Sensitive detection of GFP utilizing tyramide signal amplification to overcome gene silencing

A Local and Abscopal Effect Observed with Liposomal Encapsulation of Intratumorally Injected Oncolytic Adenoviral Therapy

This study evaluated the in vivo therapeutic efficacy of oncolytic serotype 5 adenovirus TAV255 in CAR-deficient tumors. In vitro experiments were performed with cell lines that expressed different levels of CAR (HEK293, A549, CT26, 4T1, and MCF-7). Low CAR cells, such as CT26, were poorly transduced by Ad in vitro unless the adenovirus was encapsulated in liposomes. However, the CT26 tumor in an immune-competent mouse model responded to the unencapsulated TAV255; 33% of the tumors were induced into complete remission, and mice with complete remission rejected the rechallenge with cancer cell injection. Encapsulation of TAV255 improves its therapeutic efficacy by transducing more CT26 cells, as expected from in vitro results. In a bilateral tumor model, nonencapsulated TAV255 reduced the growth rate of the locally treated tumors but had no effect on the growth rate of the distant tumor site. Conversely, encapsulated TAV255-infected CT26 induced a delayed growth rate of both the primary injected tumor and the distant tumor, consistent with a robust immune response. In vivo, intratumorally injected unencapsulated adenoviruses infect CAR-negative cells with only limited efficiency. However, unencapsulated adenoviruses robustly inhibit the growth of CAR-deficient tumors, an effect that constitutes an 'in situ vaccination' by stimulating cytotoxic T cells.

Semiquantitative Methods for GFP Immunohistochemistry and In Situ Hybridization to Evaluate AAV Transduction of Mouse Retinal Cells Following Subretinal Injection

The goal of this study was to develop methods for the evaluation of green fluorescent protein (GFP) and GFP transcript biodistribution in paraformaldehyde-fixed paraffin-embedded (PFPE) eye sections to assess the effectiveness of Adeno-associated virus (AAV) gene delivery in an experimental ocular toxicity study. Female C57BL/6NTac mice were administered AAV2-enhancedGFP vector once via subretinal injection. One group also received anti-inflammatory therapy (meloxicam). Immunohistochemistry (IHC) and RNA in situ hybridization (ISH) for GFP were performed on PFPE serial eye sections and evaluated using semiquantitative methods. On day 43, GFP labeling in both IHC and ISH sections was greatest in the retinal pigment epithelium, compared with other retinal layers in which expression was negative to moderate. Despite the presence of IHC GFP labeling in the photoreceptor layer (PRL) in some animals, only low numbers of transduced cells were detected by ISH in the PRL. Simultaneous analysis of IHC and ISH may be needed for comprehensive assessment of gene transduction and protein biodistribution. This study demonstrates approaches for semiquantitative evaluation of IHC and ISH that allow interpretation and reporting of GFP expression in toxicity studies.

Adipose-Derived Mesenchymal Stromal Cells Persist in Tissue-Engineered Vocal Fold Replacement in Rabbits

OBJECTIVES:

Cell therapies using mesenchymal stromal cells (MSCs) have been proposed as a promising new tool for the treatment of vocal fold scarring. However, the mechanisms by which MSCs promote healing as well as their duration of survival within the host vocal fold have yet to be defined. The aim of this work was to assess the persistence of embedded MSCs within a tissue-engineered vocal fold mucosal replacement in a rabbit model of vocal fold injury.

METHODS:

Male rabbit adipose-derived MSCs were embedded within a 3-dimensional fibrin gel, forming the cell-based outer vocal fold replacement. Four female rabbits underwent unilateral resection of vocal fold epithelium and lamina propria and reconstruction with cell-based outer vocal fold replacement implantation. Polymerase chain reaction and fluorescent in situ hybridization for the sex-determining region of the Y chromosome (SRY-II) in the sex-mismatched donor-recipient pairs sought persistent cells after 4 weeks.

RESULTS:

A subset of implanted male cells was detected in the implant site at 4 weeks. Many SRY-II-negative cells were also detected at the implant site, presumably representing native female cells that migrated to the area. No SRY-II signal was detected in contralateral control vocal folds.

CONCLUSIONS:

The emergent tissue after implantation of a tissue-engineered outer vocal fold replacement is derived both from initially embedded adipose-derived stromal cells and infiltrating native cells. Our results suggest this tissue-engineering approach can provide a well-integrated tissue graft with prolonged cell activity for repair of severe vocal fold scars.

Recruitment and activation of pancreatic stellate cells from the bone marrow in pancreatic cancer: a model of tumor-host interaction

Background and Aims

Chronic pancreatitis and pancreatic cancer are characterised by extensive stellate cell mediated fibrosis, and current therapeutic development includes targeting pancreatic cancer stroma and tumor-host interactions. Recent evidence has suggested that circulating bone marrow derived stem cells (BMDC) contribute to solid organs. We aimed to define the role of circulating haematopoietic cells in the normal and diseased pancreas.

Methods

Whole bone marrow was harvested from male β-actin-EGFP donor mice and transplanted into irradiated female recipient C57/BL6 mice. Chronic pancreatitis was induced with repeat injections of caerulein, while carcinogenesis was induced with an intrapancreatic injection of dimethylbenzanthracene (DMBA). Phenotype of engrafted donor-derived cells within the pancreas was assessed by immunohistochemistry, immunofluorescence and in situ hybridisation.

Results

GFP positive cells were visible in the exocrine pancreatic epithelia from 3 months post transplantation. These exhibited acinar morphology and were positive for amylase and peanut agglutinin. Mice administered caerulein developed chronic pancreatitis while DMBA mice exhibited precursor lesions and pancreatic cancer. No acinar cells were identified to be donor-derived upon cessation of cerulein treatment, however rare occurrences of bone marrow-derived acinar cells were observed during pancreatic regeneration. Increased recruitment of BMDC was observed within the desmoplastic stroma, contributing to the activated pancreatic stellate cell (PaSC) population in both diseases. Expression of stellate cell markers CELSR3, PBX1 and GFAP was observed in BMD cancer-associated PaSCs, however cancer-associated, but not pancreatitis-associated BMD PaSCs, expressed the cancer PaSC specific marker CELSR3.

Conclusions

This study demonstrates that BMDC can incorporate into the pancreas and adopt the differentiated state of the exocrine compartment. BMDC that contribute to the activated PaSC population in chronic pancreatitis and pancreatic cancer have different phenotypes, and may play important roles in these diseases. Further, bone marrow transplantation may provide a useful model for the study of tumor-host interactions in cancer and pancreatitis.

Spontaneous in vivo differentiation of embryonic stem cell-derived pancreatic endoderm-like cells corrects hyperglycemia in diabetic mice

BACKGROUND

Whole pancreas and islet transplantation are currently used for the treatment of type 1 diabetes. However, the major limitations of this potentially curative approach are an inadequate supply of cadaveric pancreata, lifelong immunosuppression, and chronic graft rejection. Therefore, there is an urgent need to develop new sources of insulin-producing cells (IPCs). Here, we investigated whether embryonic stem (ES) cells can be exploited for the derivation of IPCs, and whether their transplantation can correct hyperglycemia in diabetic mice.

METHODS

ES cells engineered to express pancreatic and duodenal homeobox 1 (Pdx1), a critical pancreatic transcription factor, were differentiated into pancreatic endoderm-like cells (PELCs) and evaluated for their potential to correct hyperglycemia after transplantation in diabetic mice.

RESULTS

After systemic injection, PELCs localized to the pancreas, liver, and kidney. They then spontaneously differentiated into IPCs that corrected hyperglycemia in diabetic mice. When transplanted under the kidney capsule, PELC-derived IPCs were equally efficient at correcting hyperglycemia. Real-time noninvasive in vivo bioluminescence imaging (BLI) of rat insulin promoter (RIP)-driven luciferase was used to monitor the fate of the transplanted PELCs. To confirm that the transplanted cells were responsible for the correction of hyperglycemia, kidneys containing the transplanted cells were nephrectomized, causing rapid hyperglycemia. Interestingly, none of the animals transplanted with PELCs developed tumors, a potential consequence of the differentiation and purification procedures.

CONCLUSIONS

Our data suggest that Pdx1-expressing PELCs are capable of spontaneously undergoing differentiation in vivo into IPCs and leading to a sustained correction of hyperglycemia in diabetic mice.

Bone marrow-derived nonreactive astrocytes in the mouse brain after permanent middle cerebral artery occlusion

We studied the effect of permanent unilateral middle cerebral artery occlusion (PMCAO) on the generation of bone marrow (BM)-derived astrocytes in female mice previously transplanted with enhanced green fluorescent protein-expressing BM from male donors. In addition to an untreated PMCAO group, one group of mice also received intracerebral infusion of transforming growth factor-alpha, resulting in a decrease in the size of the infarct. Two months after PMCAO, we found a specific type of astrocyte of BM origin in the side of the injury, near the lesion. These astrocytes did not express glial fibrillary acidic protein (GFAP) by conventional fluorescence immunostaining; however, GFAP was easily detectable by tyramide signal amplification. These cells also expressed S100β, confirming their astrocytic character. Unlike the endogenous reactive astrocytes, these BM-derived astrocytes did not proliferate during the first week of ischemia and did not contribute to the glial scar formation. Transforming growth factor-alpha infusion increased the number of BM-derived astrocytes, without affecting their distribution. Interestingly, exclusively by tyramide signal amplification staining, we found that endogenous astrocytes displaying an identical morphology were also present in control mouse and human brains. Our data demonstrate that a subpopulation of nonreactive astrocytes expressing low levels of GFAP can originate from transplanted BM in the ischemic brain. We believe that these cells represent a subpopulation of astrocytes earlier considered to be GFAP negative. The high number of astrocytes with identical morphology and chemical character in control brains suggest that these type of astrocytes may have important functional role in the central nervous system that calls for further studies.

Bone marrow-derived cells: A potential approach for the treatment of xerostomia

Transplantations of bone marrow-derived cells (BMDCs) are traditionally used for hematologic diseases, but there are increasing numbers of clinical trials using BMDC treatments for non-hematologic disorders, including autoimmune diseases. BMDCs are recently reported to improve organ functions. This paper will review available reports supporting the role of BMDCs in reducing xerostomia (i.e. re-establishing salivary gland functions) due to head and neck irradiation for cancer therapies and in Sjögren's syndrome. There are reports that BMDCs provide a beneficial effect on the saliva production. BMDCs positively affect blood vessels stability and regeneration in irradiated salivary glands. Also, BMDCs provide an immunomodulatory activity in mice with Sjögren's-like disease. While the exact mechanisms by which BMDCs improve organ functions remain controversial, there is preliminary evidence that a combination of them (such as cell transdifferentiation, vasculogenesis, and paracrine effect) occur in salivary glands.

Investigation of neuronal progenitor cell origin after transient focal cerebral ischemia in mice

Following cerebral ischemia both neuronal precursors and hematogenous cells migrate along chemokine gradients towards the injured tissue. Bone marrow derived cells are involved in the stroke related inflammatory and restaurative processes and newly born neurons are known to proliferate and migrate from the subventricular zone to the ischemic lesion. In the present study, we investigated whether hematogenous cells contribute to subpopulations of neuronal precursors using green fluorescent protein-transgenic bone marrow chimeric mice. In our experiments we found no blood-borne neuronal precursors within the ischemic site indicating that detected neuronal progenitor cells are only of brain parenchymal origin.

Detection of bone marrow-derived lung epithelial cells

Studies on the ability of bone marrow-derived cells to adopt the morphology and protein expression pattern of epithelial cells in vivo have expanded rapidly during the last decade, and hundreds of publications report that bone marrow-derived cells can become epithelial cells of multiple organs, including lung, liver, gastrointestinal tract, skin, pancreas, and others. In this review, we critically evaluate the literature related to engraftment of bone marrow-derived cells as epithelial cells in the lung. More than 40 articles focused on whether bone marrow cells can differentiate into lung epithelial cells have been published, nearly all of which claim to identify marrow-derived epithelial cells. A few investigations have concluded that no such cells are present and that the phenomenon of marrow-derived epithelial cells is based on detection artifacts. Here we discuss the problems that exist in published articles identifying marrow-derived epithelial cells, and propose standards for detection methods that provide the most definitive data. Identification of bone marrow-derived epithelial cells requires reliable and sensitive techniques for their detection, which must include cell identification based on the presence of an epithelial marker and the absence of blood cell markers as well as a marker for donor bone marrow origin. In order for these studies to be rigorous, they must also use approaches to rule out cell overlap by microscopy or single-cell isolation. Once these stringent criteria for identification of marrow-derived epithelial cells are used universally, then the field can move forward to address the critical questions about which bone marrow-derived cells are responsible for engraftment as epithelial cells, the mechanisms by which this occurs, whether these cells play a role in normal tissue repair, and whether specific cell subsets can be used for therapeutic benefit.

Combining neuropeptide Y and mesenchymal stem cells reverses remodeling after myocardial infarction

Neuropeptide Y (NPY) induced reentry of differentiated rat neonatal and adult cardiomyocytes into the cell cycle. NPY also induced differentiation of bone marrow-derived mesenchymal stem cells (MSC) into cardiomyocytes following transplantation into infarcted myocardium. Rat neonatal and adult cardiomyocytes were treated in vitro with vehicle, NPY, fibroblast growth factor (FGF; 100 ng/ml), or FGF plus NPY. DNA synthesis, mitosis, and cytokinesis were determined by immunocytochemistry. NPY-induced MSC gene expression, cell migration, tube formation, and endothelial cell differentiation were analyzed. Male rat green fluorescent protein-MSC (2 x 10(6)), pretreated with either vehicle or NPY (10(-8) M) for 72 h, were injected into the border zone of the female myocardium following left anterior descending artery ligation. On day 30, heart function was assessed, and hearts were harvested for histological and immunohistochemical analyses. NPY increased 5-bromo-2'-deoxy-uridine incorporation and promoted both cytokinesis and mitosis in rat neonatal and adult myocytes. NPY also upregulated several genes required for mitosis in MSC, including aurora B kinase, FGF-2, cycline A2, eukaryotic initiation factor 4 E, and stromal cell-derived factor-1alpha. NPY directly induced neonatal and adult cardiomyocyte cell-cycle reentry and enhanced the number of differentiated cardiomyocytes from MSC in the infarcted myocardium, which corresponded to improved cardiac function, reduced fibrosis, ventricular remodeling, and increased angiomyogenesis. It is concluded that a combined treatment of NPY with MSC is a novel approach for cardiac repair.

Allogeneic mesenchymal stem cells restore cardiac function in chronic ischemic cardiomyopathy via trilineage differentiating capacity

The mechanism(s) underlying cardiac reparative effects of bone marrow-derived mesenchymal stem cells (MSC) remain highly controversial. Here we tested the hypothesis that MSCs regenerate chronically infarcted myocardium through mechanisms comprising long-term engraftment and trilineage differentiation. Twelve weeks after myocardial infarction, female swine received catheter-based transendocardial injections of either placebo (n = 4) or male allogeneic MSCs (200 million; n = 6). Animals underwent serial cardiac magnetic resonance imaging, and in vivo cell fate was determined by co-localization of Y-chromosome (Y(pos)) cells with markers of cardiac, vascular muscle, and endothelial lineages. MSCs engrafted in infarct and border zones and differentiated into cardiomyocytes as ascertained by co-localization with GATA-4, Nkx2.5, and alpha-sarcomeric actin. In addition, Y(pos) MSCs exhibited vascular smooth muscle and endothelial cell differentiation, contributing to large and small vessel formation. Infarct size was reduced from 19.3 +/- 1.7% to 13.9 +/- 2.0% (P < 0.001), and ejection fraction (EF) increased from 35.0 +/- 1.7% to 41.3 +/- 2.7% (P < 0.05) in MSC but not placebo pigs over 12 weeks. This was accompanied by increases in regional contractility and myocardial blood flow (MBF), particularly in the infarct border zone. Importantly, MSC engraftment correlated with functional recovery in contractility (R = 0.85, P < 0.05) and MBF (R = 0.76, P < 0.01). Together these findings demonstrate long-term MSC survival, engraftment, and trilineage differentiation following transplantation into chronically scarred myocardium. MSCs are an adult stem cell with the capacity for cardiomyogenesis and vasculogenesis which contribute, at least in part, to their ability to repair chronically scarred myocardium.

Transforming growth factor alpha induces angiogenesis and neurogenesis following stroke

The cytokine transforming growth factor alpha (TGF alpha) has proangiogenic and proneurogenic effects and can potentially reduce infarct volumes. Therefore, we administered TGF alpha or vehicle directly into the area surrounding the infarct in female mice that received gender-mismatched bone marrow transplants from green fluorescent protein (GFP)-expressing males prior to undergoing permanent middle cerebral artery occlusion. Newborn cells were tracked with bromodeoxyuridine (BrdU) labeling and immunohistochemistry at 90 days after stroke onset. We also studied the ingress of bone marrow-derived cells into the ischemic brain to determine whether such cells contribute to angiogenesis or neurogenesis. Infarct volumes were measured at 90 days poststroke. The results show that TGF alpha led to significant increments in the number of newborn neurons and glia in the ischemic hemisphere. TGF alpha also led to significant increments in the number of bone marrow-derived cells entering into the ischemic hemisphere. Most of these cells did not label with BrdU and represented endothelial cells that incorporated into blood vessels in the infarct border zone. Our results also show that infarct size was significantly reduced in animals treated with TGF alpha compared with controls. These results suggest that TGF alpha can induce angiogenesis, neurogenesis and neuroprotection after stroke. At least part of the pro-angiogenic effect appears to be secondary to the incorporation of bone marrow-derived endothelial cells into blood vessels in the infarct border zone.

The combination of granulocyte colony-stimulating factor and stem cell factor significantly increases the number of bone marrow-derived endothelial cells in brains of mice following cerebral ischemia

Granulocyte colony-stimulating factor (G-CSF) induces proliferation of bone marrow-derived cells. G-CSF is neuroprotective after experimental brain injury, but the mechanisms involved remain unclear. Stem cell factor (SCF) is a cytokine important for the survival and differentiation of hematopoietic stem cells. Its receptor (c-kit or CD117) is present in some endothelial cells. We aimed to determine whether the combination of G-CSF/SCF induces angiogenesis in the central nervous system by promoting entry of endothelial precursors into the injured brain and causing them to proliferate there. We induced permanent middle cerebral artery occlusion in female mice that previously underwent sex-mismatched bone marrow transplantation from enhanced green fluorescent protein (EGFP)-expressing mice. G-CSF/SCF treatment reduced infarct volumes by more than 50% and resulted in a 1.5-fold increase in vessel formation in mice with stroke, a large percentage of which contain endothelial cells of bone marrow origin. Most cells entering the brain maintained their bone marrow identity and did not transdifferentiate into neural cells. G-CSF/SCF treatment also led to a 2-fold increase in the number of newborn cells in the ischemic hemisphere. These findings suggest that G-CSF/SCF treatment might help recovery through induction of bone marrow-derived angiogenesis, thus improving neuronal survival and functional outcome.

CD45-Positive Blood Cells Give Rise to Uterine Epithelial Cells in Mice

The uterine endometrium is composed of epithelial and stromal cells, which undergo extensive degeneration and regeneration in every estrous cycle, and dramatic changes occur during pregnancy. The high turnover of cells requires a correspondingly high level of cell division by progenitor cells in the uterus, but the character and source of these cells remain obscure. In the present study, using a novel transgenic mouse, we showed that CD45-positive hematopoietic progenitor cells colonize the uterine epithelium and that in pregnancy more than 80% of the epithelium can derive from these cells. Since we also found green fluorescent protein (GFP)-positive uterine endothelial cells in long-term GFP bone marrow-transplanted mice, we conclude that circulating CD45+ cells play an important role in regenerating the uterine epithelium.

Limitations of green fluorescent protein as a cell lineage marker

The enhanced green fluorescent protein (GFP) reporter has been widely adopted for tracking cell lineage. Here, we compare three transgenic mouse strains in which GFP is considered "ubiquitously expressed," with the GFP transgene under control of the chicken beta-actin (CBA) or human ubiquitin C (UBC) promoter. We compared the expression of GFP using flow cytometry, direct tissue fluorescence, and immunostaining with multiple commercially available anti-GFP antibodies. Mice of CBA-GFP strain 1Osb have strong but variegated expression of GFP in adult liver, kidney, small intestine, and blood. Mice of CBA-GFP strain Y01 have the highest proportion of GFP-positive peripheral blood cells yet limited GFP expression in liver, intestine, and kidney. UBC-GFP mice express GFP only weakly in solid organs and variably in blood. Direct fluorescent detection of GFP in formalin-fixed, paraffin-embedded tissue sections was the simplest approach, but it was useful only in high-expressing strains and potentially subject to artifact because of tissue autofluorescence. Immunofluorescence using either primary goat or primary rabbit antibodies was much more sensitive and allowed better discrimination of authentic signal from autofluorescence. Immunohistochemical staining was less sensitive than direct fluorescence or immunofluorescence and was subject to false-positive signal in the small intestine. In conclusion, there is considerable variability of expression within and between GFP transgenic strains. None of the tested strains gave truly ubiquitous GFP expression. A detailed analysis of GFP expression in one's tissues of interest must guide the choice of reporter mouse strain when GFP is used as a marker of cell lineage or donor origin. Disclosure of potential conflicts of interest is found at the end of this article.