Quantitative competitive reverse transcriptase-polymerase chain reaction for BCR-ABL on Philadelphia-negative leukaphereses allows the selection of low-contaminated peripheral blood progenitor cells for autografting in chronic myelogenous leukemia

The Philadelphia (Ph) translocation t(9;22) results in the creation of the BCR-ABL gene, which is now regarded as central to the mechanism that underl ies the chronic phase of chronic myelogenous leukemia (CML). From a clinica l point of view, BCR-ABL mRNA detection has become the basis for the study of minimal residual disease in CML, particularly when a complete cytogeneti c remission is achieved after interferon-alpha (IFN-alpha) therapy or allog eneic stem cell transplantation. We have recently demonstrated that it is p ossible to mobilize normal peripheral blood progenitor cells (PBPC) in high er rates if this procedure is performed during the early chronic phase. in an attempt to monitor the leukemic cell content of PBPC collections, we use d quantitative-competitive RT-PCR (QC-RT-PCR). Thirty consecutive Philadelp hia (Ph) chromosome positive patients were enrolled in this study. After ch emotherapy and G-CSF, 14 patients achieved 100% Ph-negative metaphases, nin e patients had less than or equal to 34% and seven patients >34% leukemic m etaphases. A total of 116 collection samples were studied. For each sample, BCR-ABL transcript numbers and BCR-ABL/ABL ratio were evaluated. A highly significant correlation between Ph-positive metaphases and BCR-ABL transcri pt numbers (r = 0.84, P < 0.0001) or BCR-ABL/ABL ratio (r = 0.86, P < 0.000 1) was found. For patients that underwent the procedure in early chronic ph ase, Ph-negative collections showed different levels of BCR-ABL expression. BCR-ABL transcript numbers varied from a median of 100/mu g RNA in the fir st and second leukaphereses, to 500/mu g RNA in the third and fourth leukap hereses, and 1500/mu g RNA in the fifth leukapheresis (P = 0.002). BCR-ABL/ ABL ratio values showed similar kinetics. We have also demonstrated that th ere is a correlation between low values in BCR-ABL/ABL ratio (less than or equal to 0.01) in the reinfused PBPC and the achievement of cytogenetic rem ission after autografting (chi(2) test, P = 0.01). In conclusion, this stud y demonstrates that QC-RT-PCR for BCR-ABL is a reliable and helpful method for monitoring residual leukemic load in mobilized PBPC, particularly in Ph -negative collections. Moreover, QC-RT-PCR allows selection of the best ava ilable collections for reinfusion into patients after myeloablative therapy .