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

observed in all mice. Analysis of long-term reconstitution (12 and 15
weeks post-transplant) distinguished 2 groups of mice: 1) most of them
(25 patients’ samples) had a progressive reduction in human cell engraftment,
with a majority of CD19 + cells, such as observed in mice repopulated
with normal CD34 + cells. No engraftment was detected in secondary
transplant. 2) On the contrary, a small number of mice (2 repopulated
with PMF cells and 1 with PV cells) developed a MPD-like syndrome
characterized by an increase in human cell engraftment, a majority of
CD33 + cells and even some GpA positive cells. Genotypic analysis of
human colonies demonstrated that the first group of mice contained a
majority of JAK2 WT colonies. However, in this group, we could also
observe some heterozygous colonies at 12 and 15 weeks after transplant,
in 2 mice reconstituted with cells from 2 PV patients, confirming
that the JAK2 V617F mutation is indeed present in HSCs. Genotyping
of the second group of mice is still under investigation and the results will
be presented. Conclusions. Using NOD/SCID mice we demonstrated that
the JAK2 V617F mutation is present in only a minority of HSCs in MPDs
and that it does not induce self-renewal advantage in human HSCs. We
can hypothesize that the HSCs engrafted in mice that develop a MPDlike
syndrome probably have an additional genetic event that modifies
their stem cell properties.
0444
A MOLECULAR CLASSIFICATION OF LEUKAEMIA REVEALS MDS AS A DISEASE
CONTINUUM WITH NON-LEUKAEMIA AND AML SUB GROUPS
KI. Mills, 1 A.F. Gilkes, 1 J. Hernandez, 2 W.-K. Hofmann, 3 A. Kohlmann, 4
M. Williams, 4 L. Wieczorek, 4 T. Haferlach5 1 Cardiff University, CARDIFF, United Kingdom; 2 Haematologia, SALAMAN-
CA, Spain; 3 Charite, BERLIN, Germany; 4 Roche Molecular Systems,
PLEASANTON, USA; 5 MLL, Munich Leukemia Laboratory, MUNICH, Germany
Robust gene expression signatures associated with distinct sub-classes
of paediatric and adult leukaemias have been identified from microarray
studies. Recently, the MILE (Microarray Innovations in LEukemia)
study group has compared the accuracy of gene expression profiling to
gold standard diagnostic workup for ~2000 patients within 16 acute and
chronic leukaemia subclasses, MDS, and non-leukaemia as control group
in 11 centres (ELN: 7, USA: 3, Singapore: 1). The overall cross-validation
accuracy was very high for the leukaemia subclasses: >95%. Based on
this data set a customized AmpliChip Leukemia microarray has been
designed for leukaemia classification. However, only 49.1% of the 173
MDS samples included in the study were correctly called as MDS from
their underlying gene expression profiles. The remainder were approximately
equally split between an algorithm classification call of nonleukaemia
(24%) and AML (24.6%). Our analysis showed that neither
centre nor age were a factor in differentiating between MDS, MDS with
an AML-like signature or MDS with a non-leukaemia like signature. WHO
classification was highly correlated with the microarray classification
result; specifically RAEB (I or II) was associated with AML-like signature
(p0.0001): 65% of patients with an IPSS score of
Int-2 or above were classified as AML. Individually, the blast, karyotype
and cytopenia contributions were highly significant (p