12th Congress of the European Hematology ... - Haematologica

12 th Congress of the European Hematology Association
0383
TWO DISTINCT TYPES OF GENOMIC REARRANGEMENTS INVOLVE THE C-MYB LOCUS IN
HUMAN T-CELL ACUTE LYMPHOBLASTIC LEUKEMIA, INCLUDING A TRANSLOCATION
T(6;7) DEFINING A NEW LEUKEMIC SUBGROUP IN VERY YOUNG CHILDREN
E. Clappier, 1 W. Cuccuini, 2 A. Crinquette, 2 A. Kalota, 3 J.M. Cayuela, 1
W.A. Dik, 4 A.W. Langerak, 4 B. Montpellier, 5 B. Nadel, 5 P. Walrafen, 6
O. Delattre, 7 A. Aurias, 7 T. Leblanc, 8 H. Dombret, 9 A.M. Gewirtz, 3
A. Baruchel, 8 F. Sigaux, 10 J. Soulier 2
1 Hopital Saint-Louis, PARIS, France; 2 INSERM U728, Hopital Saint-Louis,
PARIS, France; 3 University of Pennsylvania, PHILADELPHIA, USA; 4 University
Medical Center Rotterdam, ROTTERDAM, Netherlands; 5 Centre d'Immunologie
de Marseille-Luminy, MARSEILLE, France; 6 Genomic Vision,
PARIS, France; 7 INSERM U509 Institut Curie, PARIS, France; 8 Pediatric
Hematology, Hopital St-Louis, PARIS, France; 9 Adult Hematology, Hopital St-
Louis, PARIS, France; 10 IUH, Hopital Saint-Louis, PARIS, France
Background. Cytogenetics and expression studies have pointed out an
increasing number of oncogenes in T-cell acute lymphoblastic leukemias
(T-ALL), demonstrating the complexity of T-ALL oncogenesis and the
requirement for a network of cooperative oncogenic events. Classifying
T-ALL oncogenes include aberrantly activated transcription factors,
namely bHLH (TAL1, TAL2, and LYL1), homeobox genes (HOXA,
TLX1/HOX11, TLX3/HOX11L2), and CALM-AF10 and MLL fusion
genes. These oncogenes are frequently activated by chromosomal
translocation or intrachromosomal cryptic deletion. Combined analysis
of the T-ALL genetic alterations and large scale gene expression has
allowed the definition of several major T-ALL subtypes. Aims. We aimed
to identify new oncogenic alterations in T-ALL and include them in the
genetic and biological networks defining T-ALL. A series of 84 T-ALL
including 80 primary samples from children and adults, and 4 cell lines,
was investigated by conventional and molecular cytogenetics approaches.
Methods. In order to identify new T-ALL oncogenes, TCR-related
translocations were searched for using FISH flanking probes. Partner
sequences were cloned using inverse circled PCR. In addition, a genomewide
copy-number analysis was performed using a customized 4K
BAC/PAC array-CGH on the 84 T-ALL cases. Results. Two distinct recurrent
genetic events were identified that both involved the C-MYB locus
at 6q23. First, a reciprocal chromosomal translocation t(6;7)(q23;q34)
was identified that juxtaposed the TCRB and the C-MYB loci (n=4 cases
out of 84; two additional independant TCRB-MYB samples were also
studied leading to a total of 6 cases). Second, the array-CGH analysis
identified a cryptic duplication of a short genomic region including C-
MYB (n=14 cases out of 84 T-ALL, 17%). The somatic origin of the
duplication was demonstrated using paired leukemic and remission
DNA, and a minimal duplicated region of approximately 230 Kb was
mapped using 244K oligonucleotide array-CGH. RQ-PCR analysis
showed an increased C-MYB expression in both the translocated and
duplicated cases compared to other T-ALL cases and normal controls.
Strikingly, the TCRB-MYB translocation occurred in very young children
(median 2 years-old, p=10-4). Moreover, profiling of the T-ALL series by
large scale expression analysis showed that the TCRB-MYB cases
defined a unique T-ALL case cluster associated to a proliferation/mitosis
signature. By contrast, the MYB-duplicated cases were found at various
ages and in previously defined distinct T-ALL oncogenic subtypes
(SIL-TAL1, TLX1, TLX3, CALM-AF10, MLL or Immature cases). Conclusions.
The C-MYB gene has been a candidate oncogene in human hematologic
malignancies for years, based on its homology with the viral
oncogene v-Myb and frequent targeting by retroviral insertions in mouse
leukemia. This work is the first clear demonstration of the recurrent
involvement of the C-MYB locus in a human neoplasm, namely T-ALL,
in two distinct genetic alterations. The C-MYB transcription factor is
known to play a major role in early and definitive hematopoiesis, and
it has been involved at several key steps throughout the normal thymic
differentiation process. It is therefore likely that deregulated C-MYB
expression due to genomic events is oncogenic in T-ALL. Importantly,
the t(6;7) translocation defines a new subtype of T-ALL associated with
a very young age and a proliferation/mitosis signature.
140 | haematologica/the hematology journal | 2007; 92(s1)
0384
SYSTEMATIC EVALUATION OF COPY NUMBER ALTERATIONS IN CHILDHOOD ACUTE
LYMPHOBLASTIC LEUKEMIA AND THEIR ASSOCIATION WITH TREATMENT RESPONSE
D. Steinemann, 1 G. Cario, 2 M. Stanulla, 1 M. Tauscher, 1 A. Weigmann, 1
G. Göhring, 1 J. Harbott, 3 B. Radlwimmer, 4 P. Lichter, 4 M. Schrappe, 2 B.
Schlegelberger1 1 Medical School Hannover, HANNOVER; 2 University Childrens Hospital
Schleswig, KIEL; 3 Justus-Liebig-University, GIESSEN; 4 Deutsches Krebsforschungszentrum
(DKFZ), HEIDELBERG, Germany
Background. in vivo response to initial therapy, as assessed by determination
of minimal residual disease on treatment day 33 and at week 12 of
treatment, has evolved as the strongest prognostic factor in children
with acute lymphoblastic leukaemia (ALL) treated according to the BFM
regime (ALL-BFM-2000). However, it is not known so far, whether the
individual treatment response might be influenced by copy number
alterations, i.e. small deletions or amplifications, leading to altered gene
expression. Aims. We therefore aimed to systematically evaluate copy
number alterations (CNA) using high resolution array-comparative
genomic hybridization (array-CGH) in different treatment-response
groups. Methods. Leukemic DNA of 25 patients with a poor (MRD load
> 10-3 at week 12, MRD-high risk, HR) and 25 patients with a good
treatment response (no measurable MRD at weeks 5 and 12, MRD-standard
risk, SR) were compared. For array-CGH, a DNA chip containing
more than 8000 individual BAC/PAC clones leading to a genome-wide
resolution of at least 1 Mb was used. Hybridization, image analyses and
data processing was performed as described recently (Steinemann et al.
2006). Selected CNA were validated by fluorescence in situ hybridization.
Results. Copy number alterations (CNA) were found in 46 patients
(92%), in both patient groups. Microscopic alterations affecting the
whole or nearly whole chromosome arm were frequently found, e.g.
gain of 21 in 11/50, loss of 9p in 5/50, loss of 8p in 3/50, loss of 20q in
3/50 and loss of 7p in 2/50 or gain of 1q in 2/50. A gain of chromosome
1q23-qter was found in 10/25 SR-patients, whereas none of the HRpatients
showed this gain with a breakpoint in 1q23 (p