in vivo

Recent publications
Ishikawa F, Yoshida S, Saito Y,
Hijikata A, Kitamura H, Tanaka
S, Nakamura R, Tanaka T,
Tomiyama H, Saito N, Fukata M,
Miyamoto T, Lyons B, Ohshima
K, Uchida N, Taniguchi S, Ohara
O, Akashi K, Harada M, Shultz
L D. Chemotherapy-resistant
human AML stem cells home
to and engraft within the bone
marrow endsteal region. Nature
Biotechnology, 25(11):1315-21,
2007.
Figure
Femoral bone from untreated and Ara-C-treated AML-engrafted mice. In the untreated
femur, the BM space is packed with AML blasts (upper left; HE). At day 3 after
chemotherapy, there is a significant decrease in cellularity in the BM space except
at the endosteal surface of the bone (upper right and lower left; HE). TUNEL staining
confirms the massive apoptosis of cells in the central BM cavity while the cells at the
endosteal surface are relatively spared (lower right).
consistently give rise to high levels of human
hematopoietic chimerism for over six months.
In this model, human HSCs produced
mature differentiated progeny including
myelomonocytes, T and B lymphocytes,
dendritic cells, erythroid cells, and platelets.
Functionally, human B cells underwent
normal class switching, and engrafted human
T cells exhibited HLA-dependent cytotoxic
activity. Using this system, we have recently
been investigating the differentiation capacity
of myeloid and lymphoid progenitors. When
purified human myeloid progenitors and
lymphoid progenitors were intravenously
transplanted into NOD/scid/IL2rγ null newborn
mice, both progenitors displayed significant
expansion in the xenogeneic host. Human
conventional and plasmacytoid DC progeny
were found in recipients transplanted with
myeloid progenitors and those transplanted
with lymphoid progenitors, respectively. Thus,
successful short-term engraftment by lymphoid
and myeloid progenitors in the newborn NOD/
SCID/IL2rγ null mouse model enabled us to
identify the origins of human conventional DCs
and plasmacytoid DCs. The NOD/SCID/IL2rγ null
newborn transplant model is thus an excellent
system to study the properties of hematopoietic
stem and progenitor cells as well as to study the
human immune system in vivo.
Examination of human primary leukemia
stem cell biology by the development of
primary human acute myelogenous
leukemia model
While advances in chemotherapeutic
agents and stem cell transplantation have
improved survival of patients with acute
myelogenous leukemia (AML) over the last
30 years, chemoresistant disease, recurrence
after transplantation, and inability to undergo
transplantation due to lack of suitable HLAmatched
donors continue to adversely affect
clinical outcomes. Development of more
effective therapeutic agents is needed, but
the testing of such agents has so far relied on
data obtained from mouse models or in vitro
cell culture using human primary cells or cell
lines. The ability to test therapeutic agents on
human leukemic cells in vivo would be important
since it would allow for the evaluation of novel
therapeutics in a more physiologically relevant
setting, as well as the assessment of therapeutic
efficacy for individual patients.
As a proof-of-principle, we have treated
primary human AML-engrafted NOD/SCID/
IL2rγ null mice with the chemotherapeutic agent
cytarabine (AraC). By using this approach, we
were able to show that the number of human
AML cells in the peripheral blood decreased
after a single pulse treatment with AraC,
however this was followed by eventual relapse
originating from surviving leukemia stem cells
(LSCs). Importantly, the LSCs are resistant to
conventional chemotherapy, while the majority
non-stem leukemic cells are induced to undergo
apoptotic cell death. The surviving LSCs
efficiently develop AML in secondary and tertiary
recipients, suggesting that the chemoresistance
of LSCs is a major cause of AML relapse. Thus
we need to consider novel ways to eradicate
LSCs to minimize AML relapse. We are currently
investigating the mechanism underlying the
chemoresistance of LSCs.
Ishikawa F, Niiro H, Iino T,
Yoshida S, Saito N, Onohara S,
Miyamoto T, Minagawa H, Fujii
SI, Shultz LD, Harada M, Akashi
K.The developmental program of
human dendritic cells is operated
independently of conventional
myeloid and lymphoid pathways.
Blood, 2007 in press.
Shultz LD, Ishikawa F, Greiner DL.
Humanized mice in translational
biomedical research Nature
Reviews Immunol, 7:118-130,2007.
Ishikawa F, Shimazu H, Shultz LD,
Fukata M, Nakamura R, Lyons B,
Shimoda K, Shimoda S, Kanemaru
T, Nakamura K, Ito H, Kaji Y,
Perry AC, Harada M. Purified
human hematopoietic stem cells
contribute to the generation of
cardiomyocytes through cell
fusion. FASEB J 20:950-952,
2006.
Ishikawa F, Yasukawa M, Lyons B,
Yoshida S, Miyamoto T, Yoshimoto
G, Watanabe T, Akashi K, Shultz
LD, Harada M. Development of
functional human blood and
immune systems in NOD/SCID/IL2
receptor {gamma} chain null mice.
Blood 106:1565-1573, 2005.
75