Reduced-intensity conditioning in children: a reappraisal in 2008

Transplant-related mortality and morbidity (both short and long term) have limited the effectiveness of SCT in children with both malignant and nonmalignant diseases. Reduced-intensity preparative regimens permit engraftment of allogeneic cells without many of the toxicities associated with standard TBI- and non-TBI-based conditioning. We review the concepts that underlie reduced-intensity transplantation (RIT) and highlight the experience of the technique in children. Although acute organ damage may be reduced after these transplants, the overall incidence of severe infections and of GvHD may be similar to that seen after standard-intensity transplantation. The relatively small numbers of children who have received RIT and the newness of the technique preclude long-term follow-up with which to monitor the incidence of associated long-term side effects and disease-free survival. Future refinements in RIT and appropriate patient selection for these procedures will hopefully extend its utility in the future.     

Stem Cell Transplantation for Aplastic Anemia

Survival of patients with aplastic anemia treated with transplantation of bone marrow has improved significantly over the past several decades. Allogeneic bone marrow transplantation (BMT) for patients with HLA-identical siblings is now the first-line therapy, and long-term survival of approximately 90% can be expected with cyclophosphamide/antithymocyte globulin conditioning and postgrafting methotrexate/cyclosporine immunosuppression. The outcome of unrelated donor BMT has also improved significantly with the identification of a preparative regimen with less toxicity combined with the development of high-resolution DNA-based HLA typing to identify the optimal unrelated marrow donor. Patients with fully HLA-matched unrelated donors should be considered candidates for transplantation prior to exposure to repeat courses of immunosuppression. Future progress in hematopoietic stem cell transplantation for aplastic anemia will be directed toward further decreasing the acute toxicity and decreasing the delayed effects of the conditioning regimens while maintaining highly reliable rates of sustained engraftment with prevention of acute and chronic graft-versus-host disease.     

The hope and the reality of reduced intensity transplants in children with malignant diseases

Reduced intensity preparative regimens are increasingly used for conditioning prior to allogeneic stem cell transplantation. As opposed to classical methods of pre-transplant conditioning, patients receive predominantly immunosuppressive therapies that facilitate early engraftment, while cells within the graft itself promote continuation of the engraftment process. Despite early hopes that this form of transplant would be devoid of grade III and IV acute toxicities, there is a substantial amount of short-term morbidity associated with the technique. Although long-term follow-up is not yet available, it is hoped that these regimens will spare young patients many of the late effects (cataracts, growth retardation, endocrine and reproductive problems) that are often associated with classical pre-transplant conditioning regimens. Reliable engraftment and leukemic control have been demonstrated in a large number of both adult and pediatric transplant recipients of these regimens, many of whom were deemed at high risk for standard conditioning because of serious co-morbidities, previous autologous transplantation or multiply relapsed disease. A brief review of the state of the art of this technology as it applies to pediatric transplantation is presented. Preliminary results of a survey of pediatric transplant centers indicate that a variety of protocols are used for a variety of indications. The use of standardized criteria for implementation of reduced intensity preparative regimens, the use of a limited number of regimens, and more extensive data collection will permit the elaboration of prospective comparative studies of this new and exciting modality.     

Short Report: Engraftment of T-cell-depleted allogeneic haematopoietic stem cells using a reduced intensity conditioning regimen

Graft-versus-host disease (GVHD) remains a significant complication in patients undergoing allogeneic stem cell transplantation (SCT) using a reduced intensity conditioning regimen. Although T-cell depletion (TCD) reduces the risk of GVHD after a myeloablative conditioning regimen, it is associated with an increased risk of graft failure. We have therefore examined whether TCD compromises engraftment using a fludarabine-based conditioning regimen. Fifteen patients have been transplanted using such a regimen of whom 13 underwent ex vivo TCD. All but one patient demonstrated durable engraftment and no patient receiving a TCD product developed severe GVHD. Thus, TCD may play a role in GvHD prophylaxis using such regimens.     

The impact of the composition of the bone marrow graft on engraftment and graft-versus-host disease

To study the impact of the composition of the bone-marrow graft on engraftment and graft-versus-host disease (GvHD), we analyzed the data on 29 patients with acute leukemia in remission and 11 patients with aplastic anemia. All of them received bone-marrow grafts from HLA matched, MLC nonreactive, sibling donors, were nursed in laminar down-flow isolators with selective gut decontamination, and received GvHD prophylaxis with methotrexate. The number of nucleated cells in the marrow graft/kg body weight of the recipient had no relation with the rapidity of engraftment or with the occurrence and severity of GvHD. The number of hematopoietic progenitor cells (CFUc)/kg had a weak, but significant, correlation with both the number of neutrophils at day 30 post BMT and with the day at which the reticulocytes passed the 10% level. The number of T cells/kg did not show any correlation with either the occurrence or the severity of GvHD. Our data show that the concentration of hematopoietic progenitor cells in the graft correlates with the rapidity of engraftment. However, within the range of numbers of T cells infused in this study, no correlation is present between T cells in the graft and GvHD. Therefore, nearly complete depletion of marrow grafts of T cells is probably necessary to effectively decrease the incidence of GvHD.     

Bone marrow transplantation for girls with aplastic anemia utilizing modified field of total lymphoid irradiation and cyclophosphamide: with emphasis on the field of pelvic cavity

A preparative regimen for allogeneic bone marrow transplantation, consisting of total lymphoid irradiation (TLI) with 750 cGy and cyclophosphamide (CY), was used in five girls with aplastic anemia. All patients received bone marrow from HLA matched/mixed lymphocyte culture negative siblings. In our regimen the "inverted Y" field to irradiate the pelvic nodes was modified, which did not include the whole pelvic cavity in an attempt to protect the ovaries from irradiation. Although some of the pelvic nodes was supported not to be irradiated in order to protect the ovaries, engraftment occurred in all five patients including four who had been transfused prior to transplantation. All five are alive from 47 days to 1378 days (median 285 days) after transplantation without transplantation-associated complications. The calculated dose to the ovaries was sixteen percent of the entire dose of the regimen. Both of the two evaluable patients that had received transplantation just before or during the puberty are developing normal sex maturity including menstruation. This study suggests that our preparative regimen is effective not only for engraftment of the donor marrow but also for protecting the ovaries from irradiation.     

A randomized comparison of cyclophosphamide vs. reduced dose cyclophosphamide plus fludarabine for allogeneic hematopoietic cell transplantation in patients with aplastic anemia and hypoplastic myelodysplastic syndrome

Recently, a less toxic regimen comprising reduced cyclophosphamide (Cy), fludarabine, and anti-thymocyte globulin (ATG) (Cy-Flu-ATG) was used to condition high-risk patients scheduled for allogeneic hematopoietic cell transplantation (alloHSCT) instead of standard Cy-ATG in patients with severe aplastic anemia (AA). We performed a randomized phase III study to compare the regimen-related toxicities (RRTs) of two different conditioning regimens: Cy-ATG vs. Cy-Flu-ATG. Patients in the Cy-ATG arm received Cy at 200 mg/kg. Those in the Cy-Flu-ATG arm received fludarabine (Flu) at 150 mg/m(2) and Cy at 100 mg/kg. A total of 83 patients (40 in the Cy-ATG and 43 in the Cy-Flu-ATG) were enrolled. Seventy-nine patients had AA and four had MDS. All predefined RRTs were significantly lower in patients of the Cy-Flu-ATG arm (23.3 vs. 55.0 %; p = 0.003). Infection with identified causative organism and sinusoidal obstruction syndrome, hematuria, febrile episodes, and death from any cause tended to be more frequent in Cy-ATG arm but did not differ significantly between arms. There was no difference in neutrophil engraftment failure (2.5 vs. 2.33 %; p = 0.959), acute graft-versus-host disease (GvHD) (15.0 vs. 23.3 %; p = 0.388), and chronic GvHD (16.7 vs. 16.2 %; p = 0.961) between Cy-ATG and Cy-Flu-ATG arms. The 4-year survival rate did not differ between the Cy-ATG and Cy-Flu-ATG arms. Preconditioning with Cy-Flu-ATG was superior to that afforded by Cy-ATG in terms of reducing RRT levels without increasing engraftment failure.     

Allogeneic hematopoietic cell transplantation (HCT) in Hurler's syndrome using a reduced intensity preparative regimen

Allogeneic hematopoietic cell transplantation (HCT) in patients with Hurler's syndrome can improve survival and ameliorate many aspects of Hurler's syndrome including neurologic decline and cardiac compromise. Unfortunately, the toxicity of traditional preparative regimens to organs affected by the syndrome may have deleterious effects. Additionally, despite the intensity of these regimens, achieving stable donor chimerism can be difficult. We report transplant outcomes following a reduced intensity, highly immunosuppressive preparative regimen consisting of alemtuzumab, fludarabine and melphalan prior to HCT in seven patients with Hurler's syndrome treated at two centers. Six patients received grafts from unrelated donors and one received a sibling donor graft. The preparative regimen was well tolerated. All patients had initial donor engraftment at 100 days; one patient had delayed loss of donor chimerism. There was no severe acute GVHD (no GI GVHD of grade II or more, no grade IV skin GVHD). Six of the seven children are surviving at a median of 1014 (726-2222) days post transplant. This reduced intensity preparative regimen has the potential to support engraftment and improve survival and outcome in patients with Hurler's syndrome undergoing HCT.     

Non-total body irradiation containing preparative regimen in alternative donor bone marrow transplantation for severe aplastic anemia

Using non-total body irradiation (TBI) containing preparative regimens, 13 patients with severe aplastic anemia (SAA) were transplanted from an alternative donor in a single institute. In total, 12 donors were unrelated volunteers and one was an HLA one-locus mismatched sibling. Median time from diagnosis of SAA to bone marrow transplantation (BMT) was 10.1 months (range, 1.6-180.1). Nine patients had received immunosuppressive treatment with ATG before BMT, while four had not. Preparative regimens consisted of cyclophosphamide plus ATG in nine patients, cyclophosphamide plus fludarabine in two patients, and cyclophosphamide plus fludarabine plus ATG in two patients. All patients received non-T-cell depleted bone marrow from the donor. Cyclosporine plus methotrexate were given for GVHD prophylaxis. All patients engrafted on a median of day 21 (range, 15-27). Grade III-IV acute GVHD developed in three (23%) of 13 patients and extensive chronic GVHD in four (31%) of 12 evaluable patients. With a median follow-up duration of 1138 days (range, 118-1553), 10 patients are alive with durable engraftment showing 74.6% (95% confidence interval, 49.5-99.7%) of survival rate. Cause of the deaths was CNS bleeding in one and chronic GVHD in two. In conclusion, non-TBI containing preparative regimen could ensure durable engraftment in alternative donor BMT for SAA and showed promising results.     

Acute leukemia in adults: novel allogeneic transplant strategies

Acute myeloid leukemia (AML) is the most common indication for hematopoietic cell transplantation (HCT). Significant improvements in histocompatibility testing have resulted in identifying better alternative donors to provide grafts; coupled with expanding use of reduced-intensity conditioning (RIC) regimens, patient outcomes have improved. Most AML patients in complete remission now can undergo allogeneic HCT procedures with an anticipated result that approaches that obtained with sibling donors and myeloablative conditioning (MAC). Treatment-related mortality (TRM), relapse, GVHD and, for umbilical cord blood (UCB) grafts, slow engraftment/engraftment failures, however, continue to plague HCT. Newer strategies include the use of double unit UCB HCT and ex vivo expansion of UCB units using: multipotent mesenchymal stromal cells (MSCs); polyamine copper chelator tetraethylenepentamine (TEPA); and Notch ligand. Haploidentical bone marrow and blood HCT are increasing in numbers given the improved outcome with post-HCT cyclophosphamide therapy. Novel chemotherapeutic preparative regimens incorporating agents such as clofarabine and treosulfan, and novel radiation preparative regimens utilizing selective radiation approaches (helical tomotherapy) and targeted myeloablative radioimmunotherapy appear to enhance the anti-AML effect. Immunological approaches with chimeric antigen receptor-redirected T lymphocytes have been added to the armamentarium. Other novel maneuvers include more sophisticated T-cell depletion of the donor graft and post-transplant immunotherapy with regulatory T cell (Treg) therapy and MSCs for GVHD prevention. These and other strategies are improving the outlook of AML HCT recipients.     

Reduced intensity preparative regimens for allogeneic hematopoietic stem cell transplantation: a single center experience

According to recent reports, fast engraftment with minimal transplant-related toxicity and mortality (TRT, TRM) can be achieved by using reduced-intensity preparative regimens in allogeneic hematopoietic stem cell transplantation (HSCT). We report our experience with related (39%) and unrelated (61%) HSCT in 44 high risk patients (AML, ALL, CML, CLL) receiving either busulfan/fludarabine or busulfane/fludarabine/ATG or TBI/fludarabine as reduced-intensity preparative regimens. Organ toxicity was minimal with mild mucositis and no major bleeding. Acute GVHD was recorded in 64% of the patients. Twenty-three patients achieved complete remission after transplantation, and complete chimerism was obtained in all patients with stable engraftment (35 patients). Twenty-nine patients died: 15 due to relapse/progression, 14 due to TRM. Survival with median follow-up of 18.5 months was significantly better in patients with matched related transplants compared to patients with other transplants. However, there was no difference between related and unrelated transplants with regard to engraftment, TRM and GVHD. In conclusion, our results in high-risk patients transplanted in CR or with smoldering leukemia from a related donor are encouraging, although a longer follow-up and a larger group of patients is needed in order to evaluate the role of different reduced-intensity preparative regimens in unrelated and related HSCT.     

Setting the standard in T-cell-depleted haploidentical transplantation and beyond

Much progress has been made in the clinical, biological and technical aspects of the T-cell-depleted haploidentical hematopoietic stem cell transplantation (HSCT). Our experience demonstrates that infusing a megadose of extensively T-cell-depleted hematopoietic peripheral blood stem cells after an immuno-myeloablative conditioning regimen in acute leukemia patients ensures sustained engraftment with minimal GvHD without the need of any post-transplant immunosuppressive treatment. Since our first successful pilot study, our efforts have concentrated on developing new conditioning regimens, optimizing the graft processing and improving the post-transplant immunological recovery. The results we have so far achieved in high risk acute leukemia patients show that haploidentical transplantation is now a clinical reality. The present challenge is to reduce post-transplant infectious mortality and several strategies are being tested.     

The haploidentical option for high-risk haematological malignancies

Much progress has been made in the clinical, biological and technical aspects of the T-cell-depleted full-haplotype mismatched transplants for acute leukaemia. Our experience demonstrates that infusing a megadose of extensively T-cell-depleted haematopoietic peripheral blood stem cells after an immuno-myeloablative conditioning regimen in acute leukaemia patients ensures sustained engraftment with minimal GvHD without the need of any post-transplant immunosuppressive treatment. Since our first successful pilot study, our efforts have concentrated on developing new conditioning regimens, optimising the graft processing and improving the post-transplant immunological recovery. The results we have so far achieved in more than 200 high-risk acute leukaemia patients show that haploidentical transplantation is now a clinical reality. Because virtually all patients have a mismatched family member, who is immediately available, mismatched transplantation should be offered as a viable option to high-risk acute leukaemia patients who do not have, or cannot find, a matched donor.     

Increase of interleukin-18 serum levels after engraftment correlates with acute graft-versus-host disease in allogeneic peripheral blood stem cell transplantation

Purpose Acute graft-versus-host disease (GvHD) is a constant and severe complication after allogeneic stem cell transplantation regularly involving skin, liver, gut, and lungs. The cytokine interleukin-18 (IL-18) has been shown to increase in patients who develop acute GvHD after bone marrow tranplantation (BMT).Materials and methods Here, we measured IL-18 serum levels after peripheral blood stem cell transplantation (PBSCT) at several characteristic time points in 24 patients (median age 46 years). Patients received a median of 7.3×10⁶/kg bodyweight CD34-positive blood stem cells from HLA-matched family donors (n=5), matched unrelated donors (n=18), and one mismatched unrelated donor. GvHD prophylaxis consisted of cyclosporin A alone or combined with methotrexate and/or mycophenolate mofetil.Results In 14 patients we observed no GvHD or only GvHD grade I whereas ten patients developed GvHD grade II–IV post transplant. Low, intermediate, and high levels of serum IL-18 were found in patients after allogeneic PBSCT independently of GvHD after transplantation. In contrast to GvHD arising after BMT, there was no clear correlation between absolute IL-18 serum levels and GvHD grade after PBSCT. However, the individual time course of IL-18 serum level after engraftment correlates with acute GvHD after PBSCT. In detail, an increase of serum IL-18 of at least 1.6-fold after engraftment is associated with acute GvHD II or higher with a sensitivity of three out of four. Using the 1.6 cut-off for IL-18 increase after engraftment, a specificity of up to 100% can be achieved.Conclusion The time course of IL-18 serum levels might be used for GvHD prediction after PBSCT comparable to absolute serum levels after BMT.S. Scholl and H. G. Sayer contributed equally to this work.     

Reduced-toxicity conditioning with treosulfan, fludarabine and ATG as preparative regimen for allogeneic stem cell transplantation (alloSCT) in elderly patients with secondary acute myeloid leukemia (sAML) or myelodysplastic syndrome (MDS)

We investigated a dose-reduced conditioning regimen consisting of treosulfan and fludarabine followed by allogeneic stem cell transplantation (SCT) in 26 patients with secondary AML or MDS. Twenty patients were transplanted from matched or mismatched unrelated donors and six from HLA-identical sibling donors. The median age of the patients was 60 years (range, 44-70). None of the patients was eligible for a standard myeloablative preparative regimen. No graft-failure was observed, and leukocyte and platelet engraftment were observed after a median of 16 and 17 days, respectively. Acute graft-versus-host disease (GvHD) grade II-IV was seen in 23% and severe grade III GvHD in 12% of the patients. No patients experienced grade IV acute GvHD. Chronic GvHD was noted in 36% of the patients, which was extensive disease in 18%. The 2-year cumulative incidence of relapse was 21%. The relapse rate was higher in patients beyond CR1 or with intermediate two or high risk MDS (P = 0.02). The treatment-related mortality at day 100 was 28%. The 2-year estimated overall and disease-free survival was 36-34%, respectively. No difference in survival was seen between unrelated and related SCT.     

Engraftment kinetics and hematopoietic chimerism after reduced-intensity conditioning with fludarabine and treosulfan before allogeneic stem cell transplantation

Reduced-intensity conditioning with fludarabine and treosulfan before allogeneic stem cell transplantation (SCT) was introduced several years ago. Although its feasibility has recently been proven, only limited data are available on myelotoxicity, engraftment kinetics, and the significance of hematopoietic chimerism using this novel conditioning regimen. To clarify these open questions, we analyzed 27 patients with various hematological diseases, who received allogeneic SCT preceded by fludarabine/treosulfan conditioning. Further assessment endpoints included graft-vs-host disease (GvHD), mortality, and overall survival (OS). Allogeneic SCT was followed by neutropenia (absolute neutrophil count ≤ 0.5 × 10⁹/l) and thrombocytopenia (platelets ≤ 20 × 10⁹/l) in all patients. All patients showed stable neutrophil engraftment, and all except one had stable platelet engraftment. Grades II–IV acute GvHD was found in 48% of patients, whereas 52% developed chronic GvHD. The treatment-related mortality on day +100, 1 year after SCT, and at the last follow-up was 11, 26, and 33%, respectively. We found complete chimerism rates of 46, 57, and 72% on days +28, +56, and at the last follow-up or before death, respectively. The underlying malignancy tended to relapse more frequently in patients with mixed chimerism than in those with complete chimerism on day +28 as well as on day +56 (not significant). Additionally, no significant association was found between hematopoietic chimerism and donor type, GvHD, or OS, respectively. We conclude that reduced-intensity conditioning with fludarabine and treosulfan before allogeneic SCT is myeloablative, provides stable engraftment, and leads to complete chimerism in the majority of patients. Part of the abstract has been presented at the annual meeting of DGHO 2006 (Leipzig, Germany).     

Cyclosporin A in marrow transplantation for leukemia and aplastic anemia

A total of 29 consecutive patients with leukemia or aplastic anemia who received an HLA-identical marrow graft were given cyclosporin A (CyA) to prevent graft-versus-host disease (GvHD). These patients were compared with an historic group of 25 similar patients with leukemia or AA given methotrexate (MTX) for GvHD prophylaxis at this institution. Engraftment was faster in patients given CyA when compared with MTX patients, with less days of granulocytopenia (P = 0.04), a shorter interval before reaching a platelet count of 70 X 10(9)/l (P = 0.04), fewer major infections (P = 0.01), and fewer days on intravenous antibiotics (P = 0.02). There were no graft failures in CyA patients compared with four of 25 in MTX patients (P = 0.01). Early mortality was lower in CyA patients but not significantly (P = 0.06). The incidence of pulmonary complications was comparable, five of 29 and seven of 25 in CyA and MTX patients, respectively, but the clinical features of such complications differed. Interstitial pneumonia developing after day 30 was seen in MTX patients, whereas an acute respiratory distress syndrome developing between day +8 and day +18 was seen in CyA patients. Acute GvHD was less severe in CyA patients (P = 0.04), but chronic GvHD was comparable (P = 0.3). The actual one-year survival is currently 72% and 52% in CyA and MTX patients, respectively (P = 0.1). Although our initial experience with CyA is encouraging with regard to engraftment and acute GvHD, optimization of CyA protocols will probably be needed for it to be proven as having a definite advantage over MTX.     

Red blood cell-incompatible allogeneic hematopoietic progenitor cell transplantation

Transplantation of hematopoietic progenitor cells from red cell-incompatible donors occurs in 30-50% of patients. Immediate and delayed hemolytic transfusion reactions are expected complications of red cell-disparate transplantation and both ABO and other red cell systems such as Kidd and rhesus can be involved. The immunohematological consequences of red cell-incompatible transplantation include delayed red blood cell recovery, pure red cell aplasia and delayed hemolysis from viable lymphocytes carried in the graft ('passenger lymphocytes'). The risks of these reactions, which may be abrupt in onset and fatal, are ameliorated by graft processing and proper blood component support. Red blood cell antigens are expressed on endothelial and epithelial tissues in the body and could serve to increase the risk of GvHD. Mouse models indicate that blood cell antigens may function as minor histocompatibility antigens affecting engraftment. Similar observations have been found in early studies of human transplantation for transfused recipients, although current conditioning and immunosuppressive regimens appear to overcome this affect. No deleterious effects from the use of red cell-incompatible hematopoietic grafts on transplant outcomes, such as granulocyte and platelet engraftments, the incidences of acute or chronic GvHD, relapse risk or OS, have been consistently demonstrated. Most studies, however, include limited number of patients, varying diagnoses and differing treatment regimens, complicating the detection of an effect of ABO-incompatible transplantation. Classification of patients by ABO phenotype ignoring the allelic differences of these antigens also may obscure the effect of red cell-incompatible transplantation on transplant outcomes.     

Bone marrow transplantation for severe aplastic anemia: a randomized controlled study of conditioning regimens

The addition of antithymocyte globulin (ATG) to a regimen of high-dose cyclophosphamide has been advocated to enhance engraftment after allogeneic bone marrow transplantation (BMT) for severe aplastic anemia (SAA). In a prospective clinical trial, 134 patients were randomly assigned to receive cyclophosphamide alone or in combination with ATG. All patients received T-cell–replete bone marrow from an HLA-matched sibling. With a median follow-up of 6 years, the 5-year probabilities of survival were 74% for the cyclophosphamide alone group and 80% for the cyclophosphamide plus ATG group (P = .44). Graft failure and graft-versus-host disease (GVHD) rates were similar in both groups. With the survival rates achieved, this study is not adequately powered to detect significant differences between the 2 treatment groups. In conclusion, the results of allogeneic BMT for SAA have improved over time related to advances in supportive care. The addition of ATG to the preparative regimen did not significantly improve the outcome.     

Unrelated cord blood transplantation in children with idiopathic severe aplastic anemia

Early results of unrelated cord blood transplantation (UCBT) for severe aplastic anemia (SAA) were poor with a high rate of engraftment failure. This was attributed to the combination of lower graft cell dose and intact host immune system. We performed UCBT in nine children (median age 9 years) with refractory SAA using increasingly immunosuppressive preparative regimens. The time from diagnosis to UCBT was 3.4-20 months (median age 7.2 years), with all children having failed at least one course of immunosuppression. Donor/recipient HLA matching was six of six (n=1), five of six (n=2) and four of six (n=6). The median nucleated cell dose infused was 5.7 x 10(7) cells/kg (range 3.5-20 x 10(7) cells/kg). Six patients were engrafted after the first UCBT. Two of the three patients without hematopoietic reconstitution were engrafted after a second UCBT. All children receiving >or=120 mg/kg of CY in the preparative regimen were engrafted. The median time to myeloid engraftment was 25 (17-59 days) days. Acute GVHD developed in two, and chronic GVHD in five patients. Five patients developed EBV viremia post transplant (lymphoproliferative disorder in three patients). At a median follow-up of 34 months, seven patients are alive and transfusion-independent. UCBT is a feasible treatment strategy for children with refractory SAA lacking a well-matched adult donor.