title: BCR/ABL- CD34(+)HLA-DR- progenitor cells in early chronic phase, but not in more advanced phases, of chronic myelogenous leukemia are polyclonal.
abstract: Chronic myelogenous leukemia (CML) is characterized by the Philadelphia (Ph) translocation and BCR/ABL gene rearrangement which occur in a pluripotent hematopoietic progenitor cell. Ph-negative (Ph-) hematopoiesis can be restored in vivo after treatment with -interferon or intensive chemotherapy, suggesting that normal stem and progenitor cells coexist with the Ph+ clone. We have previously shown that Ph- progenitors are highly enriched in the CD34(+)HLA-DR- fraction from early chronic phase (ECP) CML patients. Previous studies have suggested that the Ph-translocation represents a secondary clonal hit occurring in an already clonally mutated Ph- progenitor or stem cells, leaving the unanswered question whether Ph- CD34(+)HLA-DR- progenitors are normal. To show the clonal nature of Ph- CD34(+)HLA-DR- CML progenitors, we have compared the expression of BCR/ABL mRNA with X-chromosome inactivation patterns (HUMARA) in mononuclear cells and in CD34(+)HLA-DR+ and CD34(+)HLA-DR- progenitors in marrow and blood obtained from 11 female CML patients (8 in chronic phase and 3 in accelerated phase [AP] disease). Steady-state marrow-derived BCR/ABL mRNA-, CD34(+)HLA-DR- progenitors had polyclonal X-chromosome inactivation patterns in 2 of 2 patients. The same polyclonal pattern was found in the progeny of CD34(+)HLA-DR- derived long-term culture-initiating cells. Mobilization with intensive chemotherapy induced a Ph-, BCR/ABL mRNA- and polyclonal state in the CD34(+)HLA-DR- and CD34(+)HLA-DR+ progenitors from 2 ECP patients. In a third ECP patient, polyclonal CD34(+) cells could only be found in the first peripheral blood collection. In contrast to ECP CML, steady-state marrow progenitors in late chronic phase and AP disease were mostly Ph+, BCR/ABL mRNA+, and clonal. Further, in the majority of these patients, a Ph-, polyclonal state could not be restored despite mobilization with intensive chemotherapy. We conclude from these studies that CD34(+)HLA-DR- cells that are Ph- and BCR/ABL mRNA- are polyclonal and therefore benign. This population is suitable for autografting in CML.
authors.affiliation: Division of Hematology, the Department of Medicine, University Hospital Gasthuisberg, Leuven, Belgium. Michel.Delforge@uz.kuleuven.ac.be
authors.forename: M
authors.initials: M
authors.lastname: Delforge
authors.forename: M A
authors.initials: MA
authors.lastname: Boogaerts
authors.forename: P B
authors.initials: PB
authors.lastname: McGlave
authors.forename: C M
authors.initials: CM
authors.lastname: Verfaillie
mesh_terms: D000328:Adult; D018952:Antigens, CD34 / Q000032:analysis*; D001854:Bone Marrow Cells / Q000473:pathology; D002478:Cells, Cultured; D002999:Clone Cells / Q000473:pathology; D005260:Female; D016044:Fusion Proteins, bcr-abl / Q000235:genetics*; D016313:Genes, abl; D006684:HLA-DR Antigens / Q000032:analysis*; D006412:Hematopoietic Stem Cells / Q000473:pathology*; D006801:Humans; D007951:Leukemia, Myeloid / Q000235:genetics / Q000473:pathology*; D016133:Polymerase Chain Reaction; D013997:Time Factors
chemical_list: D018952:Antigens, CD34; D006684:HLA-DR Antigens; D016044:Fusion Proteins, bcr-abl