Biological features of leukaemic cells associated with autonomous growth and reduced survival in acute myeloblastic leukaemia

Biomarkers of Response to Venetoclax Therapy in Acute Myeloid Leukemia

Recent progress in the use of massive sequencing technologies has greatly enhanced our understanding of acute myeloid leukemia (AML) pathology. This knowledge has in turn driven the development of targeted therapies, such as venetoclax, a BCL-2 inhibitor approved for use in combination with azacitidine, decitabine, or low-dose cytarabine for the treatment of newly diagnosed adult patients with AML who are not eligible for intensive chemotherapy. However, a significant number of AML patients still face the challenge of disease relapse. In this review, we will explore biomarkers that may predict disease progression in patients receiving venetoclax-based therapy, considering both clinical factors and genetic changes. Despite the many advances, we conclude that the identification of molecular profiles for AML patients who will respond optimally to venetoclax therapy remains an unmet clinical need.

The cytokine network in acute myeloid leukemia

Acute myeloid leukemia (AML) is a highly heterogeneous malignancy of the blood and bone marrow, characterized by clonal expansion of myeloid stem and progenitor cells and rapid disease progression. Chemotherapy has been the first-line treatment for AML for more than 30 years. Application of recent high-throughput next-generation sequencing technologies has revealed significant molecular heterogeneity to AML, which in turn has motivated efforts to develop new, targeted therapies. However, due to the high complexity of this disease, including multiple driver mutations and the coexistence of multiple competing tumorigenic clones, the successful incorporation of these new agents into clinical practice remains challenging. These continuing difficulties call for the identification of innovative therapeutic approaches that are effective for a larger cohort of AML patients. Recent studies suggest that chronic immune stimulation and aberrant cytokine signaling act as triggers for AML initiation and progression, facets of the disease which might be exploited as promising targets in AML treatment. However, despite the greater appreciation of cytokine profiles in AML, the exact functions of cytokines in AML pathogenesis are not fully understood. Therefore, unravelling the molecular basis of the complex cytokine networks in AML is a prerequisite to develop new therapeutic alternatives based on targeting cytokines and their receptors.

Targeting Apoptotic Pathways in Acute Myeloid Leukaemia

Acute Myeloid Leukaemia is a devastating disease that continues to have a poor outcome for the majority of patients. In recent years, however, a number of drugs have received FDA approval, following on from successful clinical trial results. This parallels the characterization of the molecular landscape of Acute Myeloid Leukaemia (AML) over the last decade, which has led to the development of drugs targeting newly identified recurring mutations. In addition, basic biological research into the pathobiology of AML has identified aberrant programmed cell death pathways in AML. Following on from successful outcomes in lymphoid malignancies, drugs targeting the B Cell Lymphoma 2 (BCL-2) family of anti-apoptotic proteins have been explored in AML. In this review, we will outline the preclinical and clinical work to date supporting the role of drugs targeting BCL-2, with Venetoclax being the most advanced to date. We will also highlight rationale combinations using Venetoclax, ongoing clinical trials and biomarkers of response identified from the early phase clinical trials performed.

Leukemia Associated Antigens: Their Dual Role as Biomarkers and Immunotherapeutic Targets for Acute Myeloid Leukemia

Leukemia associated antigens (LAAs) are being increasingly identified by methods such as cytotoxic T-lymphocyte (CTL) cloning, serological analysis of recombinant cDNA expression libraries (SEREX) and mass spectrometry (MS). In additional, large scale screening techniques such as microarray, single nucleotide polymorphisms (SNPs), serial analysis of gene expression (SAGE) and 2-dimensional gel electrophoresis (2-DE) have expanded our understanding of the role that tumor antigens play in the biological processes which are perturbed in acute myeloid leukemia (AML). It has become increasingly apparent that these antigens play a dual role, not only as targets for immunotherapy, but also as biomarkers of disease state, stage, response to treatment and survival. We need biomarkers to enable the identification of the patients who are most likely to benefit from specific treatments (conventional and/or novel) and to help clinicians and scientists improve clinical end points and treatment design. Here we describe the LAAs identified in AML, to date, which have already been shown to play a dual role as biomarkers of AML disease.

Autocrine GM-CSF transcription in the leukemic progenitor cell line KG1a is mediated by the transcription factor ETS1 and is negatively regulated through SECTM1 mediated ligation of CD7

BACKGROUND

CD7 expression is found on ~30% of acute myeloblastic leukemias (AML). The leukemic progenitor cell line KG1a (CD7+) constitutively expresses GM-CSF while the parental KG1 (CD7-) cell line does not. This study focuses on the molecular basis of CD7 mediated GM-CSF regulation.

METHODS

KG1a cells were treated with recombinant SECTM1-Fc protein, the PI3K kinase inhibitors wortmannin, LY292004, or PI4K activator spermine. Stable KG1-CD7+, KG1a-shCD7, KG1a-shETS1 as well as KG1a-GFP, KG1a-PKCβII-GFP cell lines were generated and the levels of CD7, GM-CSF and ETS-1 mRNA and protein were compared by real-time-PCR, western blotting, flow cytometry and ELISA.

RESULTS

SECTM1 is expressed in Human Bone Marrow Endothelial Cells (HBMEC) and its expression can be upregulated by both IFN-γ. KG1a cells demonstrated high expression levels of CD7 and ETS-1 allowing a constitutative signaling through the PI3K/Atk pathway to promote GM-CSF expression, while KG1 cells with low expression of CD7 and ETS-1 showed low GM-CSF expression. On KG1a cells GM-CSF expression could be negatively regulated by PI3K inhibitors or by recombinant SECTM1-Fc. Overexpression of CD7 in KG1 cells was insufficient to promote GM-CSF expression, while silencing of CD7 or ETS-1 resulted in reduced GM-CSF expression levels. Differentiation capable KG1a cells overexpressing PKCβII illustrated complete loss of CD7, but maintained normal levels of both ETS-1 and GM-CSF expression.

CONCLUSION

These findings add an additional layer to the previously described autocrine/paracrine signaling between leukemic progenitor cells and the bone marrow microenvironment and highlight a role for SECTM1 in both normal and malignant hematopoiesis.

GENERAL SIGNIFICANCE

This work shows that SECTM1 secreted from bone marrow stromal cells may interact with CD7 to influence GM-CSF expression in leukemic cells.

Bone marrow progenitor cells from chemically exposed workers display an intrinsic ability for autonomous proliferation

In this study, the autonomous proliferation of bone marrow progenitor cells (CFU-C), a pathological phenomenon observed in many hematological abnormalities, was investigated in 31 individuals who had been diagnosed as having neutropenia. Of these subjects, 18 had been chronically exposed (range of exposure 5-30 years) to a variety of petroleum distillates. We observed that the group of exposed individuals presented higher numbers of autonomous CFU-C when compared with those unexposed subjects. In addition, follow-up data demonstrated that 20% of the exposed population (4 of the 18) developed malignant hematological diseases. The autonomous CFU-C obtained from all individuals studied was composed predominantly of macrophages. This suggests an involvement of these cells in the development of hematological abnormalities, probably as a result of increased production of chemical myelotoxic metabolites.

Detection, isolation, and stimulation of quiescent primitive leukemic progenitor cells from patients with acute myeloid leukemia (AML)

Although many acute myeloid leukemia (AML) colony-forming cells (CFCs) and long-term culture-initiating cells (LTC-ICs) directly isolated from patients are actively cycling, quiescent progenitors are present in most samples. In the current study, (3)H-thymidine ((3)H-Tdr) suicide assays demonstrated that most NOD/SCID mouse leukemia-initiating cells (NOD/SL-ICs) are quiescent in 6 of 7 AML samples. AML cells in G(0), G(1), and S/G(2)+M were isolated from 4 of these samples using Hoechst 33342/pyroninY staining and cell sorting. The progenitor content of each subpopulation was consistent with the (3)H-Tdr suicide results, with NOD/SL-ICs found almost exclusively among G(0) cells while the cycling status of AML CFCs and LTC-ICs was more heterogeneous. Interestingly, after 72 hours in serum-free culture with or without Steel factor (SF), Flt-3 ligand (FL), and interleukin-3 (IL-3), most G(0) AML cells entered active cell cycle (percentage of AML cells remaining in G(0) at 72 hours, 1.2% to 37%, and 0% to 7.6% in cultures without and with growth factors [GFs], respectively) while G(0) cells from normal lineage-depleted bone marrow remained quiescent in the absence of GF. All 4 AML samples showed evidence of autocrine production of 2 or more of SF, FL, IL-3, and granulocyte-macrophage colony-stimulating factor (GM-CSF). In addition, 3 of 4 samples contained an internal tandem duplication of the FLT3 gene. In summary, quiescent leukemic cells, including NOD/SL-ICs, are present in most AML patients. Their spontaneous entry into active cell cycle in short-term culture might be explained by the deregulated GF signaling present in many AMLs.

The coexpression of the apoptosis-related genes bcl-2 and wt1 in predicting survival in adult acute myeloid leukemia

The Wilms tumor gene wt1 and the protooncogene bcl-2 are upregulated in acute myeloid leukemia (AML) and are known to regulate or to inhibit the onset of apoptosis. Since wt1 has been shown to regulate the expression of bcl-2, we investigated the association of the expression of these genes and their prognostic relevance in AML. Leukemic blasts from the bone marrow of 152 patients with newly diagnosed AML were analyzed for bcl-2 and wt1 mRNA expression using RT-PCR and quantitative PCR. Therapy outcome was correlated with the level of bcl-2 and wt1 transcripts. Bcl-2-specific mRNA was detectable in 127/152 (84%) patients and wt1 mRNA in 113/152 (74%) patients with AML. In monocytic subtypes the frequency of bcl-2 and wt1 transcripts was significantly lower. The expression of bcl-2 mRNA was correlated significantly with that of wt1 mRNA (P < 0.0001). In AML patients <60 years, high expression of bcl-2 and wt1 was associated with a reduced rate of continuing complete remission (CCR, P = 0.002 and P = 0.005, respectively) and increased death rate (P = 0.0002 and P = 0.04, respectively) in contrast to patients >60 years, where the expression of bcl-2 or wt1 had no prognostic impact. Based on the coexpression of bcl-2 and wt1, we established a prognostic model defining three risk groups with significant differences in CCR rate (P = 0.01), overall survival (P < 0.04) and disease-free survival (P < 0.03). Thus, bcl-2 and wt1 mRNA expression are associated with response and long-term outcome in AMLs. The coexpression of these genes allows determination of prognostic groups with high predictive value for overall and disease-free survival.

Cytokine-regulated expression of survivin in myeloid leukemia

Survivin, a member of the inhibitors-of-apoptosis gene family, is expressed in a cell-cycle-dependent manner in all the most common cancers but not in normal differentiated adult tissues. Survivin expression and regulation were examined in acute myeloid leukemia (AML). Survivin was detected by Western blot analysis in all myeloid leukemia cell lines and in 16 of 18 primary AML samples tested. In contrast, normal CD34(+) cells and normal peripheral blood mononuclear cells expressed no or very low levels of survivin. Cytokine stimulation increased survivin expression in leukemic cell lines and in primary AML samples. In cultured primary samples, single-cytokine stimulation substantially increased survivin expression in comparison with control cells, and the combination of G-CSF, GM-CSF, and SCF increased survivin levels even further. Conversely, all-trans retinoic acid significantly decreased survivin protein levels in HL-60, OCI-AML3, and NB-4 cells within 96 hours, parallel to the induction of myelomonocytic differentiation. Using selective pharmacologic inhibitors, the differential involvement of mitogen-activated protein kinase kinase (MEK) and phosphatidylinositol-3 kinase (PI3K) pathways were demonstrated in the regulation of survivin expression. The MEK inhibitor PD98059 down-regulated survivin expression in both resting and GM-CSF-stimulated OCI-AML3 cells, whereas the PI3K inhibitor LY294002 inhibited survivin expression only on GM-CSF stimulation. In conclusion, these results demonstrate that survivin is highly expressed and cytokine-regulated in myeloid leukemias and suggest that hematopoietic cytokines exert their antiapoptotic and mitogenic effects, at least in part, by increasing survivin levels.

Normal and leukemic CD34-negative human hematopoietic stem cells

Considerable progress has been made in recent years in purifying human and murine hematopoietic stem cells. The essential marker identified is the sialomucin CD34, which is expressed on primitive cells and downregulated as they differentiate into more abundant mature cells. CD34 is not unique to stem cells, however, as it is also expressed on clonogenic progenitors and some endothelial cells. Nevertheless, all clinical and experimental protocols are targeted to CD34+ cells enriched by a variety of selection methods. Recent studies in both the murine and human systems have indicated that some stem cells capable of multilineage repopulation do not express detectable levels of cell surface CD34. These studies challenge the dogma that all human repopulating cells are found in the CD34+ subset. However, the precise relationship between CD34- and CD34+ stem cells is still not well understood. In this review, the results on the discovery of the CD34- repopulating cell are summarized and the impacts this discovery may have, both clinically and in our understanding of the organization of the human hematopoietic system, are examined.

Hydroxyurea promotes the reduction of spontaneous BFU-e to normal levels in SS and S/beta thalassemic patients

We have studied the effects of hydroxyurea on growth and differentiation of early erythroid progenitor cells (BFU-e) from peripheral blood of sickle cell disease patients (five SS and two Hb S/beta-thalassemia) in the presence or absence of exogenous stimulating factors. When the mononuclear cells from the sickle cell disease patients were cultured at diagnosis (before hydroxyurea treatment), there was an increased number of BFU-e in relation to controls (p < 0.05, Wilcoxon test) when cells were grown in the presence or absence of 5637 conditioned medium and erythropoietin. Colonies that developed in the absence of added growth factors were considered "spontaneous". A significant difference was observed after hydroxyurea treatment in the number of BFU-e obtained in the presence and absence of stimulus, with a higher reduction in the spontaneous BFU-e number. As expected, there was an increased Hb F level in these patients when compared with their pretreatment levels. There was no correlation between spontaneous BFU-e and hemoglobin levels in all patients studied.

Molecular signals in anti-apoptotic survival pathways

Drug resistance, to date, has primarily been attributed to increased drug export or detoxification mechanisms. Despite correlations between drug export and drug resistance, it is increasingly apparent that such mechanisms cannot fully account for chemoresistance in neoplasia. It is now widely accepted that chemotherapeutic drugs kill tumour cells by inducing apoptosis, a genetically regulated cell death programme. Evidence is emerging that the exploitation of survival pathways, which may have contributed to disease development in the first instance, may also be important in the development of the chemoresistance. This review discusses the components of and associations between multiple signalling cascades and their possible contribution to the development of neoplasia and the chemoresistant phenotype.

Proliferative status of primitive hematopoietic progenitors from patients with acute myelogenous leukemia (AML)

One possible explanation for the competitive advantage that malignant cells in patients with acute myelogenous leukemia (AML) appear to have over normal hematopoietic elements is that leukemic progenitors proliferate more rapidly than their normal progenitor cell counterparts. To test this hypothesis, an overnight 3H-thymidine (3H-Tdr) suicide assay was used to analyze the proliferative status of malignant progenitors detected in both colony-forming cell (CFC) and long-term culture initiating cell (LTC-IC) assays from the peripheral blood of nine patients with newly diagnosed AML. Culture of AML cells in serum-free medium with 100 ng/ml Steel factor (SF), 20 ng/ml interleukin 3 (IL-3) and 20 ng/ml granulocyte colony-stimulating factor (G-CSF) for 16-24 h maintained the number of AML-CFC and LTC-IC at near input values (mean % input +/- s.d. for CFC and LTC-IC were 78 +/- 33 and 126 +/- 53, respectively). The addition of 20 muCi/ml high specific activity 3H-Tdr to these cultures reduced the numbers of both progenitor cell types from most of the patient samples substantially: mean % kill +/- s.d. for AML-CFC and LTC-IC were 64 +/- 27 and 82 +/- 16, respectively, indicating that a large proportion of both progenitor populations were actively cycling. FISH analysis of colonies from CFC and LTC-IC assays confirmed that most cytogenetically abnormal CFC and LTC-IC were actively cycling (mean % kill +/- s.d.: 68 +/- 26 and 85 +/- 13, respectively). Interestingly, in six patient samples where a significant number of cytogenetically normal LTC-ICs were detected, the % kill of these cells (74 +/- 20) was similar to that of the abnormal progenitors. These data contrast with the predominantly quiescent cell cycle status of CFC and LTC-IC previously observed in steady-state peripheral blood from normal individuals but also provide evidence that a significant proportion of primitive malignant progenitors from AML patients are quiescent and therefore may be resistant to standard chemotherapeutic regimens.

CD30 ligand (CD30L)-expressing acute myeloid leukemias: a new model of paracrine interactions for the regulation of blast cells proliferation

CD30 ligand (CD30L) is a type-II membrane glycoprotein capable of transducing signals through its specific counterstructure CD30. Even though there are indications that CD30L plays a key role as a paracrine-acting surface molecule in the deregulated cytokine cascade of Hodgkin's disease, little is known about its biological functions in other human hemopoietic malignancies, despite the demonstration of the frequent expression of CD30L in hemopoietic neoplasms of both myeloid and lymphoid origin. The present review summarises structural and biological properties of CD30L, and focuses on CD30L+ acute myeloid leukemias (AMLs) by recapitulating some phenotypic and clinical features of this subset of acute leukemias. We also discuss some mechanisms by which CD30L-expressing leukemic blasts may gain a proliferative advantage through direct interaction with specific cells, in turn expressing its specific counterreceptor CD30. In particular, data has been provided suggesting that CD30L+ AMLs may evoke a sort of polarized T-cell response with the preferential production of Th2-like cytokines, mainly IL-4, by specific CD30-expressing T cell subsets. On the other hand, leukemic blasts presenting surface CD30L, have been shown to express a peculiar cytokine-receptors pattern that makes them an ideal target for T cells-produced Th2-like cytokines. Furthermore, some Th2-like cytokines, such as IL-4, are able to enhance blast cells proliferation, as well as to up-regulate the surface expression of specific adhesion molecules that have been shown to be associated with the presence of CD30L on AML blasts.

Cooperation of p38 and extracellular signal-regulated kinase mitogen-activated protein kinase pathways during granulocyte colony-stimulating factor-induced hemopoietic cell proliferation

Hemopoietic cytokines such as interleukin-3 and granulocyte colony-stimulating factor (G-CSF) are potent activators of hemopoietic cell growth and strongly induce activation of extracellular signal-regulated kinase (ERK), c-Jun-N-terminal kinase (JNK), and p38 mitogen-activated protein (MAP) kinases. However, the role of these kinases is unclear. Using specific chemical inhibitors for MEK and p38, we demonstrate here that both ERK and p38 pathways are critically involved in the transduction of a proliferative signal and cooperate in G-CSF-induced cell proliferation. We show that, like ERK and JNK activation, activation of p38 and its downstream substrate MAP kinase-activated protein kinase 2 by interleukin-3 or G-CSF requires Ras activation. We demonstrate that two distinct cytoplasmic regions of the G-CSF receptor are involved in activation of the p38 pathway: a region within the 100 membrane-proximal amino acids is sufficient to induce low levels of p38 and MAP kinase-activated protein kinase 2 activation, whereas the membrane-distal phosphorylation site Tyr763 mediates strong activation of these kinases. The levels of p38 activation correlate closely with those of Ras activation by G-CSF, suggesting that the degree of Ras activation is a critical determinant for the extent of p38 activation by hemopoietic cytokines.

Hematopoietic growth factors and acute leukemia

Over the past decade, with the advent of hematopoietic growth factors, major strides have been made and multiple studies have attempted to define the use of these cytokines in acute leukemia. It is perhaps disappointing that, after so many studies, so many questions remain. Nevertheless, the role of cytokines in induction therapy seems to be established, although questions remain around the issue of priming therapy. Intriguing data regarding the potential for enhancing antimicrobial function should hopefully be resolved over the next few years. What is perhaps most reassuring is that the issue of safety, which for a considerable period of time precluded the development of clinical trials in acute leukemia, has been firmly laid to rest. The use of growth factors to protect normal stem cells during treatment of leukemia and to induce leukemic cell differentiation has not yet been the subject of many clinical trials. Also, growth factors are likely targets for the interruption of autocrine leukemic blast or progenitor cell growth, but again, few clinical observations are published. With the ongoing cloning of new growth factors active both in normal hematopoiesis and in leukemogenesis, the role of growth factor use in the treatment of AML will likely be the basis for much future preclinical and clinical activity.

Haematopoietic response and bcl-2 expression in patients with acute myeloid leukaemia

Bcl-2 expression, the number of apoptotic cells and the growth and differentiation of early bone marrow progenitor cells were studied in patients with confirmed diagnosis of acute myeloid leukaemia (AML). Bone marrow cells from normal individuals were used as controls. We observed an increased percentage of bcl-2-mononuclear bone marrow cells expression in AML patients in relation to controls (p =0.002). Accordingly, the number of apoptotic cells was reduced (p = 0.001) and there was a negative correlation between bcl-2 expression and the number of apoptotic cells (r=-0.664, p<0.001). In addition, bcl-2 expression was significantly increased in the chemotherapy resistant group in relation to the responsive group (p = 0.03). Lower rate of survival was observed in the group of AML patients with autonomous proliferation (p=0.01). These results suggest that a high bcl-2 expression and the presence of autonomous proliferation are related to a poor prognosis in AML.

Intraclonal heterogeneity in the in vitro daunorubicin-induced apoptosis in acute myeloid leukemia

Leukemic cells from ten patients with acute myeloid leukemia (AML) were sorted on the basis of in vitro daunorubicin (DNR) uptake. The obtained subpopulations with high and low DNR accumulation were compared with regard to induction of apoptosis, expression of bcl-2 and p53. Heterogeneous induction of apoptosis, confined to subpopulations with high DNR uptake, was observed. The size of the DNR-induced apoptotic fraction (4% to 16%) within a given AML blast population was determined by intracellular drug accumulation and was not related to the level of bcl-2 expression. All tested leukemic samples displayed expression of p53 in a growth promoter orientation, i.e. PAb1620-/PAb240+. In two samples, however, subpopulations expressing a growth suppressor orientation of p53, i.e. PAb 1620+/PAb240-, were also present. These subpopulations were confined to high-DNR-uptake fractions and associated with the induction of apoptosis. We conclude that intraclonal heterogeneity in the intracellular drug accumulation and subsequently in DNR-induced apoptosis might allow the selection of inherently drug-resistant AML clones thus contributing to relapse of leukemia.

Autonomous proliferation and bcl-2 expression involving haematopoietic cells in patients with myelodysplastic syndrome

In this work, we investigated the autonomous proliferation, bcl-2 expression and number of apoptotic cells in the bone marrow of patients with confirmed diagnosis of myelodysplastic syndromes (MDS). Normal bone marrow cells obtained from donors of the Clinical Hospital of this university were used as a control. The autonomous proliferation, evaluated by clonal culture without exogenous growth factor, and the number of apoptotic cells in bone marrow kept for 10 days in liquid cultures at 37 degrees C and 5% carbon dioxide, were significantly greater in MDS patients than in control subjects (P = 0.001, Wilcoxon). However, bcl-2 expression, measured by immunocytochemistry, was significantly lower in MDS patients than in normal individuals (P = 0.002, Wilcoxon). These results suggest that the high proliferation activity in MDS patients may be counteracted by the high level of medullar cell death, which might be related to the lower bcl-2 expression.

High expression of bcl-2 mRNA as a determinant of poor prognosis in acute myeloid leukemia

BACKGROUND

The bcl-2 oncoprotein is suggested to be directly involved in the emergence of drug resistance by disrupting or delaying the apoptotic program and promoting tumor survival.

PATIENTS AND METHODS

In order to define the clinical relevance of the bcl-2 mRNA expression in acute myeloid leukemia (AML) and its correlation to therapy outcome and prognosis, we analyzed 219 AML bone marrow (BM) samples, including 119 patients with de novo AML at presentation, 37 with AML following myelodysplastic syndrome (MDS), as well as 42 BM samples of AML in relapse and 21 in complete remission (CR) using RT-PCR. For performing quantitative measurements of bcl-2 mRNA, we developed a quantitative RT-PCR.

RESULTS

Bcl-2 mRNA was detectable in 133 of 156 (84%) patients at diagnosis and 40 of 42 (95%) at relapse. AML patients with high bcl-2 mRNA expression achieved lower CR rates than those with no or low expression. Concerning the long-term outcome, the overall (OS) and disease-free survival (DFS) was significantly worse in AML patients with high expression levels of bcl-2 mRNA. The three-year OS for all newly diagnosed AML patients was 49% and 10% (P = 0.028), respectively, and 71% and 15% (P = 0.0004) for patients < 60 years. Comparable significant differences were observed for the DFS. In AML following MDS and patients > 60 years, the bcl-2 expression was not associated with remission rate or survival.

CONCLUSIONS

The expression of bcl-2 mRNA may serve as a prognostic factor predicting remission outcome and long-term prognosis in AML.

Apoptosis and acute lymphocytic leukemia in children

We examined in vivo spontaneous and prednisolone-induced apoptosis in peripheral blood samples of 23 children with ALL by flow cytometric and morphologic methods. There was no significant spontaneous apoptosis before the therapy. Six hours after prednisolone therapy, increased apoptosis was found in 19 of 23 cases. In one case, the apoptosis of blast cells could not be compared with the clinical data, because the patient died in sepsis during the induction therapy. In 18 of 22 evaluable cases, the in vivo apoptosis correlated with the decrease of leukemic blasts during the first 8 days of prednisolone monotherapy. In 20 of 22 children, a correlation was found between in vivo prednisolone-induced apoptosis and clinical outcome. The p53 gene expression was elevated in 2 of 10 patients. No elevation in the expression of bcl-2 gene was observed. In 6 of 23 cases, the glucocorticoid receptors were measured. The correlation of clinical responsiveness and gcR mRNA shows less parallelism than does the apoptosis correlation.

Cellular Expression of Antiapoptotic BCL-2 Oncoprotein in Newly Diagnosed Childhood Acute Lymphoblastic Leukemia: A Children's Cancer Group Study

We found a marked variation in BCL-2 oncoprotein expression levels of primary leukemic cells from 338 children with newly diagnosed acute lymphoblastic leukemia (ALL). None of the high-risk features predictive of poor treatment outcome in childhood ALL, such as older age, high white blood cell (WBC) count, organomegaly, T-lineage immunophenotype, ability of leukemic cells to cause overt leukemia in severe combined immunodeficient (SCID) mice, presence of MLL-AF4, and BCR-ABL fusion transcripts were associated with high levels of BCL-2 expression. Overall, high BCL-2 levels were not associated with slow early response, failure to achieve complete remission, or poor event-free survival. High BCL-2 levels in primary leukemic cells predicted slow early response only in T-lineage ALL patients, which comprised approximately 15% of the total patient population. Even for this small subset of patients, the level of BCL-2 expression did not have a significant impact on the short-term event-free survival.

Cellular Expression of Antiapoptotic BCL-2 Oncoprotein in Newly Diagnosed Childhood Acute Lymphoblastic Leukemia: A Children's Cancer Group Study

We found a marked variation in BCL-2 oncoprotein expression levels of primary leukemic cells from 338 children with newly diagnosed acute lymphoblastic leukemia (ALL). None of the high-risk features predictive of poor treatment outcome in childhood ALL, such as older age, high white blood cell (WBC) count, organomegaly, T-lineage immunophenotype, ability of leukemic cells to cause overt leukemia in severe combined immunodeficient (SCID) mice, presence of MLL-AF4, and BCR-ABL fusion transcripts were associated with high levels of BCL-2 expression. Overall, high BCL-2 levels were not associated with slow early response, failure to achieve complete remission, or poor event-free survival. High BCL-2 levels in primary leukemic cells predicted slow early response only in T-lineage ALL patients, which comprised approximately 15% of the total patient population. Even for this small subset of patients, the level of BCL-2 expression did not have a significant impact on the short-term event-free survival.

CD30 Ligand Is Frequently Expressed in Human Hematopoietic Malignancies of Myeloid and Lymphoid Origin

CD30 ligand (CD30L) is a type-II membrane glycoprotein capable of transducing signals leading to either cell death or proliferation through its specific counterstructure CD30. Although several lines of evidence indicate that CD30L plays a key role as a paracrine- or autocrine-acting surface molecule in the deregulated cytokine cascade of Hodgkin's disease, little is known regarding its distribution and biologic significance in other human hematopoietic malignancies. By analyzing tumor cells from 181 patients with RNA studies and immunostaining by the anti-CD30L monoclonal antibody M80, we were able to show that human hematopoietic malignancies of different lineage and maturation stage display a frequent and broad expression of the ligand. CD30L mRNA and surface protein were detected in 60% of acute myeloid leukemias (AMLs), 54% of B-lineage acute lymphoblastic leukemias (ALLs), and in a consistent fraction (68%) of B-cell lymphoproliferative disorders. In this latter group, hairy cell leukemia and high-grade B-cell non-Hodgkin's lymphoma (B-NHL) expressed a higher surface density of CD30L as compared with B-cell chronic lymphocytic leukemia and low-grade B-NHL. Purified plasmacells from a fraction of multiple myeloma patients also displayed CD30L mRNA and protein. A more restricted expression of CD30L was found in T-cell tumors that was mainly confined to neoplasms with an activated peripheral T-cell phenotype, such as T-cell prolymphocytic leukemia, peripheral T-NHL, and adult T-cell leukemia/lymphoma. In contrast, none of the T-lineage ALLs analyzed expressed the ligand. In AML, a high cellular density of CD30L was detected in French-American-British M3, M4, and M5 phenotypes, which are directly associated with the presence on tumor cells of certain surface structures, including the p55 interleukin-2 receptor α-chain, the αM (CD11b) chain of β2 integrins, and the intercellular adhesion molecule-1 (CD54). Analysis of normal hematopoietic cells evidenced that, in addition to circulating and tonsil B cells, a fraction of bone marrow myeloid precursors, erythroblasts, and subsets of megakaryocytes also express CD30L. Finally, we have shown that native CD30L expressed on primary leukemic cells is functionally active by triggering both mitogenic and antiproliferative signals on CD30+ target cells. As opposed to CD30L, only 10 of 181 primary tumors expressed CD30 mRNA or protein, rendering therefore unlikely a CD30-CD30L autocrine loop in human hematopoietic neoplasms. Taken together, our data indicate that CD30L is widely expressed from early to late stages of human hematopoiesis and suggest a regulatory role for this molecule in the interactions of normal and malignant hematopoietic cells with CD30+ immune effectors and/or microenvironmental accessory cells.

Functional aspects of apoptosis in hematopoiesis and consequences of failure

Apoptosis is an internally directed, physiological method of cell destruction. Cellular components are dismantled within the confines of an intact cell membrane, and rapid ingestion by phagocytic cells prevents local inflammation. A variety of genes have now been identified as positive or negative regulators of apoptosis. Transfection experiments and studies of gene cooperation in viral transformation suggest that full cellular transformation requires not only the deregulation of proliferation, but also the inhibition of concomitant apoptosis programs. The regulation of apoptosis is fundamental to hematopoietic homeostasis. Stem cell renewal is continuously counterbalanced by apoptosis in functionally inactive or terminally differentiated cells. Extensive cell death in developing lymphocyte populations ensures that only cells recognizing non-self antigens are released into the periphery, and the finite lifespan of terminally differentiated cells enables the extensive cell turnover demanded by functional aspects of the hematopoietic system. The requirement of each hematopoietic sub-population for a specific sub-set of survival factors, provides a flexible mechanism for dictating the cellular composition of the mature population and for controlling population size. Surplus cell production and apoptosis are therefore normal features of hematopoiesis. The consequences of deregulated apoptosis are severe. Excessive apoptosis in lymphocyte populations plays a major role in the pathogenesis of acquired immunodeficiency syndrome (AIDS), whereas ineffective apoptosis has been associated with the development of inflammation, autoimmunity and hematological malignancies. The identification of various genetic abnormalities which influence apoptosis in leukaemic cells (e.g., mutant p53, Bcr-Abl and over-expression of Bcl-2), suggests that the acquisition of an anti-apoptotic lesions is an important event in the multi-step evolution of hematological malignancies. In addition, the nature of some leukaemias particularly the chronic leukemias, in which the leukemic cells are nonproliferative and long lived, suggests that anti-apoptotic lesions are early events in the pathogenesis of these diseases. It is likely that the utilization of mechanisms to evade apoptosis would facilitate disease progression in all leukemias and contribute to the development of multi-drug resistance. A better understanding of apoptosis mechanisms in hematopoietic cells, and their exploitation by leukemic cells should be useful in the development of improved cytotoxic regimes.

Quantitation of resistance to cytosine arabinoside by myeloid leukemic cells expressing bcl-2

The presence of bcl-2 in myeloid leukemias has been associated with a decrease in therapy-induced apoptosis, reduced patient survival and in vitro autonomous growth of leukemic cells. The present study focuses on the quantitation of resistance to increasing doses of 1-beta-d-arabinofuranosylcytosine (Ara-C) by using hematological tumors expressing different levels of bcl-2. Scanning densitometry of Western blots demonstrated that the myeloid U-937 cells express low levels of bcl-2 (RD = 0.008), whereas the follicular lymphoma RL-7 expressed very high levels (RD = 3.084). Colony formation was also examined following incubation with Ara-C and RL-7 cells demonstrated a higher clonogenic survival (LD50 = 0.5 microns) when compared with U-937 cells (LD50 = 0.005 microM). Similarly, the level of bcl-2 expression in each cell line was also related to apoptosis with U-937 cells demonstrating increased DNA fragmentation when compared with RL-7 cells. To further evaluate the effect of upregulated bcl-2 on Ara-C treatment, U-937 cells were transfected with a retroviral vector carrying the murine bcl-2 or vector alone. Upregulation of bcl-2 by myeloid leukemic cells increased the resistance by 3 logs to Ara-C when comparing LD50 values from clonogenic assays, and decreased apoptosis by at least 3 logs when measuring dUTP positive cells by flow cytometry.