohort (15 patients) given a busulfan-based regimen. Engraftment was achieved in 28 out of 30 patients (93%), with one case of graft failure in either group. The conditioning regimen was well tolerated in both groups, with no cases of grade III-IV regimen-related toxicity. The 7-year overall survival (OS) and disease-free survival (DFS) for the whole cohort were 100% and 93%, respectively, with a 93% DFS in both busulfan and treosulfan groups. No SCD-related adverse events occurred after engraftment in patients with complete or mixed donor chimerism. This retrospective analysis suggests that a treosulfan-based conditioning regimen is able to ensure engraftment with excellent OS/DFS and low regimen-related toxicity in patients with SCD.

Indications for allo- and auto-SCT for haematological diseases, solid tumours and immune disorders: current practice in Europe, 2015

This is the sixth special report that the European Society for Blood and Marrow Transplantation regularly publishes on the current practice and indications for haematopoietic SCT for haematological diseases, solid tumours and immune disorders in Europe. Major changes have occurred in the field of haematopoietic SCT over the last years. Cord blood units as well as haploidentical donors have been increasingly used as stem cell sources for allo-SCT, thus, augmenting the possibility of finding a suitable donor for a patient. Continuous refinement of conditioning strategies has also expanded not only the number of potential indications but also has permitted consideration of older patients or those with co-morbidity for a transplant. There is accumulating evidence of the role of haematopoietic SCT in non-haematological disorders such as autoimmune diseases. On the other hand, the advent of new drugs and very effective targeted therapy has challenged the role of SCT in some instances or at least, modified its position in the treatment armamentarium of a given patient. An updated report with revised tables and operating definitions is presented.

Immune parameter analysis of children with sickle cell disease on hydroxycarbamide or chronic transfusion therapy

Sickle cell disease (SCD) is increasingly appreciated as an inflammatory condition associated with alterations in immune phenotype and function. In this cross-sectional study we performed a multiparameter analysis of 18 immune markers in 114 paediatric SCD patients divided by treatment group [those receiving hydroxycrabamide (HC, previously termed hydroxyurea), chronic transfusion (CT), or no disease-modifying therapy] and 29 age-matched African American healthy controls. We found global elevation of most immune cell counts in SCD patients receiving no disease-modifying therapy at steady state. Despite the decrease in percentage of haemoglobin S associated with CT therapy, the abnormal cellular immune phenotype persisted in patients on CT. In contrast, in both univariate and multivariate analysis, treatment with HC was associated with normalization of the vast majority of leucocyte populations. This study provides additional support for HC treatment in SCD, as it appears that HC decreases the abnormally elevated immune cell counts in patients with SCD.

Alternative donor transplant of benign primary hematologic disorders

Hematopoietic SCT is currently the only curative therapy for a range of benign inherited and acquired primary hematologic disorders in children, including BM failure syndromes and hemoglobinopathies. The preferred HLA-matched sibling donor is available for only about 25% of such children. However, there has been substantial progress over the last four decades in the use of alternative donors for those without a matched sibling-including HLA-matched unrelated donors, HLA-haploidentical related donors and unrelated-donor umbilical cord blood-so that it is now possible to find a donor for almost every child requiring an allograft. Below, we summarize the relative merits and limitations of the different alternative donors for benign hematologic conditions, first generally, and then in relation to specific disorders, and suggest recommendations for selecting such an alternative donor.

Advances in unrelated and alternative donor hematopoietic cell transplantation for nonmalignant disorders

PURPOSE OF REVIEW

The role of hematopoietic cell transplantation in non-malignant disorders has increased exponentially with the recognition that multiple diseases can be controlled or cured if engrafted with donor-derived cells. This review provides an overview of advances made in alternative donor transplants for nonmalignant disorders.

RECENT FINDINGS

Stem cell sources, novel transplant methods, and sophisticated supportive care have simultaneously made giant strides toward improving the safety and efficacy of hematopoietic cell transplantation. This has led to the utilization of marrow, cord, peripheral blood stem cell and haploidentical stem cell sources, and novel reduced toxicity or reduced intensity conditioning regimens to transplant non-malignant disorders such as immune dysfunctions, marrow failure syndromes, metabolic disorders and hemoglobinopathies. Transplant complications such as graft rejection, infections, and graft versus host disease are better combated in this modern era of medicine, achieving better survival with decreased late effects. These aspects of transplant for non-malignant disorders are discussed.

SUMMARY

This review presents the progress made in the realm of hematopoietic cell transplantation for non-malignant disorders. It advocates the consideration of alternative donor transplants in the absence of human leukocyte antigen matched siblings when indicated by disease severity. The ultimate goal is to provide curative transplant options for more patients that can benefit from this intervention, prior to detrimental outcomes.

Smoothing the crescent curve: sickle cell disease

Sickle cell disease (SCD) is an inherited disorder secondary to a point mutation at the sixth position of the beta chain of human hemoglobin that results in the replacement of valine for glutamic acid. This recessive genetic abnormality precipitates the polymerization of the deoxygenated form of hemoglobin S that induces a major distortion of red blood cells (sickle red blood cells), which decreases sickle red blood cell deformability, leading to chronic hemolysis and vasoocclusion. These processes can result in severe complications, including chronic pain, end organ dysfunction, stroke, and early mortality. The only proven curative therapy for patients with SCD is myeloablative conditioning and allogeneic stem cell transplantation from HLA-matched sibling donors. In this review, we discuss the most recent advances in allogeneic stem cell transplantation in SCD, including more novel approaches such as reduced toxicity conditioning and the use of alternative allogeneic donors (matched unrelated donors, umbilical cord blood transplantation, haploidentical donors) and autologous gene correction stem cell strategies. Prospects are bright for new stem cell approaches for patients with SCD that will enable curative stem and genetic correction therapies for a greater number of patients suffering from this chronic and debilitating condition.

Improving cord blood unit quantity and quality at King Abdullah International Medical Research Center Cord Blood Bank

BACKGROUND

Public cord blood banks (CBBs) store cord blood unit (CBU) donations for anyone in need. However, strict regulations need to be followed to build up high-quality bank products that can be used worldwide. We established a public CBB at a tertiary hospital in Saudi Arabia. Here, we investigated the reasons behind rejecting or not collecting CBUs over 2 years (2011-2012) and which steps were implemented to improve the number and quality of storable units.

STUDY DESIGN AND METHODS

A total of 2891 mothers were evaluated. Reasons for rejecting donors, not collecting, and rejecting units before or after collection were analyzed and compared for the years 2011 and 2012.

RESULTS

A total of 1157 (40%) CBUs were not collected, mainly due to staff availability, and 564 (20%) CBUs were rejected. The main reason for rejecting donations was the mother's or neonate's health. Rejecting CBUs after collection was due to low volume. A total of 1170 (40%) CBUs were successfully collected for potential banking and sent for processing; however, 58% were rejected in the laboratory due to low total nucleated cell counts. Several changes were implemented during the 2 years including physician education and awareness, in utero collection, cesarean collection, and staff recruitment. These changes positively affected the numbers of our collected units. Out of the initially eligible mothers in 2011, only 17% were banked; this was increased to 33% in 2012.

CONCLUSIONS

We identified the problems with collecting CBUs for banking and will keep improving our selection process of recruiting more CBUs of high quality.

Concise review: umbilical cord blood transplantation: past, present, and future

Allogeneic hematopoietic stem cell transplantation is an important treatment option for fit patients with poor-risk hematological malignancies; nevertheless, the lack of available fully matched donors limits the extent of its use. Umbilical cord blood has emerged as an effective alternate source of hematopoietic stem cell support. Transplantation with cord blood allows for faster availability of frozen sample and avoids invasive procedures for donors. In addition, this procedure has demonstrated reduced relapse rates and similar overall survival when compared with unrelated allogeneic hematopoietic stem cell transplantation. The limited dose of CD34-positive stem cells available with single-unit cord transplantation has been addressed by the development of double-unit cord transplantation. In combination with improved conditioning regimens, double-unit cord transplantation has allowed for the treatment of larger children, as well as adult patients with hematological malignancies. Current excitement in the field revolves around the development of safer techniques to improve homing, engraftment, and immune reconstitution after cord blood transplantation. Here the authors review the past, present, and future of cord transplantation.

Hematopoietic stem cell transplantation for sickle cell disease: state of the science

Sickle cell disease (SCD) is an inherited disorder secondary to a point mutation at the sixth position of the beta chain of human hemoglobin resulting in the replacement of valine for glutamic acid. This recessive genetic abnormality precipitates the polymerization of the deoxygenated form of hemoglobin S inducing a major distortion of red blood cells (S-RBC), which decreases S-RBC deformability leading to chronic hemolysis and vaso-occlusion. These processes can result in severe complications including chronic pain, end-organ dysfunction, stroke, and early mortality. The only proven curative therapy for patients with SCD is myeloablative conditioning and allogeneic stem cell transplantation from HLA-matched sibling donors. In this review, we discuss the most recent advances in allogeneic stem cell transplantation in patients with SCD including more novel approaches such as reduced toxicity conditioning and the use of alternative allogeneic donors, including matched unrelated donors (MUDs), unrelated cord blood donors (UCBT), and familial haploidentical (FHI) donors. The results to date are very encouraging regarding allogeneic stem cell transplantation for patients with SCD including high survival rates and enabling a greater number of patients suffering from this chronic and debilitating condition to receive curative allogeneic stem cell therapies. However, we still have several areas to investigate and barriers to overcome to successfully cure the majority of patients with severe SCD through allogeneic stem cell therapies.

Hematopoietic stem cell transplantation for patients with sickle cell disease: progress and future directions

Research has solidified matched sibling marrow, cord blood, or mobilized peripheral blood as the best source for allogeneic hematopoietic stem cell transplantation for patients with sickle cell disease, with low graft rejection and graft-versus-host disease (GVHD) and high disease-free survival rates. Fully allelic matched unrelated donor is an option for transplant-eligible patients without HLA-matched sibling donors. Unrelated cord transplant studies reported high GVHD and low engraftment rates. Haploidentical transplants have less GVHD, but improvements are needed to increase the low engraftment rate. The decision to use unrelated cord blood units or haploidentical donors depends on institutional expertise.

Blood and marrow transplantation for sickle cell disease: is less more?

Blood and marrow transplantation is a curative therapy for patients with sickle cell disease yet this option is seldom used. Clinical studies have shown however that children transplanted for this condition can achieve excellent results. In children with sickle cell disease transplanted following conditioning with busulfan, cyclophosphamide, and anti-thymocyte globulin, cure rates in excess of 80% can be obtained when an HLA-matched sibling is used as the donor. However, the large majority of patients with sickle cell disease will not have such a donor, or will not be able to tolerate high dose conditioning regimens. Therefore novel approaches such as non-myeloablative regimes, and alternative donors such as haploidentical, unrelated, or cord blood grafts are currently being explored in clinical trials. Recent reports on non-myeloablative conditioning (HLA-matched or haploidentical donors) highlight the safety and efficacy of these approaches with low mortality and high efficacy suggesting that in the near future non-myeloablation could be the preferred type of conditioning and donor availability will not be a barrier anymore to proceed to transplant. This review will focus on the results obtained when bone marrow transplants are used to treat sickle cell disease and will discuss the results obtained with these novel approaches.

The ethics of a proposed study of hematopoietic stem cell transplant for children with “less severe” sickle cell disease

Hematopoietic stem cell transplant (HSCT) is the only cure for sickle cell disease (SCD). HSCT using an HLA-identical sibling donor is currently an acceptable treatment option for children with severe SCD, with expected HSCT survival >95% and event-free survival >85%. HSCT for children with less severe SCD (children who have not yet suffered overt disease complications or only had mild problems) is controversial. It is important to consider the ethical issues of a proposed study comparing HLA-identical sibling HSCT to best supportive care for children with less severe SCD. In evaluating the principles of nonmaleficence, respect for individual autonomy, and justice, we conclude that a study of HLA-identical sibling HSCT for all children with SCD, particularly hemoglobin SS and Sβ0-thalassemia disease, is ethically sound. Future work should explore the implementation of a large trial to help determine whether HSCT is a beneficial treatment of children with less severe SCD.

Unrelated donor allogeneic hematopoietic stem cell transplantation for patients with hemoglobinopathies using a reduced-intensity conditioning regimen and third-party mesenchymal stromal cells

Allogeneic hematopoietic stem cell transplantation for patients with a hemoglobinopathy can be curative but is limited by donor availability. Although positive results are frequently observed in those with an HLA-matched sibling donor, use of unrelated donors has been complicated by poor engraftment, excessive regimen-related toxicity, and graft-versus-host disease (GVHD). As a potential strategy to address these obstacles, a pilot study was designed that incorporated both a reduced-intensity conditioning and mesenchymal stromal cells (MSCs). Six patients were enrolled, including 4 with high-risk sickle cell disease (SCD) and 2 with transfusion-dependent thalassemia major. Conditioning consisted of fludarabine (150 mg/m(2)), melphalan (140 mg/m(2)), and alemtuzumab (60 mg for patients weighing > 30 kg and .9 mg/kg for patients weighing <30 kg). Two patients received HLA 7/8 allele matched bone marrow and 4 received 4-5/6 HLA matched umbilical cord blood as the source of HSCs. MSCs were of bone marrow origin and derived from a parent in 1 patient and from an unrelated third-party donor in the remaining 5 patients. GVHD prophylaxis consisted of cyclosporine A and mycophenolate mofetil. One patient had neutropenic graft failure, 2 had autologous hematopoietic recovery, and 3 had hematopoietic recovery with complete chimerism. The 2 SCD patients with autologous hematopoietic recovery are alive. The remaining 4 died either from opportunistic infection, GVHD, or intracranial hemorrhage. Although no infusion-related toxicity was seen, the cotransplantation of MSCs was not sufficient for reliable engraftment in patients with advanced hemoglobinopathy. Although poor engraftment has been observed in nearly all such trials to date in this patient population, there was no evidence to suggest that MSCs had any positive impact on engraftment. Because of the lack of improved engraftment and unacceptably high transplant-related mortality, the study was prematurely terminated. Further investigations into understanding the mechanisms of graft resistance and development of strategies to overcome this barrier are needed to move this field forward.

A novel reduced-intensity conditioning regimen for unrelated umbilical cord blood transplantation in children with nonmalignant diseases

Reduced-intensity conditioning (RIC) regimens have the potential to decrease transplantation-related morbidity and mortality. However, engraftment failure has been prohibitively high after RIC unrelated umbilical cord blood transplantation (UCBT) in chemotherapy-naïve children with nonmalignant diseases (NMD). Twenty-two children with a median age of 2.8 years, many with severe comorbidities and prior viral infections, were enrolled in a novel RIC protocol consisting of hydroxyurea, alemtuzumab, fludarabine, melphalan, and thiotepa followed by single UCBT. Patients underwent transplantation for inherited metabolic disorders (n = 8), primary immunodeficiencies (n = 9), hemoglobinopathies (n = 4) and Diamond Blackfan anemia (n = 1). Most umbilical cord blood (UCB) units were HLA-mismatched with median infused total nucleated cell dose of 7.9 × 10(7)/kg. No serious organ toxicities were attributable to the regimen. The cumulative incidence of neutrophil engraftment was 86.4% (95% confidence interval [CI], 65% to 100%) in a median of 20 days, with the majority sustaining > 95% donor chimerism at 1 year. Cumulative incidence of acute graft-versus-host disease (GVHD) grades II to IV and III to IV by day 180 was 27.3% (95% CI, 8.7% to 45.9%) and 13.6% (95 CI, 0% to 27.6%), respectively. Cumulative incidence of extensive chronic GVHD was 9.1% (95% CI, 0% to 20.8%). The primary causes of death were viral infections (n = 3), acute GVHD (n = 1) and transfusion reaction (n = 1). One-year overall and event-free survivals were 77.3% (95% CI, 53.7% to 89.8%) and 68.2% (95% CI, 44.6% to 83.4%) with 31 months median follow-up. This is the first RIC protocol demonstrating durable UCB engraftment in children with NMD. Future risk-based modifications of this regimen could decrease the incidence of viral infections. (www.clinicaltrials.gov/NCT00744692).

Transfusion-induced bone marrow transplant rejection due to minor histocompatibility antigens

Traditionally, alloimmunization to transfused blood products has focused exclusively on recipient antibodies recognizing donor alloantigens present on the cell surface. Accordingly, the immunologic sequelae of alloimmunization have been antibody mediated effects (ie, hemolytic transfusion reactions, platelet refractoriness, anti-HLA and anti-HNA effects, etc). However, in addition to the above sequelae, there is also a correlation between the number of antecedent transfusions in humans and the rate of bone marrow transplant (BMT) rejection-under reduced intensity conditioning with HLA-matched or HLA-identical marrow. Bone marrow transplant of this nature is the only existing cure for a series of nonmalignant hematologic diseases (eg, sickle cell disease, thalassemias, etc); however, rejection remains a clinical problem. It has been hypothesized that transfusion induces subsequent BMT rejection through immunization. Studies in animal models have observed the same effect and have demonstrated that transfusion-induced BMT rejection can occur in response to alloimmunization. However, unlike traditional antibody responses, sensitization in this case results in cellular immune effects, involving populations such as T cell or natural killer cells. In this case, rejection occurs in the absence of alloantibodies and would not be detected by existing immune-hematologic methods. We review human and animal studies in light of the hypothesis that, for distinct clinical populations, enhanced rejection of BMT may be an unappreciated adverse consequence of transfusion, which current blood bank methodologies are unable to detect.

Hematopoietic stem-cell transplantation for sickle cell disease: current evidence and opinions

With rapidly expanding evidence of benefit reported by several groups, allogeneic hematopoietic stem-cell transplantation has become an acceptable treatment option for sickle cell disease. It is currently the only curative therapy available. Hematopoietic stem-cell transplantation was offered primarily as a therapeutic option for severe sickle cell disease in the context of myeloablative matched sibling donor transplants over the last two decades and helped to establish the benefits of transplantation for this disorder. While this approach provided proof of principle, the disadvantages and limitations of transplantation became evident along the way. It has been recognized that transplantation for sickle cell disease does not need to adhere strictly to the principles of transplantation for malignant disorders, such as achievement of full donor cell chimerism. As reviewed here, in recent years the transplant community has set out to explore ways to make stem-cell transplantation more available to patients with the disease, define indications and better timing, and offset toxicities with novel approaches to conditioning and better supportive care.

Challenges and opportunities for international cooperative studies in pediatric hematopoeitic cell transplantation: priorities of the Westhafen Intercontinental Group

More than 20% of allogeneic hematopoietic cell transplantations (HCTs) are performed in children and adolescents at a large number of relatively small centers. Unlike adults, at least one-third of HCTs in children are performed for rare, nonmalignant indications. Clinical trials to improve HCT outcomes in children have been limited by small numbers and these pediatric-specific features. The need for a larger number of pediatric HCT centers to participate in trials has led to the involvement of international collaborative groups. Representatives of the Pediatric Blood and Marrow Transplant Consortium, European Group for Blood and Marrow Transplantation's Pediatric Working Group, International Berlin-Frankfurt-Munster (iBFm) Stem Cell Transplantation Committee, and Children's Oncology Group's Hematopoietic Stem Cell Transplantation Discipline Committee met on October 3, 2012, in Frankfurt, Germany to develop a consensus on the highest priorities in pediatric HCT. In addition, it explored the creation of an international consortium to develop studies focused on HCT in children and adolescents. This meeting led to the creation of an international HCT network, dubbed the Westhafen Intercontinental Group, to develop worldwide priorities and strategies to address pediatric HCT issues. This review outlines the priorities of need as identified by this consensus group.

Exposure of early pediatric trainees to blood and marrow transplantation leads to higher recruitment to the field

The National Marrow Donor Program (NMDP) projects the need for allogeneic unrelated blood and marrow transplantation (BMT) in the United States as 10,000 per year. Although the NMDP is preparing to facilitate that number by the year 2015, there are several barriers to meeting this goal, including the need to recruit more health care personnel, including BMT physicians. To learn how best to recruit BMT physicians, we examined why practicing BMT physicians chose to enter the field and why others did not. We conducted a Web-based survey among pediatric hematology/oncology (PHO) and BMT physician providers and trainees to identify the factors influencing their decision to choose or not choose a career in BMT. Out of 259 respondents (48% male, 74% of Caucasian origin), 94 self-identified as BMT physicians, 112 as PHO physicians, and 53 as PHO trainees. The PHO and BMT providers spent an average of 53% of their time in clinical activities. More than two-thirds of PHO providers reported providing BMT services at their institutions, most commonly for inpatient coverage (73%). The proportion of providers exposed to BMT early in training was significantly higher among BMT providers compared with PHO providers (51% versus 18% in medical school [P < .0001]; 70% versus 50% during residency [P < .005]). Exposure during fellowship (94%) did not differ between the 2 groups. The decision to pursue a career in BMT was made before fellowship (medical school or residency) by 50% of the respondents. A lower proportion of BMT providers than PHO providers reported current involvement in the education of medical students and residents (76% versus 98%; P < .0001). Of the 53 trainees who responded, 64% reported not contemplating a career in BMT. Of these, 68% identified inadequate exposure to BMT before PHO fellowship as the reason behind this decision. Only 26% reported receiving exposure to the BMT field while in medical school, and 43% reported exposure during residency. The 2 most common reasons cited for choosing a career as a BMT physician were the degree of intellectual and scientific challenge (89%) and the influence of role models/mentors in the field (67%). The results of this survey suggest that early exposure to BMT during medical school and residency is associated with increased interest in pursuing a career in BMT. BMT physicians and training program directors can foster interest in the field by promoting BMT-focused education and clinical inpatient and outpatient rotations during medical school and residency. This early exposure to BMT may aid recruitment of future transplantation providers.

β-globin gene transfer to human bone marrow for sickle cell disease

Autologous hematopoietic stem cell gene therapy is an approach to treating sickle cell disease (SCD) patients that may result in lower morbidity than allogeneic transplantation. We examined the potential of a lentiviral vector (LV) (CCL-βAS3-FB) encoding a human hemoglobin (HBB) gene engineered to impede sickle hemoglobin polymerization (HBBAS3) to transduce human BM CD34+ cells from SCD donors and prevent sickling of red blood cells produced by in vitro differentiation. The CCL-βAS3-FB LV transduced BM CD34+ cells from either healthy or SCD donors at similar levels, based on quantitative PCR and colony-forming unit progenitor analysis. Consistent expression of HBBAS3 mRNA and HbAS3 protein compromised a fourth of the total β-globin-like transcripts and hemoglobin (Hb) tetramers. Upon deoxygenation, a lower percentage of HBBAS3-transduced red blood cells exhibited sickling compared with mock-transduced cells from sickle donors. Transduced BM CD34+ cells were transplanted into immunodeficient mice, and the human cells recovered after 2-3 months were cultured for erythroid differentiation, which showed levels of HBBAS3 mRNA similar to those seen in the CD34+ cells that were directly differentiated in vitro. These results demonstrate that the CCL-βAS3-FB LV is capable of efficient transfer and consistent expression of an effective anti-sickling β-globin gene in human SCD BM CD34+ progenitor cells, improving physiologic parameters of the resulting red blood cells.

Hematopoietic stem cell transplantation in SCD

Hematopoietic stem cell transplantation (HSCT) is the one and only curative therapy available for patient with severe sickle cell disease (SCD). Until today, several hundreds of patients have undergone geno-identical HSCT. More than 200 patients were transplanted in France. The first indication was cerebral vasculopathy. Among both malignant and non-malignant diseases treated with HSCT, the success rate obtained in SCD patients appears as the best one. From the year 2000, more than 95% of transplanted patients survived the HSCT procedure and more than 90% are completely cured and experience a very satisfying health condition post-transplantation. However, the current standard procedure includes a myeloablative conditioning regimen for warranting engraftment. Such regime is linked to severe long-term side effects such as hypofertility. Due to the excellent obtained results, we have to think about a possible widening of indications, a decrease of conditioning intensity and toxicity, and about HSCT from alternative stem cell sources, such as mismatch family donor, unrelated volunteer donor or unrelated cord blood.

Umbilical cord blood: an evolving stem cell source for sickle cell disease transplants

Allogeneic hematopoietic stem cell transplantation has proven benefit in controlling sickle cell disease-related vasculopathy and organ damage. Myeloablative matched sibling donor cord transplants have excellent outcomes in sickle cell disease. Unrelated donor transplant options are often deferred because of a lack of suitable human leukocyte antigen-matched donors, a problem especially relevant to minority populations. Umbilical cord blood transplantation allows for more mismatching from the graft-versus-host disease perspective and the donor pool is expandable with effort and education. Drawbacks such as increased rates of graft rejection, a fixed cell dose, delayed immune reconstitution, and transplant-related mortality have deterred unrelated cord transplant efforts. However, the transplant community continues to make enormous strides in this transplant realm in areas of immunogenetics, stem cell expansion, conditioning regimens, and supportive care. This has allowed the development of new studies that are currently ongoing, exploring ways to make cord blood transplantation successful and safer. The goal is to make unrelated donor cord blood transplantation for sickle cell disease merit early consideration in patients who stand to benefit from this approach.

Allogeneic transplantation strategies including haploidentical transplantation in sickle cell disease

Sickle cell disease (SCD) is the most common inherited hemoglobinopathy. Despite antenatal counseling and neonatal screening programs implemented in higher income countries, SCD is still associated with multiple morbidities and early mortality. To date, the only curative approach to SCD is hematopoietic stem cell transplantation, but this therapy is not yet established worldwide. The registries of the European Blood and Marrow Transplant (EBMT) and the Centre for International Blood and Marrow Transplant Research (CIBMTR) account, respectively, for 611 and 627 patients receiving transplantations for SCD. Most of these patients were transplanted with grafts from an HLA-identical sibling donor. The main obstacles to increasing the number of transplantations are a lack of awareness on the part of physicians and families, the absence of reliable prognostic factors for severity, and the perceived risk that transplantation complications may outweigh the benefits of early transplantation. Results show that more than 90% of patients having undergone an HLA-identical sibling transplantation after myeloablative conditioning are cured, with very limited complications. Major improvement is expected from the use of new reduced-toxicity conditioning regimens and the use of alternative donors, including unrelated cord blood transplantations and related haploidentical bone marrow or peripheral blood stem cell transplantations.

Advances in stem cell transplantation and gene therapy in the β-hemoglobinopathies

High-level production of β-globin, γ-globin, or therapeutic mutant globins in the RBC lineage by hematopoietic stem cell gene therapy ameliorates or cures the hemoglobinopathies sickle cell disease and beta thalassemia, which are major causes of morbidity and mortality worldwide. Considerable efforts have been made in the last 2 decades in devising suitable gene-transfer vectors and protocols to achieve this goal. Five years ago, the first βE/β0-thalassemia major (transfusion-dependent) patient was treated by globin lentiviral gene therapy without injection of backup cells. This patient has become completely transfusion independent for the past 4 years and has global amelioration of the thalassemic phenotype. Partial clonal dominance for an intragenic site (HMGA2) of chromosomal integration of the vector was observed in this patient without a loss of hematopoietic homeostasis. Other patients are now receiving transplantations while researchers are carefully weighing the benefit/risk ratio and continuing the development of further modified vectors and protocols to improve outcomes further with respect to safety and efficacy.

Umbilical cord blood transplantation: a maturing technology

The use of umbilical cord blood (CB) as a source of hematopoietic progenitor cells for patients with high-risk hematologic disorders receiving allogeneic hematopoietic cell transplantations (HCTs) has increased significantly. Single-institution and registry studies have shown a decreased relapse rate and an increased transplantation-related mortality rate with similar overall survival rates after allogeneic HCT with CB compared with other donor sources. The transplantation of double CB units has overcome the dose limitation inherent in a single CB unit and thus has markedly extended the use of CB to larger children and adults. Similarly, the use of reduced intensity conditioning in the CB transplantation setting has allowed the treatment of older patients who would be unable to tolerate the myeloablative regimens used in the original CB transplantation protocols.

The Role of HLA in Cord Blood Transplantation

In recent years, umbilical cord blood (CB), a rich source of hematopoietic stem cells (HSC), has been used successfully as an alternative HSC source to treat a variety of hematologic, immunologic, genetic, and oncologic disorders. CB has several advantages, including prompt availability of the transplant, decrease of graft versus host disease (GVHD) and better long-term immune recovery, resulting in a similar long-term survival. Studies have shown that some degree of HLA mismatches is acceptable. This review is intended to outline the main aspects of HLA matching in different settings (related, pediatric, adult, or double-unit HSCT), its effect on transplantation outcome and the role of HLA in donor selection.