Successful peripheral blood stem cell mobilisation with filgrastim in patients with chronic myeloid leukaemia achieving complete cytogenetic response with imatinib, without increasing disease burden as measured by quantitative real-time PCR

Imatinib mesylate (Glivec) is a selective inhibitor of bcr-abl tyrosine kinase, the product of the Philadelphia chromosome, which is the hallmark of chronic myeloid leukaemia (CML). With imatinib, complete cytogenetic response (CCR) can be achieved in over 70% of newly diagnosed patients with CML. However, the optimal long-term management of patients who achieve CCR after imatinib is unknown. With longer follow-up, it is anticipated that some patients are likely to progress and become candidates for autologous transplantation. We studied filgrastim (r-metHuG-CSF) mobilisation of peripheral blood stem cells (PBSC) in 32 patients who have achieved CCR with imatinib. Our data demonstrate that the target CD34⁺ cell yields of ≥2.0 × 10⁶/kg were attained with filgrastim 10 μg/kg/ day, in 9/18 (50%) of patients during uninterrupted imatinib therapy, and in 10/14 (70%) when imatinib was temporarily withheld. The median CD34⁺ cell yield per aphaeresis was 0.70 × 10⁶/kg (range 0.14-2.18) and 2.90 × 10⁶/kg (range 0.15-8.71) in the two groups, respectively (P<0.005). The cell yields did not correlate with the duration of imatinib administration. There was no impact of the mobilisation procedure on the level of leukaemia as measured by serial blood bcr-abl levels using real-time quantitative PCR with either protocol. bcr-abl remained detectable at low levels in the harvests in most but not all patients. In conclusion, filgrastim can safely be used to mobilise PBSC in patients who have achieved CCR with imatinib, but CD34⁺ cell yields are significantly improved when imatinib is temporarily withheld.