Primitive progenitor cells in the blood of patients with chronic granulocytic leukemia

Lack of the adhesion molecules P-selectin and intercellular adhesion molecule-1 accelerate the development of BCR/ABL-induced chronic myeloid leukemia-like myeloproliferative disease in mice

In vitro studies show that BCR/ABL-expressing hematopoietic cells exhibit altered adhesion properties. No in vivo studies show whether the altered adhesion properties affect BCR/ABL leukemogenesis. Using mice with homozygous inactivation of genes encoding the 2 adhesion molecules P-selectin and intercellular adhesion molecule-1 (ICAM1), we show that the mutant mice develop BCR/ABL-induced chronic myeloid leukemia (CML)-like leukemia at a significantly faster rate than do wild-type (WT) mice. Lack of P-selectin and ICAM1 did not have a significant effect on the development of B-cell acute lymphoblastic leukemia (BALL) induced by BCR/ABL. Using mice deficient for P-selectin or ICAM1 alone, we show that P-selectin plays a major role in the acceleration of CML-like leukemia. Lack of P-selectin resulted in early release of BCR/ABL-expressing myeloid progenitors from bone marrow, appearing to alter the biologic properties of leukemic cells rather than their growth rate by increasing their homing to the lungs, causing fatal lung hemorrhages. These results indicate that adhesion of BCR/ABL-expressing myeloid progenitors to marrow stroma through P-selectin and ICAM1 play an inhibitory role in the development of CML-like disease, suggesting that improvement of adhesion between BCR/ABL-expressing myeloid progenitor cells and bone marrow stroma may be of therapeutic value for human CML.

p210BCR/ABL-induced alteration of pre-mRNA splicing in primary human CD34+ hematopoietic progenitor cells

Chronic myelogenous leukemia (CML) is a malignancy of the human hematopoietic stem cell (HSC) caused by the p210BCR/ABL oncoprotein. Although alternative splicing of pre-mRNA is a critical determinant of a cell's protein repertoire, it has not been associated with CML pathogenesis. We identified a BCR/ABL-dependent increase in expression of multiple genes involved in pre-mRNA splicing (eg SRPK1, RNA Helicase II/Gu, and hnRNPA2/B1) by subtractive hybridization of cDNA from p210BCR/ABL-eGFP vs eGFP-transduced umbilical cord blood CD34+ cells. beta1-integrin signaling is important to HSC maintenance and proliferation/differentiation, and is abnormal in CML. As an example of how changes in pre-mRNA processing might contribute to CML pathogenesis, we observed alternative splicing of a gene for a beta1-integrin-responsive nonreceptor tyrosine kinase (PYK2), resulting in increased expression of full-length Pyk2 in BCR/ABL-containing cells. Treatment of p210BCR/ABL-positive cells with the Abl-specific tyrosine kinase inhibitor STI571 reverted PYK2 splicing to a configuration more consistent with normal cells, and correlated with decreased expression of BCR/ABL-induced proteins involved in pre-mRNA processing. Whether altered PYK2 splicing contributes to CML pathogenesis remains undetermined; however, we propose that generic changes in pre-mRNA splicing as a result of p210BCR/ABL kinase activity may contribute to CML pathogenesis.

Inhibition of BCR-ABL Expression With Antisense Oligodeoxynucleotides Restores β1 Integrin-Mediated Adhesion and Proliferation Inhibition in Chronic Myelogenous Leukemia Hematopoietic Progenitors

Chronic myelogenous leukemia (CML) is characterized by the continuous proliferation and abnormal circulation of malignant hematopoietic progenitors. This may be related to the unresponsiveness of CML progenitors to β1 integrin adhesion receptor-mediated inhibition of progenitor proliferation by the marrow microenvironment. In hematopoietic cell lines, the BCR-ABL oncogene product, p210BCR-ABL, interacts with a variety of cytoskeletal elements important for normal integrin signaling. We studied the role of p210BCR-ABL in abnormal integrin function in CML by evaluating the effect of inhibition of BCR-ABL expression with antisense oligodeoxynucleotides (AS-ODNs) on integrin-mediated adhesion and proliferation inhibition of malignant primary progenitors from CML marrow. Preincubation of CML CD34+HLA-DR+(DR+) cells with breakpoint-specific AS-ODNs significantly increased adhesion of CML progenitors to stroma and fibronectin (FN). Pretreatment with breakpoint-specific ODNs also resulted in significant inhibition of CML progenitor proliferation after ligand or antibody-mediated β1 integrin engagement. Breakpoint-specific ODNs were significantly more effective in restoring CML progenitor adhesion and proliferation inhibition than control ODNs. BCR-ABL mRNA and p210BCR-ABL levels in CML CD34+ cells were significantly reduced after incubation with breakpoint-specific AS-ODN. These studies indicate a role for BCR-ABL in abnormal circulation and defective integrin-dependent microenvironmental regulation of proliferation of CML hematopoietic progenitors.

Inhibition of BCR-ABL Expression With Antisense Oligodeoxynucleotides Restores β1 Integrin-Mediated Adhesion and Proliferation Inhibition in Chronic Myelogenous Leukemia Hematopoietic Progenitors

Chronic myelogenous leukemia (CML) is characterized by the continuous proliferation and abnormal circulation of malignant hematopoietic progenitors. This may be related to the unresponsiveness of CML progenitors to β1 integrin adhesion receptor-mediated inhibition of progenitor proliferation by the marrow microenvironment. In hematopoietic cell lines, the BCR-ABL oncogene product, p210BCR-ABL, interacts with a variety of cytoskeletal elements important for normal integrin signaling. We studied the role of p210BCR-ABL in abnormal integrin function in CML by evaluating the effect of inhibition of BCR-ABL expression with antisense oligodeoxynucleotides (AS-ODNs) on integrin-mediated adhesion and proliferation inhibition of malignant primary progenitors from CML marrow. Preincubation of CML CD34+HLA-DR+(DR+) cells with breakpoint-specific AS-ODNs significantly increased adhesion of CML progenitors to stroma and fibronectin (FN). Pretreatment with breakpoint-specific ODNs also resulted in significant inhibition of CML progenitor proliferation after ligand or antibody-mediated β1 integrin engagement. Breakpoint-specific ODNs were significantly more effective in restoring CML progenitor adhesion and proliferation inhibition than control ODNs. BCR-ABL mRNA and p210BCR-ABL levels in CML CD34+ cells were significantly reduced after incubation with breakpoint-specific AS-ODN. These studies indicate a role for BCR-ABL in abnormal circulation and defective integrin-dependent microenvironmental regulation of proliferation of CML hematopoietic progenitors.

Interferon-alpha restores normal adhesion of chronic myelogenous leukemia hematopoietic progenitors to bone marrow stroma by correcting impaired beta 1 integrin receptor function

Treatment of chronic myelogenous leukemia (CML) with interferon-alpha frequently results in normalization of peripheral blood counts and, in up to 20% of patients, reestablishment of normal hematopoiesis. We hypothesize that interferon-alpha may restore normal adhesive interactions between CML progenitors and the bone marrow microenvironment and restore normal growth regulatory effects resulting from these progenitor-stroma interactions. We demonstrate that treatment with interferon-alpha induces a significant, dose-dependent increase in the adhesion of primitive long-term culture initiating cells and committed colony-forming cells (CFC) from CML bone marrow to normal stroma. Adhesion of CFC seen after interferon-alpha treatment could be inhibited by blocking antibodies directed at the alpha 4, alpha 5, and beta 1 integrins and vascular cell adhesion molecule, but not CD44 or intracellular adhesion molecule, suggesting that interferon-alpha induces normalization of progenitor-stroma interactions in CML. Because FACS analysis showed that the level of alpha 4, alpha 5, and beta 1 integrin expression after interferon-alpha treatment is unchanged, this suggests that interferon-alpha may restore normal beta 1 integrin function. Normalization of interactions between CML progenitors and the bone marrow microenvironment may then result in the restoration of normal regulation of CML progenitor proliferation, and explain, at least in part, the therapeutic efficacy of interferon-alpha in CML.

A comparison of the sensitivity of blood and bone marrow for the detection of minimal residual disease in chronic myeloid leukaemia

We have sought to determine whether peripheral blood or bone marrow is more sensitive for assessment of minimal residual disease in chronic myeloid leukaemia (CML). Contemporaneous blood and marrow specimens were taken from 21 patients at various times after allogeneic bone marrow transplant (BMT) and from one patient in complete cytogenetic remission on alpha-interferon. Samples were analysed for evidence of BCR-ABL mRNA by RT-PCR: four were PCR negative and 19 PCR positive. Results with blood and marrow were concordant in all cases. BCR-ABL transcripts were quantified in PCR-positive samples using a competitive PCR titration assay. Results ranged from < 10 to 2 x 10(6) BCR-ABL transcripts/micrograms RNA. In all 19 cases a high degree of concordance in BCR-ABL levels with blood and marrow (r = 0.99) was found. We conclude that either tissue may be used for residual disease studies after BMT for CML.

Cell biology of CML--a model linking the chronic and terminal phases

A model for the pathogenesis of chronic myeloid leukaemia (CML) is proposed. It relies on a comparison between normal steady-state and regenerating haemopoiesis and suggests that chronic phase CML stem cells have a finite capacity for self-renewal. According to the model, metamorphosis of the disease occurs once the potential for chronic phase cell production has been exhausted. The model considers also the generation of leukocytosis in the chronic phase and the origin of the terminal phase. Comparison with normal regenerating haemopoiesis allows discrimination between features of CML that are fundamentally abnormal and those which are normally associated with regeneration.

Regulation of growth in chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a malignant haemopoietic stem cell disorder which results in excessive production of cells of the myeloid series. It is associated with a consistent molecular abnormality, the BCR/ABL fusion gene. The product of BCR/ABL is a p210 protein tyrosine kinase but it is not known how this dictates the biological features of the disease. This review considers several key processes that can be suggested as candidate targets for the action of p210.

Rapid decline of chronic myeloid leukemic cells in long-term culture due to a defect at the leukemic stem cell level

In this report we describe a quantitative in vitro assay for the most primitive type of leukemic precursors yet defined in patients with chronic myeloid leukemia (CML). This assay is based on the recently described "long-term culture-initiating cell" (LTC-IC) assay for primitive normal human hematopoietic cells. Such cells, when cocultured with competent fibroblast feeder layers, give rise after a minimum of 5 weeks to multiple single and multilineage clonogenic progenitors detectable in secondary semisolid assay cultures. Similar cultures initiated by seeding a highly enriched source of leukemic cells from patients onto normal feeders showed the clonogenic cell output after 5 weeks to be linearly related to the input innoculum over a wide range down to limiting numbers of input cells, thus allowing absolute frequencies of leukemic LTC-ICs to be determined using standard limiting dilution analysis techniques. Leukemic LTC-IC concentrations in CML marrow were found to be decreased, on average to less than 10% of the normal LTC-IC concentration in normal marrow, but were greatly increased (up to greater than 10(5) times) in CML blood. Assessment of the number of clonogenic cells produced per leukemic LTC-IC by comparison to normal blood or marrow LTC-IC values showed this function to be unchanged in leukemic LTC-ICs [i.e., 3.1 +/- 0.4 clonogenic cells per CML LTC-IC (mean +/- SEM, n = 6) versus 3.7 +/- 1.2 (n = 3) and 4.3 +/- 0.4 (n = 5), respectively, for normal blood and marrow LTC-ICs]. In contrast, leukemic LTC-IC maintenance in LTC proved to be highly defective by comparison to normal LTC-IC of either blood or marrow origin. Thus, when cells from primary LTC were subcultured into secondary LTC-IC assays, leukemic LTC-IC rapidly declined (greater than 30-fold) within the first 10 days of culture, whereas normal LTC-IC numbers remained unchanged during this period. These findings illustrate how self-maintenance and differentiation events in primitive human hematopoietic cells can be differentially modulated by an oncogenic process and provide a framework for further studies of their manipulation, analysis, and therapeutic exploitation.

Cell interactions and gene expression in early hematopoiesis

As part of an investigation of the mechanisms controlling gene expression during lineage commitment, we have investigated the transcriptional status of hematopoietic lineage-specific genes and the interactions of early hematopoietic progenitor cells with stromal cells of the marrow microenvironment. The results indicate that a subset of otherwise lineage-restricted genes are transcriptionally active and/or DNAse I hypersensitive (i.e., "primed" for transcription) in multipotent, interleukin 3-dependent hematopoietic cells, and that they may become inaccessible and transcriptionally silent when cells are induced to adopt a single lineage during commitment. The external influences regulating gene expression in hematopoietic cells include binding interactions with stromal cells and exposure to locally presented growth factors. These interactions are thought to be essential for hematopoietic cell development and may be dysregulated in chronic myeloid leukemia.

Autologous transplantation with circulating hemopoietic stem cells

Circulating stem cells exist in sufficient numbers in mouse, dog, and man to allow collection and transplantation after ablative treatment. Preclinical studies in the mouse have shown a low concentration, with a transplantation potential ratio of bone marrow to blood of 1:100. The ratio of circulating stem cells to bone marrow stem cells is more favorable in the dog (1:10-20). Recent pilot studies carried out in different centers with 10 patients have shown that this approach is feasible in man, too. It appears that 5 X 10(8) mononuclear cells/kg of body weight collected by seven or eight leukapheresis procedures of about 4 hrs each is sufficient for fast hemopoietic recovery after marrow ablative treatment. Potential advantages of the use of blood stem cells over bone marrow stem cells are the decreased likelihood of contamination with malignant cells, the avoidance of general anesthesia, and the infusion of immunocompetent cells, which might hasten immunorecovery in the autologous setting.