Frequency of clonal B lymphocytes in chronic myelogenous leukemia evaluated by fluorescence in situ hybridization

The demonstration of the Philadelphia (Ph) chromosome in B lymphocytes from patients with chronic myelogenous leukemia (CML) has provided evidence that the disorder originates in a pluripotent progenitor cell. Divergent results, however, exist as to the degree of contribution of clonally derived cells to the B-cell compartment. To address this issue, B lymphocytes were selected from the blood of seven patients in the chronic phase of Ph-positive CML and were examined with dual-color fluoresence in situ hybridization for the presence of the Ph translocation. The purity of the B-cell preparations ranged from 88% to 97% (mean 93%). The Ph translocation was detected in 22-34% (mean, 27%) of the sorted B cells. There was no evidence that the duration of the disease affects the ratio of Ph-positive and -negative B cells. In summary, clonally derived circulating B lymphocytes were present in all patients studied but made only minor contribution to this compartment.