ORIGINAL ARTICLE Haploidentical related-donor hematopoietic cell transplantation in children using megadoses of CliniMACs-selected CD34 þ cells and a fixed CD3 þ dose CC Dvorak 1 , AL Gilman 2 , B Horn 1 , C-Y Oon 1 , EA Dunn 1 , LA Baxter-Lowe 3 and MJ Cowan 1 We conducted a prospective phase II trial utilizing the CliniMACs system to perform CD34 þ -cell selection of PBSCs from haploidentical donors to evaluate engraftment and hematoimmunological reconstitution. In total, 21 children with hematological malignancies or nonmalignant conditions underwent conditioning with 1200 cGy TBI, thiotepa, fludarabine and Thymoglobulin. Patients received megadoses of CD34 þ cells (median: 22 Â 10 6 /kg) with a fixed dose of 3 Â 10 4 /kg CD3 þ cells/kg, and engraftment occurred in 90% with prompt recovery of neutrophils and platelets. Grade II acute GVHD (aGVHD) was seen in 32% (95% confidence interval (CI), 15–54%) of evaluable patients, there was no grade III–IV aGVHD, and chronic extensive GVHD was seen in 35% (95% CI, 17–59%) of patients. The estimated 2-year EFS was 62% (95% CI, 48–83%) with a median survivor follow-up of 49 months (range: 18–119 months). Patients with nonmalignant diseases had an estimated 2-year EFS of 100% (95% CI, 56–100%) and patients with malignancies in remission had an estimated 2-year EFS of 56% (95% CI, 22–89%). Megadose CD34 þ cells with a fixed CD3 þ cell dose from haploidentical related donors resulted in good outcomes for pediatric patients with nonmalignant diseases and those with malignant diseases transplanted in remission. Bone Marrow Transplantation (2013) 48, 508–513; doi:10.1038/bmt.2012.186; published online 26 November 2012 Keywords: haploidentical; hematopoietic SCT; donor lymphocyte infusions; pediatric INTRODUCTION Many children lack an HLA-matched donor for use in allogeneic hematopoietic cell transplantation (HCT). Two alternative donor options exist for these patients: mismatched unrelated umbilical cord blood (UCB), or a haploidentical relative. An advantage of haploidentical HCT is the opportunity for post-transplant cellular therapy. However, the use of haploidentical donors is limited by three factors: (1) major HLA barriers must be overcome to prevent graft rejection and achieve engraftment; (2) stringent T-cell depletion is required to limit severe GVHD; and (3) delays in functional immune reconstitution has led to high rates of infection and relapse. 1,2 We performed haploidentical related-donor HCT in children utilizing a platform of myeloablative conditioning with megadoses of CD34 þ cells, which has been shown to overcome barriers to engraftment and accelerate recovery of neutrophils and immu- nity. 3,4 This approach is associated with severe immunodeficiency and infections soon after transplant. We addressed the profound T-cell depletion that occurs with the CliniMACs CD34 þ -cell selection system 5 by adding back a fixed CD3 þ -cell dose to the stem cell product hypothesizing that this would be associated with low rates of GVHD while promoting engraftment. We also reduced the dose of Thymoglobulin used in the conditioning regimen hypothesizing that the added T cells would prevent graft rejection. Delays in post-HCT immune reconstitution could then be managed via the use of small doses of donor lymphocytes infusions (DLI), 6 which have been shown to improve recovery of normal T-cell numbers. 6,7 To test these hypotheses, we prospectively enrolled 21 pediatric patients with high-risk diseases in a phase II trial evaluating the CliniMACs machine to prepare CD34 þ -selected cells from haploidentical related-donors, with a primary endpoint of successful engraftment. MATERIALS AND METHODS Patients and donors Eligible patients for the prospective trial presented to the University of California San Francisco Benioff Children’s Hospital or the University of North Carolina from March 2002 to July 2010 with a malignant or nonmalignant disease in need of an allogeneic HCT, and who lacked an HLA-identical related, X9/10 HLA-allele-matched unrelated or X5/6 HLA- allele-matched cord blood donor with an adequate cell dose. Patient and donor characteristics are described in Table 1. Two patients were initially enrolled on trial, but were later deemed ineligible owing to receipt of non-protocol conditioning. They were excluded from the analysis, and replacement patients were enrolled. The median patient age was 6.4 years (range: 1.4–20.5 years). Patients were considered to be in CR at transplant only if markers of minimal residual disease status (when possible for that disease) were negative. The transplant protocol was approved by the Institutional Review Boards of both institutions, and informed consent was obtained from the donors and the patient/parents in accordance with the Declaration of Helsinki. Trial conditioning regimen and GVHD prophylaxis Conditioning was based on the Perugia protocol, 1 consisting of TBI 1200 cGy (200 cGy fractions twice daily on days À 9 to À 7, with 50% lung 1 Department of Pediatrics, Division of Allergy, Immunology, and Blood and Marrow Transplant, UCSF Benioff Children’s Hospital, University of California San Francisco, San Francisco, CA, USA; 2 Division of Pediatric Blood and Marrow Transplantation, Levine Children’s Hospital, San Francisco, CA, USA and 3 Department of Surgery, University of California San Francisco, San Francisco, CA, USA. Correspondence: Dr CC Dvorak, Department of Pediatric Allergy, Immunology and Blood and Marrow Transplant, UCSF Benioff Children’s Hospital, University of California San Francisco, 505 Parnassus Avenue, M-659, San Francisco, CA 94143-1278, USA. E-mail: dvorakc@peds.ucsf.edu Received 8 May 2012; revised 21 August 2012; accepted 22 August 2012; published online 26 November 2012 Bone Marrow Transplantation (2013) 48, 508–513 & 2013 Macmillan Publishers Limited All rights reserved 0268-3369/13 www.nature.com/bmt