The influence of cyclosporin alone, or cyclosporin and methotrexate, on the incidence of mixed haematopoietic chimaerism following allogeneic sibling bone marrow transplantation for severe aplastic anaemia

Safety and Efficacy of Co-transplantation of Hematopoietic Stem Cells Combined With Human Umbilical Cord-Derived Mesenchymal Stem Cells in Children With Severe Aplastic Anemia: A Single-Center Experience

OBJECTIVES

The mostimportant problems thatlimitthe effectiveness of allogeneic hematopoietic stem cell transplantation in patients with severe aplastic anemia are graft failure and graft-versus-host disease. Mesenchymal stem cells can support normal hematopoiesis and prevent graft-versus-host disease. We aimed to analyze the effects of combined transplant of human umbilical cord-derived mesenchymal stem cells and matched donor allogeneic hematopoietic stem cells in children with severe aplastic anemia.

MATERIALS AND METHODS

We retrospectively examined 15 pediatric patients with severe aplastic anemia who received fludarabine-based reduced intensity conditioning regimen and intravenously infused human umbilical cord-derived mesenchymal stem cells at a dose of 1 × 106/kg recipient body weight within 12 to 18 hours before hematopoietic stem cells infusion. We evaluated the engraftment rate, the frequency and severity of graft-versus-host disease, and the overall survival rate.

RESULTS

No patients had adverse events related to intravenously human umbilical cord-derived mesenchymal stem cells infusion. All patients achieved successful engraftment and sustained donor chimerism. The median time for neutrophil and platelet engraftment was 14 and 25 days,respectively. The frequency was 20% for grade III/IV acute graftversus- host disease and 15.3% for chronic graftversus-host disease. Patients were followed-up for a median of 33 months (range, 2-89 months). The 5-year overall survival rate was 80%.

CONCLUSIONS

Combined transplant of matched donor hematopoietic stem cells with human umbilical cord-derived mesenchymal stem cells is safe in pediatric patients with severe aplastic anemia. The achievement of engraftment in all of our patients and the acceptable frequency of acute and chronic graft-versus-host disease and survival rate are encouraging.

Long-term follow-up of haploidentical transplantation in relapsed/refractory severe aplastic anemia: a multicenter prospective study

In recent decades, haploidentical stem cell transplantation (haplo-SCT) to treat severe aplastic anemia (SAA) has achieved remarkable progress. However, long-term results are still lacking. We conducted a multicenter prospective study involving SAA patients who underwent haplo-SCT as salvage therapy. Long-term outcomes were assessed, mainly focusing on survival and quality of life (QoL). Longitudinal QoL was prospectively evaluated during pretransplantation and at 3 and 5 years posttransplantation using the SF-36 scale in adults and the PedsQL 4.0 scale in children. A total of 287 SAA patients were enrolled, and the median follow-up was 4.56 years (range, 3.01-9.05 years) among surviving patients. During the long-term follow-up, 268 of 275 evaluable patients (97.5%) obtained sustained full donor chimerism, and 93.4% had complete hematopoietic recovery. The estimated overall survival and failure-free survival for the whole cohort at 9 years were 85.4% ± 2.1% and 84.0% ± 2.2%, respectively. Age (≥18 years) and a poorer performance status (ECOG >1) were identified as risk factors for survival outcomes. For QoL recovery after haplo-SCT, we found that QoL progressively improved from pretransplantation to the 3-year and 5-year time points with statistical significance. The occurrence of chronic graft versus host disease was a risk factor predicting poorer QoL scores in both the child and adult cohorts. At the last follow-up, 74.0% of children and 72.9% of adults returned to normal school or work. These inspiring long-term outcomes suggest that salvage transplantation with haploidentical donors can be routine practice for SAA patients without human leukocyte antigen (HLA)-matched donors.

Mixed chimerism after allogeneic hematopoietic stem cell transplantation for severe aplastic anemia

A retrospective study on 287 patients with SAA who underwent allo-HSCT between October 2012 and January 2020 was conducted to explore the outcomes, risk factors and treatment options for MC. Among 287 AA patients who excluded Fanconi anemia (FA), Congenital dyskeratosis (DKC), Paroxysmal nocturnal hemoglobinuria (PNH), etc.112 underwent matched sibling donor (MSD)-HSCT, 91 matched unrelated donor-HSCT and 84 haploidentical-HSCT. Patients were divided into the following 4 groups: group 1: Donor chimerism (DC); group 2: MC without cytopenia; group 3: MC with cytopenia; group 4: secondary graft failure (SGF).

Compared with the other three groups, SGF predicted a poor prognosis of SAA (P< 0.001). In addition, SGF was associated with the early (within 3 months after transplantation) presence of MC and the high levels of MC. Uni- and multivariate logistic regression analysis showed that donor/recipient sex-mismatching and CTX + ATG regimen were high-risk factors for MC. Of note, in MC patients with cytopenia (group 3), the effective response rate reached 55% (6/11) following enhanced immunosuppression combined with cellular therapy, while only one of the four was effective who received enhanced immunosuppression alone.

SGF was associated with poor prognosis, early presence of MC and increased levels of recipient chimerism. The donor/recipient sex-mismatching and CTX + ATG regimen based MSD-HSCT were risk factors for MC. Cellular therapy could improve the effective response rate of patients with progressive MC.

The incidence, clinical outcome, and protective factors of mixed chimerism following hematopoietic stem cell transplantation for severe aplastic anemia

OBJECTIVES

The aim of our study was to determine possible predictors and clinical course of mixed chimerism (MC) in aplastic anemia after transplantation.

METHODS

A total of 207 transplants were obtained from haploidentical donors (HID) using busulfan (Bu), cyclophosphamide (Cy), and anti-thymocyte globulin (ATG) regimens, and 69 transplants from matched related donors (MRD) and 29 transplants from unrelated donors (URD) using Cy/ATG regimens were obtained.

RESULTS

Incidences of MC were 1.93 ± 0.01%, 20.29 ± 0.01%, and 35.71 ± 0.01% in HID, MRD, and URD transplantation (p < .001). In multivariate analysis, incidence of MC was significantly higher in patients without adding Bu in conditioning (p < .001) and receiving a lower number of CD3 + cells in graft (p = .042). MC was associated with significantly lower II-IV aGvHD (3.70% vs. 27.7%, p = .007), but higher secondary graft rejection rates (14.8% vs. 0.4%, p < .001) and poorer overall survival (72.7 ± 8.9% vs. 89.6 ± 2.0%, p = .011) than those of donor chimerism cohort.

CONCLUSIONS

Mixed chimerism was an unsettling status even in non-malignancy. Haploidentical transplantation with more intense regimen by adding Bu to Cy and ATG was associated with reduced MC following HSCT for SAA. An intensified regimen should be explored in matched related or unrelated donors.

Allogeneic hematopoietic stem cell transplantation in aplastic anemia: current indications and transplant strategies

Treatment options for newly diagnosed aplastic anemia (AA) patient includes upfront allogeneic hematopoietic stem cell transplant (HSCT) or immunosuppressive therapy (IST). With recent advances in supportive care, conditioning regimens and post-transplant immunosuppression the overall survival for HSCT approaches 70-90%. Transplant eligibility needs to be assessed considering age, comorbidities, donor availability and probability of response to immunosuppressive therapy (IST). Upfront HSCT should be offered to children and young adults with matched related donor (MRD). Upfront HSCT may also be offered to children and young adults with rapidly available matched unrelated donor (MUD) who require urgent HSCT. Bone marrow (BM) graft source and cyclosporine (CsA) plus methotrexate (MTX) as graft versus host disease (GVHD) prophylaxis are preferable when using anti-thymocyte globulin (ATG) based conditioning regimens. Alemtuzumab is an acceptable alternative to ATG and is used with CsA alone and with either BM or peripheral blood stem cells (PBSC). Cyclophosphamide (CY) plus ATG conditioning is preferable for patients receiving MRD transplant, while Fludarabine (Flu) based conditioning is reserved for older adults, those with risk factors of graft failure and those receiving MUD HSCT. For haploidentical transplant, use of low dose radiotherapy and post-transplant cyclophosphamide has resulted in a marked reduction in graft failure and GVHD.

Fludarabine, Campath, and Low-Dose Cyclophosphamide (FCClow) with or without TBI Conditioning Results in Excellent Transplant Outcomes in Children with Severe Aplastic Anemia

Various reduced-intensity conditioning regimens are in use for allogeneic hematopoietic cell transplant (HSCT) in patients with idiopathic severe aplastic anemia (SAA). We describe the use of fludarabine, Campath, and low-dose cyclophosphamide (FCC^low) conditioning in 15 children undergoing related or unrelated donor transplants. Total body irradiation (TBI) of 2 Gy was added for unrelated donor HSCT. At a median follow-up of 2.3 years, the failure-free survival was 100%, with low rates of infection and toxicity. There was no occurrence of grade III to IV acute graft-versus-host disease (GVHD). All patients had full donor myeloid chimerism post-HSCT, even with mixed chimerism in the T cell lineage. The absence of chronic GVHD and long-term stable mixed donor T cell chimerism confirms immune tolerance following FCC^low (± TBI) conditioned transplantation in children with SAA.

Initial dosage optimization of ciclosporin in pediatric Chinese patients who underwent bone marrow transplants based on population pharmacokinetics

Bone marrow transplants (BMT) are an established therapeutic strategy for patients with severe aplastic anemia, acute lymphoblastic leukemia, acute myeloid leukemia or chronic myeloid leukemia. However, the successful application of BMT is limited by graft-vs.-host disease (GVHD). Ciclosporin has been widely used for treating GVHD in pediatric patients who underwent BMT. The present study aimed to optimize the dosage of ciclosporin for safety and effectiveness based on population pharmacokinetics. A non-linear mixed-effects model was used to analyze the clinical data of pediatric patients who underwent BMT between September 2016 and September 2019 at the Children's Hospital of Fudan University. Monte Carlo simulations were used to identify the optimal dose of ciclosporin. The final population pharmacokinetic model indicated that body weight and days post-transplant influenced the clearance of ciclosporin in pediatric patients who underwent BMT. The present study indicated that the optimal initial dose of ciclosporin for pediatric patients weighing 5-30 kg who underwent BMT was 6 mg/kg/day split into 2 doses.

Allogeneic hematopoietic stem cell transplantation for aplastic anemia with pre-transplant conditioning using fludarabine, reduced-dose cyclophosphamide, and low-dose thymoglobulin: A KSGCT prospective study

The optimal pre-transplant conditioning for aplastic anemia (AA) remains unclear. We performed a prospective study on allogeneic transplantation from a related or unrelated donor for adult patients with AA. We assessed whether reduced-dose cyclophosphamide (CY) could decrease toxicity while maintaining engraftment, and low-dose thymoglobulin could safely prevent graft-vs-host disease (GVHD). The pre-transplant conditioning regimen consisted of fludarabine 120 mg/m² , CY 100 mg/kg, and thymoglobulin 2.5 mg/kg with or without 2 Gy of total body irradiation. Twenty-seven patients with a median age of 36 years were analyzed. Sixteen patients received graft from related donors. The stem cell source was bone marrow in 26 patients. All of the patients but one, who died early, achieved neutrophil engraftment at a median of 19 days. Mixed chimerism was observed in six and five patients at days 30 and 90, respectively. Only one patient experienced secondary engraftment failure with complete donor-type chimerism. None of the patients developed severe acute GVHD. The cumulative incidence of chronic GVHD was 37.7% at 1 year. The overall survival rate was 96.3% at 1 year and 3 years. A high EB virus-DNA load was detected in one patient at days 60. No one developed EBV-lymphoproliferative disorder within a year. The results suggest that the conditioning regimen in this study was safe and effective. However, relatively high incidence of chronic GVHD needs further improvement.

Mixed Chimerism and Secondary Graft Failure in Allogeneic Hematopoietic Stem Cell Transplantation for Aplastic Anemia

Mixed chimerism (MC) and/or secondary graft failure (SGF) with recipient- or donor-type chimerism is a major obstacle in allogeneic transplantation for aplastic anemia (AA). From a registry database in Japan, patients with AA age >15 years who underwent a first allogeneic bone marrow or peripheral blood stem cell transplantation between 2000 and 2014 and achieved engraftment were included in this study. MC that did not require either granulocyte-colony stimulating factor (G-CSF) or transfusion support (group 1), MC (not SGF) that required G-CSF and/or transfusion support (group 2), SGF with MC or complete recipient-type chimerism (group 3), and SGF with complete donor-type chimerism (group 4) developed in 26, 16, 19, and 17 patients, respectively. The overall median duration of follow-up for survivors was 1727 days. The overall survival (OS) was 90.4% at 1 year and 83.5% at 5 years in patients without MC or SGF (n = 340), which was not different from the OS in groups 1 and 2. However, inferior OS was observed in group 3 (1 year, 52.1%; 5 years, 52.1%) and group 4 (1 year, 82.4%; 5 years, 56.3%). In multivariate analyses, the use of fludarabine (Flu) and the absence of irradiation in conditioning were associated with the development of SGF with MC or complete recipient-type chimerism, and the use of Flu in conditioning was associated with SGF with complete donor-type chimerism. In conclusion, the use of Flu may affect the occurrence of SGF with both recipient-type and donor-type chimerism.

Transplant-Associated Thrombotic Microangiopathy in Pediatric Hematopoietic Cell Transplant Recipients: A Practical Approach to Diagnosis and Management

Transplant-associated thrombotic microangiopathy (TA-TMA) is an endothelial damage syndrome that is increasingly identified as a complication of both autologous and allogeneic hematopoietic cell transplantation (HCT) in children. If not promptly diagnosed and treated, TA-TMA can lead to significant morbidity (e.g., permanent renal injury) or mortality. However, as the recognition of the early stages of TA-TMA may be difficult, we propose a TA-TMA "triad" of hypertension, thrombocytopenia (or platelet transfusion refractoriness), and elevated lactate dehydrogenase (LDH). While not diagnostic, this triad should prompt further evaluation for TA-TMA. There is increased understanding of the risk factors for the development of TA-TMA, including those which are inherent (e.g., race, genetics), transplant approach-related (e.g., second HCT, use of HLA-mismatched donors), and related to post-transplant events (e.g., receipt of calcineurin inhibitors, development of graft-vs. -host-disease, or certain infections). This understanding should lead to enhanced screening for TA-TMA signs and symptoms in high-risk patients. The pathophysiology of TA-TMA is complex, resulting from a cycle of activation of endothelial cells to produce a pro-coagulant state, along with activation of antigen-presenting cells and lymphocytes, as well as activation of the complement cascade and microthrombi formation. This has led to the formulation of a "Three-Hit Hypothesis" in which patients with either an underlying predisposition to complement activation or pre-existing endothelial injury (Hit 1) undergo a toxic conditioning regimen causing endothelial injury (Hit 2), and then additional insults are triggered by medications, alloreactivity, infections, and/or antibodies (Hit 3). Understanding this cycle of injury permits the development of a specific TA-TMA treatment algorithm designed to treat both the triggers and the drivers of the endothelial injury. Finally, several intriguing approaches to TA-TMA prophylaxis have been identified. Future work on the development of a single diagnostic test with high specificity and sensitivity, and the development of a robust risk-scoring system, will further improve the management of this serious post-transplant complication.

Mixed T Cell Chimerism After Allogeneic Hematopoietic Stem Cell Transplantation for Severe Aplastic Anemia Using an Alemtuzumab-Containing Regimen Is Shaped by Persistence of Recipient CD8 T Cells

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Clinical outcomes are excellent using an alemtuzumab-containing hematopoietic stem cell transplantation regimen for aplastic anemia.

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Outcomes are excellent despite prolonged abnormality of the T cell profile.

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Recipient-derived CD8 T cells shape persistent mixed chimerism.

Prevention of graft-versus-host disease (GVHD) is paramount for allogeneic hematopoietic stem cell transplantation (HSCT) to treat nonmalignant diseases. We previously reported that allogeneic HSCT for severe aplastic anemia (SAA) using the fludarabine, cyclophosphamide, and alemtuzumab (Campath-1H) (FCC) regimen is associated with a very low risk of GVHD and excellent clinical outcomes. We now report a single-center study of 45 patients with longer follow-up and investigation of lymphocyte recovery. Overall survival (OS) was 93%, and event-free survival (EFS) was 90.7%. Acute and chronic GVHD each occurred in 6 patients (13.3%), and only 1 case was severe. Mixed T cell chimerism was frequent and persisted after cessation of immunosuppression. T cells were extensively depleted, representing only 11.3% of lymphocytes at day 30 and rising to 43.8% by 1 year, but still significantly below normal levels (67.2%; P = .018), and deficiency persisted after immunosuppressive therapy (IST) withdrawal. Depletion of CD4 T cells was particularly profound, causing inversion of the normal CD4:CD8 T cell ratio. T cell subset composition was also abnormal, with memory and effector T cells predominating for at least 6 months after FCC HSCT. Analysis of T cell subset chimerism showed that CD4 T cells were predominantly donor-derived at 1 year, whereas recipient-derived CD8 T cells shaped mixed chimerism with a notable contribution of recipient effector CD8 T cells. The prolonged mixed T cell chimerism after IST withdrawal and low incidence of GVHD indicates the establishment of mutual tolerance, but the low incidence of viral disease suggests maintenance of antiviral immunity. Our study shows that despite the abnormal T cell profile after allogeneic HSCT for SAA using the FCC regimen, this regimen is conducive to an excellent clinical outcome.

Efficacy and safety of human umbilical cord derived mesenchymal stem cell therapy in children with severe aplastic anemia following allogeneic hematopoietic stem cell transplantation: a retrospective case series of 37 patients

The treatment of pediatric severe aplastic anemia (SAA) with allogeneic hematopoietic stem cell transplantation (allo-HSCT), presents major challenges including the risks of graft failure, septic complications, and graft-versus-host disease (GVHD). Additive infusions of human umbilical cord derived mesenchymal stem cell (hUC-MSC) may be administered to improve patient survival. We retrospectively examined 37 pediatric patients with SAA who received allo-HSCT and subsequent infusions of hUC-MSC suspension at a dose of 1.0 × 10(6 )/kg. The times and doses of hUC-MSC infusions were increased in patients with severe GVHD. All patients received hUC-MSC infusions. The median time to post-transplantation neutrophil count of greater than 0.5 × 10(9 )/L was 14 days (range, 11-20 days) and time to post-transplantation platelet count of greater than 20 × 10(9 )/L was 19 days (14-29 days). The overall frequency of acute GVHD (aGVHD) was 45.9% (17/37). These aGVHD episodes occurred at a median time of post-transplantation 47 days (15-83 days). The frequency of chronic GVHD (cGVHD) was 18.9% (7/37); cGVHD developed from aGVHD in 10.8% (4/37) of patients. The GVHD-associated mortality rate was 18.9% (7/37) and aGVHD-specific mortality rate was 8.1% (3/37). The median overall survival time was 35 months (9-67 months) and the three-year overall survival rate was 74.2% (28/37). Seven patients died of GVHD, one patient died of a severe invasive fungal infection, and one patient died of renal failure. In conclusion, post-transplantation hUC-MSC infusions seemed to be safely infused in children with SAA who have previously received allo-HSCT.

How I manage aplastic anaemia in children

Aplastic anaemia (AA) is a rare heterogeneous condition in children. 15-20% of cases are constitutional and correct diagnosis of these inherited causes of AA is important for appropriate management. For idiopathic severe aplastic anaemia, a matched sibling donor (MSD) haematopoietic stem cell transplant (HSCT) is the treatment of choice. If a MSD is not available, the options include immunosuppressive therapy (IST) or unrelated donor HSCT. IST with horse anti-thymocyte globulin (ATG) is superior to rabbit ATG and has good long-term results. In contrast, IST with rabbit ATG has an overall response of only 30-40%. Due to improvements in outcome over the last two decades in matched unrelated donor (MUD) HSCT, results are now similar to that of MSD HSCT. The decision to proceed with IST with ATG or MUD HSCT will depend on the likelihood of finding a MUD and the differing risks and benefits that each therapy provides.

Alemtuzumab with fludarabine and cyclophosphamide reduces chronic graft-versus-host disease after allogeneic stem cell transplantation for acquired aplastic anemia

We evaluated a novel alemtuzumab-based conditioning regimen in HSCT for acquired severe aplastic anemia (SAA). In a multicenter retrospective study, 50 patients received transplants from matched sibling donors (MSD; n = 21) and unrelated donors (UD; n = 29), using fludarabine 30 mg/m2 for 4 days, cyclophosphamide 300 mg/m2 for 4 days, and alemtuzumab median total dose of 60 mg (range:40-100 mg). Median age was 35 years (range 8-62). Overall survival at 2 years was 95% ± 5% for MSD and 83% for UD HSCT (p 0.34). Cumulative incidence of graft failure was 9.5% for MSD and 14.5% for UD HSCT. Full-donor chimerism (FDC) in unfractionated peripheral blood was 42%; no patient achieved CD3 FDC. Acute GVHD was observed in only 13.5% patients (all grade I-II) and only 2 patients (4%) developed chronic GVHD. A low incidence of viral infections was seen. Factors influencing overall survival were HSCT comorbidity 2-year index (92% with score 0-1 vs 42% with score ≥ 2, P < .001) and age (92% for age < 50 years vs 71% ≥ 50 years, P < .001). Our data suggest that the use of an alemtuzumab-based HSCT regimen for SAA results in durable engraftment with a low incidence of chronic GVHD.

Aplastic Anemia: First-line Treatment by Immunosuppression and Sibling Marrow Transplantation

Newly diagnosed aplastic anemia is a serious condition, with more than 75% (higher in young patients) becoming long-term survivors if diagnosed and treated appropriately. First-line treatment approaches include immunosuppressive treatment using the combination of antithymocyte globulin and cyclosporine A for patients without a sibling donor and HLA identical sibling transplant for patients younger than age 40 with a donor. Best transplant strategies have been defined and include conditioning with cyclophosphamide and antithymocyte globulin, marrow as a stem cell source, and graft-versus-host diease prophylaxis using cyclosporine A and methotrexate. It is against these standard treatment approaches that any therapeutic progress has to be measured.

Prognostic utility of routine chimerism testing at 2 to 6 months after allogeneic hematopoietic cell transplantation

The utility of routine chimerism analysis as a prognostic indicator of subsequent outcomes after allogeneic hematopoietic cell transplantation (HCT) with myeloablative conditioning regimens remains controversial. To address this controversy, routine chimerism test results at 2 to 6 months after HCT with myeloablative conditioning regimens were evaluated for association with subsequent risk of chronic graft-versus-host disease (GVHD), nonrelapse mortality (NRM), relapse, and overall mortality. Only 70 of 1304 patients (5%) had < 95% donor-derived cells in the marrow. Low donor chimerism in the marrow occurred more often in patients with low-risk diseases compared with those with higher-risk diseases and was significantly associated with a reduced risk of chronic GVHD. Among 673 patients evaluated, 164 (24%) had < 85% donor-derived T cells in the blood. Low donor T cell chimerism was more frequent in patients with low-risk diseases compared with those with higher-risk diseases, in those who received conditioning with busulfan compared with those who received conditioning with total body irradiation, and in those with lower-grade acute GVHD. Low donor T cell chimerism in the blood was significantly associated with a reduced risk of chronic GVHD but not with a reduced risk of relapse, NRM, or overall mortality. Routine testing of chimerism in the marrow and blood at 2 to 6 months after HCT with myeloablative conditioning regimens may be helpful in documenting engraftment in clinical trials, but provides only limited prognostic information in clinical practice.

Treatment strategies for patients with severe aplastic anemia

Treatment strategies for patients with severe aplastic anemia (SAA), depend on the severity of the disease, the age of the patient and the availability of a family donor. Progress in the past has included the early use of combined immunosuppressive therapy (IST) and better matching strategies to select unrelated donors. Currently, the actuarial 10-year survival in 2479 patients registered within the European Group for Blood and Marrow Transplantation (EBMT), is 73 and 68% for patients receiving first-line BMT or IST. The outcome of BMT has significantly improved since 1996, and this is true for both matched sibling donor BMT as well as for alternative donor BMT. Survival is significantly better in children (<16 years) as compared with adults (79 vs 68%, P<0.0001). In contrast, there has been no significant improvement over time for patients receiving IST. Again, results were significantly better in children compared with adults (81 versus 70%, P=0.001), especially in very severe aplasia (83 versus 62%, P=0.0002). This report outlines some of these results as a basis for treatment strategies in SAA.

Worse outcome and more chronic GVHD with peripheral blood progenitor cells than bone marrow in HLA-matched sibling donor transplants for young patients with severe acquired aplastic anemia

We analyzed the outcome of 692 patients with severe aplastic anemia (SAA) receiving transplants from HLA-matched siblings. A total of 134 grafts were peripheral blood progenitor cell (PBPC) grafts, and 558 were bone marrow (BM) grafts. Rates of hematopoietic recovery and grades 2 to 4 chronic graft-versus-host disease (GVHD) were similar after PBPC and BM transplantations regardless of age at transplantation. In patients older than 20 years, chronic GVHD and overall mortality rates were similar after PBPC and BM transplantations. In patients younger than 20 years, rates of chronic GVHD (relative risk [RR] 2.82; P = .002) and overall mortality (RR 2.04; P = .024) were higher after transplantation of PBPCs than after transplantation of BM. In younger patients, the 5-year probabilities of overall survival were 73% and 85% after PBPC and BM transplantations, respectively. Corresponding probabilities for older patients were 52% and 64%. These data indicate that BM grafts are preferred to PBPC grafts in young patients undergoing HLA-matched sibling donor transplantation for SAA.