in vivo 26: 9-18 (2012)
Repopulation of the Irradiation Damaged
Lung with Bone Marrow-derived Cells
MARK E. BERNARD1, HYUN KIM1, MALOLAN S. RAJAGOPALAN1, BRANDON STONE1,
UMAR SALIMI1, JEAN-CLAUDE RWIGEMA1, MICHAEL W. EPPERLY1, HONGMEI SHEN2,
JULIE P. GOFF1, DARCY FRANICOLA1, TRACY DIXON1, SHAONAN CAO1, XICHEN ZHANG1,
HONG WANG1, DONNA B. STOLZ3 and JOEL S. GREENBERGER1
1Department
of Radiation Oncology, University of Pittsburgh Cancer Institute, Pittsburgh, PA, U.S.A.;
of Surgery, University of Pittsburgh School of Medicine, Pittsburgh, PA, U.S.A.;
3Department of Cell Biology and Physiology, University of Pittsburgh Medical Center, Pittsburgh, PA, U.S.A.
2Department
Abstract. Aim: The effect of lung irradiation on reduction of
lung stem cells and repopulation with bone marrow-derived
cells was measured. Materials and Methods: Expression of
green fluorescent protein positive cells (GFP+) in the lungs of
thoracic irradiated FVB/NHsd mice (Harlan Sprague Dawley,
Indianapolis, IN, USA) was determined. This was compared to
the repopulation of bone marrow-derived cells found in the
lungs from naphthalene treated male FVB/NHsd mice and
gangciclovir (GCV) treated FeVBN GFP+ male marrow
chimeric HSV-TK-CCSP. The level of mRNA for lung stem cell
markers clara cell (CCSP), epithelium 1 (FOXJ1) and
surfactant protein C (SP-C), and sorted single cells positive for
marrow origin epithelial cells (GFP+CD45–) was measured.
Results: The expression of pulmonary stem cells as determined
by PCR was reduced most by GCV, then naphthalene, and least
by thoracic irradiation. Irradiation, like GCV, reduced mRNA
expression of CCSP, CYP2F2, and FOXJ1, while naphthalene
reduced that of CCSP and CYP2F2. Ultrastructural analysis
showed GFP+ pulmonary cells of bone marrow origin, with the
highest frequency being found in GCV-treated groups.
Conclusion: Bone marrow progenitor cells may not participate
in the repopulation of the lung following irradiation.
The bone marrow origin of epithelial cells remains a topic of
intense controversy. Initial reports of the reconstitution of total-
This article is freely accessible online.
Correspondence to: Joel S. Greenberger, MD, Department of
Radiation Oncology, University of Pittsburgh Cancer Institute, 5150
Centre Avenue, Rm. 533, Pittsburgh, PA 15232, U.S.A. Tel: +1 412
647 3602, Fax: +1 412 647 1161, e-mail: greenbergerjs@upmc.edu
Key Words: CCSP, GCV, bone marrow, lung repair, GFP, surfactant
protein C, FOXJ1.
0258-851X/2012 $2.00+.40
body irradiated mice with a single hematopoietic stem cell (1)
were confirmed by multiple reports of bone marrow-derived
cells capable of repopulating the lung (2-11), esophagus (1215), and other organs (16). Other studies suggested that the
level of repopulation of lung epithelial organs with cells of
bone marrow origin was either nonexistent or very low (17-22).
Most bone marrow-derived cells in the lung were determined to
be hematopoietic. While the bone marrow origin of epithelial
cells in irradiation-damaged tissue remains controversial, there
is clear evidence that bone marrow transplantation ameliorates
the toxicity of subtotal or total-body irradiation (16, 23, 24).
The magnitude of the contribution of bone marrow-derived
cells in ameliorating the acute toxicity of lung irradiation
damage remains controversial.
Mouse models of lung irradiation damage demonstrate
genetic strain-dependent variation (25-26), as well as a
histopathologic difference between acute radiation
pneumonitis and late irradiation alveolitis/fibrosis (24, 2729). To determine the role of bone marrow cells in the repair
of lung irradiation damage, a positive control model for the
specific removal of lung stem cells is required.
We have taken advantage of a unique model of the depletion
of pulmonary stem cells in HSV-TK-CCSP transgenic mice
(30-33). These mice demonstrate Herpes simplex virus (HSV)
thymidine kinase (TK) expression linked to the lung stem cell
(Clara-cell)-specific promoter (CCSP) (33) and when they are
treated by mini-Alzet pump administration of gangciclovir
(GCV) demonstrate a drug dose-dependent depletion of
pulmonary stem cells (30-32). Furthermore, GCV-treated HSVTK-CCSP mice demonstrate primitive lung stem cell depletion
in addition to committed pulmonary progenitor cell depletion
associated with naphthalene toxicity (30-33).
In the present studies, we utilized the FVB/NHsd (Harlan
Sprague Dawley, Indianapolis, IN, USA) background strain
mice, and a transgenic strain containing the green fluorescent
protein expressed in all cells (FVB.Cg-Tg(ACTB-
9
in vivo 26: 9-18 (2012)
EGFP)B5Nagy/J). The HSV-TK-CCSP strain mice (FVB/
NHsd background) were the positive control to evaluate the
relative effects of total lung irradiation on pulmonary toxicity
compared to the known lung toxicity induced by naphthalene
or GCV treatment. We evaluated toxin-induced depletion of
lung-specific mRNA levels, their elevation during repair of
lung damage, and the contribution of cells of bone marrow
origin in the repair and repopulation process. We utilized
HSV-TK-CCSP recipient mice, chimeric for sex-mismatched
GFP+ bone marrow to determine the bone marrow origin of
both hematopoietic marked CD45+ cells, as well as CD45–
epithelial cells of bone marrow origin in the irradiated lung.
Materials and Methods
Animals. All animal experiments and procedures were approved by
the Institutional Animal Care and Use Committee (IACUC) at
University of Pittsburgh. Experiments were performed on
FVB/NHsd (wild-type) and HSV-TK-CCSP transgenic littermates
of 6-10 weeks of age.
Naphthalene treatment. Naphthalene administration was performed
in FVB/NHsd mice as previously described to target lung cell
populations for destruction (34). Briefly, naphthalene (Sigma
Chemical, St. Louis, MO, USA) was dissolved in corn oil and
administered at a concentration of 20 mg/ml. Each animal received
200 mg naphthalene per kilogram body weight through an
intraperitoneal injection. Naphthalene was also given with or without
our manganese superoxide dismutase plasma liposome (MnSODPL), which has been shown to reduce oxidative stress in response to
irradiation (35-36), and bone marrow transplantation (BMT).
Irradiation of FVB/NHsd mice. Irradiation was administered to
FVB/NHsd female or to FeVB/n female (FVB.Cg-Tg(ACTBEGFP)B5Nagy/J male marrow chimeric) mice by a linear
accelerator to a dose of 19 Gy to the thorax with head and abdomen
shielded (37). Mice were followed up for one and two weeks after
irradiation and then real time polymerase chain reaction (RT-PCR)
studies were performed on lungs as described below. Chimeric
FVB/NHsd then received a combination of granulocyte colony
stimulating factor (G-CSF) (PeproTech, Rocky Hill, NJ, USA) and
bone marrow transplantation (BMT) to promote homing of bone
marrow including donor marrow origin GFP+ bone marrow
progenitor cells to the lung (27).
HSV-TK-CCSP Transgenic mice and GCV. Generation of and
characterization of HSV-TK-CCSP transgenic mice has been
previously described (38). Transgenic mice were treated with GCV
(Roche Applied Science, Indianapolis, IN, USA) which was
delivered over a 24 h period via mini osmotic pumps (ALZET, Palo
Alto, CA, USA) as described previously (38). Briefly, GCV was
dissolved in normal saline at concentrations of either 25 or 50 mg/ml
and loaded into mini osmotic pumps. Pumps which were designed
to discharge over 24 h were subcutaneously implanted and were then
retrieved after 5-7 days. Control mice were implanted with mini
osmotic pumps filled with normal saline. Mice were allowed ad
libitum access to food and water and their weights were carefully
monitored both prior to treatment and daily thereafter.
10
Tissue collection and RT-PCR analysis of lung-specific mRNA levels.
After sacrificing the mouse, the heart was perfused with up to 10
ml of PBS buffer to clear the lungs of circulatory blood. The right
lung was then inflated, fixed in 2% paraformaldehyde in PBS (pH
7.4) and placed into 2% paraformaldehyde in PBS solution at 4˚C
overnight. Fixed lungs were immersed in 30% sucrose overnight at
4˚C, then frozen in liquid nitrogen-cooled 2-methylpentane. Frozen
lungs were stored at –80˚C until sectioned.
The left lung lobes were tied off prior to inflation and fixation of
the right lung and were immediately removed and frozen on dry ice.
Using a standard Trizol-based methodology (TRIzol reagent,
Invitrogen, Carlsbad, CA, USA), DNA was extracted, and cDNA
was generated using a reverse transcription kit (High Capacity
cDNA Reverse Transcriptase Kit; Applied Biosystems, Foster City,
CA, USA). mRNA expression of pulmonary stem cell markers
CCSP (clara cell secretory protein) which is a pulmonary progenitor
cell; CYP2F2 (cytochrome P450, family 2, subfamily f, polypeptide
2; Gene Bank: NM 007817.2), a gene responsible for the
metabolism of compounds in Clara cells; FOXJ1 (Forkhead box
protein J1; Gene Bank: NM 008240.3); and SPC (surfactant protein
c; Gene Bank: NM 011359.2), responsible for the production of
surfactant, were quantified by RT-PCR. RT-PCR was performed
using a robotic automated pipetting system (39) (EPMotion 5070;
Eppendorf AG, Hamburg, Germany) to ensure high precision and
throughput and run on an RT-PCR machine (Realplex 2 S;
Eppendorf AG). mRNA expression was compared using the ΔΔCt
method and a standard pooled total lung RNA preparation as the
calibrator and with the GUSB gene as the housekeeping gene.
Bone marrow transplantation. Allogeneic BMT from GFP positive
FVB/NHsd mice was conducted in some mice after lung toxicant
administration to determine whether this would aid in repair and
repopulation of depleted cells. Bone marrow was isolated from the tibia
and femurs of FVB.Cg-Tg(ACTB-EGFP)B5Nagy/J mice and 1×106
bone marrow cells were intravenously injected into recipient mice (27).
Generation of GFP+ chimeric mice. Generation of HSV-TK-CCSP
marrow chimeric and FVB/NHsd marrow chimeric mice has been
previously described (40-41). Bone marrow was harvested from the
femur of male GFP+ homozygous FVB.Cg-Tg(ACTB-EGFP)
B5Nagy/J GFP+ transgenic mice. HSV-TK-CCSP or FVB/NHsd
female recipient mice received 10 Gy total body irradiation using a
137Cs irradiator (27). After irradiation, 1×106 GFP+ cells were injected
into the recipient mice via the tail vein. Percentage of chimerism was
then measured 60 days later using flow cytometry for GFP+
peripheral blood cells representing over 70% of cells.
Explant of lung and sorting for GFP+ cells. An experiment to
determine whether BMT stimulated homing of GFP+ donor cells to
the lungs in drug-treated or irradiated mice was carried out. Mice
were sacrificed, and the circulatory system was perfused with 10 ml
of PBS. Next 1 ml dispase (50U/ml; Becton Dickinson, Franklin
Lakes, NJ, USA) and 1 ml 1% LMP agarose were instilled into the
lungs by intratracheal cannulation and the lungs were then
immediately covered in ice. Right lung lobes were then removed,
minced and incubated with 2 μg/ml collegenase/dispase (In
Vitrogen, Carlsbad, CA, USA) in PBS for 45 minutes in a highhumidity incubator at 37˚C for digestion. Cells were then
cytocentrifuged and resuspended in Dulbecco’s Modified Eagle
Medium (DMEM) (Mediatech, Inc., Manassas, VA, USA), drawn
Bernard et al: Bone Marrow-derived Cells in Lung Repair
through proportionately smaller gauge needles up to a 27-gauge
needle and filtered twice through 40 μm cell strainers to remove cell
clumps. Cells were then resuspended in red blood cell lysis buffer
for 4 minutes, washed in DMEM/10% fetal bovine serum (FBS) and
resuspended in PBS/10% FBS at a density of approximately
1×106/100 μl. Cells were then incubated in Ter119 antibody and
CD45 antibody for 20 minutes to select and remove blood cells.
Propidium iodide (2 μg/ml) was added to the cells for
discrimination of dead cells. The GFP+CD45+ and GFP+CD45– cells
were then isolated by flow cytometry.
Immunofluorescence analysis of lungs. Lungs were sectioned at 6
μm and affixed to charged slides (Superfrost/Plus; Fisher, Pittsburgh,
PA, USA). Tissue was rinsed three times in PBS, rinsed three times
in PBS containing 0.5% BSA (BSA Buffer) and blocked in 2% BSA
in PBS for 30 min at room temperature. Primary antibodies diluted in
BSA buffer were added to sections for 1 h at room temperature.
Primary antibodies used were: rabbit anti-GFP (1:100; Abcam,
Cambridge, MA, USA); rat anti-mouse CD45 (1:100; BD
Pharmingen, San Diego, CA, USA) and goat anti-surfactant protein
C (1:100; Santa Cruz Biotechnology, Santa Cruz, CA, USA).
Sections were washed five times in BSA Buffer then fluorescently
tagged secondary antibodies, diluted in BSA buffer, were added to
the sections for 1 h at room temperature. Secondary antibodies used
here were donkey anti-rabbit Alexa 488 (1:500; Invitrogen, Carlsbad,
CA, USA), donkey anti-rat Cy3 and donkey anti-goat Cy3 (1:1000;
Jackson ImmunoLabs, West Grove, PA, USA). Tissue were washed
three times in PBG buffer, three times in PBS, then nuclei were
stained using 0.001% Hoechst dye (bis benzimide) in double-distilled
water for 30 s. Following a wash in PBS, the tissue was coverslipped
using gelvatol (23 g poly(vinyl alcohol) 2000, 50 ml glycerol, 0.1%
sodium azide in 100 ml PBS) and viewed on an Olympus Fluoview
1000 confocal microscope (Olympus Corporation, Center Valley, PA,
USA). Collages were prepared using Photoshop CS software (Adobe
Systems Incorporated, San Jose, CA, USA).
Transmission electron microscopy of GFP+-sorted lung cells. Cell
suspensions were fixed in 2.5% glutaraldehyde in PBS then immediately
pelleted in a 1.5 ml microfuge tube at 300 × g. After 1 h fixation, the
supernatant was removed and the cell pellets were washed three times in
PBS then post-fixed in 1% OsO4, 1% K3Fe(CN)6 for 1 h. Following
three additional PBS washes, the pellet was dehydrated through a graded
series of 30-100% ethanol, then placed in 100% propylene oxide, then
infiltrated in a 1:1 mixture of propylene oxide Polybed 812 epoxy resin
(Polysciences, Warrington, PA, USA) for 1 h. After several changes of
100% resin over 24 h, the pellet was embedded in a final change of
resin, cured at 37˚C overnight, followed by additional hardening at 65˚C
for two more days. Ultrathin (60 nm) sections were collected on 200
mesh copper grids, stained with 2% uranyl acetate in 50% methanol for
10 min, followed by 1% lead citrate for 7 min. Sections were imaged at
80 kV using a JEOL JEM 1011 transmission electron microscope
(Peabody, MA, USA) fitted with a side mount AMT 2k digital camera
(Advanced Microscopy Techniques, Danvers, MA, USA).
Results
Thoracic irradiation causes less depletion of primitive lung
stem cells than does naphthalene treatment of FVB/NHsd mice.
The changes in pulmonary mRNA levels of CCSP, CYP2F2,
FOXJ1, and SPC were quantitated by robotic semi-automated
Table I. Effect of irradiation compared to naphthalene on lung-associated
markers in FVB/NHsd mice.
Group (n=3)
CCSP
Naphthalene+ 19.6%±06.5
MnSOD-PL (p=0.0008)*
(p=0.9601)κ
Naphthalene+ 19.6%±0.11
MnSOD-PL+ (p=0.0002)*
BMT
(p=0.9316)κ
Naphthalene+ 7.2%±1.0
BMT
(p<0.0001)*
(p=0.0367)κ
Naphthalene
20%±4.0
(p=0.0003)*
15 Gy day 7
62.8%±9.4
(p=0.0262)*
(p=0.0277)Φ
15 Gy day 14 30%±0.0177
(p=0.0003)Φ
Control
100%
CYP2F2
37.0±21.8
(p=0.0105)*
(p=0.9722)κ
42%±08.1
(p=0.0043)*
(p=0.7216)κ
18.9%±3.1
(p=0.0002)*
(p=0.1028)κ
37.6%±8.3
(p=0.0035)*
45.2%±6.0
(p=0.0662)*
(p=0.0028)Φ
65.1%±0.053
(p=0.0110)Φ
100%
FOX1
SPC
53.7%±20.5 32.6%±09.9
(p=0.0949)* (p=0.0042)*
(p=0.2412)κ (p=0.1332)κ
80.8%±31.7 49.5%±0.7
(p=0.5836)* (p=0.0010)*
(p=0.8336)κ (p=0.305)κ
40.5%±5.3
30.9%±4
(p=0.0016)* (p=0.0006)*
(p=0.0401)κ (p=0.089)κ
88.7%±15.1 69.2%±16.7
(p=0.5232)* (p=0.1558)*
69.3%±8.6 96.6%±2.3
(p=0.1154)* (p=0.6113)*
(p=0.0415)Φ (p=0.9221)Φ
49.6%±0.047 123.3%±0.363
(p=0.0025)Φ (p=0.5599)Φ
100%
100%
FVB/NHsd mice were treated with naphthalene or a combination of
naphthalene along with MnSOD-PL and BMT. Mice were sacrificed 3
days later and the left lobes excised, then mRNA extracted and tested for
levels of CCSP, CYP2F2, FOXJ1, and SPC. Other FVB/NHsd mice were
irradiated to 15 Gy to the thorax then 7 or 14 days later the left lobes
excised, tested for mRNA concentrations of CCSP, CYP2F2, FOXJ1, and
SPC as described in the Materials and Methods. *signifies p-value
compared to control, κ signifies naphthalene alone, and Φ signifies 15
Gy day 7 or day 14.
RT-PCR in FVB/NHsd mice treated with lung irradiation to 15
Gy or with naphthalene (Table I and Figure 1). Naphthalene
reduced expression of CCSP and CYP2F2 compared to the
control untreated group after 3 days. Injection of bone marrow
following naphthalene treatment may be able to prevent the
decrease in primitive lung stem cells by providing a source of
hematopoietic pluripotential stem cells, however naphthalene
plus BMT resulted in reduction of CCSP, CYP2F2, FOXJ1,
and SPC. Pretreatment with MnSOD-PL which has been
demonstrated to protect the lung from the development of
organizing alveolitis or fibrosis following irradiation (37) alone
or with BMT did not protect the lung stem cells as seen by
reduced expression of CCSP, CYP2F2 , and SPC.
Thoracic irradiation reduced the mRNA expression of
CCSP, CYP2F2, and FOXJ1 at seven and fourteen days after
irradiation when compared to the controls (Table I and
Figure 1). There was no significant change in SPC mRNA
expression at day 7 or 14 after irradiation. Thoracic
irradiation caused less depletion of early pulmonary cell
markers by RT-PCR assay than did naphthalene treatment.
GCV treatment of FVB/NHsd background HSV-TK-CCSP
mice causes the greatest depletion of primitive stem cell
markers measured by RT-PCR. Gene expression by
11
in vivo 26: 9-18 (2012)
Figure 1. Levels of mRNA expression for CCSP, CYP2F2, FOXJ1, and SPC in naphthalene treated or thoracic irradiated FVB/NHsd mice. Lungs were
isolated from FVB/NHsd mice which had received naphthalene, naphthalene plus MnSOD-PL, naphthalene plus bone marrow transplant (BMT) or
naphthalene plus MnSOD-PL and BMT 3 days previously. The lungs from other FVB/NHsd mice which had been irradiated to 15 Gy were isolated
7 days and 14 days after irradiation with mRNA extracted and RT-PCR performed to measure gene expression for CCSP, CYP2F2, FOXJ1 and SPC.
measuring mRNA levels for CCSP, CYP2F2, FOXJ1, and
SPC in HSV-TK-CCSP mice was tested after mice received
either 25 mg/ml of GCV, 50 mg/ml of GCV, or saline
compared to untreated control mice (Table II and Figure 2).
As shown in Table II, 25 mg/ml or 50 mg/ml of GCV
reduced mRNA expression for CCSP, CYP2F2, and FOXJ1
compared to the untreated control group. There was no
detectable change in SPC expression. Saline treatment
reduced mRNA expression of FOXJ1 and SPC, but did not
change levels of CCSP or CYP2F2.
Cell sorting reveals that the greatest removal of primitive
lung stem cells follows GCV treatment in GFP+ chimeric
HSV-TK-CCSP mice. The number of GFP+CD45– and
GFP+CD45+ cells collected from the lungs of GFP+ chimeric
transgenic CCTK mice treated with thoracic irradiation
(Table III) or GCV for 7 days (Table IV) was determined by
flow cytometry of excised lungs. There were low numbers of
12
GFP+CD45- cells detected in both irradiated and GCVtreated HSV-TK-CCSP GFP+ chimeric mice.
Immunohistochemical staining and ultrastructural examination
of GFP+ CD45– and GFP+ CD45+ cells in lungs of chimeric
HSV-TK-CCSP (FVB/NHsd) mice reveals rare epithelial cells
of bone marrow origin. Staining and cell characterization of
lung samples is shown in Figures 3-5. The chimeric FVB/NHsd
mice had few GFP+ cells which were positive for the pulmonary
marker SPC, characteristic of type II pneumocytes. Sorted cells
from chimeric FVB/NHsd female mice receiving different
treatments were examined by transmission electron
microscopically to determine whether the GFP+ cells were
differentiated lung cells displaying microvilli and intracellular
multilammelar bodies. This would demonstrate that bone
marrow cells can differentiate into mature alveolar type 2 cells.
GFP+CD45– cells were found (Figure 5); however, GFP+CD45+
cells were noted predominantly.
Bernard et al: Bone Marrow-derived Cells in Lung Repair
Table II. Impact of gangciclovir (GCV) treatment on expression of mRNA
of lung-associated markers in HSV-TK-CCSP mice.
Group (n=3)
25 mg/ml GCV
CCSP
4.3%±1.6
(p<0.0001)
50 mg/ml GCV
2.3%±2.1
(p<0.0001)
Saline
15.0%±2.2
FOXJ1
30.5%±6.0 268.3%±133.0
(p<0.0001) (p=0.0004)
11%±10.2
SPC
9.3%±5.7
(p=0.2827)
184.6%±46.9
(p=0.0010) (p=0.0001)
(p=0.1589)
102.5%±12.2 86.0%±11.3 49.6%±4.9
31.8%±12.8
(p=0.9499)
Control
CYP2F2
100%
(p=0.2144) (p=0.0008)
100%
100%
(p=0.0056)
100%
HSV-TK-CCSP mice were treated with either 25 mg/ml of GCV, 50
mg/ml of GCV, or saline (n=3/group). Mice were sacrificed 7 days later
and the left lobes excised and mRNA extracted, then concentrations of
CCSP, CYP2F2, FOXJ1, and SPC were measured as described in the
Materials and Methods. P-values compare treated mice to controls.
Figure 2. Levels of mRNA expression for CCSP, CYP2F2, FOXJ1, and
SPC in GCV-treated HSV-TK-CCSP mice. Lungs were isolated from
mice that had received either 25 or 50 mg/ml of GCV, saline or control
mice 7 days after the pumps were implanted. RT-PCR was performed
on mRNA extracted from the lungs to determine gene expression.
Table III. Quantitation of migration of GFP+ cells from bone marrow
transplant to the irradiated lung.
Treatment
group
GFP+ CD45– lung cells
n
0 Gy
450±95
GFP+ CD45+ lung cells
% per
100,000 cells
N
% per
100,000 cells
0.4±0.1
9298±713
9.2±0.8
10023±1546
10.1±1.5
12539±1773
12.5±1.8
Table IV. Quantitation of migration of GFP+ cells from bone marrow
transplant to the gangciclovir-treated lungs of HSV-TK-CCSP mice.
Treatment
group
GFP+ CD45– lung cells
n
% per
100,000
lung cells
81±39
126±8.3
(p=0.979)
0.1±0.1
0.1±0.1
(p=0.4542)
(p=0.0341*) (p=0.0242*)
19 Gy
310±16
0.3±0.1
(p=0.0187*) (p=0.0072*)
19 Gy+G-CSF
189±37
0.2±0.1
Control
GCV
(p=0.0699Φ) (p=0.0693Φ)
19
Gy+GFP+
bone marrow
19 Gy+GFP+
299±36
0.3±0.1
8118±555
8.1±0.6
11475±198
11.5±0.2
(p=0.0004Φ)
(p=0.0004Φ)
(p=0.0766*) (p=0.1053*)
206±21
0.3±0.1
bone marrow+ (p=0.0372*) (p=0.0252*)
G-CSF
FVB/NHsd female mice were irradiated to 10 Gy total body irradiation
followed by intravenous injection of 1×106 bone marrow cells from GFP+
male mice. Sixty days later mice were divided into 5 treatment groups: 1)
control nonirradiated mice; 2) irradiation to 19 Gy to the thoracic cavity
(head and abdomen shielded); 3) 19 Gy followed by G-CSF injection; 4)
19 Gy followed by GFP+ intravenous injection with bone marrow 5 days
later, and 5) 19 Gy plus bone marrow and G-CSF. Thirty days later, mice
were sacrificed and lungs excised. Left lungs were fixed, sectioned, and
examined for GFP+ cells and surfactant. Right lungs were prepared as
single cell suspensions and sorted for GFP+CD45– and GFP+CD45+ cells
by flow cytometry. Irradiation resulted in few GFP+CD45– lung cells. GCSF treatment resulted in no greater numbers of GFP+CD45– cells but
increased the detectable number of GFP+CD45+ cells. *Versus 19 Gy plus
G-CSF; Φ versus 19 Gy plus bone marrow plus G-CSF.
GFP+ CD45+ lung cells
n
% per
100,000
lung cells
309±102
0.3±0.1
10035±1226 10.0±1.2
(p=0.0011) (p=0.0012)
HSV-TK-CCSP female mice were total-body irradiated to 10 Gy
followed by injection of 1×106 bone marrow cells from male GFP+
mice. Sixty days later mice were implanted with mini-Alzet pumps
containing either saline (control) or 25 mg/ml gangcyclovir (GCV) and
treated for 14 days. Mice were sacrificed 30 days later. The left lungs
were removed and examined for GFP+ cells and surfactant. The right
lungs were prepared as single cell suspensions and sorted for
GFP+CD45– and GFP+CD45+ cells. GCV treatment resulted in a
significant increase of GFP+CD45+ cells but not of GFP+CD45– cells.
Discussion
Thoracic irradiation causes acute and chronic (late) toxicity
(23-24). Acute radiation pneumonitis in patients is dependent
upon total irradiation dose, fraction size, and the duration of
radiation treatment (42-48). In models of single fraction
irradiation damage, a decrease in inflammatory cytokines
13
in vivo 26: 9-18 (2012)
Figure 3. Immunofluorescent staining for GFP+ cells in the lung of thoracic-irradiated female FVB/NHsd mouse chimeric for male GFP+ bone
marrow. Mice received 15 Gy thoracic irradiation, bone marrow transplant (BMT), and/or G-CSF as described in the Materials and Methods. Sixty
days after treatment, mice were sacrificed, the left lung lobes removed, sectioned and stained for GFP (green), pulmonary surfactant protein c (red),
and DNA (blue). A: Image shows a surfactant+ GFP+ cell (arrow) within the lung parenchyma (×600). B: Surfactant+ GFP+ cell (arrow) shown in
relation to alveolar spaces shown in A in a differential interference microscopy overlay (×600). C: Higher magnification image (×1200) with arrow
indicating GFP+ cell with cytoplasmic GFP and intracellular vacuolar-surfactant protein c staining (red). Bar represents 10 μm in each panel.
Figure 4. Immunofluorescent staining for GFP+ cells in lung of GCV treated female HSV-TK-CCSP mouse chimeric for GFP+ male bone marrow.
Mice received 25 mg/ml of GCV by mini Alzet pumps as described in the Methods. Sixty days after treatment, mice were sacrificed, the left lung lobes
excised, sectioned, and stained for GFP (green), CD45 (red), and DNA (blue). A: Image shows GFP+CD45+ cells (×400) which represent a large
number of GFP+ cells. B and C: Arrows indicate macrophages (×600 and ×1200, respectively). GFP+CD45+ cells were also abundant, with very
few GFP+CD45– cells observed in the sections. Bar represents 10 μm in each panel.
and migration into the lungs of lymphocytes,
polymorphonuclear leukocytes, and macrophages has been
demonstrated (36-37). Irradiation damage is associated with
depletion of intrinsic lung macrophages, endothelial cells in
the microvasculature, and swelling of both vascular and
epithelial compartments in the lung (23-24). Following
recovery from pneumonitis, there is a latent period during
which histopathologic evidence of lung damage is absent. A
late phase of organizing alveolitis/fibrosis is then detected at
around 100 to 150 days in the C57BL/6J model (27, 36). In
14
other mouse strains, radiation pneumonitis may be more
severe and lung fibrosis less dramatic (25-26). Mouse strains
both sensitive and relatively resistant to lung irradiation have
been described (25). Pulmonary toxicity in humans follows
the same patterns dependent upon total dose, fraction size,
and volume of lung treated (49-51). Acute radiation
pneumonitis remains a clear radiation dose-limiting toxicity
in thoracic radiotherapy and can be fatal, particularly in a
setting of opportunistic bacterial or viral infection, and
toxicity of concomitant or sequential chemotherapy (52-53).
Bernard et al: Bone Marrow-derived Cells in Lung Repair
Figure 5. Transmission electron micrographs of isolated lung cells from thoracic irradiated female HSV-TK-CCSP female mouse chimeric for GFP+
male bone marrow treated with 25 mg/ml of GCV. Chimeric HSV-TK-CCSP female mice were sacrificed 60 days after GCV treatment, the right
lung lobes excised, and single cell suspensions sorted for GFP+CD45– and GFP+CD45+ cells using flow cytometry. Sorted cells were then processed
for transmission electron microscopy as described. A: Type II alveolar pneumocyte isolated from the GFP+CD45– fraction. Characteristic
intracellular multilammelar bodies (arrows) and membrane-associated microvilli (arrowheads) are present. B: Morphology of hematopoietic cells
found in the GFP+CD45+ fraction, which include neutrophils, macrophages, and lymphocytes.
There has been excitement in recent years regarding the
reported plasticity of bone marrow stem cells with respect to
their capacity to differentiate to cells of epithelial origin (1,
54-56). Since the initial reports of bone marrow origin of
pulmonary epithelial cells, there has been much controversy
and publications both confirm (2-11) or fail to confirm (1722) the capacity of bone marrow stem cells to differentiate
into pulmonary epithelial cells. A major obstacle in resolving
this controversy has been the unavailability of an appropriate
animal model for selected removal of lung stem cells in
preparation of the ‘niche’ or homing cell-site for circulating
stem cell progenitors of bone marrow origin. We took
advantage of an appropriate positive control model that
selectively eliminates lung stem cells. HSV-TK-CCSP mice
demonstrate GCV-mediated effective removal of CCSPsensitive lung stem cells in a dose-dependent manner.
Primitive lung stem cells are removed in a quantifiable
fashion, measurable by both drop in levels of mRNA for lung
stem cell-specific markers, and through histopathologic
evidence of depletion of cells at the bronchial/alveolar
margin (30-33, 38). During recovery, repopulation of the
lung is associated with return to normal levels of mRNA for
lung cell-specific markers (38). In the present studies, we
utilized the HSV-TK-CCSP mouse strain to measure
migration of bone marrow-derived cells to the lung in sexmismatched FVB.Cg-Tg(ACTB-EGFP)B5Nagy/J chimeric
mice treated with GCV compared to thoracic irradiation, and
the pulmonary toxin naphthalene.
GCV treatment of HSV-TK-CCSP chimeric mice resulted
in detectable clearing of stem cells that may have allowed
migration to the lung of chimeric bone marrow-derived
GFP+CD45– cells shown by both histochemistry in situ, and
by transmission electron microscopy of removed sorted cells,
to be epithelial in origin. However, the majority of bone
marrow-derived cells migrating into the lungs were of
hematopoietic origin and GFP+CD45+. Both thoracicirradiated and naphthalene-treated mice demonstrated a lower
level of bone marrow-derived progenitor cell migration into
the lungs. These studies confirm and extend previous
publications demonstrating that GCV treatment in HSV-TKCCSP mice specifically removes primitive hematopoietic
stem cells compared to naphthalene treatment. Furthermore,
data support the notion that the stem cell niche in the lung
must be cleared by GCV treatment to allow a suitable homing
site for bone marrow-derived cells (38). In an attempt to
enhance homing to niche-cleared sites, we treated mice with
the bone marrow mobilization drug, G-CSF. Other mice were
treated by intratracheal injection of MnSOD-PL (37), shown
15
in vivo 26: 9-18 (2012)
to facilitate improved tolerance to thoracic irradiation by
removal of oxidative stress. In the present studies, BMT alone
led to the highest degree of measurable GFP+CD45– cells of
bone marrow origin in the lung. Further studies will be
required to determine whether an optimized schedule of GCSF administration and/or MnSOD-PL intrapulmonary
delivery can facilitate a greater degree of homing of bone
marrow-derived cells to the lungs in GCV-treated mice. In
contrast, naphthalene treatment resulted in non-specific
toxicity of multiple lung cell phenotypes and did not lead to
increased bone marrow-derived cell migration into the lungs.
Thoracic irradiation did not significantly remove lung stem
cells nor did it facilitate migration into the lungs of bone
marrow-derived stem cells, detectable neither by mRNA level
measurements, nor by bone marrow-derived cells found in
single-cell suspensions of sorted lung cells after BMT. Thus,
the present studies establish a relatively low level of lung
stem cell depletion by single fraction thoracic irradiation.
Whether fractionated irradiation depletes stem cells to a
greater degree is the subject of current investigation.
In contrast to the paucity of evidence for bone marrowderived progenitors of lung epithelium in the acute phase of
irradiation damage, there is evidence that bone marrowderived cells play a role in the late injury of organizing
alveolitis/radiation fibrosis (27-29). This late injury is
associated with migration into the lungs of a separate
population of cells known as bone marrow stromal cells
(mesenchymal stem cells, mesenchymal stromal cells).
Further studies are required to determine whether effective
clearance of the bone marrow stem cell niche in a setting of
less oxidative stress and less toxicity can result in improved
migration into the lungs of bone marrow-derived stem cells
of epithelial progenitors facilitating irradiation repair (27).
The mechanism by which late radiation fibrosis/organizing
alveolitis is associated with robust support to the lungs of
bone marrow-derived cells, although of a different cell
phenotype, may be attributable to lung production of
chemotactic marrow mobilizing cytokines (27-29). Further
studies will be required to confirm this proposed mechanism.
The present results showed that thoracic irradiation
minimally eliminates stem cells, specifically Clara cells, in
lungs and this decrease is modestly present for up to 14 days
after treatment. This time coincides with irradiation having
a toxic effect upon rapidly dividing cells which is seen
clinically in total-body irradiation and is part of the regimen
for BMT in order to eliminate the bone marrow’s progenitor
population (57-58).
Naphthalene treatment reduced pulmonary stem cells and
treatment with antioxidant MnSOD-PL did help to attenuate
the depletion of pulmonary Clara cells which was correlated
with MnSOD-PL protection of esophageal and lung cells
from ionizing irradiation (13, 61). Both swallowed
administration of MnSOD-PL and inhaled administration of
16
MnSOD-PL has also shown to increase homing of GFP+
bone marrow cells to irradiated esophagus and lung,
respectively (13, 27, 62-63). Therefore, it is possible that
MnSOD-PL increases homing of GFP+ bone marrow
progenitors into the lung without altering the initial decrease
in lung progenitor cells caused by the toxin exposure.
We also showed that G-CSF did not increase homing of
GFP+ bone marrow progenitor cells into the lung. While G-CSF
is responsible for increase mobilization of the bone marrow
progenitor cells (20), the amount of inflammation associated
with thoracic irradiation (64-66) could have prevented the
mobilized progenitor cells from homing to the lung.
Clearing stem cells by GCV treatment of HSV-TK-CCSP
mice was most effective. Both 25 mg/ml and 50 mg/ml GCV
caused a dramatic decrease in CCSP expression. Since 50
mg/ml had a toxic effect, we used 25 mg/ml of GCV for the
experiments to determine whether these cleared stem cell
niches can be repopulated with bone marrow progenitor
cells. GFP+CD45– cells were present in the lungs of GCVtreated chimeric transgenic CCTK mice. The CD45+ antigen
is a marker for hematopoietic cells (59-60). Since
GFP+CD45– cells of bone marrow origin were also present,
these were likely cells that differentiated into lung
epithelium. After sorting, transmission electron microscopy
showed few cells to be epithelial. Immunohistochemical
staining was positive for GFP+, and SPC, showing a bone
marrow origin. Lower numbers of cells of bone marrow
origin were detected in the lungs of chimeric FVB/NHsd
mice treated with 19 Gy thoracic irradiation.
Further studies will be required to determine if bone
marrow progenitor cells contribute significantly to damage
repair of the irradiated lung or rather represent rare and
insignificant events.
Acknowledgements
This study was supported by grants from the NIH/CA119927 and
T32-AG21885.
The Authors thank Drs. Barry Stripp from the Division of
Pulmonary, Allergy, and Critical Care Medicine, Department of
Medicine, Duke University Medical Center, Durham, NC and Susan
Reynolds from the Department of Pediatrics, National Jewish
Medical and Research Center, Denver, CO for HSV-TK-CCSP mice,
reagents for rtPCR testing, and many helpful discussions.
References
1 Kraus DS, Theise ND, Collector MI, Henegariu O, Hwang S,
Gardner R, Neutzel S and Sharkis SJ: Multi-organ, multi-lineage
engraftment by a single bone marrow-derived stem cell. Cell
105: 369-377, 2011.
2 Gomperts BN, Belperio JA, Burdick MD and Strieter RM:
Mobilization of circulating progenitor epithelial cells with
keratinocyte growth factor aids in airway repair. Blood 108(11):
87a, 2006.
Bernard et al: Bone Marrow-derived Cells in Lung Repair
3 Zomorodian TJ, Greer D, Wood K, Foster B, Demers D, Johnson
K, Quesenberry PJ and Abedi M: Mac-1 and F4/80 surface
markers are present on murine hematopoietic stem cells. ASH
Meeting Abstracts. Blood 108(11): 1677, 2006.
4 Aliotta J, Keaney P, Passero M, Dooner M, Pimentel J, Greer D,
Demers D, Foster B, Peterson A, Dooner G, Theise N, Abedi M,
Colvin G and Quesenberry P: Bone marrow production of lung
cells: the impact of G-CSF, cardiotoxin, graded doses of irradiation,
and subpopulation phenotype. Exp Hem 34: 230-241, 2006.
5 Albera C, Polak JM, Janes S, Griffiths MJD, Alison MR, Wright
NA, Navaratnarasah S, Poulsom R, Jeffrey R, Fisher C, Burke
M and Bishop AE: Repopulation of human pulmonary
epithelium by bone marrow cells: a potential means to promote
repair. Tissue Eng 11: 7-8, 2005.
6 Suratt BT, Cool CD, Seris AE, Chen L, Varella-Garcia M, Shpall
EJ, Brown KK and Worthen GS: Human pulmonary chimerism
after hematopoietic stem cell transplantation. Am J Respir Crit
Care Med 168: 318-322, 2003.
7 Mattson J, Jansson M, Wernerson A and Hassa M: Lung epithelial
cells and type II pneuomocytes of donor origin after allogeneic
hematopoietic stem cell transplantation. Transplantation 78: 154157, 2004.
8 Kleeberger W, Versmold A, Rothamel T, Glockner S, Bredt M,
Haverich A, Lehmann U and Kreipe H: Increased chimerism of
bronchial and alveolar epithelium in human lung allografts
undergoing chronic injury. Am J Pathol 162: 1487-1494, 2003.
9 Spencer H, Rampling D, Aurora P, Bonnet D, Hart SL and Jaffe
A: Transbronchial biopsies provide longitudinal evidence for
epithelial chimerism in children following sex mismatched lung
transplantation. Thorax 60: 60-62, 2005.
10 Bittmann I, Dose T, Baretton GB, Muller C, Schwaiblmair M,
Kur F and Lohrs U: Cellular chimerism of the lung after
transplantation: an interphase cytogenetic study. Am J Clin
Pathol 115: 525-533, 2001.
11 Bruscia EM, Price JE, Cheng EC, Weiner S, Caputo C, Ferreira
EC, Egan M and Krause DS: Assessment of cystic fibrosis
transmembrane conductance regulator (CFTR) activity in CFTRnull mice after bone marrow transplantation. Proc Natl Acad Sci
USA 103(8): 2965-2970, 2006.
12 Epperly MW, Shen H, Jefferson M and Greenberger JS: In vitro
differentiation capacity of esophageal progenitor cells with
capacity for homing and repopulation of the ionizing irradiationdamaged esophagus. In Vivo 18(6): 675, 2004.
13 Niu Y, Epperly MW, Shen H, Smith T, Lewis D, Gollin S and
Greenberger JS: Intraesophageal MnSOD-plasmid liposome
administration enhances engraftment and self-renewal capacity
of the bone marrow-derived progenitors of esophageal squamous
epithelium. Gene Ther 15: 347-356, 2008.
14 Epperly MW, Zhang X, Nie S, Cao S, Kagan V, Tyurin V and
Greenberger JS: MnSOD-plasmid liposome gene therapy effects
on ionizing irradiation-induced lipid peroxidation of the
esophagus. In Vivo 19: 997-1004, 2005.
15 Epperly MW, Shen H, Zhang X, Nie S, Cao S and Greenberger JS:
Protection of esophageal stem cells from ionizing irradiation by
MnSOD-plasmid liposome gene therapy. In Vivo 19: 965-974, 2005.
16 Greenberger JS and Epperly M: Bone marrow-derived stem cells
and radiation response. Semin Radiat Oncol 19: 133-139, 2009.
17 Chang J, Summer R, Sun Xi, Fitzsimmons K and Fine A: Evidence
that bone marrow cells do not contribute to the alveolar epithelium.
Am J Respir Cell Mol Biol 33: 335-342, 2005.
18 Kotton DN, Fabian AJ and Mulligan RC: Failure of bone
marrow to reconstitute lung epithelium. Am J Respir Cell Mol
Biol 33: 328-334, 2005.
19 Davies JC, Potter M, Bush A, Rosenthal M, Geddes DM and
Alton EW: Bone marrow stem cells do not repopulate the healthy
upper respiratory tract. Pediatr Pulmonol 34: 251-256, 2002.
20 Zander DS, Bez MA, Cogle CR, Visner GA, Theise ND and
Crawford JM: Bone marrow-derived stem-cell repopulation
contributes minimally to the type II pneumocyte pool in
transplanted human lungs. Transplantation 80: 206-212, 2005.
21 Chang JC, Summer R, Sun X, Fitzsimmons F and Fine A:
Evidence that bone marrow cells do not contribute to the alveolar
epithelium. Am J Respir Cell Mo Biol 33: 335-342, 2005.
22 Kotton DN, Fabian AJ and Mulligan RC: Failure of bone
marrow to reconstitute lung epithelium. Am J Respir Cell Mol
Biol 33: 328-334, 2005.
23 Hall EJ: Radiobiology for the Radiologist (4th Edition). J.B.
Lippincott, Inc., Philadelphia, PA, 1999.
24 Rubin P and Cassarett GW: Clinical Radiation Pathology. W.B.
Saunders, Philadelphia, PA, 1968.
25 Dileto CL and Travis EL: Fibroblast radiosensitivity in vitro and
lung fibrosis in vivo: comparison between a fibrosis-prone and
fibrosis-resistant mouse strain. Radiat Res 146(1): 61-67, 1996.
26 Franko AJ and Sharplin J: Development of fibrosis after lung
irradiation in relation to inflammation and lung function in a
mouse strain prone to fibrosis. Radiat Res 140(3): 347-355, 1994.
27 Epperly MW, Guo H, Gretton JE and Greenberger JS: Bone
marrow origin of myofibroblasts in irradiation pulmonary
fibrosis. Am J Respir Cell Mol Biol 29: 213-224, 2003.
28 Ortiz LA, Gambelli F, McBride C, Gaupp D, Baddoo M,
Kaminski N and Phinney DG: Mesenchymal stem cell
engraftment in lung is enhanced in response to bleomycin
exposure and ameliorates its fibrotic effects. Proc Natl Acad Sci
USA 100(14): 8407-8411, 2003.
29 Hashimoto N, Jin H, Liu T, Chensue SW and Phan SH: Bone
marrow-derived progenitor cells in pulmonary fibrosis. J Clin
Invest 113(2): 243-251, 2004.
30 Reynolds SD, Giangreco A, Hong KU, McGrath KE, Ortiz LA
and Stripp BR: Airway injury in lung disease pathophysiology:
selective depletion of airway stem and progenitor cell pools
potentiates lung inflammation and alveolar dysfunction. Am J
Physiol Lung Cell Mol Physiol 287: L1256-L1265, 2004.
31 Hong KU, Reynolds SD, Watkins S, Fuchs E and Stripp BR:
Basal cells are a multipotent progenitor capable of renewing the
bronchial epithelium. Am J Path 164(2): 577-588, 2004.
32 Stripp BR and Reynolds SD: Bioengineered lung epithelium:
implications for basic and applied studies in lung tissue
regeneration. Am J Respir Cell Mol Biol 32: 85-86, 2005.
33 Yoshikawa S, Miyahara T, Reynolds SD, Stripp BR, Anghelescu
M, Eyal FG and Parker JC: Clara cell secretory protein and
phospholipase A2 activity modulate acute ventilator-induced
lung injury in mice. J Appl Physiol 98: 1264-1271, 2005.
34 Stripp BR, Maxson K, Mera R and Singh G: Plasticity of airway
cell proliferation and gene expression after acute naphthalene
injury. Am J Physiol 269(6 Pt1): L791-L799, 1995.
35 Guo HL, Seixas-Silva JA, Epperly MW, Gretton JE, Shin DM
and Greenberger JS: Prevention of irradiation-induced oral
cavity mucositis by plasmid/liposome delivery of the human
manganese superoxide dismutase (MnSOD) transgene. Radiat
Res 159: 361-370, 2003.
17
in vivo 26: 9-18 (2012)
36 Epperly MW, Bernarding M, Gretton J, Jefferson M, Nie S and
Greenberger JS: Overexpression of the transgene for manganese
superoxide dismutase (MnSOD) in 32D cl 3 cells prevents
apoptosis induction by TNF-α, IL-3 withdrawal and ionizing
irradiation. Exp Hematol 31: 465-474, 2003.
37 Carpenter M, Epperly MW, Agarwal A, Nie S, Hricisak L, Niu Y
and Greenberger JS: Inhalation delivery of manganese superoxide
dismutase-plasmid/liposomes (MnSOD-PL) protects the murine
lung from irradiation damage. Gene Therapy 12: 685-690, 2005.
38 Reynolds SD, Hong KU, Giangreco A, Mango GW, Guron C,
Morimoto Y and Stripp BR: Conditional clara cell ablation
reveals a self-renewing progenitor function of pulmonary
neuroendocrine cells. Am J Physiol Lung Cell Mol Physiol
278(6): L1256-L1263, 2000.
39 Rajagopalan MS, Stone B, Rwigema J-C, Salimi U, Epperly MW,
Goff J, Franicola D, Dixon T, Cao S, Zhang X, Buchholz BM,
Bauer AJ, Choi S, Bakkenist C, Wang H and Greenberger JS:
Intraesophageal manganese superoxide dismutase-plasmid
liposomes ameliorates novel total body and thoracic irradiation
sensitivity of homologous deletion recombinant negative nitric
oxide synthase-1 (NOS1–/–) mice. Radiat Res 174: 297-312, 2010.
40 Sengupta N, Caballero S, Mames RN, Butler JM, Scott EW and
Grant MB: The role of adult bone marrow-derived stem cells in
choroidal neovascularization. Invest Ophthalmol Vis Sci 44(11):
4908-4913, 2003.
41 Hashimoto N, Jin H, Liu T, Chensue SW and Phan SH: Bone
marrow-derived progenitor cells in pulmonary fibrosis. J Clin
Invest 113(2): 243-252, 2004.
42 Gopal R, Tucker SL, Komaki R, Liao Z, Forster KM, Stevens C,
Kelly JF and Starkschall G: The relationship between local dose
and loss of function for irradiated lung. Int J Radiat Oncol Biol
Phy 56(1): 106-113, 2003.
43 Yorke ED, Jackson A, Rosenzweig KE, Merrick SA, Gabrys D,
Venkatraman ES, Burman CM, Leibel SA and Ling CC: Dosevolume factors contributing to the incidence of radiation
pneumonitis in non-small cell lung cancer patients treated with
three-dimensional conformal radiation therapy. Int J Radiat
Oncol Biol Phy 54(2): 329-339, 2002.
44 Marks LB: Dosimetric predictors of radiation-induced lung
injury. Int J Radiat Oncol Biol Phy 54(2): 313-316, 2002.
45 Wu VWC, Kwong DLW and Sham JST: Target dose conformity
in 3-dimensional conformal radiotherapy and intensity
modulated radiotherapy. Radiother Oncol 71: 201-206, 2004.
46 Roof KS, Fidias P, Lynch TJ, Ancukiewicz M and Choi NC:
Radiation dose escalation in limited-stage small cell lung cancer.
Int J Radiat Oncol Biol Phy 57(3): 701-708, 2003.
47 Rosenman JG, Halle JS, Socinski MA, Deschesne K, Moore DT,
Johnson H, Fraser R and Morris DE: High-dose conformal
radiotherapy for treatment of stage IIIA/IIIB non-small cell lung
cancer: technical issues and results of a phase I/II trial. Int J
Radiat Oncol Biol Phy 54(2): 348-356, 2002.
48 Socinski MA, Rosenman JG, Halle J, Schell MJ, Lin Y, Rivera
SP, Clark J, Limentani S, Fraser R, Mitchell W and Detterbeck
FC: Dose-escalating conformal thoracic radiation therapy with
induction and concurrent carboplatin/paclitaxel in unresectable
stage IIIA/B non-small cell lung carcinoma. A modified phase
I/II trial. Cancer 92: 1213-1223, 2001.
18
49 Wu K-L, Jiang G-L, Liao Y, Qian H, Wang L-J, Fu X-L and
Zhao S: Three-dimensional conformal radiation therapy for nonsmall cell lung cancer: A phase I/II dose escalation clinical trial.
Int J Radiat Oncol Biol Phy 57(5): 1336-1344, 2003.
50 Gopal R, Starkschall G, Tucker SL, Cox J, Liao Z, Hanus M,
Kelly JF, Stevens CW and Komaki R: Effects of radiotherapy
and chemotherapy on lung function in patients with non-small
cell lung cancer. Int J Radiat Oncol Biol Phy 56(1): 114-120,
2003.
51 Emami B, Mirkovic N, Scott C, Byhardt R, Graham MV, James
AE, John MHA, Urtasun R, Asbell SO, Perez CA and Cox J:
The impact of regional nodal radiotherapy (dose/volume) on
regional progression and survival in unresectable non-small cell
lung cancer: an analysis of RTOG data. Lung Cancer 41(2): 207214, 2003.
52 Scagliotti GV and Turrisi AT 3rd: Docetaxel-based combinedmodality chemoradiotherapy for locally advanced non-small cell
lung cancer. Oncologist 8(4): 361-374, 2003.
53 Rakovitch E, Tsao M, Ung Y, Pignol J-P, Cheung P and Chow E:
Comparison of the efficacy and acute toxicity of weekly versus
daily chemoradiotherapy for non-small cell lung cancer: a metaanalysis. Int J Radiat Oncol Biol Phy 58(1): 196-203, 2004.
54 Weiss DJ, Berberich MA, Borok Z, Gail DB, Kolls IK, Penland
C and Prockop DJ: Adult stem cells, lung biology, and lung
disease. Proc Am Thorac Soc 3: 193-207, 2006.
55 Stripp BR, Maxson K, Mera R and Singh G: Plasticity of airway
cell proliferatin and gene expression after acute Naphthalene
injury. Am J Physiol Lung Cell Mol Physiol 269: L791-L799,
1995.
56 Reynolds SD, Hong KU, Giangreco A, Mango G Guron C,
Morimoto Y and Stripp BR: Conditional clara cell ablation
reveals a self-renewing progenitor function of pulmonary
neuroendocrine cells. Am J Physiol Lung Cell Mol Physiol 278:
L1256-L1263, 2000.
57 Cao X, Wu X, Frassica D, Yu B, Pang L, Xian L, Wan M, Lei
W, Armour M, Tryggestad E, Wong J, Wen CY, Lu WW and
Frassica FJ: Irradiation induces bone injury by damaging bone
marrow microenvironment for stem cells. Proc Natl Acad Sci
USA 108(4): 1609-1614, 2011.
58 Knope WH, Blom J and Grosby WH: Regeneration of locally
irradiated bone marrow. I. Dose dependent, long-term changes
in the rat with particular emphasis upon vascular and stoma
reaction. Blood 28: 398-415, 1966.
59 Shah VO, Civin CI and Loken MR: Flow cytometric analysis of
human bone marrow. IV. Differential quantitative expression of
T-200 common leukocyte antigen during normal hemopoiesis. J
Immunol 140(6): 1861-1867, 1988.
60 Ahmed N, Vogel B, Rohde E, Strunk D, Grifka J, Schulz MB
and Grassel S: CD45- positive cells of haematopoietic origin
enhance chondrogenic marker gene expression in rat marrow
stromal cells. Int J Mol Med 18(2): 233-240, 2006.
Received July 28, 2011
Revised September 16, 2011
Accepted September 19, 2011