Mutation of the WT1 gene in myelodysplastic syndrome and acute myeloid leukaemia post myelodysplastic syndrome

Wilms' tumor gene (WT1) is predominantly expressed in clonal hematopoietic cells in myelodysplastic syndromes

To determine the expression of Wilms' tumor gene (WT1) in clonal hematopoietic cells in patients with myelodysplastic syndromes (MDS), immunochemistry labelling (alkaline phosphatase anti-alkaline phosphatase) and fluorescence in situ hybridization (FISH) were coperformed on bone marrow cytospins from 18 patients whose abnormal karyotypes had been determined by G-binding analysis. Compared to 12 healthy donors, WT1 positive nucleated cells in MDS marrows were significantly higher (t = 2.30; P = 0.032). Moreover, WT1 was expressed predominantly in MDS clonal cells (with abnormal FISH signals) rather than in non-clonal cells (residual normal cells) (t = 2.19; P = 0.043).

Mutation of the Wilms' tumor 1 gene is a poor prognostic factor associated with chemotherapy resistance in normal karyotype acute myeloid leukemia: the United Kingdom Medical Research Council Adult Leukaemia Working Party

PURPOSE

To determine the clinical relevance of Wilms' tumor 1 (WT1) gene mutations in acute myeloid leukemia (AML) with normal karyotype (NK).

PATIENTS AND METHODS

Exons 7 and 9 of WT1 were screened in samples from 470 young adult NK AMLs using a combination of direct sequencing and high-resolution capillary electrophoresis.

RESULTS

Overall, 51 mutations were detected in 47 cases (10%): 46 frameshift mutations with insertion/deletion of one to 28 base pairs in exon 7 (n = 45) or exon 9 (n = 1), with a median mutant level of 45% (range, 8% to 86%), and five substitutions in exon 9: D396N (n = 3), H397Y (n = 1) and H397Q (n = 1). Patients with WT1 mutations had an inferior response to induction chemotherapy compared with wild-type cases (complete remission rate, 79% v 90%, odds ratio [OR] = 3.02; 95% CI, 1.17 to 7.82; P = .02), a higher rate of resistant disease (15% v 4%; OR = 9.33; 95% CI, 2.38 to 36.6; P = .001), an increased cumulative incidence of relapse (67% v 43%, hazard ratio [HR] = 3.02; 95% CI, 1.69 to 5.38; P = .0008), with a reduction in both relapse-free survival (22% v 44%; HR = 2.16; 95% CI, 1.32 to 3.55; P = .005) and overall survival (26% v 47%; HR = 1.91; 95% CI, 1.23 to 2.95; P = .007) at 5 years. In multivariate analysis, which included FLT3 internal tandem duplication and NPM1 mutation status, the presence of a WT1 mutation remained an independent adverse prognostic factor.

CONCLUSION

WT1 mutations are a negative prognostic indicator in NK AML and may be suitable for the development of targeted therapy.

Wilms' tumor 1 gene mutations independently predict poor outcome in adults with cytogenetically normal acute myeloid leukemia: a cancer and leukemia group B study

PURPOSE

To analyze the prognostic impact of Wilms' tumor 1 (WT1) gene mutations in cytogenetically normal acute myeloid leukemia (CN-AML). PATIENTS AND METHODS We studied 196 adults younger than 60 years with newly diagnosed primary CN-AML, who were treated similarly on Cancer and Leukemia Group B (CALGB) protocols 9621 and 19808, for WT1 mutations in exons 7 and 9. The patients also were assessed for the presence of FLT3 internal tandem duplications (FLT3-ITD), FLT3 tyrosine kinase domain mutations (FLT3-TKD), MLL partial tandem duplications (MLL-PTD), NPM1 and CEBPA mutations, and for the expression levels of ERG and BAALC.

RESULTS

Twenty-one patients (10.7%) harbored WT1 mutations. Complete remission rates were not significantly different between patients with WT1 mutations and those with unmutated WT1 (P = .36; 76% v 84%). Patients with WT1 mutations had worse disease-free survival (DFS; P < .001; 3-year rates, 13% v 50%) and overall survival (OS; P < .001; 3-year rates, 10% v 56%) than patients with unmutated WT1. In multivariable analyses, WT1 mutations independently predicted worse DFS (P = .009; hazard ratio [HR] = 2.7) when controlling for CEBPA mutational status, ERG expression level, and FLT3-ITD/NPM1 molecular-risk group (ie, FLT3-ITD(negative)/NPM1(mutated) as low risk v FLT3-ITD(positive) and/or NPM1(wild-type) as high risk). WT1 mutations also independently predicted worse OS (P < .001; HR = 3.2) when controlling for CEBPA mutational status, FLT3-ITD/NPM1 molecular-risk group, and white blood cell count.

CONCLUSION

We report the first evidence that WT1 mutations independently predict extremely poor outcome in intensively treated, younger patients with CN-AML. Future trials should include testing for WT1 mutations as part of molecularly based risk assessment and risk-adapted treatment stratification of patients with CN-AML.

WT1 in acute leukemia, chronic myelogenous leukemia and myelodysplastic syndrome: therapeutic potential of WT1 targeted therapies

Among clinicians, initial awareness of the Wilms' tumor gene was limited mostly to pediatric oncologists. Almost a decade ago, overexpression of Wilms' tumor 1 (WT1) was observed in adult acute leukemia. Subsequent studies indicated that WT1 overexpression occurs in most cases of acute myelogenous leukemia, acute lymphoblastic leukemia, chronic myelogenous leukemia (CML), and myelodysplastic syndrome (MDS). Limited tissue expression of WT1 in adults suggests that WT1 can be a target for leukemia/MDS therapy. WT1 expression in stem/progenitor cells remains unsettled. However, lack of progenitor cell suppression by WT1 antisense or WT1-specific cytotoxic T cells provide some assurance that WT1 expression in progenitor cells is minimal or absent. Immunotherapy-based WT1 approaches are furthest along in preclinical development. WT1-specific cytotoxic lymphocytes can be generated from normals and leukemic patients. In mice, WT1 vaccines elicit specific immune responses without evidence of tissue damage. In this paper, we review studies validating the immunogenicity of WT1 and propose that leukemia and MDS may be a good clinical model to test the efficacy of a WT1 vaccine.

Role of the WT1 tumor suppressor in murine hematopoiesis

The WT1 tumor-suppressor gene is expressed by many forms of acute myeloid leukemia. Inhibition of this expression can lead to the differentiation and reduced growth of leukemia cells and cell lines, suggesting that WT1 participates in regulating the proliferation of leukemic cells. However, the role of WT1 in normal hematopoiesis is not well understood. To investigate this question, we have used murine cells in which the WT1 gene has been inactivated by homologous recombination. We have found that cells lacking WT1 show deficits in hematopoietic stem cell function. Embryonic stem cells lacking WT1, although contributing efficiently to other organ systems, make only a minimal contribution to the hematopoietic system in chimeras, indicating that hematopoietic stem cells lacking WT1 compete poorly with healthy stem cells. In addition, fetal liver cells lacking WT1 have an approximately 75% reduction in erythroid blast-forming unit (BFU-E), erythroid colony-forming unit (CFU-E), and colony-forming unit-granulocyte macrophage-erythroid-megakaryocyte (CFU-GEMM). However, transplantation of fetal liver hematopoietic cells lacking WT1 will repopulate the hematopoietic system of an irradiated adult recipient in the absence of competition. We conclude that the absence of WT1 in hematopoietic cells leads to functional defects in growth potential that may be of consequence to leukemic cells that have alterations in the expression of WT1.

Tumor suppressor genes in normal and malignant hematopoiesis

Over the last decade, a growing number of tumor suppressor genes have been discovered to play a role in tumorigenesis. Mutations of p53 have been found in hematological malignant diseases, but the frequency of these alterations is much lower than in solid tumors. These mutations occur especially as hematopoietic abnormalities become more malignant such as going from the chronic phase to the blast crisis of chronic myeloid leukemia. A broad spectrum of tumor suppressor gene alterations do occur in hematological malignancies, especially structural alterations of p15(INK4A), p15(INK4B) and p14(ARF) in acute lymphoblastic leukemia as well as methylation of these genes in several myeloproliferative disorders. Tumor suppressor genes are altered via different mechanisms, including deletions and point mutations, which may result in an inactive or dominant negative protein. Methylation of the promoter of the tumor suppressor gene can blunt its expression. Chimeric proteins formed by chromosomal translocations (i.e. AML1-ETO, PML-RARalpha, PLZF-RARalpha) can produce a dominant negative transcription factor that can decrease expression of tumor suppressor genes. This review provides an overview of the current knowledge about the involvement of tumor suppressor genes in hematopoietic malignancies including those involved in cell cycle control, apoptosis and transcriptional control.