Plerixafor in poor stem cell mobilizers: the Belgian Compassionate Use Program

Currently available stem cell mobilizing regimens (G-CSF +/- chemotherapy) show high failure rates, especially in heavily pretreated patients. Plerixafor, a new stem cell mobilizing agent blocking the CXCR4-SDF-1 interaction, offers a new strategy for stem cell mobilization, especially in poor mobilizers.This study reports on the outcome of the Belgian compassionate use program (CUP).

Between July 2008 and July 2009, 14 Belgian transplant centres participated in plerixafor CUP. In total, 22 poor stem cell mobilizers were included. Patients who previously failed stem cell mobilization received a combination of G-CSF (morning of Day 1-5) and plerixafor (evening of Day 4). Apheresis was performed on Day 5. G-CSF, plerixafor and apheresis were continued until at least 2 x 10(6)/kg CD34+ cells were obtained in a maximum of 3 collections.

A mean of 2 plerixafor administrations was needed to reach > or = 2 x 10(6)/kg CD34+ cells. The overall cumulative success rate (defined as the proportion of patients achieving a successful collection after a maximum of 3 apheresis days) was 64%. Half of the heavily pretreated patients ( 3 prior chemotherapy regimens) could be mobilized successfully. Patients who received < or = 2 prior chemotherapy regimens mobilized successfully in 75% of the cases. Thirteen patients (59.1%) underwent autologous stem cell transplantation with normal neutrophil and platelet recovery times.

For patients failing previous mobilization attempts, the combination of plerixafor and G-CSF is a successful mobilizing strategy, even in poor mobilizers who received > or = 3 prior chemotherapy regimens.