Optimizing drug therapy in pediatric SCT: focus on pharmacokinetics.

Given age-related differences in drug metabolism and indications for hematopoietic SCT (HSCT), personalized drug dosing of the conditioning regimen and post-transplant immunosuppression may reduce graft rejection, relapse rates and toxicity in pediatric HSCT recipients. This manuscript summarizes the pharmacokinetic/dynamic data of HSCT conditioning and post-grafting immunosuppression, presented at the First Annual Pediatric Bone Marrow Transplant Consortium (PBMTC) meeting in April 2013. Personalized dosing of BU to a target plasma exposure reduces graft rejection in children and improves relapse/toxicity rates in adults. Current weight-based dosing achieves the target BU exposure in only a minority (24.3%) of children. The initial BU dose should be based on the European Medicines Agency nomogram or population pharmacokinetic models to improve the numbers of children achieving the target exposure. There are limited pharmacokinetic data for treosulfan, CY, fludarabine and alemtuzumab as HSCT conditioning in children. For post-grafting immunosuppression, mycophenolic acid (MPA) clearance may be increased in younger children (<12 years). The preferred MPA pharmacokinetic monitoring parameters and target range are still evolving in HSCT recipients. Multi-institutional trials incorporating properly powered pharmacokinetic/dynamic studies are needed to assess the effect of variability in the plasma exposure of drugs/metabolites on clinical outcomes in pediatric HSCT recipients.

Sequential myeloablative autologous stem cell transplantation and reduced intensity allogeneic hematopoietic cell transplantation is safe and feasible in children, adolescents and young adults with poor-risk refractory or recurrent Hodgkin and non-Hodgkin lymphoma.

The outcome of children, adolescents and young adults (CAYA) with poor-risk recurrent/refractory lymphoma is dismal (⩽30%). To overcome this poor prognosis, we designed an approach to maximize an allogeneic graft vs lymphoma effect in the setting of low disease burden. We conducted a multi-center prospective study of myeloablative conditioning (MAC) and autologous stem cell transplantation (AutoSCT), followed by a reduced intensity conditioning (RIC) and allogeneic hematopoietic cell transplantation (AlloHCT) in CAYA, with poor-risk refractory or recurrent lymphoma. Conditioning for MAC AutoSCT consisted of carmustine/etoposide/cyclophosphamide, RIC consisted of busulfan/fludarabine. Thirty patients, 16 Hodgkin lymphoma (HL) and 14 non-Hodgkin lymphoma (NHL), with a median age of 16 years and median follow-up of 5years, were enrolled. Twenty-three patients completed both MAC AutoSCT and RIC AlloHCT. Allogeneic donor sources included unrelated cord blood (n=9), unrelated donor (n=8) and matched siblings (n=6). The incidence of transplant-related mortality following RIC AlloHCT was only 12%. In patients with HL and NHL, 10 year EFS was 59.8% and 70% (P=0.613), respectively. In summary, this approach is safe, and long-term EFS with this approach is encouraging considering the poor-risk patient characteristics and the use of unrelated donors for RIC AlloHCT in the majority of cases.

New frontiers in pediatric Allo-SCT.

The inaugural meeting of 'New Frontiers in Pediatric Allogeneic Stem Cell Transplantation' organized by the Pediatric Blood and Transplant Consortium (PBMTC) was held at the American Society of Pediatric Hematology and Oncology Annual Meeting. This meeting provided an international platform for physicians and investigators active in the research and utilization of pediatric Allo-SCT in children and adolescents with malignant and non-malignant disease (NMD), to share information and develop future collaborative strategies. The primary objectives of the conference included: (1) to present advances in Allo-SCT in pediatric ALL and novel pre and post-transplant immunotherapy; (2) to highlight new strategies in alternative allogeneic stem cell donor sources for children and adolescents with non-malignant hematological disorders; (3) to discuss timing of immune reconstitution after Allo-SCT and methods of facilitating more rapid recovery of immunity; (4) to identify strategies of utilizing Allo-SCT in pediatric myeloproliferative disorders; (5) to develop diagnostic and therapeutic approaches to hematological complications post pediatric Allo-SCT; (6) to enhance the understanding of new novel cellular therapeutic approaches to pediatric malignant and non-malignant hematological disorders; and (7) to discuss optimizing drug therapy in pediatric recipients of Allo-SCT. This paper will provide a brief overview of the conference.

The pharmacokinetics and safety of twice daily i.v. BU during conditioning in pediatric allo-SCT recipients.

Intravenous BU divided four times daily (q6 h) has been shown to be safe and effective in pediatric allo-SCT recipients. Though less frequent dosing is desirable, pharmacokinetic (PK) data on twice daily (q12 h) i.v. BU administration in pediatric allo-SCT recipients is limited. We prospectively examined the PK results in a cohort of pediatric allo-SCT recipients receiving i.v. BU q12 h as part of conditioning before allo-SCT. BU levels were obtained after the first dose of conditioning. PK parameter analysis (n=49) yielded the following 95% confidence intervals (CI95): weight-normalized volume of distribution: 0.65-0.73 L/kg; t(1/2): 122-147 min; weight-normalized clearance (CL(n)): 3.4-4.3 mL/min/kg; and area under the curve: 1835-2180 mmol × min/L. From these results, a steady state concentration was calculated with CI95 between 628-746 ng/mL. Comparison between recipients ≤4 vs >4 years old revealed significant differences in t(1/2) (mean: 115 vs 146 min, P=0.008) and CL(n) (mean: 4.4 vs 3.5 mL/min/kg, P=0.038). Intravenous BU q12 h had a comparable PK to i.v. BU q6 h PK seen in the literature, and in pediatric allo-SCT recipients, is a feasible, attractive alternative to i.v. q6h dosing.

Reduced intensity allogeneic umbilical cord blood transplantation in children and adolescent recipients with malignant and non-malignant diseases.

There is a significant amount of morbidity and mortality following myeloablative umbilical cord blood transplantation (UCBT). Reduced intensity (RI) conditioning offers an alternative to myeloablative conditioning before UCBT. We investigated RI-UCBT in 21 children and adolescents with malignant (n=14), and non-malignant diseases (n=7). RI conditioning consisted of fludarabine (150-180 mg/m2) with either busulfan (< or = 8 mg/kg)+rabbit antithymocyte globulin (R-ATG; n=16) or cyclophosphamide+R-ATG+/-etoposide (n=5). Human leukocyte antigen match: 4/6 (n=13), 5/6 (n=5) and 6/6 (n=3). The median total nucleated cell and CD34+ cell dose per kilogram were 3.58 x 10(7) and 2.54 x 10(5), respectively. The median time for neutrophil and platelet engraftment was 17.5 and 52 days, respectively. There were six primary graft failures (chronic myelogenous leukemia (CML), beta-thalassemia, hemophagocytic lymphohistiocytosis (HLH) and myelodysplastic syndrome (MDS)). The probability of developing grade II to grade IV acute graft-versus-host disease (GVHD) and chronic GVHD was 28.6 and 16.7%, respectively. Incidence of transplant-related mortality (TRM) was 14%. The 5 years overall survival (OS) in all patients was 59.8%. The 5 years OS for patients with average versus poor-risk malignancy was 77.8 versus 22.2% (P=0.03). RI-UCBT may result in graft failure in specific high-risk chemo-naïve patients (CML, beta-thalassemia, HLH and MDS), but in more heavily pretreated pediatric and adolescent recipients results in rapid engraftment and may be associated with decreased severe GVHD and TRM.