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Acute lymphoblastic leukemia (ALL) in second complete remission is one of the most common indications for allogeneic hematopoietic stem cell transplantation (HSCT) in pediatric patients. We compared the outcome after HCST of adolescents, aged 14 to 18 years, with that of children (ie, patients < 14 years of age). Enrolled in the study were 395 patients given the allograft between January 1990 and December 2007; both children (334) and adolescents (61) were transplanted in the same pediatric institutions. All patients received a myeloablative regimen that included total body irradiation in the majority of them. The donor was an HLA-identical sibling for 199 patients and an unrelated volunteer in the remaining 196 patients. Children and adolescents had a comparable cumulative incidence of transplantation-related mortality, disease recurrence, and of both acute and chronic graft-versus-host disease. The 10-year probability of overall survival and event-free survival for the whole cohort of patients were 57% (95% confidence interval, 52%-62%) and 54% (95% confidence interval, 49%-59%), respectively, with no difference between children and adolescents. This study documents that adolescents with ALL in second complete remission given HSCT in pediatric centers have an outcome that does not differ from that of patients younger than 14 years of age.

Gene transfer into hematopoietic stem cells by gamma-retroviral vectors (RVs) is an effective treatment for inherited blood disorders, although potentially limited by the risk of insertional mutagenesis. We evaluated the genomic impact of RV integration in T lymphocytes from adenosine deaminase-deficient severe combined immunodeficiency (ADA-SCID) patients 10 to 30 months after infusion of autologous, genetically corrected CD34(+) cells. Expression profiling on ex vivo T-cell bulk population revealed no difference with respect to healthy controls. To assess the effect of vector integration on gene expression at the single-cell level, primary T-cell clones were isolated from 2 patients. T-cell clones harbored either 1 (89.8%) or 2 (10.2%) vector copies per cell and displayed partial to full correction of ADA expression, purine metabolism, and T-cell receptor-driven functions. Analysis of RV integration sites indicated a high diversity in T-cell origin, consistently with the polyclonal T-cell receptor-Vbeta repertoire. Quantitative transcript analysis of 120 genes within a 200-kb window around RV integration sites showed modest (2.8- to 5.2-fold) dysregulation of 5.8% genes in 18.6% of the T-cell clones compared with controls. Nonetheless, affected clones maintained a stable phenotype and normal in vitro functions. These results confirm that RV-mediated gene transfer for ADA-SCID is safe, and provide crucial information for the development of future gene therapy protocols. The trials described herein have been registered at http://www.clinicaltrials.gov as #NCT00598481 and #NCT00599781.