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Blood, Vol. 91 No. 10 (May 15), 1998:
pp. 3688-3692
Engraftment of Cultured Human Hematopoietic Cells in Sheep
By
Yoshifumi Shimizu,
Makio Ogawa,
Masao Kobayashi,
Graca Almeida-Porada, and
Esmail D. Zanjani
From the Department of Medicine, Medical University of South
Carolina, Charleston, SC; and Department of Veterans
Affairs Medical Centers, Charleston, SC and Reno, NV.
 |
ABSTRACT |
In an effort to expand human hematopoietic progenitors and stem
cells in vitro, we cultured human
CD34+c-kitlow bone marrow cells in suspension
in the presence of KIT ligand, FLK2/FLT3 ligand, interleukin-6 (IL-6),
and erythropoietin with or without IL-3 and tested their engrafting
capabilities by injecting them into sheep fetuses. As markers for
engraftment, we analyzed CD45+ cells and karyotypes of
the colonies grown in methylcellulose culture. In three separate
experiments, day-60 engraftment in the bone marrow was seen with both
fresh cells and cells cultured in the presence or absence of IL-3. When
fetuses were allowed to be born and analyzed for CD45+
cells, no long-term engraftment was seen with cultured cells. We then
pooled the CD45+ cells of the fetal samples and
transplanted them into secondary recipient fetuses. Day-60 engraftment
in the secondary recipients was again noted when transplantation in the
primary recipients was initiated with fresh cells. There were 3 cases
in which cultured cells showed signs of engraftment in the secondary
recipients, but the remaining 24 cases showed no signs of engraftment.
These data documented that suspension culture for 2 weeks of enriched adult human bone marrow cells can maintain short-term (2 months) engrafting cells, but may not maintain longer term engrafting cells.
This sheep/human xenograft model may serve as an excellent method for
the evaluation of the engraftment potential of in vitro-expanded cells.
| |
INTRODUCTION |
IF IT WERE POSSIBLE to increase the
number of hematopoietic stem cells in vitro, it would have a profound
impact on future allogeneic and autologous stem cell transplantation.
Therefore, the subject of in vitro (ex vivo) expansion of hematopoietic
stem cells is currently one of the major emphases in
hematology-oncology fields.1-3 Many investigators have
documented that it is possible to increase in culture the number of
hematopoietic progenitors such as colony-forming cells and long-term
culture initiating cells (LTC-IC).1-3 Although some
investigators attempted to expand the population of murine stem cells
with in vivo reconstituting ability, the results to date remain
controversial.4-9 In general, these investigators used the
cytokines that have been shown to regulate cycling of primitive
progenitors, such as c-kit ligand (KL), flt3/flk-2 ligand (FL),
interleukin-1 (IL-1), IL-3, IL-6, IL-11, and granulocyte-macrophage
colony-stimulating factor (GM-CSF).10 However, observations
in our laboratory indicated that both IL-3 and IL-1 negatively affect
in vitro expansion of stem cells with long-term engraftment
capability.11,12
We describe here our initial attempt to expand in culture human
hematopoietic stem cells with in vivo engrafting capabilities. Because
in vitro assays for human hematopoietic stem cells are not available,
we used human/sheep xenogeneic transplantation as an assay for human
stem cells.13 We earlier documented that human
hematopoietic stem cells with long-term engrafting capabilities are in
the c-kitlow population of the CD34+ marrow
cells using the sheep/human xenograft model.14 Therefore, we cultured CD34+c-kitlow bone marrow cells in
serum-free medium supplemented with KL, FL, and IL-6. We show here that
human bone marrow cells cultured in the presence of combinations of
cytokines can engraft sheep fetuses for at least 2 months
posttransplantation. The sheep/human xenograft model is a useful assay
for in vitro manipulation of human hematopoietic stem cells.
| |
MATERIALS AND METHODS |
Cytokines.
Recombinant human KL and FL were provided by Dr S. Lyman (Immunex,
Seattle, WA). Recombinant human IL-3 was supplied by the Genetics
Institute (Cambridge, MA). Recombinant human IL-6 was a gift from Dr M. Naruto (Toray Industries, Yokohama, Japan). Recombinant human
erythropoietin (EP) was provided by Dr F.-K. Lin (Amgen Biologicals,
Thousand Oaks, CA).
Clonal cell culture of donor cells.
Aliquots of the human cells were cultured in 35-mm Falcon suspension
culture dishes (Becton Dickinson Labware, Lincoln Park, NJ) using the
methylcellulose culture technique described previously.14 The culture medium consisted of  -medium, 1.2%
1,500-centipoise methylcellulose (Shinetsu Chemical, Tokyo, Japan),
30% fetal calf serum (FCS; Intergen Corp, Purchase, NY), 1% bovine
serum albumin (BSA), 100 U/mL IL-3, 100 ng/mL IL-6, 100 ng/mL KL, and 2 U/mL EP. Dishes were incubated at 37°C in a humidified atmosphere
of 5% CO2/95% air (vol/vol). On day 14 of culture,
colonies were scored on an inverted microscope.
Donor cell preparation and suspension culture.
Bone marrow CD34+c-kitlow cells were prepared
as described previously.15 One day after cell separation,
portions of these cells were injected into sheep fetuses as fresh
cells. The remainders of the cells were suspended in
-medium (ICN, Irvine, CA) containing 2% deionized,
crystallized BSA (Sigma, St Louis, MO), 300 µg/mL iron-saturated
human transferrin (Sigma), 6 µg/mL cholesterol (Sigma), 10 µg/mL
lecithin (Sigma), 1 × 10 7 mol/L
sodium selenite (Sigma), 10 µg/mL insulin (Sigma), and a combination
of 100 ng/mL KL, 100 ng/mL FL, 100 ng/mL IL-6, 100 U/mL IL-3, and 2 U/mL EP. The cells were incubated at 37°C in a humidified
atmosphere of 5% O2/5% CO2/90%
N2 (vol/vol). The media was changed once on day 7. After 2 weeks of incubation, the cells were harvested and fractions were
injected into sheep fetuses.
In utero transplantation.
Donor cells were injected into preimmune fetal sheep recipients using
the amniotic bubble procedure described previously.13,16,17 Both fresh cells and cultured cells were resuspended in
-medium containing 20% FCS and 50 U/mL each of
recombinant human IL-3 and GM-CSF and transferred to Reno, NV by
overnight mail. Two thousand (experiments no. 1 and 2) to 3,000 (experiment no. 3) fresh cells or the whole cells expanded from 3,000 (experiments no. 1 and 3) to 6,000 (experiment no. 2) fresh cells were
transplanted intraperitoneally into each fetus at the gestational ages
of 58 to 63 days. Some of the recipient fetuses were killed on day 60 posttransplantation, and the bone marrow cells were analyzed for the
presence of human cells. The remainders were allowed to be born and
were examined monthly for signs of engraftment. In other experiments,
CD45+ cells were collected by panning from pooled fetal
samples that were positive for human cells and retransplanted into
preimmune fetal sheep at 0.4 to 3.0 × 106
cells/fetus. Secondary recipient fetuses were killed on day 60 posttransplantation, and the bone marrow cells were analyzed for signs
of human cell engraftment.
Assessment of donor cell engraftment.
Bone marrow mononuclear cells from the fetal and newborn sheep
transplanted with human cells were analyzed for the presence of human
cells by flow cytometry (CD45+ cells), karyotype analysis,
and clonal culture assays, as described previously.16,17
CD45+ cells at 0.1% were considered positive.
| |
RESULTS |
Expansion of human hematopoietic cells and progenitors.
Although there were significant differences in the magnitude of
expansion among the three experiments, the total nucleated cell counts
(TNCC) increased after 14 days of incubation with KL, FL, IL-6,
and EP (Table 1). Progenitor populations
also expanded except in one culture without IL-3. In all three
experiments, IL-3 enhanced production of both TNCC and progenitors.
Engraftment of human cells in primary recipients (fetuses).
Table 2 shows engraftment of human cells in
primary recipient fetuses on day 60 posttransplantation. In the three
experiments, 8 of the total of 13 recipients injected with fresh cells
became chimeric. The frequencies of CD45+ cells in the bone
marrow ranged from 0.42% to 5.3%. Of the total of 22 fetuses
receiving cultured cells, 15 fetuses became chimeric. In this group,
CD45+ cells in the bone marrow ranged from 0.4% to 7.8%.
All fetal samples that were positive for CD45+ cells
contained multipotential progenitors (colony-forming units-mix [CFU-Mix]) and/or granulocyte-macrophage progenitors
(colony-forming units-granulocyte-macrophage [CFU-GM])
of human origin. Both the frequencies of the chimeric fetuses and the
levels of CD45+ were very similar between the fresh cells
group and the cultured cells group. The presence of IL-3 in the
suspension culture did not have consistent influence on the levels of
engraftment. These data indicated that the ability of cells to support
engraftment in vivo for 2 months is maintained by the cells in culture
for 2 weeks with or without IL-3.
Engraftment of human cells in primary recipients (newborn animals).
Some of the fetuses injected with fresh cells and those injected with
cultured cells were allowed to be born. They were examined monthly for
signs of engraftment. The results are presented in Table 3. In many animals injected with
fresh cells, CD45+ cells were detected as late as 3 months
after birth, which is approximately 6 months posttransplantation. In
contrast, only 2 animals injected with the cultured cells showed signs
of engraftment by human cells 1 week after birth. No animals showed the
presence of CD45+ cells 1 month after the birth of the
animals.
Engraftment of human cells in secondary recipients (fetuses).
The analysis of the newborn animals presented in Table 3 may be
interpreted to suggest that true stem cells with long-term engrafting
capabilities are not maintained under current cell culture conditions.
This hypothesis was tested in another transplantation model, namely
transplantation to secondary recipients. The primary recipient fetuses
were killed 60 days after the first transplantation and the secondary
recipient fetuses were killed again 60 days later. Therefore, the total
span of observation was 120 days after the first transplantation of the
cells. The results of the positive samples are presented in
Table 4. The frequencies of chimeric animals were significantly (P < .01 by the Student's
t-test) higher in the fetuses transplanted with fresh cells
than in those transplanted with cultured cells. Of the 13 secondary
recipients tested for engraftment by fresh cells, a total of 10 recipients showed the presence of CD45+ cells. The levels
of CD45+ cells in the bone marrow of these fetuses ranged
from 1.1% to 7.2%. In contrast, of the total of 27 secondary
recipient fetuses tested for engraftment by cultured cells, only 3 recipients showed signs of engraftment. The levels of the
CD45+ cells in the bone marrow ranged from 0.3% to 1.3%.
There were statistically significant differences in the levels of
CD45+ cells between the fresh cells group and the cultured
cells group in experiment no. 3. However, the number of cells injected
did not seem to be a significant factor in whether the animals became chimeric. For instance, the number of CD45+ cells from
donors receiving fresh cells and injected into secondary fetuses was
0.4 to 3 × 106 cells/fetus, with an equal
distribution of positives and negatives between the low and high doses.
Ten of 13 of these animals were positive. The amount of
CD45+ cells administered to secondary fetuses from animals
that received cultured cells was 1.5 to 3.4 × 106
cells/fetus, and only 3 of 27 animals were positive. This study was
consistent with the results presented in Table 3 and indicated that
long-term engraftment capability of the stem cells is impaired during 2 weeks of incubation under current culture conditions.
| |
DISCUSSION |
Stem cell transplantation provides definitive therapy for a variety of
malignant and inherited diseases. Recently, transplantation of stem
cells harvested from the umbilical cord blood became an important
therapy for leukemia and other malignancies of children. However, the
limited quantity of cord blood harvest is thought to be a serious
obstacle for use of cord blood stem cell transplantation in older
children and adults. In vitro expansion of the population of stem cells
would significantly extend the indication of cord blood stem cell
transplantation. Furthermore, gene transduction into hematopoietic stem
cells in gene therapy may be facilitated under similar culture
conditions. For these reasons, in vitro expansion of human
hematopoietic stem cells is an important current research interest.
Already, several investigators have shown that it is possible to
increase in culture the number of human hematopoietic progenitors, such
as colony-forming cells and LTC-IC, but none studied engraftment
potentials of the cultured human cells.18-24
Recently, Brugger et al25 and Williams et al26
reported transplantation of cultured autologous cells after high-dose
chemotherapy of the patients. Because of the autologous nature of the
transplantation, contributions by the cultured cells to the
hematopoietic reconstitution could not be quantitated. We used the in
utero human/sheep xenograft model to assay the engrafting capability of
cultured cells. It appears that this system is sufficiently
reproducible and quantitative and demonstrated repeatedly the
engrafting capabilities of the freshly prepared cells. The study showed
that short-term (2 months) engraftment capability of the human
hematopoietic progenitors is maintained during the 2-week incubation
period. We earlier documented the negative effects of IL-3 on the in
vitro maintenance of long-term engrafting capabilities of murine
hematopoietic stem cells.11,12 Therefore, we wished also to
test if human IL-3 possesses negative effects on human hematopoietic
stem cells. IL-3 did not affect negatively the short-term engraftment
capability of the cultured cells. Unfortunately, only 1 of 6 animals
transplanted with cultured cells showed chimerism at 4 months after
cell transplantation and only 3 of the 27 secondary transplantation
recipients of cultured cells became chimeric. In addition, the levels
of chimerism were significantly lower than those of fresh cells group.
Therefore, we are not certain of the long-term engrafting capability of
cultured cells or the effects of IL-3 on human stem cell expansion.
After submission of this manuscript to Blood, investigators in
two laboratories reported their studies of in vitro expansion of
transplantable cord blood stem cells using nonobese diabetes/SCID (NOD/SCID) mice. Bhatia et al27 observed a twofold to
fourfold increase in the SCID-repopulating cells after a 4-day
suspension culture of CD34+CD38 human
cord blood cells. Their cytokines consisted of KL, FL, IL-3, and IL-6.
Conneally et al28 performed a suspension culture of
CD34+CD38 human cord blood cells in
serum-free culture containing KL, FL, IL-3, IL-6, and G-CSF for 5 to 8 days and observed the statistically significant twofold increase in the
competitive repopulating units. Although the cytokine combinations used
were similar, there are significant differences between their and our
studies. We used adult human marrow cells rather than cord blood cells
and our assay was in utero transplantation to sheep fetuses rather than transplantation to NOD/SCID mice. In addition, our suspension culture
was significantly longer than that of the reported studies. Nonetheless, their results and our observations are in agreement in
that the suspension culture with similar cytokine combinations can
maintain cells that are capable of engrafting xenogeneic hosts for up
to 2 months. However, our studies suggested that the current culture
system may not be able to maintain longer term engrafting cells.
Further studies are needed for the determination of precise combinations and concentrations of cytokines for the optimal expansion of the stem cells that are capable of long-term engraftment. Both the
NOD/SCID murine model and in utero transplantation to sheep may
complement each other and be useful in this endeavor.
| |
FOOTNOTES |
Submitted August 22, 1997;
accepted January 12, 1998.
Supported by the National Institute of Health Grants No. DK/HL 48714 and DK 32294, by the Office of Research and Development, Medical
Research Service, Department of Veterans Affairs, and by a grant from
Amgen.
Address reprint requests to Makio Ogawa, MD, PhD, Ralph H. Johnson
Department of Veterans Affairs Hospital, 109 Bee St, Charleston, SC
29401-5799.
The publication costs of this article were defrayed in part by page
charge payment. This article must therefore be hereby marked
"advertisement" in accordance with 18 U.S.C. section
1734 solely to indicate this fact.
| |
ACKNOWLEDGMENT |
The authors thank Dr Haiqun Zeng for assistance in cell sorting and Dr
Pamela Pharr and Anne G. Leary for discussion and preparation of this
manuscript.
| |
REFERENCES |
1.
Williams DA:
Ex vivo expansion of hematopoietic stem and progenitor cells Robbing Peter to pay Paul?
Blood
81:3169,
1993[Free Full Text]
2.
Verfaillie CM:
Can human hematopoietic stem cells be cultured ex vivo?
Stem Cells
12:466,
1994[Medline]
[Order article via Infotrieve]
3.
Emerson SG:
Ex vivo expansion of hematopoietic precursors, progenitors, and stem cells: The next generation of cellular therapeutics.
Blood
87:3082,
1996[Free Full Text]
4.
Rebel VI,
Dragowska W,
Eaves CJ,
Humphries RK,
Lansdorp PM:
Amplification of Sca-1+LinWGA+ cells in serum-free cultures containing steel factor, interleukin-6, and erythropoietin with maintenance of cells with long-term in vivo reconstituting potential.
Blood
83:128,
1994[Abstract/Free Full Text]
5.
Knobel KM,
McNally MA,
Berson AE,
Rood D,
Chen K,
Kilinski L,
Tran K,
Okarma TB,
Lebkowski JS:
Long-term reconstitution of mice after ex vivo expansion of bone marrow cells: Differential activity of cultured bone marrow and enriched stem cell populations.
Exp Hematol
22:1227,
1994[Medline]
[Order article via Infotrieve]
6. Peters SO, Kittler ELW, Ramshaw HS, Quesenberry PJ: Murine marrow
cells expanded in culture with IL-3, IL-6, IL-11, and SCF acquire an
engraftment defect in normal hosts. Exp Hematol 23:461,1995
7.
Peters SO,
Kittler ELW,
Ramshaw HS,
Quesenberry PJ:
Ex vivo expansion of murine marrow cells with interleukin-3 (IL-3), IL-6, IL-11, and stem cell factor leads to impaired engraftment in irradiated hosts.
Blood
87:30,
1996[Abstract/Free Full Text]
8. Spangrude GJ, Brooks DM, Tumas DB: Long-term repopulation of
irradiated mice with limiting numbers of purified hematopoietic stem
cells: In vivo expansion of stem cell phenotype but not function. Blood
85:1006,1995
9.
Holyoake TL,
Freshney MG,
McNair L,
Parker AN,
McKay PJ,
Steward WP,
Fitzsimons E,
Graham GJ,
Pragnell IB:
Ex vivo expansion with stem cell factor and interleukin-11 augments both short-term recovery posttransplant and the ability to serially transplant marrow.
Blood
87:4589,
1996[Abstract/Free Full Text]
10.
Ogawa M:
Differentiation and proliferation of hematopoietic stem cells.
Blood
81:2844,
1993[Abstract/Free Full Text]
11.
Yonemura Y,
Ku H,
Hirayama F,
Souza LM,
Ogawa M:
Interleukin-3 or interleukin-1 abrogates the reconstituting ability of hematopoietic stem cells.
Proc Natl Acad Sci USA
93:4040,
1996[Abstract/Free Full Text]
12.
Yonemura Y,
Ku H,
Lyman SD,
Ogawa M:
In vitro expansion of hematopoietic progenitors and maintenance of stem cells: Comparison between FLT3/FLK2 ligand and KIT ligand.
Blood
89:1915,
1997[Abstract/Free Full Text]
13.
Zanjani ED,
Almeida-Porada G,
Flake AW:
The human/sheep xenograft model: A large animal model of human hematopoiesis.
Int J Hematol
63:179,
1996[Medline]
[Order article via Infotrieve]
14. Ogawa M, Leary AG: Erythroid progenitors, in Golde DW (ed):
Methods in Hematology, Hematopoiesis. New York, NY,
Churchill Livingstone, 1984, p 123
15.
Kawashima I,
Zanjani ED,
Almeida-Porada G,
Flake AW,
Zeng HQ,
Ogawa M:
CD34+ human marrow cells that express low levels of kit protein are enriched for long-term marrow-engrafting cells.
Blood
87:4136,
1996[Abstract/Free Full Text]
16.
Zanjani ED,
Pallavicini MG,
Ascensao JL,
Flake AW,
Langlois RG,
Reitsma M,
Mackintosh FR,
Stutes D,
Harrison MR,
Tavassoli M:
Engraftment and long-term expression of human fetal hemopoietic stem cells in sheep following transplantation in utero.
J Clin Invest
89:1178,
1992
17.
Zanjani ED,
Flake AW,
Rice H,
Hedrick M,
Tavassoli M:
Long-term repopulating ability of xenogeneic transplanted human fetal liver hematopoietic stem cells in sheep.
J Clin Invest
93:1051,
1994
18.
Brugger W,
Mocklin W,
Heimfeld S,
Berenson RJ,
Mertelsmann R,
Kanz L:
Ex vivo expansion of enriched peripheral blood CD34+ progenitor cells by stem cell factor, interleukin-1 , IL-6, IL-3, interferon- , and erythropoietin.
Blood
81:2579,
1993[Abstract/Free Full Text]
19.
Srour EF,
Brandt JE,
Briddell RA,
Grigsby S,
Leemhuis T,
Hoffman R:
Long-term generation and expansion of human primitive hematopoietic progenitor cells in vitro.
Blood
81:661,
1993[Abstract/Free Full Text]
20.
Henschler R,
Brugger W,
Luft T,
Frey T,
Mertelsmann R,
Kanz L:
Maintenance of transplantation potential in ex vivo expanded CD34+-selected human peripheral blood progenitor cells.
Blood
84:2898,
1994[Abstract/Free Full Text]
21.
Sui X,
Tsuji K,
Tanaka R,
Tajima S,
Muraoka K,
Ebihara Y,
Ikebuchi K,
Yasukawa K,
Taga T,
Kishimoto T,
Nakahata T:
gp130 and c-kit signalings synergize for ex vivo expansion of human primitive hemopoietic progenitor cells.
Proc Natl Acad Sci USA
92:2859,
1995[Abstract/Free Full Text]
22.
McKenna HJ,
deVries P,
Brasel K,
Lyman SD,
Williams DE:
Effect of flt3 ligand on the ex vivo expansion of human CD34+ hematopoietic progenitor cells.
Blood
86:3413,
1995[Abstract/Free Full Text]
23.
Petzer AL,
Hogge DE,
Lansdorp PM,
Reid DS,
Eaves CJ:
Self-renewal of primitive human hematopoietic cells (long-term-culture-initiating cells) in vitro and their expansion in defined medium.
Proc Natl Acad Sci USA
93:1470,
1996[Abstract/Free Full Text]
24.
Soma T,
Yu JM,
Dunbar CE:
Maintenance of murine long-term repopulating stem cells in ex vivo culture is affected by modulation of transforming growth factor- but not macrophage inflammatory protein-1 activities.
Blood
87:4561,
1996[Abstract/Free Full Text]
25.
Brugger W,
Heimfeld S,
Berenson RJ,
Mertelsmann R,
Kanz L:
Reconstitution of hematopoiesis after high-dose chemotherapy by autologous progenitor cells generated ex vivo.
N Engl J Med
333:283,
1995[Abstract/Free Full Text]
26.
Williams SF,
Lee WJ,
Bender JG,
Zimmerman T,
Swinney P,
Blake M,
Carreon J,
Schilling M,
Smith S,
Williams DE,
Oldham F,
Van Epps D:
Selection and expansion of peripheral blood CD34+ cells in autologous stem cell transplantation for breast cancer.
Blood
87:1687,
1996[Abstract/Free Full Text]
27.
Bhatia M,
Bonnet D,
Kapp U,
Wang JCY,
Murdoch B,
Dick JE:
Quantitative analysis reveals expansion of human hematopoietic repopulating cells after short-term ex vivo culture.
J Exp Med
186:619,
1997[Abstract/Free Full Text]
28.
Conneally E,
Cashman J,
Petzer A,
Eaves C:
Expansion in vitro of transplantable human cord blood stem cells demonstrated using a quantitative assay of their lympho-myeloid repopulating activity in nonobese diabetic-scid/scid mice.
Proc Natl Acad Sci
94:9836,
1997[Abstract/Free Full Text]
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Abstract
Introduction
Abstract