Peripheral blood is a source of BCR-ABL-negative pre-progenitors in early chronic phase chronic myeloid leukemia

Abstract

Manipulation of autologous bone marrow cells (BM) for transplantation in chronic myeloid leukemia (CML) to enrich for normal cells is a novel approach that may improve survival for patients not suitable for allogeneic transplantation. Limitations of this technique include the reported low frequency of normal stem cells in CML and the difficulties in obtaining sufficient BM for manipulation. To address these problems we compared the apheresis product with the diagnostic bone marrow at diagnosis as a source of primitive BCR/ABL-negative progenitors. We analyzed the CD34⁺ HLA-DR⁻ and CD34⁺CD38⁻ populations in five CML patients to evaluate the frequency of BCR-ABL-negative progenitors and pre-progenitors in these populations. Progenitor analysis was performed by RT-PCR of individual hemopoietic colonies from a standard CFU-GM assay. Analysis of pre-progenitors involved RT-PCR of secondary colonies derived from a stroma-free pre-CFU assay. Our results show variable levels of BCR-ABL-negative progenitors in the 34⁺DR⁻ population but very low levels of BCR-ABL-negative progenitors in the 34⁺38⁻ population in blood. Analysis of pre-progenitors from the 34⁺DR⁻ fraction of peripheral blood (PB) and BM showed 80–100% and 85–100% of colonies were BCR-ABL negative at days 14 and 28, respectively. Analysis of pre-progenitors from the 34⁺38⁻ fraction of PB and BM showed 23–100% and 42–100% of colonies were BCR-ABL negative at days 14 and 28, respectively. In summary, pre-progenitors from the 34⁺DR⁻ and 34⁺38⁻ populations are predominantly BCR-ABL negative in both marrow and blood at diagnosis. Apheresis product collected at diagnosis is a more abundant source of BCR-ABL-negative pre-progenitors than BM. Thus, apheresis product could potentially be utilized as a source of BCR-ABL-negative stem cells in CML.