LEUKEMIAS - BIOLOGY, CYTOGENETICS AND MOLECULAR MARKERS IN DIAGNOSIS AND PROGNOSIS: GENETIC ADVANCES IN ALL
Early T-Cell Precursor-ALL in Adult T-ALL.
Eckhard Thiel1 and
Claudia D Baldus*,1
1 Medical Department III, Hematology and Oncology, Charité University Hospital Benjamin Franklin, Berlin, Germany, 2 Medical Department II, Hematology/Oncology, Goethe University Hospital, Frankfurt/M, Germany, 3 MLL Munich Leukemia Laboratory, Munich, Germany, 4 Medical Department III, University Hospital Mannheim, Mannheim, Germany
Introduction: Recently, a small subgroup of pediatric acute T-lymphoblasticleukemia (T-ALL) was described, which is closely associatedwith the gene expression profile of early T-cell precursors(ETPs). This subtype, termed ETP-ALL, showed a highly unfavorableoutcome compared to non-ETP(='typical')-ALL. Based on the resultsof Coustan-Smith et al. (Lancet Oncology, 2009), the Italiannational study Associazione Italiana Ematologia Oncologia Pediatrica(AIEOP) and St-Jude Children's hospital modified their treatmentin children with ETP-ALL to a more intensive regime includingstem cell transplantation. ETP-ALL is characterized by a specificimmunophenotype (CD1a-, CD8-, CD5weak with expression of stemcell or myeloid markers). Here we explored the existence ofETP-ALL in adults and further studied the molecular characteristicsof this specific T-ALL subtype.
Patients and methods: We examined the gene expression profiles of 86 adult T-ALL patientsobtained from the Microarray Innovations in LEukemia (MILE)multicenter study (HG-U133 Plus 2.0, Affymetrix, Haferlach etal., JCO in press). In addition, bone marrow of 296 patientsfrom the German Acute Lymphoblastic Leukemia Multicenter StudyGroup (GMALL) were analyzed by flow cytometry and expressionlevels of BAALC, IGFBP7, MN1, and WT1 were determined by real-time-PCR.
Results: Using the published list of differentially expressed genes inETPs (Coustan-Smith et al. 2009) we performed unsupervised clusteringanalyses of the 86 T-ALL samples. A cluster of 17 samples (19.8%)displayed an ETP-associated gene expression profile and weredefined as ETP-ALL. Comparing the gene expression profiles ofETP-ALL and typical T-ALL, 2065 probe sets were differentiallyexpressed in ETP-ALL (FDR 0.05). In addition to genes used forclassification, we also identified genes known to be involvedin the pathogenesis of T-ALL (e.g. PROM1, BCL2, LMO2, LYL1).In particular, stem cell associated genes such as, BAALC (2.52-fold,p=0.003), IGFBP7 (2.76-fold, p=0.002) or MN1 (3.41-fold, p<0.001)were upregulated in ETP-ALL, whereas HOX11 (45-fold, p=0.004),a marker for thymic T-ALL, was downregulated. An independentcohort of 297 patient samples from the GMALL study group wasexamined by flow cytometry and real-time PCR. 19 (6.4%) samplesrevealed the ETP-ALL immunophenotype. As expected, all patientsamples were found in the group of early T-ALL, representing23.5% of all early T-ALLs. There was a significant correlationbetween a lower leukocyte count at first diagnosis and the classificationof ETP-ALL (p=0.001). Gene expression measured by real-time-PCRwas performed for genes associated with poor outcome in T-ALL:BAALC (2.11-fold, p<0.001) and IGFBP7 (3.59-fold, p=0.003)were significantly upregulated in the group of ETP-ALL. Similarly,the genes MN1 (4.52-fold, p<0.001) and WT1 (2.76-fold, p=0.036),described as poor prognostic markers in cytogenetically normalAML, were also upregulated in ETP-ALL.
Conclusion: In adult T-ALL, a subset of patients shares the gene expressionprofil and immunophenotype of ETP-ALL, which is in line withrecent findings in pediatric patients. The gene expression profileof this subset is significantly correlated to stem cell associatedmarkers predictive for inferior outcome in T-ALL. Interestingly,adverse factors in CN-AML are also aberrantly expressed in ETP-ALLsuggesting a myeloid origin of ETPs and indicating a closerrelationship between ETP-ALL and AML. The prognostic impactand the determination of the most appropiate set of markersneeds to be further investigated. These results support theGMALL strategy to regard early T-ALL patients as high risk withassignment to stem cell transplantation.