Wilms tumor gene (WT1) expression as a panleukemic marker

Dendritic Cell-Based Immunotherapy of Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a type of blood cancer characterized by the uncontrolled clonal proliferation of myeloid hematopoietic progenitor cells in the bone marrow. The outcome of AML is poor, with five-year overall survival rates of less than 10% for the predominant group of patients older than 65 years. One of the main reasons for this poor outcome is that the majority of AML patients will relapse, even after they have attained complete remission by chemotherapy. Chemotherapy, supplemented with allogeneic hematopoietic stem cell transplantation in patients at high risk of relapse, is still the cornerstone of current AML treatment. Both therapies are, however, associated with significant morbidity and mortality. These observations illustrate the need for more effective and less toxic treatment options, especially in elderly AML and have fostered the development of novel immune-based strategies to treat AML. One of these strategies involves the use of a special type of immune cells, the dendritic cells (DCs). As central orchestrators of the immune system, DCs are key to the induction of anti-leukemia immunity. In this review, we provide an update of the clinical experience that has been obtained so far with this form of immunotherapy in patients with AML.

Studies of Wilms’ Tumor (WT1) Gene Expression in Adult Acute Leukemias in Singapore

Biomarkers provide certain values for diagnosis, monitor treatment efficacy, or for the development of novel therapeutic approach for particular diseases. Thus, the identification of specific of biomarkers for specific medical problems, including malignant diseases may be valuable in medical practice. In the study, we have used the Wilms’ tumor gene ( WT1) as a biomarker to evaluate its expression in local adult patients with newly diagnosed acute leukemia, including both acute myeloid and lymphoid leukemias (AML and ALL).

Aim

To investigate WT1 gene expression in adult patients with acute leukemia at diagnosis.

Methods

Eighteen patients with acute leukemia diagnosed at Singapore General Hospital, Singapore, between September, 2004 and July, 2005 were included in this study. There were fifteen AML and three ALL cases aged from 18 to 71 years old. Total RNA and DNA was extracted from peripheral blood mononuclear cells (PBMCs). Expression of WT1 was detected by nested reverse-transcription polymerase chain reaction (Nested RT-PCR). K562, and 3T3 cells were used as positive- and negative-controls. The results were revalidated using real-time PCR. HLA-A genotyping was performed using sequence specific oligonucleotide polymorphism (SSOP) analysis.

Results

WT1 gene was exclusively expressed in all eighteen, including three ALL and fifteen AML, patients. In contrast with WT1 gene, the HLA-A genotyping was remarkably heterogeneous in these patients.

Conclusions

WT1 gene expression was observed in local patients with acute leukemia at diagnosis. It may be used as a potential molecular marker for diagnosis, clinical progression of the diseases or monitoring the response to treatment, as well as a target for the development of novel therapeutic approaches.

miR-590 regulates WT1 during proliferation of G401 cells

Nephroblastoma (Wilms' tumor) is frequently associated with mortality in children. MicroRNAs (miRNAs) are important for tumor development serving as oncogenes or tumor suppressors. In the present study, miRNA-590 (miR-590) was identified to be upregulated in Wilms' tumor tissues compared with the normal adjacent tissues. Additionally, the levels of miR-590 were consistent with their clinical stage. Wilms' tumor 1 (WT1) was considered to be a tumor suppressor in certain tumor types, and it has been detected at low expression levels in various types of cancer with high cell proliferation and aggressive behavior. The expression levels of miR-590 were quantified using reverse transcription-quantitative polymerase chain reaction. Cell proliferation was measured using 5-ethynyl-20-deoxyuridine assays. The protein expression levels of WT1 were investigated by western blot analysis. To the best of our knowledge, the present study was the first to determine that WT1 was a target gene of miR-590 as miR-590 was able to negatively regulate WT1 expression level by binding to the specific target site within the 3′-untranslated region (3′-UTR) of WT1 in G401 cells. Additionally, overexpression of miR-590 promoted G401 cell proliferation which was consistent with the effect of small interfering RNA-WT1. Subsequently, the present study determined that the cell phenotype altered by miR-590 overexpression may be reversed by upregulation of WT1 in G401 cells. In conclusion, the observations indicated that miR-590 may function as an oncogene via targeting WT1 to induce G401 cell proliferation. These results may contribute to current understanding of the function of miR-590 in nephroblastoma.

Induction of Immune Response after Allogeneic Wilms' Tumor 1 Dendritic Cell Vaccination and Donor Lymphocyte Infusion in Patients with Hematologic Malignancies and Post-Transplantation Relapse

Relapse of hematologic malignancies is the primary cause of treatment failure after allogeneic hematopoietic stem cell transplantation (HCT). Treatment for post-HCT relapse using donor lymphocyte infusion (DLI) has limited utility, particularly in the setting of acute leukemia, and can result in the development of graft-versus-host disease (GVHD). The Wilms' tumor 1 (WT1) gene product is a tumor-associated antigen that is expressed in acute leukemia and other hematologic malignancies, with limited expression in normal tissues. In this pilot trial, we assessed safety and feasibility of a WT1 peptide-loaded donor-derived dendritic cell (DC) vaccine given with DLI designed to enhance and direct the graft-versus-leukemia effect. Secondary objectives were to evaluate immunologic and clinical responses. A total of 5 subjects, median age 17 years (range, 9 to 19 years), with post-HCT relapse were enrolled. Disease subtypes included acute lymphoblastic leukemia (n = 3), acute myelogenous leukemia (n = 1), and Hodgkin lymphoma (n = 1). Successful vaccine production was feasible from all donors. DC vaccination and DLI were well tolerated. One recipient developed grade 1 skin GVHD not requiring systemic therapy. The most common adverse events included grade 1 reversible pain and pruritus at the vaccine injection and delayed-type hypersensitivity (DTH) skin testing sites. There were no grade 3 or higher adverse events related to the research. Immune responses consisted of ELISpot response in 3 recipients and positive DTH tests to WT1 peptide cocktail in 2 subjects. Our study provides 1 of the first attempts to apply tumor-specific vaccine therapy to the allogeneic setting. Preliminary results show the DC-based vaccination is safe and feasible after allogeneic HCT, with a suggestion that this approach can be used to sensitize the repopulated allogeneic-donor immune system to WT1. Future directions may include testing of vaccination strategies in the early post-transplantation setting for relapse prevention.

In vitro generation of mature, naive antigen-specific CD8(+) T cells with a single T-cell receptor by agonist selection

Peripheral blood T cells transduced with a tumor-specific T-cell receptor (TCR) face problems of auto-reactivity and lack of efficacy caused by cross-pairing of exogenous and endogenous TCR chains, as well as short term in vivo survival due to activation and growth factor-induced differentiation. We here studied an alternative strategy for the efficient generation of naive CD8(+) T cells with a single TCR. TCR-transduced human postnatal thymus-derived and adult mobilized blood-derived hematopoietic progenitor cells (HPCs) were differentiated to CD4(+)CD8(+) double-positive T cells using OP9-Delta-like 1 (OP9-DL1) cultures. Addition of the agonist peptide induced double positive cells to cross-present the peptide, leading, in the absence of co-stimulation, to cell cycle arrest and differentiation into mature CD8(+) T cells. Comprehensive phenotypic, molecular and functional analysis revealed the generation of naive and resting CD8(+) T cells through a process similar to thymic positive selection. These mature T cells show a near complete inhibition of endogenous TCRA and TCRB rearrangements and express high levels of the introduced multimer-reactive TCR. Upon activation, specific cytokine production and efficient killing of tumor cells were induced. Using this strategy, large numbers of high-avidity tumor-specific naive T cells can be generated from readily available HPCs without TCR chain cross-pairing.

Wilms' tumor gene 1: a possible new proangiogenic factor in Hodgkin lymphoma

INTRODUCTION

Wilms' tumor gene 1 (WT1) was recently found to play a role in solid and hematologic malignancies and serves as a marker of prognosis and minimal residual disease in acute leukemia. WT1 was also found to be involved in tumor angiogenesis. There are no data concerning the involvement of WT1 in angiogenesis in lymphoproliferative tumors. The aim of this study was to explore the involvement of WT1 in Hodgkin lymphoma.

METHODS

The expression of WT1, neuropilin 1, and VEGF was tested by immunohistochemistry in lymph nodes biopsies of 20 Hodgkin patients and 7 reactive lymph nodes.

RESULTS

WT1 was expressed in endothelial cells, in 95% of the malignant lymph nodes. The average of WT1 expression scale was higher in the malignant lymph nodes than in reactive lymph nodes. We found a positive correlation between WT1 expression scale and the angiogenesis scale (0.53) that was statistically significant (P<0.05). As the number of vessels increases, the expression of WT1 is more intense.

CONCLUSIONS

We found, for the first time, that WT1 is expressed in endothelial cells in Hodgkin lymphoma. The clinical implications of these findings should be tested in a future study.

NCI First International Workshop on the Biology, Prevention, and Treatment of Relapse after Allogeneic Hematopoietic Stem Cell Transplantation: report from the Committee on Disease-Specific Methods and Strategies for Monitoring Relapse following Allogeneic Stem Cell Transplantation. Part I: Methods, acute leukemias, and myelodysplastic syndromes

Relapse has become the major cause of treatment failure after allogeneic stem cell transplantation. Outcome of patients with clinical relapse after transplantation generally remains poor, but intervention prior to florid relapse improves outcome for certain hematologic malignancies. To detect early relapse or minimal residual disease, sensitive methods such as molecular genetics, tumor-specific molecular primers, fluorescein in situ hybridization, and multiparameter flow cytometry (MFC) are commonly used after allogeneic stem cell transplantation to monitor patients, but not all of them are included in the commonly employed disease-specific response criteria. The highest sensitivity and specificity can be achieved by molecular monitoring of tumor- or patient-specific markers measured by polymerase chain reaction-based techniques, but not all diseases have such targets for monitoring. Similar high sensitivity can be achieved by determination of donor chimerism, but its specificity regarding detection of relapse is low and differs substantially among diseases. Here, we summarize the current knowledge about the utilization of such sensitive monitoring techniques based on tumor-specific markers and donor cell chimerism and how these methods might augment the standard definitions of posttransplant remission, persistence, progression, relapse, and the prediction of relapse. Critically important is the need for standardization of the different residual disease techniques and to assess the clinical relevance of minimal residual disease and chimerism surveillance in individual diseases, which in turn, must be followed by studies to assess the potential impact of specific interventional strategies.

High expression of WT1 gene in acute myeloid leukemias with more predominant WT1+17AA isoforms at relapse

Real-time quantitative reverse transcriptase polymerase chain reaction method was established for detecting the expression levels of WT1 gene and WT1+17AA isoforms in 226 acute myeloid leukemia (AML) bone marrow (BM) cells. The results showed that WT1 gene was 2-3 logarithms expressed more in AML BM cells at initial diagnosis or relapse than in normal BM cells (p<0.001), with predominant WT1+17AA isoforms expression (the ratio of WT1+17AA/WT1 more than 0.50). Interestingly the ratio of WT1+17AA/WT1 was statistically higher in relapsed AMLs than in initially diagnosed (p=0.01), speculating that WT1+17AA isoforms might participate in AML relapse.

WT1 protein expression in childhood acute leukemia

In patients with acute leukemia, Wilms' tumor gene 1 (WT1) has been used as a target for the detection of minimal residual disease (MRD) by PCR techniques. The expression of WT1 protein, however, has not been extensively studied. To determine the relation between expression of WT1 transcripts and of the encoded protein, we examined leukemic cell lines and primary childhood leukemia samples using both real-time quantitative PCR (RQ-PCR) and flow cytometry. WT1 protein was highly expressed in the leukemic cell lines K562, HL-60, PLB 985, KG-1a and CEM. By contrast, 40 primary samples of acute lymphoblastic leukemia (ALL; B-ALL, n = 15 and T-ALL, n = 10) and acute myeloid leukemia (n = 15) expressed low levels of WT1 protein. RQ-PCR detected WT1 transcript levels in the same range as reported in earlier studies in childhood acute leukemia. The results of this study indicate the following: (i) there are considerable discrepancies between WT1 transcripts and protein expression; (ii) WT1 is not a suitable marker for flow cytometric MRD detection in childhood acute leukemia.

Clinical implications of minimal residual disease monitoring by quantitative polymerase chain reaction in acute myeloid leukemia patients bearing nucleophosmin (NPM1) mutations

To explore the validity and prognostic significance of minimal residual disease detection by quantitative polymerase chain reaction (qPCR) in patients of acute myeloid leukemia (AML) bearing Nucleophosmin (NPM1) mutations, we quantified mutants in 194 bone marrow samples from 38 patients with a median follow-up time of 20.6 months. Following induction chemotherapy, a median of 2.78 log decline in mutant copy number was observed. Relapse was always accompanied by significant increase of mutant numbers (P<0.001). After achieving complete remission (CR), the mutant copy number was significantly higher in patients with subsequent relapse than in those remaining in continuous CR (P<0.001). Presence of detectable mutants after treatment predicted relapse if no further chemotherapy was administered. Furthermore, the patients with any rise of mutant signals during serial follow-up had 3.2-fold increase of relapse risk compared to those with persistently low or undetectable signals (P<0.001). Patients who could achieve mutant reduction to <0.1% of internal control had significantly longer overall survival (OS) (P=0.004) and relapse-free survival (RFS) (P<0.001). Failure to achieve 2 logs of reduction after consolidation predicted shorter OS (P=0.01) and RFS (P=0.001). In conclusion, qPCR monitoring may have prognostic impact in AML patients with NPM1 mutations.

Increased midkine gene expression in childhood B-precursor acute lymphoblastic leukemia

Midkine (MK) is a heparin-binding growth factor that is overexpressed in a number of solid cancers. However, expression in acute leukemia has not been clarified. We examined MK gene expression using real-time PCR in 94 children with acute leukemia. In 30 of the 41 patients with B-precursor ALL, MK gene expression was overexpressed than normal BM. MK gene was also overexpressed in more than half of patients with FAB M1 and M2 types of AML. Quantification of MK gene by real-time PCR offers particular promise as a prognostic marker and a marker for minimal residual disease in children with B-precursor ALL.

Wilms' tumor gene 1 (WT1) expression in childhood acute lymphoblastic leukemia: a wide range of WT1 expression levels, its impact on prognosis and minimal residual disease monitoring

Wilms' tumor gene 1 (WT1) is overexpressed in the majority (70-90%) of acute leukemias and has been identified as an independent adverse prognostic factor, a convenient minimal residual disease (MRD) marker and potential therapeutic target in acute leukemia. We examined WT1 expression patterns in childhood acute lymphoblastic leukemia (ALL), where its clinical implication remains unclear. Using a real-time quantitative PCR designed according to Europe Against Cancer Program recommendations, we evaluated WT1 expression in 125 consecutively enrolled patients with childhood ALL (106 BCP-ALL, 19 T-ALL) and compared it with physiologic WT1 expression in normal and regenerating bone marrow (BM). In childhood B-cell precursor (BCP)-ALL, we detected a wide range of WT1 levels (5 logs) with a median WT1 expression close to that of normal BM. WT1 expression in childhood T-ALL was significantly higher than in BCP-ALL (P<0.001). Patients with MLL-AF4 translocation showed high WT1 overexpression (P<0.01) compared to patients with other or no chromosomal aberrations. Older children (> or =10 years) expressed higher WT1 levels than children under 10 years of age (P<0.001), while there was no difference in WT1 expression in patients with peripheral blood leukocyte count (WBC) > or =50 x 10(9)/l and lower. Analysis of relapsed cases (14/125) indicated that an abnormal increase or decrease in WT1 expression was associated with a significantly increased risk of relapse (P=0.0006), and this prognostic impact of WT1 was independent of other main risk factors (P=0.0012). In summary, our study suggests that WT1 expression in childhood ALL is very variable and much lower than in AML or adult ALL. WT1, thus, will not be a useful marker for MRD detection in childhood ALL, however, it does represent a potential independent risk factor in childhood ALL. Interestingly, a proportion of childhood ALL patients express WT1 at levels below the normal physiological BM WT1 expression, and this reduced WT1 expression appears to be associated with a higher risk of relapse.

Monitoring of minimal residual disease in acute myeloid leukemia

Monitoring minimal residual disease (MRD) becomes increasingly important in the risk-adapted management of patients with acute myeloid leukemia (AML). The two most sensitive and quantitative methods for MRD detection are multiparameter flow cytometry (MFC) and real-time polymerase chain reaction (QRT-PCR). Fusion gene-specific PCR in AML is based on the RNA level, and thus in contrast to MFC expression levels rather than cell counts are assessed. For both methods independent prognostic values have been shown. The strong power of MFC has been shown mainly in the assessment of early clearance of the malignant clone. MRD levels in AML with fusion genes have the strongest prognostic power after the end of consolidation therapy. In addition, with QRT-PCR highly predictive initial expression levels can be assessed. With both methods early detection of relapse is possible. So far, validated PCR-based MRD was done with fusion genes that are detectable in only 20-25% of all AML MFC is superior since it is applicable for most AML. However, QRT-PCR is still more sensitive in most cases. Thus, it is desirable to establish new molecular markers for PCR-based studies. Large clinical trials will determine the role and place of immunologic and PCR-based monitoring in the prognostic stratification of patients with AML.

Expression of Wilms' tumor gene 1 at different stages of acute myeloid leukemia and analysis of its major splice variants

WT1 is a transcription factor involved in differentiation and proliferation of acute myeloid leukemia (AML) blasts and is expressed in 90% of cases, as determined by nested reverse transcription polymerase chain reaction (RT-PCR). It is proposed to be a key molecule in leukemia promotion. To assess the relevance of WT1 expression, we analyzed blood and bone marrow samples from 58 AML patients (37 at diagnosis, 8 in hematological remission, and 13 at relapse) for the level of WT1 expression, using quantitative real-time RT-PCR. In addition, 21 randomly chosen samples were also analyzed for the quantitative expression of the main WT1 splice variants. As expected, samples from patients at the time of diagnosis or relapse showed significantly higher WT1 expression compared to samples from patients in remission or control samples. No striking difference in expression levels was found between various French-American-British (FAB) subtypes. The level of WT1 expression observed in patients at the time of initial diagnosis was similarly high in patients at relapse. Expression of the four main isoforms (E5+/KTS+, E5-/KTS+, E5+/KTS-, and E5-/KTS-) was found in all samples with significantly higher expression levels of the E5+ variants. Together, these findings support the potential of WT1 as a target for novel treatment approaches in AML.

Usefulness of quantitative assessment of Wilms tumor suppressor gene expression in chronic myeloid leukemia patients undergoing imatinib therapy

The Wilms tumor suppressor gene (WT1) is overexpressed in a number of human hematological malignancies, including chronic myeloid leukemia (CML). Although at present, the biological significance of WT1 expression in CML in still unclear, this marker could represent a useful tool for molecular monitoring of CML patients prior to and post imatinib therapy. In fact, the use of real-time polymerase chaine reaction (PCR) to quantitatively measure the WT1 transcript amount may be a predictor of patient response to imatinib therapy.