Polyclonal haemopoieses associated with long-term persistence of the AML1-ETO transcript in patients with FAB M2 acute myeloid leukaemia in continous clinical remission

Silencing AML1-ETO gene expression leads to simultaneous activation of both pro-apoptotic and proliferation signaling

The t(8;21)(q22;q22) rearrangement represents the most common chromosomal translocation in acute myeloid leukemia (AML). It results in a transcript encoding for the fusion protein AML1-ETO (AE) with transcription factor activity. AE is considered to be an attractive target for treating t(8;21) leukemia. However, AE expression alone is insufficient to cause transformation, and thus the potential of such therapy remains unclear. Several genes are deregulated in AML cells, including KIT that encodes a tyrosine kinase receptor. Here, we show that AML cells transduced with short hairpin RNA vector targeting AE mRNAs have a dramatic decrease in growth rate that is caused by induction of apoptosis and deregulation of the cell cycle. A reduction in KIT mRNA levels was also observed in AE-silenced cells, but silencing KIT expression reduced cell growth but did not induce apoptosis. Transcription profiling of cells that escape cell death revealed activation of a number of signaling pathways involved in cell survival and proliferation. In particular, we find that the extracellular signal-regulated kinase 2 (ERK2; also known as mitogen-activated protein kinase 1 (MAPK1)) protein could mediate activation of 23 out of 29 (79%) of these upregulated pathways and thus may be regarded as the key player in establishing the t(8;21)-positive leukemic cells resistant to AE suppression.

Measurements of treatment response in childhood acute leukemia

Measuring response to chemotherapy is a backbone of the clinical management of patients with acute leukemia. This task has historically relied on the ability to identify leukemic cells among normal bone marrow cells by their morphology. However, more accurate ways to identify leukemic cells have been developed, which allow their detection even when they are present in small numbers that would be impossible to be recognized by microscopic inspection. The levels of such minimal residual disease (MRD) are now widely used as parameters for risk assignment in acute lymphoblastic leukemia (ALL) and increasingly so in acute myeloid leukemia (AML). However, different MRD monitoring methods may produce discrepant results. Moreover, results of morphologic examination may be in stark contradiction to MRD measurements, thus creating confusion and complicating treatment decisions. This review focusses on the relation between results of different approaches to measure response to treatment and define relapse in childhood acute leukemia.

Forced expression of AML1–AMP19, a fusion transcript generated from a radiation-associated t(19;21) leukemia, blocks myeloid differentiation

We isolated and characterized a novel AML1 (also termed Runx1) fusion transcript from a radiation-associated acute myeloid leukemia with a t(19;21). This fusion transcript, termed AML1-AMPl9, was joined out of frame, resulting in a truncated AML1 protein that inhibits activation of AML1 target promoters. It is now becoming clear that truncations of AMLl are more common in leukemia than previously thought. To analyze the effect of truncated AML1 species on myeloid differentiation and proliferation, AML1-AMPl9 was retrovirally transduced into the IL-3-dependent 32D cells. 32D cells over-expressing AML1-AMPl9 failed to differentiate normally when stimulated with G-CSF, but continued to proliferate and maintained a primitive phenotype. However, AML1-AMPl9 did not transform the cells to cytokine independence, implying that for full transformation of a myeloid progenitor by truncated AML1 another genetic lesion is required.

Role of RUNX in autoimmune diseases linking rheumatoid arthritis, psoriasis and lupus

Recent studies investigating the genetic susceptibility of systemic lupus erythematosus, rheumatoid arthritis and psoriasis have revealed a potential role for the RUNX proteins in the development of autoimmune disease. A new pathway of disease pathogenesis opens new avenues of research with thousands of questions that remain to be answered. In this review I attempt to propose how the RUNX proteins might be involved in these diseases and review current knowledge on this very interesting trio of transcription factors that was previously only suspected to be involved in cancer.

Effects of the leukemia-associated AML1-ETO protein on hematopoietic stem and progenitor cells

Insights into the pathogenesis of human leukemia have relied heavily on studies of the identified chromosomal translocations found in this group of malignant diseases. Acquired, balanced translocations in acute myelogenous leukemia (AML) generally involve transcriptional regulatory genes, whereas in the myeloproliferative disorders tyrosine kinases are frequently involved. These rearrangements alter the function of at least one and often both of the involved genes. In this review, we focus on the AML1-ETO (a.k.a. RUNX1-ETO) fusion protein, which is found in t(8;21)+ AML. Expression of AML1-ETO in human hematopoietic stem cells (HSCs) preferentially enhances their maintenance, as opposed to their differentiation. The direct effects of AML1-ETO on human and murine HSCs, and the potentially cooperating events that may contribute to its leukemogenic properties, are discussed.

Monitoring of acute myeloid leukemia by flow cytometry

Monitoring of minimal residual disease (MRD) becomes increasingly important in the risk-adapted management of patients with acute myeloid leukemia (AML). In selected patients with AML, multiparameter flow cytometry has shown accuracy and sensitivity in the quantification of MRD levels with independent prognostic impact. The applicability of this approach is superior to that of other methods such as quantitative polymerase chain reaction: Up to 80% of all patients can be monitored by flow cytometry. Nonetheless, significant technical advances are anticipated to extend the applicability of flow cytometry to 100% and to improve its sensitivity. Large clinical trials will determine the role of immunologic monitoring in the prognostic stratification of patients with AML.

Assessment of minimal residual disease (MRD) in CBFbeta/MYH11-positive acute myeloid leukemias by qualitative and quantitative RT-PCR amplification of fusion transcripts

The inv(16)(p13q22) chromosomal rearrangement associated with FAB M4Eo acute myeloid leukemia (AML) subtype is characterized by the presence of the CBFbeta/MYH11 fusion transcript that can be used to detect minimal residual disease (MRD). However, qualitative RT-PCR studies of MRD have so far produced conflicting results and seem of limited prognostic value. We have evaluated retrospectively MRD in a large series of CBFbeta/MYH11-positive patients employing both qualitative and quantitative (real-time PCR) approaches. 186 bone marrow samples from 36 patients were examined with a median follow-up of 27.5 months; 15 patients relapsed during follow-up. In qualitative studies, carried out by 'nested' RT-PCR assay, all patients in complete remission (CR) immediately after induction/consolidation therapy were found to be PCR positive. However, follow-up samples at later time points were persistently negative (except one case) in patients remaining in continuous CR (CCR) for more than 12 months. 16 patients were evaluated by quantitative real-time PCR assay: CBFbeta/MYH11 transcript copy number was normalized for expression of the housekeeping gene ABL, expressed as fusion gene copy number per 10(4) copies of ABL. A 2-3 log decline in leukemic transcript copy number was observed after induction/consolidation therapy. After achieving CR, the mean copy number was significantly higher in patients destined to relapse compared to patients remaining in CCR (151 vs 9, P < 0.0001 by Mann-Whitney test). Moreover, in CCR patients, the copy number dropped below the detection threshold after the treatment protocol was completed and remained undetectable in subsequent MRD analysis in accordance with results obtained by qualitative RT-PCR. On the contrary, in the seven patients who relapsed, the copy number in CR never declined below the detection threshold; thus a cut-off value discriminating these two groups of patients could be established. The findings of our study, if confirmed, might confer an important predictive value to quantitative real-time PCR determinations of MRD in patients with inv(16) leukemia.

Is AML1/ETO gene expression a good prognostic factor in pediatric acute myeloblastic leukemia?

To assess the clinical significance of AML1/ETO gene detected by nested reverse transcriptase polymerase chain reaction, the outcome of 7 patients with acute myeloblastic leukemia between 3 and 14 years of age were presented. All patients had complete remission (CR) at the end of induction (AML-MRC 10 protocol) and 4 underwent unpurged autologous, 2 allogeneic (from matched siblings) non-T-cell-depleted bone marrow transplantations (BMT) in first CR. One patient died due to allogeneic BMT-related complications, and 4 patients relapsed at 13, 17, 18, and 26 months. Only one patient achieved second CR. All relapsed patients died between 18 and 36 months with resistant disease (n = 3) or infection during salvage chemotherapy (n = 1). Two patients who had autologous BMT are alive and disease free at 44 and 50 months. Although statistical significance could not be shown, event-free survival and overall survival rates of AML1/ETO-positive patients (28.57 and 28.57%, respectively) at 3.5 years were even lower than those of AML1/ETO-negative patients. The results confirm some previous reports that AML1/ETO gene in children and adolescents is not a favorable prognostic factor.

AML1/ETO-expressing nonleukemic stem cells in acute myelogenous leukemia with 8;21 chromosomal translocation

Leukemia-specific AML1/ETO transcripts are detectable in most patients with t(8;21) acute myelogenous leukemia (AML) in long-term remission. To understand the inconsistency between the clinical cure and the presence of "residual disease" at a molecular level, we separated and identified the cells expressing AML1/ETO by phenotype and function. Here we demonstrate that AML1/ETO transcripts are present in a fraction of stem cells, monocytes, and B cells in remission marrow, and in a fraction of B cells in leukemic marrow, but not in T cells. AML1/ETO transcripts also were demonstrated in a fraction of colony-forming cells of erythroid, granulocyte-macrophage, and/or megakaryocyte lineages in both leukemic and remission marrow. These data strongly suggest that the acquisition of the t(8;21) occurs at the level of stem cells capable of differentiating into B cells as well as all myeloid lineages, and that a fraction of the AML1/ETO-expressing stem cells undergo additional oncogenic event(s) that ultimately leads to transformation into AML.

Molecular monitoring of minimal residual disease in acute myeloblastic leukemia with t(8;21) by RT-PCR

The t(8;21) is one of the most common translocations in acute myeloid leukaemia (AML) occurring in approximately 20% of adult and 40% of paediatric AML-M2. This translocation fuses the AML1 gene on chromosome 21q to the MTG8 (ETO) gene on chromosome 8q to produce the fusion gene AML1-MTG8. Transcripts for the AML1-MTG8 fusion gene have been detected in the majority of patients in remission by qualitative RT-PCR methods. Thus for such patients these methods are unsuitable for monitoring minimal residual disease (MRD). Furthermore, the diverse form of transcripts for this fusion gene was found in patients at different phases of their disease, which rules out the usefulness of the expression of any particular set of transcripts as a marker for monitoring MRD in those patients. On the other hand a quantitative RT-PCR method we developed, was able to assess the effectiveness of treatment and predict relapse up to four months before the onset of haematological relapse. This method should distinguish patients in stable remission from those at high risk of relapse and therefore identify patients who would require additional or new treatment such as BMT.

Minimal residual disease in acute myelogenous leukemia with PML/RAR alpha or AML1/ETO mRNA and phenotypic analysis of possible T and natural killer cells in bone marrow

Here we studied minimal residual disease (MRD) of patients with acute myeloid leukemia (AML) who have PML/RAR alpha or AML1/ETO as well as the phenotypic analysis of lymphocyte subsets involved in antitumor immunity. Eight patients in long-term (LT; 3 to 15 years) and 15 patients in short-term (ST; up to 3 years) remission were studied. Using the reverse transcription-polymerase chain reaction (RT) assay, the limit of detection was 10(-5) to 10(-6) for PML/RAR alpha transcript and 10(-4) to 10(-5) for the AML1/ETO transcript. Simultaneously, T lymphocyte subsets and NK cells from the peripheral blood (PB) and bone marrow (BM) were investigated by flow cytometric analysis. Four of the eight patients in LT and 7 of the 15 patients in ST remission were MRD-positive. Although all MRD-positive patients in LT remission are still until now event-free, 3 of the 7 MRD-positive (MRD+) patients in ST remission soon relapsed. The total populations of CD4+, CD8+ and CD56+ [possible T-cell and natural killer (T/NK) populations] in the BM of ST patients and MRD+/LT patients were significantly (p < .01) low. The CD8+ CD28+ population showed the same tendency (p < .01-.02). The T/NK subsets in the BM of MRD-negative (MRD-) LT (MRD-/LT) patients showed similar numbers of cells as normal volunteers. Basically, the total percentage of the CD4+, CD8+ and CD56+ cell populations in the BM was increased and in the following order: MRD-/LT patients, normal volunteers, MRD+/LT patients and MRD+ or -/ST patients. The percentages of the T/NK-cell subsets in the PB were not significantly different among these groups. Thus, the difference of the possible T/NK-cell phenotype in the BM may strongly influence clinical and molecular remission. These results still remain to be confirmed by further studies of the functional anti-tumor immunity of T/NK cells of AML in remission.

Detection of a t(8;21)(q22;q22) in a case of M5 acute monoblastic leukemia

Although the translocation (8;21) is the single most common structural rearrangement reported in acute myeloblastic leukemia (AML), it is rarely seen in AML FAB type M5. We describe a case of a 51-year-old male with a diagnosis of acute monoblastic leukemia (AML M5b with hemophagocytic component) whose karyotype showed at (8;21)(q22;22). To our knowledge, this is the first report of this translocation in an AML M5b. The t(8;21) has been associated with a good prognosis, but our patient suffered a fast and fatal evolution.

Diagnosis and treatment of childhood acute myelogenous leukemia

Acute myelogenous leukemia (AML) accounts for about 20% of the acute leukemias seen in children. In contrast to childhood acute lymphoblastic leukemia (ALL), there has only been a modest improvement in the cure rate of children with AML during the past two decades. Approximately 40% of children treated with chemotherapy alone are long-term survivors. The outcome is somewhat better for those children who are given bone marrow transplants from histocompatible sibling donors early in the first remission. During the last decade, however, new insights into the molecular basis of AML has increased our understanding of the pathogenesis and biology of this group of leukemias and are beginning to provide us with new therapeutic strategies.

Significance of quantitative analysis of AML1/ETO transcripts in peripheral blood stem cells from t(8;21) acute myelogenous leukemia

Autologous peripheral blood stem cell transplantation (PBSCT) is replacing autologous bone marrow transplantation (BMT) in the treatment of leukemia. One of the potential advantages of autologous PBSCT is the possibility that peripheral blood stem cells (PBSC) are less likely to be contaminated by leukemic cells than bone marrow grafts. However, the major problem still remains the high incidence of leukemic relapse following autologous PBSCT, which may be caused by the reinfusion of PBSC contaminated by leukemic cells. Recently, we have developed a quantitative assay using competitive reverse transcriptase polymerase chain reaction that estimates the number of AML1/ETO transcripts in t(8;21) acute myelogenous leukemia (AML), in order to determine the degree of leukemic cell contamination in PBSC harvests, and to monitor minimal residual disease (MRD) quantitatively in patients with t(8;21) AML. Our data indicate that although PBSC harvests collected after consolidation chemotherapy are contaminated by leukemic cells, the degree of leukemic cell contamination decreases with repeated cycles of chemotherapy. Furthermore, the MRD in PBSC harvests is less than in the corresponding bone marrow obtained on the day of the PBSC collection. There appears to be no relationship between the number of AML1/ETO transcripts found in the infused PBSC harvests and the incidence of leukemic relapse following autologous PBSCT in our study. However, a substantial decrease of AML1/ETO transcripts was seen following autologous PBSCT. Thus, the quantitative analysis of AML1/ETO transcripts may be clinically useful in patients with t(8;21) AML.