Scholarly article on topic 'HLA-identical sibling peripheral blood stem cell transplantation in children and adolescents'

HLA-identical sibling peripheral blood stem cell transplantation in children and adolescents Academic research paper on "Clinical medicine"

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Abstract of research paper on Clinical medicine, author of scientific article — Tsutomu Watanabe, Yoichi Takaue, Yoshifumi Kawano, Kenichi Koike, Atsushi Kikuta, et al.

Abstract Allogeneic peripheral blood stem cell transplantation (PBSCT) was performed in children and adolescents for the treatment of malignant (n = 49) and nonmalignant hematological disease (n = 8). Granulocyte colony-stimulating factor (G-CSF)-mobilized PBSCs were apheresed from 57 HLA-matched siblings aged 9 months to 24 years (median, 8 years) without any serious adverse, effects. No abnormalities were found in these donors for a median follow-up of 25 months (range, 6-56 months). Patients were conditioned with a TBI-containing regimen (n = 17) or a non-TBI regimen (n = 40). GVHD prophylaxis consisted of methotrexate (MTX) plus cyclosporine A (CSP) for 23 patients, CSP plus methylprednisolone (mPDN) for 22 patients, MTX only for 7 patients, CSP only for 4 patients, and MTX plus CSP plus mPDN for 1 patient. Engraftment was prompt, with a median number of days to reach an absolute neutrophil count (ANC) above 0.5 x 10(9)/L of 13 days (range, 8-23 days), with 1 graft failure. Acute GVHD (grades II-IV) occurred in 8 (16%) of 49 evaluable patients, and chronic GVHD developed in 23 (64%) of 36 evaluable patients. Notably, two thirds of chronic GVHD was extensive. The Kaplan-Meier estimate of 3-year disease-free survival was 0% for refractory disease (n = 6), 37.2% +/- 11.8% for high-risk malignancies (n = 25), 81.4% +/- 9.7% for standard-risk malignancies (n = 18), and 100% for nonmalignant disease (n = 8). The estimated 100-day nonrelapse mortality rate was 9.9% +/- 4.2%. In conclusion, allogeneic PBSCT is feasible in a pediatric population. Although the grade of acute GVHD was set low, as in Japanese BMT studies, the incidence and severity of chronic GVHD appears to be relatively high. For nonmalignant disease, the question arises of whether the higher incidence and severity of chronic GVHD is a drawback of this procedure. For high-risk malignancies, whether or not a graft-versus-leukemia effect prevents relapse needs to be clarified in future comparative studies with BMT. Biol Blood Marrow Transplant 2002;8(1):26-31.

Academic research paper on topic "HLA-identical sibling peripheral blood stem cell transplantation in children and adolescents"

Biology of Blood and Marrow Transplantation 8:26-31 (2002) © 2002 American Society for Blood and Marrow Transplantation

HLA-Identical Sibling Peripheral Blood Stem Cell Transplantation in Children and Adolescents

Tsutomu Watanabe,1 Yoichi Takaue,2 Yoshifumi Kawano,3 Kenichi Koike,4 Atsushi Kikuta,5 Masue Imaizumi,6 Arata Watanabe,7 Haruhiko Eguchi,8 Shigeru Ohta,9 Yasuo Horikoshi,10 Asayuki Iwai,11 Atsushi Makimoto,2 Yasuhiro Kuroda,1 the PBSCT Study Group of Japan

'University of Tokushima School of Medicine, Tokushima; 2National Cancer Center Hospital, Tokyo; 3Kyushu Cancer Center, Fukuoka; 4University of Shinshu School of Medicine, Matsumoto; 5Fukushima Medical University School of Medicine, Fukushima; 6University of Tohoku School of Medicine, Sendai; 7Nakadori Hospital, Akita; 8Kurume University, Kurume; 9Shiga Medical School, Ohtsu; 10Shizuoka Children's Hospital, Shizuoka; ''Kagawa Children's Hospital, Zentuji, Japan

Correspondence and reprint requests: Tsutomu Watanabe, Department of Pediatrics, University of Tokushima School of Medicine, 3-18-15 Kuramoto-cho, Tokushima 770-8305, Japan (e-mail: twatanab@clin.med.tokushima-u.ac.jp).

Received August 15, 2001; accepted October 24, 2001

ABSTRACT

Allogeneic peripheral blood stem cell transplantation (PBSCT) was performed in children and adolescents for the treatment of malignant (n = 49) and nonmalignant hematological disease (n = 8). Granulocyte colony-stimulating factor (G-CSF)-mobilized PBSCs were apheresed from 57 HLA-matched siblings aged 9 months to 24 years (median, 8 years) without any serious adverse effects. No abnormalities were found in these donors for a median follow-up of 25 months (range, 6-56 months). Patients were conditioned with a TBI-containing regimen (n = 17) or a non-TBI regimen (n = 40). GVHD prophylaxis consisted of methotrexate (MTX) plus cyclosporine A (CSP) for 23 patients, CSP plus methylprednisolone (mPDN) for 22 patients, MTX only for 7 patients, CSP only for 4 patients, and MTX plus CSP plus mPDN for 1 patient. Engraftment was prompt, with a median number of days to reach an absolute neutrophil count (ANC) above 0.5 X 109/L of 13 days (range, 8-23 days), with 1 graft failure. Acute GVHD (grades II-IV) occurred in 8 (16%) of 49 evaluable patients, and chronic GVHD developed in 23 (64%) of 36 evaluable patients. Notably, two thirds of chronic GVHD was extensive. The Kaplan-Meier estimate of 3-year disease-free survival was 0% for refractory disease (n = 6), 37.2% ±11.8% for high-risk malignancies (n = 25), 81.4% ±9.7% for standard-risk malignancies (n = 18), and 100% for nonmalignant disease (n = 8). The estimated 100-day nonre-lapse mortality rate was 9.9% ±4.2%. In conclusion, allogeneic PBSCT is feasible in a pediatric population. Although the grade of acute GVHD was set low, as in Japanese BMT studies, the incidence and severity of chronic GVHD appears to be relatively high. For nonmalignant disease, the question arises of whether the higher incidence and severity of chronic GVHD is a drawback of this procedure. For high-risk malignancies, whether or not a graft-versus-leukemia effect prevents relapse needs to be clarified in future comparative studies with BMT.

KEY WORDS

Allogeneic peripheral blood stem cell transplantation patients • Pediatric donors

HLA-matched sibling donor • Pediatric

INTRODUCTION

Granulocyte colony-stimulating factor (G-CSF)-mobilized peripheral blood stem cells (PBSCs) from healthy donors have been used in place of bone marrow (BM) in adult allogeneic hematopoietic stem cell transplantation [1]. There are practical advantages to using PBSCs rather than BM as a stem cell source, including rapid hematopoietic reconstitution, fewer infectious complications, and possible enhance-

ment of the graft-versus-leukemia (GVL) effect [2-5]. The benefit of PBSCs for donors is elimination of the need for general anesthesia and hospitalization associated with BM aspiration. However, in children, technical difficulties of PBSC harvest by apheresis, such as overcoming the problems of extracorporeal volume and blood access [6] and a concern for the use of G-CSF in healthy children, have restricted the use of PBSCs in the allogeneic setting [7,8]. Although safe

Table 1. Patient and Donor Characteristics

Patients (n = 57) Donors (n = 57)

Median age (range) 10 y (6 mo to 19 y) 8 y (9 mo to 24 y)

Sex, M/F 28/29

Median body weight, kg (range) 29 (5-71)

Disease

Malignancy 49

ALL 23

First CR 4

Second CR 6

Third or more CR 10

Refractory 3

AML 18

First CR 8

Second or more CR 10

Refractory 2

Non-Hodgkin's Lymphoma 4

Nonmalignancy 8

Severe aplastic anemia 6

Chronic granulomatous disease 1 Kostmann's disease 1

and effective PBSC harvesting procedures have been demonstrated in the autologous setting [9,10], we should be more careful with normal donors, and the long-term toxicities of G-CSF treatment must be carefully assessed.

In the present report, we describe our experience with allogeneic PBSC transplantation (PBSCT) in pediatric patients with HLA-matched sibling donors. Although this study was hampered by differences in the approaches used at 10 different institutions with regard to PBSC collection methods, preparative regimens, and supportive care issues, we believe that the observed data may still be useful for assessing the value of this procedure in pediatric patients.

METHODS

Patients and Donors

The characteristics of the patients and donors are shown in Table 1. The clinical protocols for PBSCT were approved by the institutional review boards at the participating institutions. Patients were eligible for enrollment if allogeneic stem cell transplantation was indicated for their disease and they had an HLA-identical sibling. Written informed consent was obtained from the patient's guardian (or the patient if he/she was more than 16 years old). Before stem cell collection, the details of the procedure and risks of both BM harvest and PBSC collection were fully explained. The decision to agree to PBSC harvest was made by the donor's guardian alone (if the donor was less than 10 years old), by both the donor's guardian and the donor (if more than 10 but less than 16 years old), or by the donor alone (if more than 16 years old), and written informed consent was obtained. This choice was based on the medical condition of the donor in 18 transplantations or the medical condition of the patient in 32 transplantations. For the remaining 7 donors, PBSC harvest was the donor's preference. The medical conditions of the donors included the risks associated

with the use of general anesthesia such as bronchial asthma (n = 12), difficulties in BM harvest such as obesity (n = 4), or body weight differences between the donor and the patient (n = 2). The medical conditions of the patients included the anticipation of rapid engraftment after allogeneic PBSCT because the patients were at high risk for life-threatening infection (n = 7), and the anticipation of possible GVL effects for high-risk malignancies or second transplantations (n = 15). In the remaining 10 cases, the physician's preference was the only reason for the choice of PBSC.

PBSC Harvest

All of the donors received G-CSF at a dosage of 7.5 to 10 |ig/kg per day by subcutaneous injection for 5 to 6 days. On days 4 and 5 or 5 and 6 of G-CSF treatment, donors underwent apheresis using continuous blood cell separators (Baxter CS3000 Plus: n = 29; COBE Spectra: n = 28). For 12 donors weighing less than 20 kg, the extracorporeal circuit was preprimed with 75 to 200 mL of autologous blood or allogeneic irradiated leukocyte-depleted packed red blood cells, depending on the machine and separating chamber. For blood access, a radial artery was used in 35 donors (mostly less than 10 years old) and a cubital vein was used in 14 donors (10 years old or more). Eight donors had central venous (CV) catheter placement (inguinal, 5; subclavian, 3) if peripheral blood access was not achieved. Ketamine was used to sedate donors when a CV catheter was inserted, whereas no sedation was used when a radial artery or a cubital vein was accessed in donors, except in 3 donors. The target volume of processed blood per apheresis was 200 to 300 mL/kg for children and 10 L for adolescents. PBSCs from 52 donors were frozen using a programmed freezer (n = 3) or an uncontrolled method without a programmed freezer as described elsewhere (n = 49) [11]; and they were stored in a deep freezer (n = 33) or the vapor phase of liquid nitrogen (n = 19) until transplantation according to each institution's protocol. PBSCs from 5 donors were infused without freezing on day 0. T cells were not depleted from any of the grafts. For cell evaluation, CD34+ and CD3+ cells were analyzed by flow cytometry, and colony-forming units-granulo-cyte/macrophage (CFU-GM) were analyzed by in vitro colony assay at each institution.

Donors were followed up every 6 months or 1 year for blood counts and a medical check-up.

Transplantation Procedures

Preparative regimens and graft-versus-host disease (GVHD) prophylaxis are shown in Table 2. The diagnosis of GVHD was based mainly on clinical symptoms, and if the diagnosis was in doubt, a biopsy was performed. The grades of GVHD were determined according to 1994 Consensus Conference criteria [12]. Cyclosporine A (CSP) was tapered beginning 60 to 100 days following transplantation and was reduced by 10% per week in most cases if no GVHD was observed.

Statistical Methods

The date of final analysis was December 31, 2000. The time required to attain an absolute neutrophil count (ANC) of at least 0.5 X 109/L or a platelet count of at least 20 X 109/L without platelet transfusion was calculated using the Kaplan-Meier method [13]. Overall survival and disease-free

Table 2. Preparative Regimens and GVHD Prophylaxis*

Preparative regimens (n = 57)

Malignant disease (n = 49) Nonmalignant disease (n = 8) GVHD prophylaxis (n = 57)

TBI-containing regimen 15 TBI-containing regimen 2 CSP plus MTX 23

Plus CY/VP-16 5 Plus CY 1 CSP plus mPDN 22

Plus CY/Ara-C 3 Plus CY/ALG 1 MTX only 7

Plus L-PAM 2 Non-TBI regimen 6 CSP only 4

Plus CY 1 CY/ATG 2 CSP/MTX/mPDN 1

Plus Ara-C 1 Bu/CY 1

Plus L-PAM/VP-16 1 Bu/CY/TLI 1

Plus L-PAM/Ara-c 1 CY/TLI 1

Plus Bu/L-PAM 1 CY/TLI/ALG 1

Non-TBI regimen 34

Bu/L-PAM 18

Bu/CY 6

MCVAC 3

Bu/Ara-C/VP-16 2

Bu/CY/TEPA 1

CY/TEPA 1

Bu/MCNU/CY 1

Bu/TEPA 1

VP-16/TEPA/CBDCA 1

*TBI indicates total body irradiation; mPDN, methylprednisolone; CY, cyclophosphamide; VP-16, etoposide; Ara-C, cytosine arabinoside; ALG, antilymphocyte globulin; L-PAM, melphalan; ATG, antithymocyte globulin; Bu, busulfan; TLI, total lymphoid irradiation; MCVAC, MCNU plus cytosine arabinoside plus etoposide plus cyclophosphamide; TEPA, thiotepa; CBDCA, carboplatinum.

survival were calculated using Kaplan-Meier methods and evaluated using the log-rank test with 95% confidence interval (CI). Disease-free survival was calculated from date of transplantation to date of relapse or death by any cause if there was no relapse.

RESULTS

Mobilization and Collection of PBSCs

During G-CSF treatment, 7 donors (17.5%), most older than 10 years, complained of lumbago or bone pain, and 3 donors (5.3%) complained of headache, which was relieved by nonsteroidal anti-inflammatory agents. Although very young children could not complain, they appeared to be fine during G-CSF treatment. Only 1 donor had a very high white blood cell count (72.0 X 109/L), and the dose of G-CSF was reduced. The procedure for PBSC harvest was well tolerated, and neither hemodynamic instability, clinical evidence of severe hypocalcemia, nor vaso-vagal reflex was noted during PBSC collection. Mild hypocalcemia was observed in 10 donors and relieved with an increased infusion of calcium gluconate. The average number of aphereses was 2 (range, 1-4), and an average of 480 mL/kg (range, 2121266 mL/kg) of blood was processed. The platelet count decreased in all of the donors, falling to less than 100 X 109/L in 51 donors (89.5%) and less than 50 X 109/L in 6 donors (10.5%). However, there was no clinically significant bleeding, and platelet counts returned to the normal range within 7 to 10 days after the last apheresis. This decrease in the platelet count became prominent following multiple aphereses, and 6 donors required reinfusion of their own platelet-rich plasma, which was obtained during cell processing. Forty donors could be followed, and blood examination showed no abnormalities in any of these donors within a median follow-up of 25 months (range, 6-56 months).

Engraftment Results

The patients received a median of 8.1 X 108/kg (range, 2.7-16.8) mononuclear cells, 5.2 X 106/kg (range, 1.7-16.9 X 106/kg) CD34+ cells, 3.6 X 108/kg (range, 1.7-7.1 X 108/kg) CD3+ cells, and 8.1 (range, 0.4-31.7 X 105/kg) CFU-GM. All of the patients recovered their peripheral blood cell counts, except for 1 patient with engraftment failure who received allogeneic PBSCT as a second transplantation after failed engraftment with BM. The median number (±SE) of days to an ANC of greater than 0.5 X 109/L on 3 consecutive days was 13.0 ±0.62 days (95% CI, 8-23 days). G-CSF was used in 27 patients following transplantation. The median number of days to reach ANC above 500 was 13.1 ±4.2 days (range,

8-18 days) for patients with G-CSF and 14.2 ±3.1 days (range, 8-23 days) for patients without G-CSF. This difference was not statistically significant. The median number of days to a platelet count of greater than 20 X 109/L was 15.0 ±1.04 days (range, 8-115 days). Seven patients did not reach a platelet count of greater than 50 X 109/L. In the remaining 42 patients, the median number of days to a platelet count of greater than 50 X 109/L was 17 days (range,

9-49 days). We compared the methotrexate (MTX) group and the non-MTX group to study the effect of MTX, which was used for GVHD prophylaxis, on engraftment. The median number of days to reach an ANC above 500 was 14.2 ± 3.1 for the MTX group and 11.0 ± 2.3 for the non-MTX group (P = .0049). Thus, the use of MTX significantly affected engraftment.

Graft-Versus-Host Disease

Forty-nine patients who survived more than 60 days were evaluable for acute GVHD, and 36 patients who survived 100 days or more were evaluable for chronic GVHD (Table 3). Eight patients (16.3%) showed clinical grade II to IV acute GVHD, and 1 patient died because of acute

Table 3. Graft-Versus-Host Disease

n (%) >

Acute GVHD 49 La

Grade 0 28 (57) S l/l

Grade I 13(27)

Grade II 5 (10) U QJ

Grade III 1 (2) C

Grade IV 2 (4) o

Grades II-IV 8 (16)

Grades III-IV 3 (6) 3

Chronic GVHD (n = 36) 23 (64) ■Q o

Limited 6 (26) & Oh

Extensive 17(74)

Organs involved

Oral mucosa 20 (56)

Skin 15 (42)

Eyes 10 (28)

Lungs 6 (17) fl

Liver 4 (11) L. □

Gastrointestinal tract 3 (8) <Z)

GVHD-associated infection. In 36 evaluable patients, chronic GVHD developed in 23 patients (64%). Seventeen patients had extensive forms, involving the oral mucosa, eyes, upper gastrointestinal tract, liver, and lung. Two patients showed clinical symptoms and findings similar to those of systemic sclerosis. Three patients died from progressive lung disease probably related to chronic GVHD. A higher dose of prednisolone or methylprednisolone was used to control acute GVHD in all cases. Various immunosuppressive agents, including steroids, FK 506, azathiopurine, and antilymphocyte globulin, were used to control chronic GVHD.

Outcomes and Survival

Nine patients (15.8%) relapsed or exhibited refractory disease during this study (Table 4). Thirteen patients (22.8%) died from transplantation-related toxicities. Transplantation-related toxicities included GVHD or associated complications (n = 4), infection (n = 3), pulmonary toxicity (n = 3), veno-occlusive disease of the liver (n = 2), intracranial bleeding (n = 1), and graft failure (n = 1). Deaths related to transplantation-related complications occurred 26, 30, 39, 48, 49,

Table 4. Causes of Failure for Malignant Disease

Standard

Refractory High Risk Risk

(n = 6) (n = 13) (n = 3)

Refractory disease 2

Relapse 3 2 2

GVHD 4

Acute 1

Chronic 3

Transplantation-related toxicity 1 7 1

Infection 1 2

Veno-occlusive disease 2

Pulmonary 3 1

Bleeding 1

Graft failure 1

Standard-risk

High-risk

Refractory

12 3 4

Years After Transplantation

High-risk

Refractory

0 12 3 4

Years After Transplantation

Figure 1. Overall survival (A) and disease-free survival (B) for hematological malignancies. Overall survival and disease-free survival were assessed according to 3 categories: high-risk hematological malignancies, standard-risk hematological malignancies, and refractory malignant disease.

54, 65, 90, 140, 195, 235, 248, and 539 days following transplantation. The estimated 100-day nonrelapse mortality rate was 9.9% (95% CI, 5.7%-14.1%). Survival was assessed according to 4 groups (Figure 1): high-risk hematological malignancy, standard-risk hematological malignancy, refractory malignant disease, and nonmalignancy. The first category included transplantations following the second or more complete remission (CR) of acute myelogenous leukemia (AML) or the third or more CR of acute lymphoblastic leukemia (ALL); high-risk myelodysplastic syndrome (MDS) (refractory anemia with excess blasts); and chronic myelogenous leukemia (CML) in blastic crisis (n = 25). The second category included hematological malignancies following the first CR of AML or first or second CR of ALL and low-risk MDS (refractory anemia) (n = 18). The risk features that allowed patients to undergo allogeneic transplantation in the first CR included Philadelphia chromosome- or MLL-positive or infant ALL or AML except AML with t(8,21) and inv. 16. The third category included transplantations at relapse or refractory disease (n = 6). The fourth category included severe aplastic anemia (n = 6), chronic granulomatous disease (n = 1), and Kostmann's disease (n = 1). The Kaplan-Meier estimate of 3-year overall

Figure 2. Overall survival and chronic GVHD. The relationship between chronic GVHD and overall survival was assessed for 35 patients with hematological malignancies according to the presence (n = 23) or absence (n = 12) of GVHD.

survival was 37.6% (95% CI, 26.0%-49.2%) for high-risk malignancies, 78.4% (95% CI, 66.8%-90.0%) for standard-risk malignancies, and 16.7% (95% CI, 0.5%-31.9%) for refractory malignant disease. The Kaplan-Meier estimate of 3-year disease-free survival was 37.2% (95% CI, 25.4%-59.0%) for high-risk malignancies, 81.4% (95% CI, 71.7%-91.1%) for standard-risk malignancies, and 0% for refractory malignant disease. All of the patients with nonmalignant disease have been alive and disease-free for a median of 1112 days (range, 356-1908 days; data not shown).

We also analyzed the relationship between chronic GVHD and overall survival for 35 evaluable patients with malignancies. There was a trend toward increased survival in patients with chronic GVHD compared to those without GVHD, although this difference was not statistically significant (P = .088) (Figure 2). In addition, only 3 of 23 patients with GVHD developed relapse, whereas 4 of 14 patients without GVHD relapsed. Again, this difference was not statistically significant.

DISCUSSION

When PBSCs are collected from pediatric donors, 2 major issues should be considered: the short-term and long-term effects of G-CSF on normal children and the safety of PBSC harvest procedures. The results of this study suggest that the collection of PBSCs from pediatric donors is feasible with acceptable adverse effects, although the long-term effects of G-CSF administration should be monitored for a longer period. Although G-CSF has a theoretical risk of clonal evolution [14], no adverse clinical or hematological events have occurred with, at most, a 5-year follow-up in a limited number of donors [15,16]. For a safe apheresis procedure, problems associated with extracorporeal blood volume, blood access, hypocalcemia due to acid-citrate-dextrose solution A (ACD-A) toxicity (anticoagulant), and the vago-vagal reflex should be overcome. For blood access to obtain sufficient blood flow, placement of a CV line may not be justified in this donor population. Placement of CV catheters is accompanied by serious complications such as pneumothorax, per-

foration of the superior vena cava, and venous thrombosis [17,18]. Further, placement of a CV catheter requires general anesthesia in small children. Thus, peripheral blood access should be used. In children weighing less than 20 kg, the cell separator must be primed with blood to avoid circulatory collapse, and autologous blood must be used to avoid the potential risk of allogeneic blood transfusion [19]. Thus, for normal pediatric donors, the choice of PBSCs should be based on these risks and benefits, balanced against the risks of general anesthesia and BM harvesting.

In this study, only 8 of the 49 evaluable patients (16%) developed grade II to IV acute GVHD. It has been well documented that both the incidence and severity of GVHD in Japan are less than those in other countries, because of a more homogenous distribution of HLA [20]. Thus, the data are compatible with our historical data. On the other hand, 23 of 36 evaluable patients (66%) developed chronic GVHD, mostly extensive forms involving oral mucosa and skin, whereas this incidence was only 22% in matched-sibling BMT in our recent report [21]. Five patients suffered from severe chronic GVHD; 3 of them died from progressive lung disease probably related to chronic GVHD, and 2 patients showed clinical symptoms and findings similar to those of systemic sclerosis, a severe form of chronic GVHD. Although the grade of acute GVHD was set low, the incidence and severity of chronic GVHD might be rather high considering that all of the patients were Japanese children who received a graft from a matched sibling. This high incidence of chronic GVHD might have been due to a variety of factors, such as the type of prophylaxis against GVHD, the preparative regimen, and the length of follow-up. In this study, about half of the patients did not receive MTX for GVHD prophylaxis, consistent with the widely accepted practice in the Japanese transplantation society. Furthermore, because of high-risk disease features, strong GVHD prophylaxis might not have been used in anticipation of GVL effects. Nevertheless, in other countries it is well recognized that the omission of MTX contributes to a higher incidence of chronic GVHD [22]. On the other hand, an increased incidence of GVHD may contribute to a decreased incidence of leukemia relapse by inducing a GVL effect [23,24], although this issue is still controversial [25,26]. A limitation of our study was the lack of a control such as BMT with regard to survival, and we cannot be certain that allogeneic PBSCT has a greater GVL effect than BMT. Careful controlled randomized studies are needed to determine whether PBSCs might have significant GVL effects. Thus, for nonmalignant disease and standard-risk hematological malignancies, the use of PBSCs in the pediatric population might be limited because of a high incidence of chronic GVHD and poor posttransplantation quality of life, unless the donor's condition would support PBSCs [27].

ACKNOWLEDGMENTS

We thank all of the involved stem cell transplantation physicians and nurses for providing excellent patient care. We also thank the PBSCT Study Group investigators for the opportunity to evaluate the data collected on patients and donors.

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