Abstract Book 2010 - CIMT Annual Meeting

084 Chen | Tumor biology & interaction with the immune system
Disturbed NK cell function in CML patients at diagnosis does
not recover under treatment with imatinib mesylate
Christiane I-U. Chen 1 , Steffen Koschmieder 2 , Linda Kamp 2 , Holden T Maecker 3 , Wolfgang
Berdel 2 , Heribert Jürgens, 1 Peter P Lee 4 , Claudia Rössig 1
1 Department of Pediatric Hematology and Oncolocy, University Hospital Muenster, Germany
2 Department of Medicine, Division of Hematology and Oncology, University Hospital Muenster, Germany
3 Human Immune Monitoring Center, Stanford University School of Medicine, USA
4 Department of Medicine, Division of Hematology, Stanford University, USA
Even though the tyrosine kinase inhibitor imati-
nib mesylate (imatinib) has become the first-line
therapy for patients with chronic myeloid leukemia
(CML), allogeneic hematopoietic stem cell transplantation
(HSCT) remains the only curative treatment.
The important contribution of the immune
system to curing CML is evidenced by the potent
therapeutic effects of donor lymphocyte infusions.
In addition to cytotoxic T cells, natural killer (NK)
cells may be involved in immunologic control of the
disease. Here, we used a transgenic tet-off inducible
CML mouse model as well as peripheral blood
samples from CML patients to explore the role of
NK cells in CML.
Splenic lymphocyte subpopulations from CML
mice were analyzed by flow cytometry. Under continuous
tetracycline treatment (tet-on), these mice
have a bcr-abl-negative phenotype, whereas withdrawal
of tetracycline induces bcr-abl transgene
expression, resulting in initiation of leukemia and
manifestation of a CML-like phenotype (tet-off, bcrabl+).
Bcr-abl+ mice had significantly decreased
relative numbers of NK cells compared to control
mice (5.5% vs 13.8%, p = 0.045). While ex vivo expansion
of purified NK cell populations from tet-on
and tet-off mice demonstrated similar proliferative
responses to stimulation with high-dose interleukin-2
(IL-2), the cytolytic capacity of NK cells expanded
from bcr-abl+ mice against K-562 cells was
significantly reduced (10.7% vs. 27.3% at an E:T
ratio of 1:1, p < 0.05).
To address the functionality of NK cells in human
CML, we quantified NK cells in peripheral blood
samples from 13 patients at diagnosis and at several
time points during imatinib-induced remission
(range 10-59 months). Compared to age-matched
healthy controls, NK cells were decreased at diagnosis
(4,4% vs 13%, p < 0.05) and did not recover
to normal levels under imatinib treatment (6.2% vs
10%, p < 0.05). Functional experiments revealed
reduced expansion of NK cells in response to coincubation
with K-562/4-1BBL/mbIL-15 stimulator
cells in CML patients versus healthy controls
(26-fold expansion vs 48-fold expansion within 10
days, p < 0.05). Moreover, the cytolytic activity of
human CML NK cells was reduced both at diagnosis
(8.3% lysis of K-562 target cells at an E:T ratio
of 1:1) and under treatment with imatinib (11%)
compared to control (18.9%, p < 0.05).
We conclude that patients with CML have both
quantitative and qualitative defects within their
NK cell compartment, which can be reproduced
by transgenic bcr-abl expression in mice. NK cells
do not recover to normal levels and normal function
under imatinib treatment, even after obtaining
complete remission. Further work will aim at
identifying the underlying mechanisms of NK cell
deficiency in CML, and the development of strategies
to exploit NK cells for immunotherapy of the
disease.
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