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P. 268
progenitor characteristics in MCF10A non-malignant human mammary epithelial cells. These data are
consistent with the cell of origin hypothesis since an incremental increase in stem/progenitor cell
56
population is thought to increase cancer risk. Here we compared the effect of 600 MeV/amu Fe versus
X-rays on stem/progenitor phenotype and self-renewal in the progeny of irradiated MCF10A cells. A
reporter for Let7c microRNA, whose absence indicates the frequency of undifferentiated cells, increased
in a Notch dependent manner in MCF10A that were irradiated with low LET and treated with TGFβ (Tang,
Stem Cell, 2013). Here, Let7c negative cells also increased in cultures irradiated with equal doses (50 cGy)
56
of Fe ions (1.8 fold, p< 0.05) or X-rays (3.5 fold, p<0.005) compared to control cultures. This effect was
Notch and TGFβ-dependent. We next evaluated MCF10A functional self-renewal using a mammosphere
assay. TGFβ reduced mammosphere formation, consistent with its known inhibition of self-renewal and
56
proliferation. The progeny of cells irradiated 5-6 days before with 10, 50, or 80 cGy of either high LET Fe
ions or low LET X-rays showed decreased mammosphere forming capacity as measured by a quantitative
limiting dilution assay. Notably, this decrement was blocked when cells were treated with TGFβ. Thus,
irradiation with either high or low LET similarly expand a rare population of Let7c negative MCF10A cells,
which requires TGFβ and Notch cooperation. However, functional stem cell self-renewal is compromised
in the daughters of irradiated cells, which is offset by TGFβ in a Notch independent manner.
(PS4-55) Mesenchymal stem cells reduce lung injury and prevent infection-related mortality following
irradiation. Erzsebet Szilagyi; Flavia Neri; Mark M. Gajjar; David Polchert; Mallory L. Sears; Nabil T.
Makhlouf; Brett Smith; and Amelia Bartholomew, University of Illinois, Chicago, IL
Background: Mesenchymal Stem Cells (MSC) can theoretically suppress host defenses by
suppressing T and antigen presenting cell proliferation and by reducing the numbers of pro-inflammatory
IL-1 producing M1 macrophages. MSC also can increase pro-regenerative IL-10 producing M2
macrophages, accelerating regeneration. Using a sublethal radiation exposure, we tested whether tissue
regeneration or increased mortality due to global immunosuppression would predominate with MSC
treatment. Methods: C57BL6 mice were irradiated to induce severe neutropenia and lymphopenia and
treated with autologous mesenchymal stem cells or vehicle control 24 hours post-radiation. Klebsiella
pneunomiae, was delivered intratracheally 4 days after radiation when white blood counts were low.
Results: Animals treated with radiation or Klebsiella alone had 100% survival. Animals exposed to both
radiation and Klebsiella had 25% survival, demonstrating the synergy between of radiation-related tissue
damage and infection on mortality. MSC treatment increased survival to 75%, p=0.04 and demonstrated
a significant increase in GR1+ and CD3+CD4+ T cells on day 3 (p=0.01) sustaining elevated levels through
day 18, suggesting increased production and/or release. GR-1+ cells maintained significantly higher levels
than control values, first observed on day 3 (p=0.04). Lung histology revealed decreased parenchymal
necrosis and decreased inflammatory infiltrate. Lung tissue IL-10 was increased (p=0.05) and IL-1 was
decreased with MSC treatment. Conclusion: The observed reduction of tissue injury and increased IL-10
content suggest MSC may facilitate a macrophage switch from M1 to M2 within the lung parenchyma.
Restoration of tissue integrity was associated with resistance to infection, similar to control animals
exposed to infection alone. These findings suggest a paradigm shift in the current understanding of MSC
therapeutic potential, in which the immunosuppressive effect of MSC for tissue regeneration
hierarchically supersedes immunosuppressive effects on host defense mechanisms.
266 | P a g e
consistent with the cell of origin hypothesis since an incremental increase in stem/progenitor cell
56
population is thought to increase cancer risk. Here we compared the effect of 600 MeV/amu Fe versus
X-rays on stem/progenitor phenotype and self-renewal in the progeny of irradiated MCF10A cells. A
reporter for Let7c microRNA, whose absence indicates the frequency of undifferentiated cells, increased
in a Notch dependent manner in MCF10A that were irradiated with low LET and treated with TGFβ (Tang,
Stem Cell, 2013). Here, Let7c negative cells also increased in cultures irradiated with equal doses (50 cGy)
56
of Fe ions (1.8 fold, p< 0.05) or X-rays (3.5 fold, p<0.005) compared to control cultures. This effect was
Notch and TGFβ-dependent. We next evaluated MCF10A functional self-renewal using a mammosphere
assay. TGFβ reduced mammosphere formation, consistent with its known inhibition of self-renewal and
56
proliferation. The progeny of cells irradiated 5-6 days before with 10, 50, or 80 cGy of either high LET Fe
ions or low LET X-rays showed decreased mammosphere forming capacity as measured by a quantitative
limiting dilution assay. Notably, this decrement was blocked when cells were treated with TGFβ. Thus,
irradiation with either high or low LET similarly expand a rare population of Let7c negative MCF10A cells,
which requires TGFβ and Notch cooperation. However, functional stem cell self-renewal is compromised
in the daughters of irradiated cells, which is offset by TGFβ in a Notch independent manner.
(PS4-55) Mesenchymal stem cells reduce lung injury and prevent infection-related mortality following
irradiation. Erzsebet Szilagyi; Flavia Neri; Mark M. Gajjar; David Polchert; Mallory L. Sears; Nabil T.
Makhlouf; Brett Smith; and Amelia Bartholomew, University of Illinois, Chicago, IL
Background: Mesenchymal Stem Cells (MSC) can theoretically suppress host defenses by
suppressing T and antigen presenting cell proliferation and by reducing the numbers of pro-inflammatory
IL-1 producing M1 macrophages. MSC also can increase pro-regenerative IL-10 producing M2
macrophages, accelerating regeneration. Using a sublethal radiation exposure, we tested whether tissue
regeneration or increased mortality due to global immunosuppression would predominate with MSC
treatment. Methods: C57BL6 mice were irradiated to induce severe neutropenia and lymphopenia and
treated with autologous mesenchymal stem cells or vehicle control 24 hours post-radiation. Klebsiella
pneunomiae, was delivered intratracheally 4 days after radiation when white blood counts were low.
Results: Animals treated with radiation or Klebsiella alone had 100% survival. Animals exposed to both
radiation and Klebsiella had 25% survival, demonstrating the synergy between of radiation-related tissue
damage and infection on mortality. MSC treatment increased survival to 75%, p=0.04 and demonstrated
a significant increase in GR1+ and CD3+CD4+ T cells on day 3 (p=0.01) sustaining elevated levels through
day 18, suggesting increased production and/or release. GR-1+ cells maintained significantly higher levels
than control values, first observed on day 3 (p=0.04). Lung histology revealed decreased parenchymal
necrosis and decreased inflammatory infiltrate. Lung tissue IL-10 was increased (p=0.05) and IL-1 was
decreased with MSC treatment. Conclusion: The observed reduction of tissue injury and increased IL-10
content suggest MSC may facilitate a macrophage switch from M1 to M2 within the lung parenchyma.
Restoration of tissue integrity was associated with resistance to infection, similar to control animals
exposed to infection alone. These findings suggest a paradigm shift in the current understanding of MSC
therapeutic potential, in which the immunosuppressive effect of MSC for tissue regeneration
hierarchically supersedes immunosuppressive effects on host defense mechanisms.
266 | P a g e
