Mobilization of hematopoietic stem cells by plerixafor alone in children: A sequential Bayesian trial

Background: The rapid kinetics of hematopoietic stem cells induced by Plerixafor (Mozobil (R), Genzyme) should be of particular interest in children. We therefore conducted a prospective trial to determine whether a one-day mobilization by plerixafor alone was efficient enough in children with cancer. Methods: Children with solid malignancies were consecutively recruited for this phase-IIA, Bayesian single-center prospective study. Mobilization consisted in one subcutaneous injection of 240 mu g plerixafor/kg body weight at 8 a.m. (h0). Collection by apheresis began at h5 provided that CD34+ count exceeded 10 x 10(6)/L. Our main evaluation criterion was percent of children in which at least 5 x 10(6) CD34+/kg could be collected during the first apheresis. Results: No patients fulfilled the success criterion, and so a stopping criterion was met after 5 patients. All patients reached the threshold value of 10 x 10(6) CD34+ cells/L post-injection and so all were eligible for apheresis. Peak CD34+ cell values were ranged from 11 to 44 x 106/L and were reached in 4 h to 6 h. No side-effects were observed. Median number of CD34+ cells collected per patient BW was 1.62 x 10(6) [0.47-3.5]. In 3 of the 5 patients, collection was >1.5 x 10(6) CD34+/kg BW. Conclusion: In children, a 'one-day' mobilization regimen consisting of one injection of 240 mu g/kg plerixafor alone in hematological steady state provides a faster and shorter mobilization than in adults. This strategy may be an attractive option for completing an insufficient graft. More studies are warranted to optimize the use of plerixafor in children. (C) 2013 Elsevier Ltd. All rights reserved.