Sickle cell disease is a chronic illness with significant morbidity and mortality. The most frequent adverse events are painful vaso-occlusive crises (VOC) that often require hospitalisation (Platt et al, 1991, 1994). VOC are recurrent and unpredictable and associated with higher mortality (Platt et al, 1994). In addition, children with sickle cell disease have a 10% risk of developing an overt stroke and a 20–25% risk of experiencing a silent cerebral infarction (Ohene-Frempong et al, 1998; Steen et al, 2003a). Cerebral infarction can cause impaired cognitive abilities with devastating physical impairments (Fowler et al, 1988; Swift et al, 1989; Brown et al, 1993; Armstrong et al, 1996; DeBaun et al, 1998; Brown et al, 2000; Steen et al, 2003b). Most recently, it has been recognised that 30% of adults with sickle cell disease develop pulmonary hypertension, which is strongly associated with a high rate of sudden death (Gladwin et al, 2004). Similar rates of pulmonary hypertension have been observed in children (Suell et al, 2005; Qureshi et al, 2006). The severity of these complications warrants the institution of therapeutic interventions that prevent and eliminate these life-threatening events. It has been shown previously that haematopoietic stem cell transplantation (HCT) can cure patients with sickle cell disease and is currently the only known cure for this disease (Ferster et al, 1992; Walters et al, 1996; Vermylen et al, 1998; Bernaudin, 1999). However, its toxicity limits broader application. Recent attempts to decrease the toxicity of HCT by employing a non-myeloablative transplant conditioning regimen have not been successful due to a high rate of disease recurrence after HCT (Iannone et al, 2003, 2005). Newer, reduced-intensity regimens are being tested to overcome this problem of graft rejection. Until an optimal regimen is identified, it is important to present updated results of myeloablative HCT from multiple centres to assist clinicians who must choose among various treatment options for children with severe sickle cell disease. We report outcomes after myeloablative HCT for sickle cell disease utilising data reported over a 13-year period to the Center for International Blood and Marrow Transplant Research (CIBMTR) from 30 transplant centres worldwide.
We report outcomes after myeloablative haematopoietic cell transplantation (HCT) from human leucocyte antigen (HLA)-matched sibling donors in 67 patients with sickle cell disease transplanted between 1989 and 2002. The most common indications for transplantation were stroke and recurrent vaso-occlusive crisis in 38% and 37% of patients respectively. The median age at transplantation was 10 years and 67% of patients had received >10 red blood cell transfusions before HCT. Twenty-seven percent of patients had a poor performance score at transplantation. Ninety-four percent received busulfan and cyclophosphamide-containing conditioning regimens and bone marrow was the predominant source of donor cells. Most patients achieved haematopoietic recovery and no deaths occurred during the early post-transplant period. Rates of acute and chronic graft-versus-host disease were 10% and 22% respectively. Sixty-four of 67 patients are alive with 5-year probabilities of disease-free and overall survival of 85% and 97% respectively. Nine patients had graft failure with recovery of sickle erythropoiesis, eight of who had recurrent sickle-related events. This report confirms and extends earlier reports that HCT from HLA-matched related donors offers a very high survival rate, with few transplant-related complications and the elimination of sickle-related complications in the majority of patients who undergo this therapy.
Patient and methods
The CIBMTR is a working group of over 500 voluntary transplant centres worldwide that contribute patient-, disease- and, transplant-characteristics and outcome data on allogeneic transplant recipients to a Statistical Center at the Medical College of Wisconsin. Participating centres register consecutive transplants. Detailed demographic and clinical data are collected on a representative sample of registered patients using a weighted randomisation scheme. Patients are followed longitudinally. Computerised error checks, physician review of submitted data and on-site audits of participating centres ensure data quality. The Institutional Review Board of the Medical College of Wisconsin approved this study.
The study includes patients with sickle cell disease who received a first HCT from a human leucocyte antigen (HLA)-matched sibling after a myeloablative transplant-conditioning regimen between 1989 and 2002. The decision to proceed to HCT and all aspects of the transplant regimen were at the discretion of the transplant centre. One hundred and twenty-six patients were eligible for the study and comprehensive data were available in 67 patients. Thus, the study population consisted of 67 transplant recipients from 30 transplant centres worldwide. Patient, disease, and transplant characteristics and overall survival rates were similar among patients with and without comprehensive data.
Neutrophil recovery was defined as an absolute neutrophil count (ANC) of at least 0·5 × 109/l for three consecutive days; platelet recovery, as achieving a platelet count of at least 20 × 109/l, unsupported by transfusions for at least 7 days. Diagnosis of acute and chronic graft-versus-host disease (GVHD) was based on local institutional criteria with overall grade of acute GVHD assigned retrospectively by the CIBMTR based on stage of involvement reported for each individual organ (Atkinson et al, 1990; Przepiorka et al, 1995). Disease-free survival was defined as survival with a sickle haemoglobin level of less than 50%.
The probabilities of disease-free and overall survival were calculated using the Kaplan–Meier estimator (Klein & Moeschberger, 2003). For analysis of survival rates, death from any cause was considered an event, and data on patients who were alive at last follow-up were censored. For disease-free survival, disease recurrence (sickle haemoglobin >50% with or without clinical disease symptoms) or death from any cause was considered an event, and data on patients who were alive were censored at last follow-up. The probabilities of neutrophil and platelet recovery and acute and chronic GVHD were calculated using the cumulative incidence estimator (Klein & Moeschberger, 2003). For haematopoietic recovery and GVHD, death without an event was the competing event. Data on patients who were alive were censored at last follow-up. Confidence intervals (CI) were calculated using a log transformation (Klein & Moeschberger, 2003). Analyses were completed with the use of SAS software, version 9·1 (SAS Institute, Carey, NC, USA).
Patient, disease and transplant characteristics
Patient, disease and transplant characteristics are shown in Table I. The median age at HCT was 10 years (range: 2–27) and three patients were older than 21 years of age. Forty-two of 67 (63%) patients were male. Sickle cell genotype was known in 63 patients and homozygous sickle haemoglobin (haemoglobin SS) was the predominant genotype. Most patients had received more than 10 red blood cell transfusions before HCT and 10 patients had red cell alloimmunisation. Pretransplant serum ferritin level was available in 42 of 67 patients. Of these, the ferritin level was <1000 μg/l in 18 patients and ≥1000 μg/l in 24 patients. Only 10 patients received chelation therapy prior to HCT. Many of the patients had experienced typical complications of sickle cell disease before HCT that included vaso-occlusive crises and acute chest syndrome (Table I). Seven patients had sickle nephropathy and eight osteonecrosis prior to HCT. Indications for transplantation varied; stroke (n = 24) and VOC (n = 25) were the most frequent cited. Others included acute chest syndrome (n = 6), chronic red blood cell transfusion/iron overload (n = 5), severe disability (n = 1), recurrent priapism (n = 1), and recurrent pneumonia (n = 1). Indication for HCT was not reported for four patients. Despite a history of VOC in 23 patients, only 11 received hydroxycarbamide before HCT. Most patients received a myeloablative combination of busulfan and cyclophosphamide for transplant conditioning. Over half the patients were transplanted after 1999 and therefore after completion of the Multi-center Collaborative Sickle Cell transplantation study (Walters et al, 1996). As the CIBMTR does not collect information on enrolment or clinical trials, we were unable to determine the actual number of patients in this report and the report by Walters et al (1996). The median follow-up among surviving patients was 61 months (range: 3–178). Sixty of 64 surviving patients were followed for longer than 1-year post-HCT.
|Age at transplant, years|
|Karnofsky Performance score pretransplant|
|Patient's sickle cell genotype|
|Hb SS||59 (94)|
|Hb Sβ+thalassemia||1 (1)|
|Number of blood transfusions pretransplant|
|Transfusion received, number unknown||1 (2)|
|No transfusions received||2 (3)|
|Stroke prior to transplant|
|Acute chest syndrome prior to transplant|
|Recurrent vaso-occlusive crises requiring hospitalisation within 2 years prior to transplant|
|<3 crises per year||11 (17)|
|≥3 crises per year||23 (36)|
|Required hospitalisation, number of years unknown||8 (13)|
|Not required hospitalisation||22 (34)|
|Recurrent priapism prior to transplant|
|BU + CY ⊆ othera||63 (94)|
|Source of stem cellsc|
|Bone marrow||54 (81)|
|Peripheral blood stem cell||9 (13)|
|Umbilical cord blood||4 (6)|
|MTX +CsA ⊆ other||52 (78)|
|MTX ⊆ other||1 (1)|
|Tacrolimus ⊆ other||2 (3)|
|CsA ⊆ other||7 (11)|
|T cell depletion||3 (4)|
|Median follow-up of survivors, months||61 (3–178)|
All patients achieved neutrophil recovery (Table II). The median time to recovery was 18 days and the probabilities of recovery were 90% and 100%, at day 28 and day 100 respectively. Fifty-seven of 59 patients achieved platelet recovery (Table II). The median time to recovery was 24 days and the probability of recovery at day 100 was 96%.
|Outcome||n||Probability (95% confidence interval)|
|Absolute neutrophil count >0·5 × 109/l|
|At 28 days||67||90 (82–95)|
|At 100 days||100 (0–100)|
|Platelet count ≥20 × 109/l|
|At 100 days||59||96 (91–99)|
|Acute graft-versus-host disease At 100 days, grades (2–4)||67||10 (4–19)|
|Chronic graft-versus-host diseasea|
|At 1 year||67||16 (8–26)|
|At 3 years||22 (13–34)|
|At 5 years||22 (13–34)|
|At 1 year||65||85 (74–92)|
|At 3 years||85 (74–92)|
|At 5 years||85 (74–92)|
|At 1 year||67||97 (91–100)|
|At 3 years||97 (91–100)|
|At 5 years||97 (91–100)|
Acute and chronic GVHD
Eight of 67 patients developed grade 2–4 acute GVHD with an overall probability of 10% at day 100 (Table II). Only two patients developed grade 3–4 acute GVHD. Thirteen of 67 patients developed chronic GVHD. The 5-year probability of chronic GVHD was 22% (Table II). Of the 13 patients with chronic GVHD, nine had limited and three had extensive chronic GVHD. The severity of chronic GVHD was not reported for the remaining patient. Of the patients who developed extensive chronic GVHD, two received bone marrow grafts and one peripheral blood. The proportion of patients with GVHD did not differ by age at HCT (<10 years vs. ≥10 years).
Examining GVHD by donor graft type, of the 54 patients who received bone marrow graft type, six patients developed acute GVHD and 11 developed chronic GVHD. Of the nine patients who received peripheral blood stem cells, one developed acute GVHD and one chronic GVHD. Of the four patients who received umbilical cord blood, one developed acute GVHD and one chronic GVHD.
Six of 13 patients with chronic GVHD (all received bone marrow grafts) reported the duration of immunosuppressive therapy. The median duration of immunosuppressive therapy for these patients with limited chronic GVHD was 12 months (range: 6–16) and for those with extensive chronic GVHD, 11 months (10–12). Of the patients who developed chronic GVHD, all except one remained disease-free.
Fifty-five patients remained free of sickle cell symptoms (recurrent stroke, vaso-occlusive crises or acute chest syndrome) with haemoglobin S level <50% at a median of 5-years after HCT. However, 11 of these patients experienced seizures in the immediate post-HCT period (i.e. within the first 100 days after HCT) consistent with that described in the study by Walters et al (1996). The 5-year probability of disease-free survival was 85% (95% CI: 74–92; Fig 1). At last follow up, nine patients had haemoglobin S level ≥50%, of which eight had return of symptoms.
Characteristics and outcome of patients with haemoglobin S>50% post-transplantation
All nine patients who had haemoglobin S levels ≥50% were <l6 years of age at HCT (median age 9 years, range 3–16 years) and half of the transplantations occurred prior to 1999. Seven of the patients were males. Three patients had pre-HCT Karnofsky performance scores of <90. Four of the nine patients had received >10 red blood cell transfusions prior to HCT. Of the nine patients, one had red blood cell alloimmunisation, one received chelation therapy prior to HCT and one had been on hydroxycarbamide therapy prior to HCT. Three patients had suffered a stroke prior to HCT. The primary indication for HCT was recurrent VOC in six patients and stroke in the remaining three patients.
All patients received a busulfan and cyclophosphamide conditioning regimen. The stem cell sources for the nine patients are as follows: six received bone marrow and three received peripheral blood stem cells. The cell dose for bone marrow recipients were 0·08, 2·3, 3·0, 3·9, 4·1 and 5·4 × 108/kg. They all received T-replete grafts and clacinuerin inhibitor containing GVHD prophylaxis regimen (cyclosporine + short course methotrexate in five patients and cyclosporine alone in one patient). All six bone marrow recipients achieved neutrophil recovery at a median of 28 days. This was slower than in those bone marrow recipients who were disease-free (haemoglobin S ≤50%), who achieved neutrophil recovery at a median of 18 days.
For peripheral blood recipients, the total nucleated cell dose infused was 3·92 and 30·7 × 108/kg in two patients. Both these patients received in-vitro T-cell depletion (Campath). The cell dose infused for the remaining patient is not known. This patient received an un-manipulated graft and cyclosporine and short course methotrexate for GVHD prophylaxis. Times to neutrophil recovery were 12, 19 and 12 d. In comparison, for patients who are disease-free, median time to neutrophil recovery was 12·5 d.
None of these nine patients developed acute GVHD. One patient developed extensive chronic GVHD 3·9 months after HCT and, at last follow-up, maintained a haemoglobin S level >50%. Five of nine patients received a second infusion from the same donor and without a second conditioning regimen. All patients were alive at last follow up with haemoglobin S level >50%.
Sixty-four of 67 patients were alive after HCT with a 5-year probability of overall survival of 97% (95% CI: 91–100; Fig 1). Though four patients developed veno-oclusive disease post-HCT, there were no deaths attributed to this complication. One of these four patients received intravenous busulfan and one oral busulfan. The method of busulfan administration was not reported for the remaining two patients. Overall, there were three deaths and all occurred beyond 3 months after HCT. Patient 1 died of central nervous system haemorrhage 4·5 months post-HCT at 7 years of age and had experienced both acute and chronic GVHD. Patient 2 died from multi-organ failure 11·5 months post-HCT at 15 years of age. This patient had not had any acute or chronic GVHD. Patient 3 died of unknown causes 8 years post-HCT at 10 years of age and had experienced chronic GVHD. None of these three patients reported disease recurrence (haemoglobin S >50%) prior to death. There were no reports of malignancy after HCT.
The results of the current study confirm and extend earlier findings of successful HCT for sickle cell disease (Ferster et al, 1992; Vermylen et al, 1993, 1998; Vermylen & Cornu, 1994; Walters et al, 1996, 1997, 2000, 2001; Bernaudin, 1999) With disease-free and overall survival rates of 85% and 97%, respectively, HCT is a suitable treatment option that can be applied with a curative intent when an HLA-matched sibling donor is available. Our observations are supported by the ongoing utilisation of HCT for sickle cell disease by affected families and their physicians after completion of the national clinical trial, even though alternative supportive therapies, such as hydroxycarbamide and chronic red blood cell transfusions, are readily available.
In our cohort, disease recurrence and chronic GVHD were the most common serious complications of HCT. Nine patients experienced return of disease within the first year after HCT, as demonstrated by sickle haemoglobin levels >50%. It is unclear what risk feature predisposed to this complication. Approximately half of these patients received more than 10 blood transfusions before HCT, which might have contributed to disease recurrence. However, the small number of patients and the relatively few events in this cohort limited our ability to perform multivariate analysis to explore potential risk factors for disease recurrence. A history of exposure to multiple blood transfusions prior to HCT was associated with an increased risk of graft rejection in other non-malignant diseases, such as aplastic anaemia (Storb et al, 1980; Anasetti et al, 1986; Stucki et al, 1998). Further, Walters and colleagues in their prospective clinical trial also reported a trend towards disease recurrence in patients who received chelation therapy for iron overload, implying that frequent blood transfusions may have increased the risk of graft rejection in sickle cell disease (Walters et al, 1996, 1997, 2001).
Thirteen patients developed chronic GVHD with an overall rate of 22%; the rate of chronic GVHD observed here was similar to rates reported for other non-malignant diseases at similar ages (Kahl et al, 2005). Very few patients in our study experienced severe chronic GVHD, making HCT a very good treatment option for patients with sickle cell disease.
Transplantation with stable engraftment of donor cells eliminates vaso-occlusive events related to sickle cell disease (Walters et al, 2000, 2001; Walters, 2004). The long-term outcomes of patients with sickle cell disease who have undergone HCT are encouraging, even with the risk of chronic GVHD (Walters et al, 2000, 2001; Walters, 2004). Specifically, patients had improved growth and stable or improved lung function and central nervous system findings after HCT for stroke. These data argue for early referral and HCT in sickle cell disease patients who have an HLA-matched sibling donor so that HCT may be performed in younger patients with minimal exposure to red blood cell transfusions.
As with all reports utilising an observational database, the decision to proceed to HCT, the rationale for stem cell source, and other aspects of post-HCT follow-up were determined at the discretion of individual centres. Thus, we do not have information on donor-recipient chimerism in all the patients in this study and it appears that transplant centres were most likely to measure the haemoglobin S fraction as the sole method of disease status assessment post-HCT. In addition, the transplant centres did not systematically perform pre- and post-HCT magnetic resonance imaging studies of the brain, which limited our ability to analyse outcomes related to central nervous system disease in these patients.
Predicting the severity of sickle cell disease has been largely based on the development of clinical symptoms and it is difficult to determine severity prior to the onset of these complications. However, improved characterisation of the extent of morbidity caused by this disease has occurred recently. Specifically, we now know that pulmonary hypertension affects 30% of adults with sickle cell disease and is associated with an increased risk of early mortality, that children with increased cerebral arterial velocity in the large intracranial vessels are at high-risk for stroke, and that silent stroke affects at least 22% of patients and results in impaired cognitive functioning (Kinney et al, 1999; Schatz et al, 2001; Gladwin et al, 2004; Adams & Brambilla, 2005). Therapies to decrease the morbidity and mortality related to sickle cell disease include hydroxycarbamide and chronic blood transfusions. Hydroxycarbamide is not effective in all patients and requires life-long compliance. Blood transfusion therapy, although highly effective, has complications of alloimmunisation, iron overload, and risk of blood-borne infections. These limitations of supportive care make HCT an important and vital treatment option for sickle cell disease. Children who have full-siblings and who experience these severe complications of sickle cell disease should undergo HLA typing with consideration of HCT if a suitable donor is available. Future research in the safety and feasibility of unrelated HCT is a logical next step to broaden the number of children who might undergo HCT.
The CIBMTR is supported by Public Health Service Grant U24-CA76518 from the National Cancer Institute, the National Institute of Allergy and Infectious Diseases, and the National Heart, Lung and Blood Institute; Office of Naval Research; Health Services Research Administration (DHHS); and grants from Abbott Laboratories; Aetna; American International Group, Inc.; American Red Cross; Amgen, Inc.; Anonymous donation to the Medical College of Wisconsin; AnorMED, Inc.; Astellas Pharma US, Inc.; Baxter International, Inc.; Berlex Laboratories, Inc.; Biogen IDEC, Inc.; BloodCenter of Wisconsin; Blue Cross and Blue Shield Association; Bristol-Myers Squibb Company; BRT Laboratories, Inc.; Cangene Corporation; Celgene Corporation; CellGenix, Inc.; Cell Therapeutics, Inc.; CelMed Biosciences; Cylex Inc.; Cytonome, Inc.; CytoTherm; DOR BioPharma, Inc.; Dynal Biotech, an Invitrogen Company; Enzon Pharmaceuticals, Inc.; Gambro BCT, Inc.; Gamida Cell, Ltd; Genzyme Corporation; Gift of Life Bone Marrow Foundation; GlaxoSmithKline, Inc.; Histogenetics, Inc.; HKS Medical Information Systems; Kirin Brewery Co., Ltd; Merck & Company; The Medical College of Wisconsin; Millennium Pharmaceuticals, Inc.; Miller Pharmacal Group; Milliman USA, Inc.; Miltenyi Biotec, Inc.; MultiPlan, Inc.; National Marrow Donor Program; Nature Publishing Group; Novartis Pharmaceuticals, Inc.; Osiris Therapeutics, Inc.; Pall Medical; Pfizer, Inc.; Pharmion Corporation; PDL BioPharma, Inc; Roche Laboratories; Sanofi-aventis; Schering Plough Corporation; StemCyte, Inc.; StemSoft Software, Inc.; SuperGen, Inc.; Sysmex; The Marrow Foundation; THERAKOS, Inc.; University of Colorado Cord Blood Bank; ViaCell, Inc.; ViraCor Laboratories; Wellpoint, Inc.; and Zelos Therapeutics, Inc. The views expressed in this article do not reflect the official policy or position of the National Institute of Health, the Department of the Navy, the Department of Defense, or any other agency of the U.S. Government.