Bcr-Abl efficiently induces a myeloproliferative disease and production of excess interleukin-3 and granulocyte-macrophage colony-stimulating factor in mice: a novel model for chronic myelogenous leukemia

The bcr-abl oncogene plays a critical role in causing chronic myelogenous leukemia (CML). Effective laboratory animal models of CML are needed to study the molecular mechanisms by which the bcr-abl oncogene acts in the disease progression of CML. We used a murine stem cell retroviral vector (MSCV) to transduce the bcr-abl/p210 oncogene into mouse bone marrow cells and found that expression of Bcr-Abl/p210 induced a myeloproliferative disorder that resembled the chronic phase of human CML in 100% of bone marrow transplanted mice in about 3 weeks. This CML-like disease was readily transplanted to secondary recipient mice. Multiple clones of infected cells were expanded in the primary recipients, but the leukemia was primarily monoclonal in the secondary recipient mice. Mutation analysis demonstrated that the protein tyrosine kinase activity of Bcr-Abl/p210 was essential for its leukemogenic potential in vivo. Interestingly, we found that the leukemic cells expressed excess interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF) in the diseased mice. These studies demonstrate that expression of Bcr-Abl can induce a CML-like leukemia in mice much more efficiently and reproducibly than in previously reported mouse CML models, probably due to efficient expression in the correct target cell(s). Our first use of this model for analysis of the molecular mechanisms involved in CML raises the possibility that excess expression of hematopoietic growth factors such as IL-3 and GM-CSF may contribute to the clinical phenotype of CML.     

An animal model of leukemogenesis using transgenic mice

The bcr/abl chimeric oncoprotein is considered to be implicated in the pathogenesis of Philadelphia chromosome-positive human leukemias. To investigate its biological function and the role in leukemogenesis in vivo, we generated transgenic mice expressing p210bcr/abl driven by the metallothionein promoter. Two of six founder mice and the transgenic progeny of one leukemic founder mouse developed leukemias several months after birth. Phenotypically, each leukemic mouse showed a thymic enlargement, a marked splenomegaly, and/or lymphnode swellings. Pathological examination revealed that leukemic cells were infiltrated in all tissues examined, especially in thymus, spleen, liver, and lymphnode. Expression of the p210bcr/abl transgene product and increased phosphorylation of cellular proteins in leukemic tissues were detected by the Western blot analysis. In addition, the expressed p210bcr/abl protein was demonstrated to possess an enhanced kinase activity by the in vitro immunecomplex kinase assay. These results indicate that hematopoietic precursor cells expressing the p210bcr/abl transgene product acquired a proliferative advantage and eventually developed leukemias in transgenic mice. The p210bcr/abl transgenic mice are considered to be an excellent animal model to investigate p210bcr/abl function and its role in leukemogenesis in vivo.     

The hypereosinophilic variant of Ph''-positive chronic myeloleukemia

AIM: To confirm clonal nature of idiopathic hypereosinophilic syndrome (IHES), its relevance to Ph'-positive chronic myeloid leukemia. MATERIALS AND METHODS: 3 cases of idiopathic hypereosinophilic syndrome are reported with morphologic analysis of bone marrow cells and cytogenetic examinations. In one patient the presence of Ph'-chromosome was confirmed at fluorescent in situ hybridization (FISH) and molecular-genetic analysis (bcr/abl). Samples of bone marrow, spleen and liver were examined pathohistologically. RESULTS: The presence of chromosome anomaly t(9;22), i.e. Ph'-chromosome, associated with chronic myeloid leukemia (CML) was identified in all the 3 cases. There was also myeloid hyperplasia in the bone marrow (with primarily mature, eosinophilic granulocytes), spleen and liver, depression of megakaryocyto- and erythropoiesis. 2 patients had similar clinical symptoms which was not typical for CML in chronic phase: fever, elevated ESR, clear-cut anemia and thrombocytopenia. In the absence of hyperleukocytosis, blood and bone marrow eosinophils remained high (42.5, 21.5, 42.5% and 21.4, 7.1, 6.5%, respectively) due to "mature" forms. The number of blasts in the bone marrow was maximum 2.4%. CONCLUSION: The literature and the obtained data suggest closeness of idiopathic hypereosinophilic syndrome and Ph'-positive CML within myeloproliferative diseases.     

Importance of mixed chimerism to predict relapse in persistently BCR/ABL positive long survivors after allogeneic bone marrow transplantation for chronic myeloid leukemia

Determination of hematological chimerism could be helpful in understanding the biology of leukemic relapse after allogeneic bone marrow transplant (BMT) for chronic myeloid leukemia (CML), because the detection of malignant residual cells carrying the bcr/abl message by qualitative RT-PCR is of limited value in predicting disease progression for individual patients. We have studied the chimerism pattern and the bcr/abl status by Southern-blot in 15 CML patients (M/F:6/9) transplanted with unmanipulated BM from HLA identical sibling donors, persistently bcr/abl positive by RT-PCR. The median age of the series was 31 years (18-49) and disease status at BMT was: chronic phase: 11, accelerated phase: 3 and blast crisis: 1 patient. Of the 15 patients, 9 are alive and in complete remission (CR), 4 have died in CR and 2 are alive but suffered relapse at + 19 and +26 months post-BMT. The median follow-up is 81 months (13,7-168). Rearrangement of the BCR gene was performed by Southern-blot using P32-labeled transprobe-1. PCR analysis of chimerism was assessed using primers for the following VNTR loci: D1S80, D1S111, 33.1, APO-B, YNZ-22, lambdag3 and DXS52. Seventy-nine samples were analyzed (median per patient 5 (range 2-9)). Thirteen patients showed complete chimerism and lacked BCR rearrangement over time by Southern-blot. The 2 patients who relapsed showed mixed chimera status from +9 and +5 months respectively until the end of the study. Persistent BCR rearrangement was observed in these 2 patients from +12 and +11 months respectively. Our data suggest that mixed chimerism may predict hematologic or cytogenetic relapse by several months in those patients who are persistently PCR-positive post-BMT.     

Chronic myelogenous leukemia

Chronic myelogenous leukemia is a clonal hematopoietic malignancy characterized by a balanced translocation between chromosomes 9 and 22 that results in the generation of an abnormal bcr/abl fusion protein with increased tyrosine kinase activity. This abnormal fusion protein has transforming activity for hematopoietic cells in vitro and causes chronic myelogenous leukemia-like myelopoiesis in mice. Chronic myelogenous leukemia progenitor cells display abnormalities in their interactions with bone marrow stroma, perhaps due to defective adhesion molecule function. Conventional therapies for chronic myelogenous leukemia include hydroxyurea, busulfan, or interferon. Treatment with interferon may prolong overall survival, especially in patients who achieve a cytogenetic response. Related donor marrow transplantation can result in long-term survival in more than 65% of patients treated early in the course of disease. For patients without an available matched sibling donor, unrelated donor marrow transplantation or autologous marrow transplantation are alternative therapeutic options.     

Innovative therapy for chronic myelogenous leukemia

Innovative therapies for chronic myelogenous leukemia (CML) have focused mainly on combining autologous transplantation with another modality of therapy for purging of the graft or treatment of the patient after transplant. Of the three categories of innovative therapies, two are based on studies that demonstrate the bcr/abl gene rearrangement in the pathogenesis of CML, whereas the third is based on the observation that allogeneic disparity is important to maintain remissions in CML. The rationale and data supporting these innovative approaches are reviewed in this article and future strategies are discussed.     

Capping of bcr-abl antisense oligonucleotides enhances antiproliferative activity against chronic myeloid leukemia cell lines

Leukemia due to a chromosomal translocation offers an attractive model for the design and testing of antisense agents because the sequence at the translocation junction is unique to the leukemic cell population. Chronic myeloid leukemia is the most common such translocation-induced leukemia. We have found antisense phosphodiester oligonucleotides directed at the bcr-abl junction to be ineffective in inhibiting the growth of CML cell lines. Therefore, we have investigated the effects produced by certain structural modifications of bcr-abl antisense oligonucleotides. For assay purposes we used K562 cells which have the bcr exon 3/abl exon 2 junction and BV173 cells which have the bcr exon 2/abl exon 2 junction. We have found that 5'-capping with a dimethoxytrityl group and 3'-capping with an amino-2-hydroxypropyl group confer antiproliferative activity. The enhancement of activity by capping appears at least partly attributable to exonuclease resistance since stability in serum-containing medium is increased.     

Chronic myelogenous leukemia: molecular and cellular aspects

Chronic myelogenous leukemia (CML) originates in a pluripotent hematopoietic stem cell of the bone marrow and is characterized by greatly increased numbers of granulocytes in the blood. Myeloid and other hematopoietic cell lineages are involved in the process of clonal proliferation and differentiation. After a period of 4-6 years the disease progresses to acute-stage leukemia. On the cellular level, CML is associated with a specific chromosome abnormality, the t(9; 22) reciprocal translocation that forms the Philadelphia (Ph) chromosome. The Ph chromosome is the result of a molecular rearrangement between the c-ABL proto-oncogene on chromosome 9 and the BCR (breakpoint cluster region) gene on chromosome 22. Most of ABL is linked with a truncated BCR. The BCR/ABL fusion gene codes for an 8-kb mRNA and a novel 210-kDa protein which has higher and aberrant tyrosine kinase activity than the normal c-ABL-coded counterpart. Phosphorylation of a number of substrates such as GAP, GRB-2, SHC, FES, CRKL, and paxillin is considered a decisive step in transformation. An etiological connection between BCR/ABL and leukemia is indicated by the observation that transgenic mice bearing a BCR/ABL DNA construct develop leukemia of B, T, and myeloid cell origin. CML cells proliferate and expand in an almost unlimited manner. Adhesion defects in bone marrow stromal cells have been proposed to explain the increased number of leukemic cells in the peripheral blood. However, findings of our laboratory have shown that the BCR/ABL chimeric protein that is expressed in transfected cells may, under certain conditions, also increase the adhesion to fibronectin via enhanced expression of integrin. Our previous immunocytological studies on the expression of beta1 and beta2 integrins have found no qualitative differences between normal and CML hematopoietic cells in vitro. Even long-term-cultured CML bone marrow or blood cells continuously express those adhesion molecules that are characteristic of the cytological type. Recent experiments indicate that certain early CML progenitors may adhere to the stromal layer in vitro similarly to their normal counterparts. They cannot be completely removed by long-term culture on allogeneic stromal cells. At present, the only curative therapy is transplantation of allogeneic hematopoietic stem cells. Based on the molecular and cellular state of knowledge of CML, new therapies are being developed. BCR/ABL antisense oligonucleotides, inhibitors of tyrosine kinase, peptide-specific adoptive immunotherapy or peptide vaccination, and restoration of hematopoiesis by autologous stem cell transplantation following CML cell purging are examples of important approaches to improving CML treatment.     

Acute transformation of chronic myelomonocytic leukemia with t(1;3) (p36;q21) abnormality

A 66-year-old man was given a peripheral blood test because of low grade fever. Leukocytosis was detected, and the blood and bone marrow findings were consistent with those of chronic myelomonocytic leukemia. Three months later the hematological findings were: WBC 58,800/microliter (19% blastoid cells, 22% monocytes), Hb 9.0 g/dl, and a platelet count of 116 x 10(4)/microliters. A bone marrow examination revealed the presence of 52.6% blastoid cells and dysmegakaryocytopoiesis, including micromegakaryocytes. Serum and urinary lysozyme levels were elevated. Karyotypic analysis detected t(1; 3) (p36;q21), but not major bcr/abl mRNA. The patient was given a diagnosis of acute transformation of chronic myelomonocytic leukemia. Despite treatment, he died about 3 months later. t(1;3) is occasionally observed in cases of myelodysplastic syndrome (MDS) and leukemia. Patients with t(1;3) often exhibit dysmegakaryocytopoiesis; furthermore, acute leukemia develops more readily in those who also have MDS. Cases of long-term survival are rare.     

Cytotoxic T cells overcome BCR-ABL-mediated resistance to apoptosis

Chronic myeloid leukemia is a disease marked by expanded clonal hematopoiesis; it is incurable by chemotherapy or radiation but is cured in a majority of patients receiving bone marrow transplantation from nonidentical sibling donors, an outcome generally attributed to a T cell-mediated graft-versus-leukemia effect. In this report, we examine the effect of the P210BCR-ABL fusion protein of the BCR-ABL oncogene, the molecular hallmark of chronic myelogenous leukemia, on the sensitivity of mouse cell lines to apoptosis induced by chemotherapy, radiation, or activated cytotoxic T lymphocytes (CTLs). We find that, although cells expressing P210BCR-ABL by gene transfer are more resistant than their normal counterparts to apoptosis induced by chemotherapy or radiation, they are equally susceptible to apoptosis induced by alloreactive CTLs. These results show that CTLs overcome BCR-ABL-mediated resistance to apoptosis and, therefore, provide a biological correlation for the success of allogeneic bone marrow transplantation in chronic myelogenous leukemia.     

Development of an outcomes management program at an academic medical center

Donor CD4+ and CD8+ T cells mediate graft-vs.-leukemia (GVL) responses in the allogeneic bone marrow transplantation (alloBMT) setting. To evaluate the role of functional T cell subsets in the mediation of GVL, alloreactive donor CD4+ (Th1/Th2) and CD8+ (Tc1/Tc2) T cells of defined cytokine phenotype were generated by in vitro culture. A leukemia/transplantation model (B6 into B6C3F1; 1050 cGy host irradiation) was established using the bcr/abl-transfected myeloid leukemia line, 32Dp210 (P210; H-2k). Leukemia control mice (1X10(4) P210 cells per recipient) died at day 12.0 post-BMT. Recipients of the CD4+, Th1-type or CD8+, Tc1-type populations were conferred a survival advantage (death at 20.7 and 23.5 days post-BMT, respectively). In contrast, the CD4+, Th2-type population did not mediate GVL (death at 12.3 days). Furthermore, cell mixing experiments demonstrated that the Th2 subset abrogated both Th1- and Tc1-mediated GVL. The CD8+, Tc2 population, which secreted type II cytokines and lysed the P210 leukemia target in vitro, mediated GVL in some experiments; interestingly, the magnitude of Tc2-mediated GVL was inversely related to the level of interleukin-10 (IL-10) secreted in vitro by the Tc2 population. These studies therefore indicate that alloreactive T cells of type I phenotype maximally generate GVL, and that type I/type II interactions are an important consideration for allogeneic transplantation in the setting of leukemic hosts.     

Genetic marking shows that Ph+ cells present in autologous transplants of chronic myelogenous leukemia (CML) contribute to relapse after autologous bone marrow in CML

Relapse after autologous bone marrow transplantation for chronic myelogenous leukemia (CML) can be due either to the persistence of leukemia cells in systemic tissues following preparative therapy, or due to the persistence of leukemia cells in the autologous marrow used to restore marrow function after intensive therapy. To help distinguish between these two possible causes of relapse, we used safety-modified retroviruses, which contain the bacterial resistance gene NEO, to mark autologous marrow cells that had been collected from patients early in the phase of hematopoietic recovery after in vivo chemotherapy. The cells were then subjected to ex vivo CD34 selection following collection and 30% of the bone marrow were exposed to a safety-modified virus. This marrow was infused after delivery of systemic therapy, which consisted of total body irradiation (1,020 cGy), cyclophosphamide (120 mg/kg), and VP-16 (750 mg/m2). RT PCR assays specific for the bacterial NEO mRNA, which was coded for by the virus, and the bcr-abl mRNA showed that in two evaluable CML patients transplanted with marked cells, sufficient numbers of leukemia cells remained in the infused marrow to contribute to systemic relapse. In addition, both normal and leukemic cells positive for the retroviral transgenome persisted in the systemic circulation of the patients for at least 280 days posttransplant showing that the infused marrow was responsible for the return of hematopoiesis following the preparative therapy. This observation shows that it is possible to use a replication-incompetent safety-modified retrovirus in order to introduce DNA sequences into the hematopoietic cells of patients undergoing autologous bone marrow transplantation. Moreover, this data suggested that additional fractionation procedures will be necessary to reduce the probability of relapse after bone marrow transplantation in at least the advanced stages of the disease in CML patients undergoing autologous bone marrow transplantation procedures.     

Blastic transformation of p53-deficient bone marrow cells by p210bcr/abl tyrosine kinase

Blastic transformation of chronic myelogenous leukemia (CML) is characterized by the presence of nonrandom, secondary genetic abnormalities in the majority of Philadelphia1 clones, and loss of p53 tumor suppressor gene function is a consistent finding in 25-30% of CML blast crisis patients. To test whether the functional loss of p53 plays a direct role in the transition of chronic phase to blast crisis, bone marrow cells from p53+/+ or p53-/- mice were infected with a retrovirus carrying either the wild-type BCR/ABL or the inactive kinase-deficient mutant, and were assessed for colony-forming ability. Infection of p53-/- marrow cells with wild-type BCR/ABL, but not with the kinase-deficient mutant, enhanced formation of hematopoietic colonies and induced growth factor independence at high frequency, as compared with p53+/+ marrow cells. These effects were suppressed when p53-/- marrow cells were coinfected with BCR/ ABL and wild-type p53. p53-deficient BCR/ABL-infected marrow cells had a proliferative advantage, as reflected by an increase in the fraction of S+G2 phase cells and a decrease in the number of apoptotic cells. Immunophenotyping and morphological analysis revealed that BCR/ABL-positive p53-/- cells were much less differentiated than their BCR/ABL-positive p53+/+ counterparts. Injection of immunodeficient mice with BCR/ABL-positive p53-/- cells produced a transplantable, highly aggressive, poorly differentiated acute myelogenous leukemia. In marked contrast, the disease process in mice injected with BCR/ABL-positive p53+/+ marrow cells was characterized by cell infiltrates with a more differentiated phenotype and was significantly retarded, as indicated by a much longer survival of leukemic mice. Together, these findings directly demonstrate that loss of p53 function plays an important role in blast transformation in CML.     

Purification and characterization of a male-specific protein in the hemolymph of the wax moth, Galleria mellonella L

The aim of the current study was to determine whether immunization with synthetic peptides corresponding to the joining region segment of p210 bcr-abl chimeric protein can elicit CD8+ cytotoxic T lymphocytes (CTLs) capable of specifically lysing leukemia cells. BALB/c mice were immunized with peptides identical to the joining region segment of p210 bcr-abl protein. Class I major histocompatibility complex (MHC)-restricted bcr-abl peptide-specific CD8+ CTLs were elicited. The CTL clones were H-2 Kd restricted and specifically recognized a nonamer peptide of the combined sequence of bcr-abl amino acids but neither bcr nor abl amino acid sequence alone. Despite specificity and substantial lytic potential against syngeneic cell line incubated with exogenously supplied peptides, the bcr-abl peptide-specific CTLs failed to lyse syngeneic murine leukemia cells expressing human p210 bcr-abl protein containing the same bcr-abl joining region peptide sequence. Similarly, the bcr-abl peptide-specific CTLs did not lyse human bcr-abl-positive chronic myelogenous leukemia cells expressing murine class I MHC antigen (i.e., K562 cells infected with vaccinia virus expressing H-2 Kd). The appropriateness of the joining region segment of bcr-abl protein to serve as a T cell target depends upon whether that segment is presented by class I MHC in a concentration high enough to stimulate CTLs. The current experiments using murine peptide-specific CTLs could not establish that the joining region of bcr-abl protein is processed and presented by class I MHC antigen-processing pathway, but the possibility was not ruled out. Alternative models and/or strategies are necessary.