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

Ex vivo cytokine expansion of peripheral blood Ph-negative cells in chronic myeloid leukaemia

Hematopoietic progenitors can be expanded ex vivo in the presence of various cytokine combinations. Since normal early progenitor or stem cells persist in the blood and bone marrow of patients with Philadelphia chromosome [Ph]-positive chronic myeloid leukaemia (CML), the selection of normal (Ph-negative) progenitor cells from CML patients would be of considerable clinical value for ex vivo purging and autologous transplantation. To obtain these cells, CD34-positive (progenitor) cells from the peripheral blood (PB) of CML patients were either pretreated or not with 5-fluorouracil (5FU) and then grown in suspension culture for 7 days with a combination of cytokines. We compared different combinations of cytokines containing interleukin-1 alpha (IL1), interleukin-3 (IL3), stem cell factor (SCF), leukemia inhibitor factor (LIF), Flt3-ligand (FLT3L), and thrombopoietin (TPO). 5FU decreased cell proliferation in the liquid culture but concurrently increased the expansion of CFU-GM. While the addition of cytokines such as FLT3L and TPO improved CFU-GM expansion. FISH and RT-PCR analysis showed that this method significantly favored a higher frequency of Ph-negative cells after expansion in liquid culture. Therefore ex vivo expansion of putatively normal hematopoietic progenitor cells from cytapheresis is feasible in CML.

Stem Cell Factor as a Single Agent Induces Selective Proliferation of the Philadelphia Chromosome Positive Fraction of Chronic Myeloid Leukemia CD34+ Cells

The interaction between p145c-KIT and p210bcr-abl in transduced cell lines, and the selective outgrowth of normal progenitors during long-term culture of chronic myeloid leukemia (CML) cells on stroma deficient in stem-cell factor (SCF) suggests that the response of CML cells to SCF may be abnormal. We examined the proliferative effect of SCF(100 ng/mL), provided as the sole stimulus, on individual CD34+ cells from five normal donors and five chronic-phase CML patients. Forty-eight percent of isolated single CML CD34+ cells proliferated after 6 days of culture to a mean of 18 cells, whereas only 8% of normal CD34+ cells proliferated (mean number of cells generated was 4). SCF, as a single agent, supported the survival and expansion of colony-forming unit–granulocyte-macrophage (CFU-GM) from CML CD34+CD38+ cells and the more primitive CML CD34+CD38− cells. These CFU-GM colonies were all bcr-abl positive, showing the specificity of SCF stimulation for the leukemic cell population. Coculture of CML and normal CD34+ cells showed exclusive growth of Ph+cells, suggesting that growth in SCF alone is not dependent on secretion of cytokines by CML cells. SCF augmentation of β1-integrin–mediated adhesion of CML CD34+cells to fibronectin was not increased when compared with the effect on normal CD34+ cells, suggesting that the proliferative and adhesive responses resulting from SCF stimulation are uncoupled. The increased proliferation may contribute to the accumulation of leukemic progenitors, which is a feature of CML.

Biology of CD34+CD38- cells in lymphohematopoiesis

Since the discovery of the CD34 stem/progenitor cell antigen, considerable progress has been made in further purifying human lymphohematopoietic stem cells (HSC). These studies have identified a number of antigens which can be targeted to subfractionate the CD34+ cell population. In particular, several lines of evidence suggest that the rare CD38(-)subpopulation of CD34+ cells may be enriched in HSC. This review briefly summarizes relevant knowledge concerning the CD38 molecule and the results of in vitro and in vivo studies of CD34+38(-)cells. Possible clinical uses for purified CD34+38(-)cells are outlined.

Stem Cell Factor as a Single Agent Induces Selective Proliferation of the Philadelphia Chromosome Positive Fraction of Chronic Myeloid Leukemia CD34+ Cells

The interaction between p145c-KIT and p210bcr-abl in transduced cell lines, and the selective outgrowth of normal progenitors during long-term culture of chronic myeloid leukemia (CML) cells on stroma deficient in stem-cell factor (SCF) suggests that the response of CML cells to SCF may be abnormal. We examined the proliferative effect of SCF(100 ng/mL), provided as the sole stimulus, on individual CD34+ cells from five normal donors and five chronic-phase CML patients. Forty-eight percent of isolated single CML CD34+ cells proliferated after 6 days of culture to a mean of 18 cells, whereas only 8% of normal CD34+ cells proliferated (mean number of cells generated was 4). SCF, as a single agent, supported the survival and expansion of colony-forming unit–granulocyte-macrophage (CFU-GM) from CML CD34+CD38+ cells and the more primitive CML CD34+CD38− cells. These CFU-GM colonies were all bcr-abl positive, showing the specificity of SCF stimulation for the leukemic cell population. Coculture of CML and normal CD34+ cells showed exclusive growth of Ph+cells, suggesting that growth in SCF alone is not dependent on secretion of cytokines by CML cells. SCF augmentation of β1-integrin–mediated adhesion of CML CD34+cells to fibronectin was not increased when compared with the effect on normal CD34+ cells, suggesting that the proliferative and adhesive responses resulting from SCF stimulation are uncoupled. The increased proliferation may contribute to the accumulation of leukemic progenitors, which is a feature of CML.

BCR-ABL-positive progenitors in chronic myeloid leukaemia patients in complete cytogenetic remission after treatment with interferon-alpha

To determine the source of residual disease detected in patients with chronic myeloid leukaemia (CML) in complete cytogenetic remission (n=8) after treatment with interferon-alpha (IFN-alpha), we have tested CFU-GM colonies grown from bone marrow mononuclear cells or from plastic-adherent (Pdelta) cells for BCR-ABL mRNA using a nested multiplex RT-PCR. We compared our results with those obtained by analysis of colonies from newly diagnosed patients (n=4) and patients achieving no cytogenetic response (n=1) or incomplete cytogenetic response to treatment with IFN-alpha (n=5). A total of 1239 informative colonies were analysed. A small proportion of BCR-ABL-positive colonies was detected in all eight patients in complete cytogenetic remission, suggesting the persistence of leukaemia that could potentially lead to relapse. The overall proportion of BCR-ABL-positive colonies in patients achieving a cytogenetic response to IFN-alpha correlated with the levels of BCR-ABL transcripts detected in the peripheral blood by competitive RT-PCR (P=0.004). We conclude that residual disease detected in the peripheral blood of complete cytogenetic responders to IFN-alpha is at least partly derived from clonogenic myeloid cells. It is probable that the leukaemia clone in CML is only very rarely or never entirely eradicated by treatment with IFN-alpha.

Establishment of a Reproducible Model of Chronic-Phase Chronic Myeloid Leukemia in NOD/SCID Mice Using Blood-Derived Mononuclear or CD34+ Cells

An animal model of chronic myeloid leukemia (CML) will help characterize leukemic and normal stem cells and also help evaluate experimental therapies in this disease. We have established a model of CML in the NOD/SCID mouse. Infusion of ≥4 × 107chronic-phase CML peripheral blood cells results in engraftment levels of ≥1% in the bone marrow (BM) of 84% of mice. Engraftment of the spleen was seen in 60% of mice with BM engraftment. Intraperitoneal injection of recombinant stem cell factor produced a higher level of leukemic engraftment without increasing Philadelphia-negative engraftment. Granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor did not increase the level of leukemic or residual normal engraftment. Assessment of differential engraftment of normal and leukemic cells by fluorescence in situ hybridization analysis with bcr and abl probes showed that a median of 35% (range, 5% to 91%) of engrafted cells present in the murine BM were leukemic. BM engraftment was multilineage with myeloid, B-cell, and T-cell engraftment, whereas T cells were the predominant cell type in the spleen. BM morphology showed evidence of eosinophilia and increased megakaryocytes. We also assessed the ability of selected CD34+ CML blood cells to engraft NOD/SCID mice and showed engraftment with cell doses of 7 to 10 × 106 cells. CD34− cells failed to engraft at cell doses of 1.2 to 5 × 107. CD34+ cells produced myeloid and B-cell engraftment with high levels of CD34+ cells detected. Thus, normal and leukemic stem cells are present in CD34+ blood cells from CML patients at diagnosis and lead to development of the typical features of CML in murine BM. This model is suitable to evaluate therapy in CML.

Establishment of a Reproducible Model of Chronic-Phase Chronic Myeloid Leukemia in NOD/SCID Mice Using Blood-Derived Mononuclear or CD34+ Cells

An animal model of chronic myeloid leukemia (CML) will help characterize leukemic and normal stem cells and also help evaluate experimental therapies in this disease. We have established a model of CML in the NOD/SCID mouse. Infusion of ≥4 × 107chronic-phase CML peripheral blood cells results in engraftment levels of ≥1% in the bone marrow (BM) of 84% of mice. Engraftment of the spleen was seen in 60% of mice with BM engraftment. Intraperitoneal injection of recombinant stem cell factor produced a higher level of leukemic engraftment without increasing Philadelphia-negative engraftment. Granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor did not increase the level of leukemic or residual normal engraftment. Assessment of differential engraftment of normal and leukemic cells by fluorescence in situ hybridization analysis with bcr and abl probes showed that a median of 35% (range, 5% to 91%) of engrafted cells present in the murine BM were leukemic. BM engraftment was multilineage with myeloid, B-cell, and T-cell engraftment, whereas T cells were the predominant cell type in the spleen. BM morphology showed evidence of eosinophilia and increased megakaryocytes. We also assessed the ability of selected CD34+ CML blood cells to engraft NOD/SCID mice and showed engraftment with cell doses of 7 to 10 × 106 cells. CD34− cells failed to engraft at cell doses of 1.2 to 5 × 107. CD34+ cells produced myeloid and B-cell engraftment with high levels of CD34+ cells detected. Thus, normal and leukemic stem cells are present in CD34+ blood cells from CML patients at diagnosis and lead to development of the typical features of CML in murine BM. This model is suitable to evaluate therapy in CML.