PBPC mobilization with chemotherapy and G-CSF in patients with chronic myeloid leukemia: quantification of bcr/abl-positive cells by interphase fluorescence in situ hybridization and competitive PCR

BACKGROUND: Autografting of normal stem cells mobilized after chemotherapy is increasingly used in chronic myeloid leukemia (CML). Thus, quantificatio n of possible contamination of progenitor cell apheresis with breakpoint cl uster region (bcr)/Abelson murine leukemia (abl)positive cells is of great clinical interest. STUDY DESIGN AND METHODS: Two molecular methods were compared to quantify bcr/abl positivity in leukapheresis components obtained after mobilizing chemother apy in six patients with CML. To document the efficacy of in vivo purging, the leukapheresis procedures were monitored with interphase fluorescence in situ hybridization (FISH) and quantitative competitive PCR (QC-PCR) as a r atio of bcr/abl:abl. RESULTS: From the first to the last leukapheresis, bcr/ abl positivity in F ISH increased from a median of 11 percent to 33 percent. For bcr/abl transc ripts, a simultaneous increase in consecutive leukapheresis procedures was seen. The median percentage of bcr cells in a bcr/abl:abl ratio was 3.1 per cent in the first apheresis. In the last apheresis after the mobilization w ith mRNA, the QC-PCR showed a median of 19.5 percent. FISH and QC-PCR showe d a statistical significant increase of bcr/ abl positivity from the first to the last apheresis. CONCLUSIONS: Both FISH and QC-PCR were reliable methods of quantifying bcr/ abl positivity, and they allowed selection of the optimal apheresis compone nt for autologous transplantation. In both methods, a significant increase in bcr/abl positivity was seen from the first to the last leukapheresis. Wi th FISH, results can be obtained within 24 hours. This method may prevent a dditional contaminated leukapheresis in case of increasing percentages of b cr/abl-positive cells.