A Pediatric Study of a Plerixafor Containing Regimen In Second Allogeneic Stem Cell Transplantation

Patients with refractory hematologic malignancies, including those who develop recurrent disease after allogeneic hematopoietic stem cell transplantation (HSCT) have a dismal prognosis. Historically, both regimen-related mortality and disease recurrence have been significant causes of treatment failure in this heavily pre-treated patient population. Novel therapeutic agents that target molecular signaling mechanisms and increase the sensitivity of leukemic cells to apoptosis may clearly play a role in this setting. This study hypothesizes that interrupting the SDF-1/CXCR4 axis using the selective CXCR4 antagonist plerixafor may be useful as a leukemic stem cell mobilizing agent for patients who are refractory to standard dose chemotherapy and in relapse after an allogeneic transplant. This hypothesis is based on the dependence of leukemia cells on MSCs for survival signals as described above and on the preclinical data that suggest increased efficacy by antileukemia agents when leukemia cells are separated from MSCs. In the present trial, the study proposes to add plerixafor to enhance the conditioning regimen cytotoxicity. At this time the goal is to determine the maximum tolerated dose (MTD) of plerixafor through the process of dose limiting toxicity (DLT) evaluation. Pharmacokinetic studies will be conducted. Additional studies will quantify and the content of leukemia cells and key regulatory and effector T cell populations in the bone marrow and blood before and after exposure to this medication. If the observed outcomes of this trial are promising, it could serve as a platform on which to study further use of plerixafor as a complimentary agent with conditioning as well as other chemotherapeutic regimens for patients with relapsed or refractory hematologic malignancies.