Intracerebral Xenotransplantation of GFP Mouse Bone Marrow Stromal Cells in Intact and Stroke Rat Brain: Graft Survival and Immunologic Response

A Comparison of Immune Responses Exerted Following Syngeneic, Allogeneic, and Xenogeneic Transplantation of Mesenchymal Stem Cells into the Mouse Brain

Due to their multifactorial aspects, mesenchymal stem cells (MSCs) have been widely established as an attractive and potential candidate for the treatment of a multitude of diseases. A substantial number of studies advocate that MSCs are poorly immunogenic. In several studies, however, immune responses were observed following injections of xenogeneic donor MSCs. In this study, the aim was to examine differences in immune responses exerted based on transplantations of xenogeneic, syngeneic, and allogeneic MSCs in the wild-type mouse brain. Xenogeneic, allogeneic, and syngeneic MSCs were intracerebrally injected into C57BL/6 mice. Mice were sacrificed one week following transplantation. Based on immunohistochemical (IHC) analysis, leukocytes and neutrophils were expressed at the injection sites in the following order (highest to lowest) xenogeneic, allogeneic, and syngeneic. In contrast, microglia and macrophages were expressed in the following order (highest to lowest): syngeneic, allogeneic, and xenogeneic. Residual human MSCs in the mouse brain were barely detected after seven days. Although the discrepancy between leukocytes versus macrophages/microglia infiltration should be resolved, our results overall argue against the previous notions that MSCs are poorly immunogenic and that modulation of immune responses is a prerequisite for preclinical and clinical studies in MSC therapy of central nervous system diseases.

Comparison of MSC-Neurogenin1 administration modality in MCAO rat model

Intracerebral (IC) grafting of mesenchymal stem cells (MSCs) is not currently used in humans due to its potential complications. On the other hand, intra-arterial (IA) administration can be facilitated for engrafting of intensifed MSCs in the injured human brain. The study is designed to compare the two methods of MSC administration using IA and IC routes through the parameters of behavior, infarct volume, cell distribution, and MSC identification. An ischemic stroke model was generated in Sprague Dawley male rats. This experiment used MSCs/Ngn1 that express Neurogenin1 (Ngn1) to ensure grafted MSC maintenance. MSCs/Ngn1 or normal saline was administrated via the IC or IA route on day 3. All animals were randomly assigned into four groups (five rats in each group): IC-control, IA-control, IC-MSCs/Ngn1, or IA-MSCs/Ngn1. Motor behaviors, infarct volume, and distribution of superparamagnetic iron oxide (SPIO)-labeled cells on magnetic resonance imaging (MRI) were compared from each group. There were no baseline differencess in motor behaviors or infarct volume between IC-MSCs/Ngn1 and IA-MSCs/Ngn1. Hovever, the IA-MSCs/Ngn1 group showed the greatest recovery on Rotarod testing and adhesive removal tests (p = 0.003 and p = 0.009 vs. IC-MSCs/Ngn1, respectively). The IA-MSCs/Ngn1 group also had more evenly distributed SPIO-labeled cells on MRI. The results suggest that IA administration is likely to be benefcial for humans based on its ability to improve behavioral outcomes and ensure even MSC engrafting.

Differential Clearance of Rat and Human Bone Marrow-Derived Mesenchymal Stem Cells from the Brain after Intra-arterial Infusion in Rats

Intra-arterial (IA) delivery of bone marrow-derived mesenchymal stem cells (BM-MSCs) has shown potential as a minimally invasive therapeutic approach for stroke. The aim of the present study was to determine the whole-body biodistribution and clearance of technetium-99m (99mTc)-labeled rat and human BM-MSCs after IA delivery in a rat model of transient middle cerebral artery occlusion (MCAO) using single-photon emission computed tomography (SPECT). Our hypothesis was that xenotransplantation has a major impact on the behavior of cells. Male RccHan: Wistar rats were subjected to sham operation or MCAO. Twenty-four hours after surgery, BM-MSCs (2×106 cells/animal) labeled with 99mTc were infused into the external carotid artery. Whole-body SPECT images were acquired 20 min, 3 h, and 6 h postinjection, after which rats were sacrificed, and organs were collected and weighed for measurement of radioactivity. The results showed that the majority of the cells were located in the brain and especially in the ipsilateral hemisphere immediately after cell infusion both in sham-operated and MCAO rats. This was followed by fast disappearance, particularly in the case of human cells. At the same time, the radioactivity signal increased in the spleen, kidney, and liver, the organs responsible for destroying cells. Further studies are needed to demonstrate whether differential cell behavior has any functional impact.

Short-, middle- and long-term safety of superparamagnetic iron oxide-labeled allogeneic bone marrow stromal cell transplantation in rat model of lacunar infarction

Recently, both basic and clinical studies demonstrated that bone marrow stromal cell (BMSC) transplantation therapy can promote functional recovery of patients with CNS disorders. A non-invasive method for cell tracking using MRI and superparamagnetic iron oxide (SPIO)-based labeling agents has been applied to elucidate the behavior of transplanted cells. However, the long-term safety of SPIO-labeled BMSCs still remains unclear. The aim of this study was to investigate the short-, middle- and long-term safety of the SPIO-labeled allogeneic BMSC transplantation. For this purpose, BMSCs were isolated from transgenic rats expressing green fluorescent protein (GFP) and were labeled with SPIO. The Na/K ATPase pump inhibitor ouabain or vehicle was stereotactically injected into the right striatum of wild-type rats to induce a lacunar lesion (n = 22). Seven days after the insult, either BMSCs or SPIO solution were stereotactically injected into the left striatum. A 7.0-Tesla MRI was performed to serially monitor the behavior of BMSCs in the host brain. The animals were sacrificed after 7 days (n = 7), 6 weeks (n = 6) or 10 months (n = 9) after the transplantation. MRI demonstrated that BMSCs migrated to the damage area through the corpus callosum. Histological analysis showed that activated microglia were present around the bolus of donor cells 7 days after the allogeneic cell transplantation, although an immunosuppressive drug was administered. The SPIO-labeled BMSCs resided and started to proliferate around the route of the cell transplantation. Within 6 weeks, large numbers of SPIO-labeled BMSCs reached the lacunar infarction area from the transplantation region through the corpus callosum. Some SPIO nanoparticles were phagocytized by microglia. After 10 months, the number of SPIO-positive cells was lower compared with the 7-day and 6-week groups. There was no tumorigenesis or severe injury observed in any of the animals. These findings suggest that BMSCs are safe after cell transplantation for the treatment of stroke.

Bone marrow stromal cells as a therapeutic treatment for ischemic stroke

Cerebral ischemia remains the most frequent cause of death and quality-of-life impairments due to neurological deficits, and accounts for the majority of total healthcare costs. However, treatments for cerebral ischemia are limited. Over the last decade, bone marrow stromal cell (BMSC) therapy has emerged as a particularly appealing option, as it is possible to help patients even when initiated days or even weeks after the ischemic insult. BMSCs are a class of multipotent, self-renewing cells that give rise to differentiated progeny when implanted into appropriate tissues. Therapeutic effects of BMSC treatment for ischemic stroke, including sensory and motor recovery, have been reported in pre-clinical studies and clinical trials. In this article, we review the recent progress in BMSC-based therapy for ischemic stroke, focusing on the route of delivery and pre-processing of BMSCs. Selecting an optimal delivery route is of particular importance. The ideal approach, as well as the least risky, for translational applications still requires further identification. Appropriate preprocessing of BMSCs or combination therapy has the benefit of achieving the maximum possible restoration. Further pre-clinical studies are required to determine the time-window for transplantation and the appropriate dosage of cells.

The role of astrocytes in mediating exogenous cell-based restorative therapy for stroke

Astrocytes have not been a major therapeutic target for the treatment of stroke, with most research emphasis on the neuron. Given the essential role that astrocytes play in maintaining physiological function of the central nervous system and the very rapid and sensitive reaction astrocytes have in response to cerebral injury or ischemic insult, we propose to replace the neurocentric view for treatment with a more nuanced astrocytic centered approach. In addition, after decades of effort in attempting to develop neuroprotective therapies, which target reduction of the ischemic lesion, there are no effective clinical treatments for stroke, aside from thrombolysis with tissue plasminogen activator, which is used in a small minority of patients. A more promising therapeutic approach, which may affect nearly all stroke patients, may be in promoting endogenous restorative mechanisms, which enhance neurological recovery. A focus of efforts in stimulating recovery post stroke is the use of exogenously administered cells. The present review focuses on the role of the astrocyte in mediating the brain network, brain plasticity, and neurological recovery post stroke. As a model to describe the interaction of a restorative cell-based therapy with astrocytes, which drives recovery from stroke, we specifically highlight the subacute treatment of stroke with multipotent mesenchymal stromal cell therapy.

Cholinergic Neuron-Like Cells Derived from Bone Marrow Stromal Cells Induced by Tricyclodecane-9-yl-Xanthogenate Promote Functional Recovery and Neural Protection after Spinal Cord Injury

The rate of neuronal differentiation of bone marrow stromal cells (BMSCs) in vivo is very low; therefore, it is necessary to elevate the number of BMSC-derived neurons to cure neurodegenerative diseases. We previously reported that tricyclodecane-9-yl-xanthogenate (D609), an inhibitor of phosphatidylcholine-specific phospholipase C (PC-PLC), induced BMSCs to differentiate into neuron-like cells in vitro. However, the neuronal type is not clear, and it is still unknown whether these neuron-like cells possess physiological properties of functional neurons and whether they can contribute to the recovery of neuron dysfunction. To answer these questions, we investigated their characteristics by detecting neuronal function-related neurotransmitters and calcium image. The results showed that these cells exhibited functional cholinergic neurons in vitro. Transplantation of these cholinergic neuron-like cells promoted the recovery of spinal cord-injured mice, and they were more effective than BMSCs. The number of cholinergic neurons was increased after injection with BMSC-derived cholinergic neuron-like cells, indicating their high differentiation rate in vivo. Moreover, the proportion of cholinergic neurons in host cells and secretion of acetylcholine were increased, and preservation of neurofilament was also observed in the lesion of mice implanted with BMSC-derived neurons, suggesting the neuronal protection of BMSC-derived neurons. Our findings provide both a simple method to induce the differentiation of BMSCs into cholinergic neuron-like cells and a putative strategy for the therapy of spinal cord injuries.

Baby STEPS: a giant leap for cell therapy in neonatal brain injury

We advance Baby STEPS or Stem cell Therapeutics as an Emerging Paradigm in Stroke as a guide in facilitating the critical evaluation in the laboratory of the safety and efficacy of cell therapy for neonatal encephalopathy. The need to carefully consider the clinical relevance of the animal models in mimicking human neonatal brain injury, selection of the optimal stem cell donor, and the application of functional outcome assays in small and large animal models serve as the foundation for preclinical work and beginning to understand the mechanism of this cellular therapy. The preclinical studies will aid our formulation of a rigorous human clinical trial that encompasses not only efficacy testing but also monitoring of safety indices and demonstration of mechanisms of action. This schema forms the basis of Baby STEPS. Our goal is to resonate the urgent call to enhance the successful translation of cell therapy from the laboratory to the clinic.

Long-term magnetic resonance imaging of stem cells in neonatal ischemic injury

OBJECTIVE

Quantitative magnetic resonance imaging (MRI) can serially and noninvasively assess the degree of injury in rat pup models of hypoxic ischemic injury (HII). It can also noninvasively monitor stem cell migration following iron oxide prelabeling. Reports have shown that neural stem cells (NSCs) may help mediate neuroprotection or stimulate neuroreparative responses in adult and neonatal models of ischemic injury. We investigated the ability of high-field MRI to monitor and noninvasively quantify the migration, proliferation, and location of iron oxide-labeled NSCs over very long time periods (58 weeks) in real time while contemporaneously correlating this activity with the evolving severity and extent of neural damage.

METHODS

Labeled clonal murine NSCs (mNSCs) were implanted 3 days after unilateral HII in 10-day-old rat pups into the contralateral striatum or ventricle. We developed methods for objectively quantifying key aspects of dynamic NSC behavior (eg, viability; extent, and speed of migration; degree of proliferation; extent of integration into host parenchyma). MRI images were validated with histological and immunohistochemical assessments.

RESULTS

mNSCs rapidly migrated (100 μm/day) to the lesion site. Chains of migrating NSCs were observed in the corpus callosum. In pups subjected to HII, though not in intact control animals, we observed a 273% increase in the MR-derived volume of mNSCs 4 weeks after implantation (correlating with the known proliferative behavior of endogenous and exogenous NSCs) that slowly declined over the 58-week time course, with no adverse consequences. Large numbers of now quiescent mNSCs remained at the site of injury, many retaining their iron oxide label.

INTERPRETATION

Our studies demonstrate that MRI can simultaneously monitor evolving neonatal cerebral injury as well as NSC migration and location. Most importantly, it can noninvasively monitor proliferation dynamically for prolonged time periods. To be able to pursue clinical trials in newborns using stem cell therapies it is axiomatic that safety be insured through the long-term real time monitoring of cell fate and activity, particularly with regard to observing unanticipated risks to the developing brain. This study supports the feasibility of reliably using MRI for this purpose.

Short-time survival and engraftment of bone marrow stromal cells in an ectopic model of bone regeneration

In tissue-engineered applications bone marrow stromal cells (BMSCs) are combined with scaffolds to target bone regeneration; animal models have been devised and the cells' long-term engraftment has been widely studied. However, in regenerated bone, the cell number is severely reduced with respect to the initially seeded BMSCs. This reflects the natural low cellularity of bone but underlines the selectivity of the differentiation processes. In this respect, we evaluated the short-term survival of BMSCs, transduced with the luciferase gene, after implantation of cell-seeded scaffolds in a nude mouse model. Cell proliferation/survival was assessed by bioluminescence imaging: light production was decreased by 30% on the first day, reaching a 50% loss within 48 h. Less than 5% of the initial signal remained after 2 months in vivo. Apoptotic BMSCs were detected within the first 2 days of implantation. Interestingly, the initial frequency of clonogenic progenitors matched the percentage of in vivo surviving cells. Cytokines and inflammation may contribute to the apoptotic onset at the implant milieu. However, preculturing cells with tumor necrosis factor alpha enhanced survival, allowing detection of 8.1% of the seeded BMSCs 2 months after implantation. Thus culturing conditions may reduce the apoptotic overload of seeded osteoprogenitors, strengthening the constructs' osteogenic potential.

Bone grafts cultured with bone marrow stromal cells for the repair of critical bone defects: an experimental study in mice

Tissue engineering of autologous bone combined with osteoprogenitor cells is a suitable strategy for filling large bone defects. The aim of this study was to evaluate the osteogenicity of a xenogenic bone graft cultured with allogenic bone marrow stromal cells (BMSC) in a mouse critical size craniotomy. Bovine trabecular bone grafts were made free of bone marrow cells or debris and were delipidated. BMSC were harvested from C57BL/6-Tg(ACTbEGFP)1Osb/J mice (GFP+ cells) and were cultured 14 days on bone grafts in control or osteogenic medium. Engineered grafts were implanted in calvarial defect in C57BL/6 mice. Four groups were studied: graft with BMSC differentiated in osteoblasts (G-Ob), graft with BMSC (G-BMSC), graft without cells (G) and no graft. Calvariae were studied 2 and 8 weeks after implantation by radiographic and histomorphometric analyses. G group: the bone ingrowth was limited to the edges of the defect. The center of the graft was filled by a fibrovascular connective tissue. G-BMSC or G-Ob groups: bone formation occurred early in the center of the defect and did not increase between 2 and 8 weeks; the newly formed woven bone was partially replaced by lamellar bone. The preoperative osteoblastic differentiation of BMSC did not allow faster and better bone regeneration. After 2 weeks, GFP+ cells were observed around the grafted bone but no GFP+ osteocyte was present in the newly formed bone. No GFP+ cell was noted after 8 weeks. However, pre-implantation culture of the biomaterial with allogenic BMSC greatly enhanced the bone regeneration.

Cellular immune response to intrastriatally implanted allogeneic bone marrow stromal cells in a rat model of Parkinson's disease

BACKGROUND

Marrow stromal cells (MSC), the non-hematopoietic precursor cells in bone marrow, are being investigated for therapeutic potential in CNS disorders. Although in vitro studies have suggested that MSC may be immunologically inert, their immunogenicity following transplantation into allogeneic recipients is unclear. The primary objective of this study was to investigate the cellular immune response to MSC injected into the striatum of allogeneic recipients (6-hydroxydopamine [6-OHDA]-hemilesioned rats, an animal model of Parkinson's disease [PD]), and the secondary objective was to determine the ability of these cells to prevent nigrostriatal dopamine depletion and associated motor deficits in these animals.

METHODS

5-Bromo-2-deoxyuridine (BrdU) - labeled MSC from two allogeneic sources (Wistar and ACI rats) were implanted into the striatum of adult Wistar rats at the same time as 6-OHDA was administered into the substantia nigra. Behavioral tests were administered one to two weeks before and 16-20 days after 6-OHDA lesioning and MSC transplantation. Immunocytochemical staining for T helper and T cytotoxic lymphocytes, microglia/macrophages, and major histocompatibility class I and II antigens was performed on post-transplantation days 22-24. MSC were detected with an anti-BrdU antibody.

RESULTS

Tissue injury due to the transplantation procedure produced a localized cellular immune response. Unexpectedly, both sources of allogeneic MSC generated robust cellular immune responses in the host striatum; the extent of this response was similar in the two allograft systems. Despite these immune responses, BrdU+ cells (presumptive MSC) remained in the striatum of all animals that received MSC. The numbers of remaining MSC tended to be increased (p = 0.055) in rats receiving Wistar MSC versus those receiving ACI MSC. MSC administration did not prevent behavioral deficits or dopamine depletion in the 6-OHDA-lesioned animals.

CONCLUSION

MSC, when implanted into the striatum of allogeneic animals, provoke a marked immune response which is not sufficient to clear these cells by 22-24 days post-transplantation. In the experimental paradigm in this study, MSC did not prevent nigrostriatal dopamine depletion and its associated behavioral deficits. Additional studies are indicated to clarify the effects of this immune response on MSC survival and function before initiating trials with these cells in patients with PD or other neurodegenerative disorders.

Hemispheric brain injury and behavioral deficits induced by severe neonatal hypoxia-ischemia in rats are not attenuated by intravenous administration of human umbilical cord blood cells

Neonatal hypoxia-ischemia (HI) is an important cause of mortality and morbidity in infants. Human umbilical cord blood (HUCB) is a potential source of cellular therapy in perinatology. We investigated the effects of HUCB cells on spatial memory, motor performance, and brain morphologic changes in neonate rats submitted to HI. Seven-day-old rats underwent right carotid artery occlusion followed by exposure to 8% O(2) inhalation for 2 h. Twenty-four hours after HI, rats received either saline solution or HUCB cells i.v. After 3 wk, rats were assessed using a Morris Water Maze and four motor tests. Subsequently, rats were killed for histologic, immunohistochemical, and polymerase chain reaction (PCR) analyses. HI rats showed significant spatial memory deficits and a volumetric decrease in the hemisphere ipsilateral to arterial occlusion. These deficits and decreases were not significantly attenuated by the injection of HUCB cells. Moreover, immunofluorescence and PCR analysis revealed few HUCB cells located in rat brain. Intravenous administration of HUCB cells requires optimization to achieve improved therapeutic outcomes in neonatal hypoxic-ischemic injury.

Neural progenitors derived from human embryonic stem cells are targeted by allogeneic T and natural killer cells

Neural progenitor cells (NPC) of foetal origin or derived from human embryonic stem cells (HESC) have the potential to differentiate into mature neurons after transplantation into the central nervous system, opening the possibility of cell therapy for neurodegenerative disorders. In most cases, the transplanted NPC are genetically unrelated to the recipient, leading to potential rejection of the transplanted cells. Very few data provide reliable information as to the potential immune response of allogeneic neural progenitors derived from HESC. In this study, we analyzed in vitro the allogeneic immune response of T lymphocytes and natural killer (NK) cells to NPC derived from HESC or of foetal origin. We demonstrate that NPC induce T-cell stimulation and a strong NK cytotoxic response. NK-cell activity is unrelated to MHC-I expression but driven by the activating NKG2D receptor. Cyclosporine and dexamethasone previously used in clinical studies with foetal NPC did not only fail to prevent NK alloreactivity but strongly inhibited the terminal maturation from NPC into mature neurons. We conclude that allogenic transplantation of NPC in the central nervous system will most likely require an immunosuppressive regimen targeting allogenic T and NK cells, whereas possible interference with the differentiation of NPC needs to be carefully evaluated.

TSP-1 secreted by bone marrow stromal cells contributes to retinal ganglion cell neurite outgrowth and survival

Background

Bone marrow stromal cells (BMSCs) are pluripotent and thereby a potential candidate for cell replacement therapy for central nervous system degenerative disorders and traumatic injury. However, the mechanism of their differentiation and effect on neural tissues has not been fully elucidated. This study evaluates the effect of BMSCs on neural cell growth and survival in a retinal ganglion cell (RGCs) model by assessing the effect of changes in the expression of a BMSC-secreted protein, thrombospondin-1 (TSP-1), as a putative mechanistic agent acting on RGCs.

Methods and Findings

The effect of co-culturing BMSCs and RGCs in vitro was evaluated by measuring the following parameters: neurite outgrowth, RGC survival, BMSC neural-like differentiation, and the effect of TSP-1 on both cell lines under basal secretion conditions and when TSP-1 expression was inhibited. Our data show that BMSCs improved RGC survival and neurite outgrowth. Synaptophysin, MAP-2, and TGF-β expression are up-regulated in RGCs co-cultured with BMSCs. Interestingly, the BMSCs progressively displayed neural-like morphology over the seven-day study period. Restriction display polymerase chain reaction (RD-PCR) was performed to screen for differentially expressed genes in BMSCs cultured alone or co-cultured with RGCs. TSP-1, a multifactorial extracellular matrix protein, is critically important in the formation of neural connections during development, so its function in our co-culture model was investigated by small interfering RNA (siRNA) transfection. When TSP-1 expression was decreased with siRNA silencing, BMSCs had no impact on RGC survival, but reduced neurite outgrowth and decreased expression of synaptophysin, MAP-2 and TGF-β in RGCs. Furthermore, the number of BMSCs with neural-like characteristics was significantly decreased by more than two-fold using siRNA silencing.

Conclusions

Our data suggest that the TSP-1 signaling pathway might have an important role in neural-like differentiation in BMSCs and neurite outgrowth in RGCs. This study provides new insights into the potential reparative mechanisms of neural cell repair.

Experimental Study on Trace Marking and Oncogenicity of Neural Stem Cells Derived from Bone Marrow

It has been well accredited that the neural stem cells (NSCs) derived from bone marrow stroma cells (BMSCs) can be used as the therapeutic application. However, their efficacy and safety in therapeutic application are uncertain. In this experiment, the trace marking and oncogenicity of NSCs derived from BMSCs (BMSCs-D-NSCs) were studied. The BMSCs were harvested by gradient centrifugation and cultured in "NSCs medium" in vitro. The verified CD133/Nestin-positive BMSCs-D-NSCs were then transplanted into nude mice to detect the oncogenicity, into the right lateral cerebral ventricle or right caudae putamen and substantia nigra to examine, whether the symptoms were improved in Parkinson's Disease (PD) models after transplantation, by both SPECT image assay of dopamine transporter (DAT) in corpus striatum and its average standard uptake value (SUVave) in corpus striatum and thalamus. Tissue samples and surviving model animals were studied at 1, 3, and 6 months post-transplantation. Before transplantation, the cells were labeled with BrdU or rAAV-GFP for the pathological sections, and with Feridex for the in vivo trace by MRI assay. The concanavalin A (ConA) agglutination test, stop-dependence test with soft agar, karyotype analysis of chromosome G zone in BMSCs-D-NSCs, and the nude mouse neoplasia test were also performed. The BrdU, rAAV-GFP or Feridex can be used as trace markers of BMSCs-D-NSCs during transplantation. The transplanted BMSCs-D-NSCs displayed neither toxicity nor neoplasia up to 6 months in vivo, but could play an important role in improving the symptoms of the animals with degenerative diseases like PD.

Bone marrow-derived mesenchymal stromal cells for the repair of central nervous system injury

Transplantation of bone marrow-derived mesenchymal stromal cells (MSCs) into the injured brain or spinal cord may provide therapeutic benefit. Several models of central nervous system (CNS) injury have been examined, including that of ischemic stroke, traumatic brain injury and traumatic spinal cord injury in rodent, primate and, more recently, human trials. Although it has been suggested that differentiation of MSCs into cells of neural lineage may occur both in vitro and in vivo, this is unlikely to be a major factor in functional recovery after brain or spinal cord injury. Other mechanisms of recovery that may play a role include neuroprotection, creation of a favorable environment for regeneration, expression of growth factors or cytokines, vascular effects or remyelination. These mechanisms are not mutually exclusive, and it is likely that more than one contribute to functional recovery. In light of the uncertainty surrounding the fate and mechanism of action of MSCs transplanted into the CNS, further preclinical studies with appropriate animal models are urgently needed to better inform the design of new clinical trials.

Overexpression of D2/D3 receptors increases efficacy of ropinirole in chronically 6-OHDA-lesioned Parkinsonian rats

Ropinirole, which is a non-ergot dopamine agonist derivative, exerts therapeutic benefits in Parkinson's disease (PD). Based on recent studies implicating dopamine receptors 2 and 3 (D2R and D3R) as possible targets of ropinirole, we over-expressed these dopamine receptor genes in the dopamine-denervated striatum of rodents to reveal whether their over-expression modulated ropinirole activity. Adult Sprague-Dawley rats initially received unilateral 6-hydroxydopamine lesion of the medial forebrain bundle. At 1 month after surgery, successfully lesioned animals (3 or less forelimb akinesia score, and 8 or more apomorphine-induced rotations/min over 1 h) were randomly assigned to intrastriatal injection (ipsilateral to the lesion) of blank lentiviral vector, D2R, D3R or both genes. At about 5 months post-lesion, ropinirole (0.2 mg/kg, i.p.) was administered daily for 9 consecutive days. The subtherapeutic dose of ropinirole improved the use of previously akinetic forelimb and produced robust circling behavior in lesioned animals with striatal over-expression of both D2R and D3R compared to lesioned animals that received blank vector. In contrast, the subtherapeutic dose of ropinirole generated only modest motor effects in lesioned animals with sole over-expression of D2R or D3R. Western immunoblot and autoradiographic assays showed enhanced D2R and D3R protein levels coupled with normalized D2R and D3R binding in the ventral striatum of lesioned animals with lentiviral over-expression of both D2R and D3R relative to vehicle-treated lesioned animals. Immunohistochemical analyses showed that D2R and D3R GFP fluorescent cells colocalized with enkephalin and substance P immunoreactive medium spiny neurons. These data support the use of the subtherapeutic dose of ropinirole in a chronic model of PD.

Trophic factor induction of human umbilical cord blood cells in vitro and in vivo

The mononuclear fraction of human umbilical cord blood (HUCBmnf) is a mixed cell population that multiple research groups have shown contains cells that can express neural proteins. In these studies, we have examined the ability of the HUCBmnf to express neural antigens after in vitro exposure to defined media supplemented with a cocktail of growth and neurotrophic factors. It is our hypothesis that by treating the HUCBmnf with these developmentally-relevant factors, we can expand the population, enhance the expression of neural antigens and increase cell survival upon transplantation. Prior to growth factor treatment in culture, expression of stem cell antigens is greater in the non-adherent HUCBmnf cells compared to the adherent cells (p < 0.05). Furthermore, treatment of the non-adherent cells with growth factors, increases BrdU incorporation, especially after 14 days in vitro (DIV). In HUCBmnf-embryonic mouse striata co-culture, a small number of growth factor treated HUCBmnf cells were able to integrate into the growing neural network and express immature (nestin and TuJ1) and mature (GFAP and MAP2) neural markers. Treated HUCBmnf cells implanted in the subventricular zone predominantly expressed GFAP although some grafted HUCBmnf cells were MAP2 positive. While short-term treatment of HUCBmnf cells with growth and neurotrophic factors enhanced proliferative capacity in vitro and survival of the cells in vivo, the treatment regimen employed was not enough to ensure long-term survival of HUCBmnf-derived neurons necessary for cell replacement therapies for neurodegenerative diseases.

Axonal sprouting into the denervated spinal cord and synaptic and postsynaptic protein expression in the spinal cord after transplantation of bone marrow stromal cell in stroke rats

We investigated whether compensatory reinnervation in the corticospinal tract (CST) and the corticorubral tract (CRT) is enhanced by the administration of bone marrow stromal cells (BMSCs) after experimental stroke. Adult male Wistar rats were subjected to permanent right middle cerebral artery occlusion (MCAo). Phosphate-buffered saline (PBS, control, n=7) or 3x10(6) BMSCs in PBS (n=8) were injected into a tail vein at 1 day postischemia. The CST of the left sensorimotor cortices was labeled with DiI 2 days prior to MCAo. Functional recovery was measured. Rats were sacrificed at 28 days after MCAo. The brain and spinal cord were removed and processed for vibratome sections for laser-scanning confocal analysis and paraffin sections for immunohistochemistry. Normal rats (n=4) exhibited a predominantly unilateral pattern of innervation of CST and CRT axons. After stroke, bilateral innervation occurred through axonal sprouting of the uninjured CRT and CST. Administration of BMSCs significantly increased the axonal restructuring on the de-afferented red nucleus and the denervated spinal motoneurons (p<0.05). BMSC treatment also significantly increased synaptic proteins in the denervated motoneurons. These results were highly correlated with improved functional outcome after stroke (r>0.81, p<0.01). We conclude that the transplantation of BMSCs enhances axonal sprouting and rewiring into the denervated spinal cord which may facilitate functional recovery after focal cerebral ischemia.

Bone marrow-derived stem cells in neurological diseases: stones or masons?

In spite of the commonly held belief that ‘the brain does not regenerate’, it is now accepted that postnatal neurogenesis does occur. Thus, one wonders whether cellular-replacement therapy might be used to heal the brain in diseases caused by neuronal cell loss. The existence of neural stem cells has been demonstrated by many scientists and is now generally accepted. The exact role of these cells, how their numbers are regulated and how they participate in CNS and spinal cord regeneration in postnatal life are still not well known. There are many reviews summarizing work on these cells; consequently, I will focus instead on other cells that may participate in postnatal neurogenesis: bone marrow-derived stem cells. The possibility that bone marrow-derived stem cells populate the CNS and differentiate into various neural elements is certainly not universally accepted.

Stem Cells in Cell Transplantation

This commentary documents the increased number of stem cell-related research reports recently published in the cell transplantation field in the journal Cell Transplantation. The journal covers a wide range of issues in cell-based therapy and regenerative medicine and is attracting clinical and preclinical articles from around the world. It thereby complements and extends the basic coverage of stem cell physiology reported in Stem Cells and Development. Sections in Cell Transplantation cover neuroscience, diabetes, hepatocytes, bone, muscle, cartilage, skin, vessels, and other tissues, as well as tissue engineering that employs novel methods with stem cells. Clearly, the continued use of biomedical engineering will depend heavily on stem cells, and these two journals are well positioned to provide comprehensive coverage of these developments.

Human umbilical cord blood cells do not improve sensorimotor or cognitive outcome following transient middle cerebral artery occlusion in rats

The present study investigated effects of human umbilical cord blood (HUCB) cells on sensorimotor, cognitive, and histological outcome in rats subjected to transient middle cerebral artery occlusion (MCAO). Halothane anesthetized adult male Wistar rats were subjected to transient MCAO for 2 h. HUCB cells (mononuclear 1-5x10(7) or Lin(-) cells 1-5x10(5)) were administered intravenously after 24 h recovery. The limb-placing test was performed on postoperative days 2, 4, 6, 9, 12, 16, and 20. In addition, beam-walking and cylinder tests were used to assess sensorimotor function at baseline, and on postoperative days 4, 12, and 20. Morris water-maze was used to assess cognitive performance on postoperative days 22-24. Subsequently, rats were perfused for measurement of infarct volumes and detection of HUCB cells by immunohistochemistry (MAB1281). MCAO rats showed a partial spontaneous recovery in sensorimotor function during the follow-up. However, the recovery profile was similar in MCAO controls and in MCAO rats that received HUCB cells. HUCB did not affect impaired water-maze performance of MCAO rats. Only few human nuclei-specific MAB1281-positive cells were detected in the ipsilateral hemisphere in MCAO rats that received HUCB cells. Infarct volumes did not differ between the experimental groups. A group of additional rats were used to further study biodistribution of intravenously given (111)In-oxine-labelled mononuclear HUCB cells in MCAO and sham-operated rats. SPECT imaging data indicated a high tracer uptake in the lung, liver, spleen, and kidney, but not in the brain immediately after administration or 24 h post-administration. The present study suggests that HUCB cells do not improve functional recovery or histological outcome in MCAO rats after systemic administration because of limited migration of cells in the ischemic brain.

Transplants of human mesenchymal stem cells improve functional recovery after spinal cord injury in the rat

Human mesenchymal stem cells (hMSCs) derived from adult bone marrow represent a potentially useful source of cells for cell replacement therapy after nervous tissue damage. They can be expanded in culture and reintroduced into patients as autografts or allografts with unique immunologic properties. The aim of the present study was to investigate (i) survival, migration, differentiation properties of hMSCs transplanted into non-immunosuppressed rats after spinal cord injury (SCI) and (ii) impact of hMSC transplantation on functional recovery. Seven days after SCI, rats received i.v. injection of hMSCs (2x10(6) in 0.5 mL DMEM) isolated from adult healthy donors. Functional recovery was assessed by Basso-Beattie-Bresnahan (BBB) score weekly for 28 days. Our results showed gradual improvement of locomotor function in transplanted rats with statistically significant differences at 21 and 28 days. Immunocytochemical analysis using human nuclei (NUMA) and BrdU antibodies confirmed survival and migration of hMSCs into the injury site. Transplanted cells were found to infiltrate mainly into the ventrolateral white matter tracts, spreading also to adjacent segments located rostro-caudaly to the injury epicenter. In double-stained preparations, hMSCs were found to differentiate into oligodendrocytes (APC), but not into cells expressing neuronal markers (NeuN). Accumulation of GAP-43 regrowing axons within damaged white matter tracts after transplantation was observed. Our findings indicate that hMSCs may facilitate recovery from spinal cord injury by remyelinating spared white matter tracts and/or by enhancing axonal growth. In addition, low immunogenicity of hMSCs was confirmed by survival of donor cells without immunosuppressive treatment.

Marrow stromal cells transplanted to the adult brain are rejected by an inflammatory response and transfer donor labels to host neurons and glia

Abstract The remarkable plasticity of marrow stromal cells (MSCs) after transplantation to models of neurological disease and injury has been described. In this report, we investigated the plasticity and long-term survival of MSCs transplanted into the normal brain. MSCs were isolated from green fluorescent protein (GFP) transgenic rats and double-labeled with 5-bromo-2-deoxyuridine (BrdU) and bis benzamide (BBZ) prior to transplantation into the adult hippocampus or striatum. Surgery elicited an immediate inflammatory response. MSC grafts were massively infiltrated by ED1-positive microglia/macrophages and surrounded by a marked astrogliosis. By 14 days, graft volume had retracted and GFP immunoreactivity was absent, indicating complete donor rejection. Consequently, MSCs did not exhibit plasticity formerly identified in other studies. However, BrdU- and BBZ-labeled cells were detected up to 12 weeks. Control transplants of nonviable MSCs demonstrated the transfer of donor labels to host cells. Unexpectedly, BrdU labeling was colocalized to host phagocytes, astrocytes, and neurons in both regions. Our results indicate that MSCs transplanted to the intact adult brain are rejected by an inflammatory response. Moreover, use of the traditional cell labels BrdU and BBZ may provide a misleading index of donor survival and differentiation after transplantation.

Umbilical cord blood-derived stem cells and brain repair

Human umbilical cord blood (HUCB) is now considered a valuable source for stem cell-based therapies. HUCB cells are enriched for stem cells that have the potential to initiate and maintain tissue repair. This potential is especially attractive in neural diseases for which no current cure is available. Furthermore, HUCB cells are easily available and less immunogenic compared to other sources for stem cell therapy such as bone marrow. Accordingly, the number of cord blood transplants has doubled in the last year alone, especially in the pediatric population. The therapeutic potential of HUCB cells may be attributed to inherent ability of stem cell populations to replace damaged tissues. Alternatively, various cell types within the graft may promote neural repair by delivering neural protection and secretion of neurotrophic factors. In this review, we evaluate the preclinical studies in which HUCB was applied for treatment of neurodegenerative diseases and for traumatic and ischemic brain damage. We discuss how transplantation of HUCB cells affects these disorders and we present recent clinical studies with promising outcome.

Tumorigenicity issues of embryonic carcinoma-derived stem cells: relevance to surgical trials using NT2 and hNT neural cells

Cell therapy is a rapidly moving field with new cells, cell lines, and tissue-engineered constructs being developed globally. As these novel cells are further developed for transplantation studies, it is important to understand their safety profiles both prior to and posttransplantation in animals and humans. Embryonic carcinoma-derived cells are considered an important alternative to stem cells. The NTera2/D1 teratocarcinoma cell-line (or NT2-N cells) gives rise to neuron-like cells called hNT neurons after exposure to retinoic acid. NT2 cells form tumors upon transplantation into the rodent. However, when the NT2 cells are treated with retinoic acid to produce hNT cells, they terminally differentiate into post-mitotic neurons with no sign of tumorigenicity. Preliminary human transplantation studies in the brain of stroke patients also demonstrated a lack of tumorigenicity of these cells. This review focuses on the use of hNT neurons in cell transplantation for the treatment in central nervous system (CNS) diseases, disorders, or injuries and on the mechanism involved in retinoic acid exposure, final differentiation state, and subsequent tumorigenicity issues that must be considered prior to widespread clinical use.

Limitations of intravenous human bone marrow CD133+ cell grafts in stroke rats

We examined the effects of timing and routes of transplantation on survival and functional benefits of human bone-marrow-derived CD133+ cells in experimentally stroke Sprague-Dawley rats. At day 7 post-stroke, both immediate and delayed intracerebral transplantation resulted in similar graft survival (7%) that was localized within the original transplant site and reduction of motor (27%) and neurological (40%) deficits. In contrast, graft survival (0.01-0.04%) was only detected in delayed intravenous transplantation, characterized by cell migration throughout the ipsilateral stroke hemisphere. Behavioral improvement, however, was limited to neurological response and only apparent in immediate intravenous transplantation. Reduction of cerebral infarct (25%) was only noted in intracerebral transplantation. Intravenous transplantation requires optimization for improved therapeutic outcome of CD133+ cell grafts in stroke.

Mesenchymal stem cells in autoimmune disease

Autoimmune diseases afflict more than 3% of the U.S. population. Current therapy for mild to moderate cases is symptomatic, however advanced cases suffer high morbidity and mortality. Advanced patients have benefited from stem cell therapy in the form of bone marrow transplantation in conjunction with high-dose cytotoxic therapy. Broader application of stem cell therapy requires better understanding of how adult stem cells affect development and foster treatment of autoimmune pathologies, and of better ways to manipulate the host immune responses. While extensive research documents the role of hematopoietic stem cells (HSCs) in autoimmune disease, few studies have addressed if and how mesenchymal stem cells (MSCs) contribute to their etiopathology. Recent characterization of MSCs and their role in hematopoiesis and immune modulation suggest that their potential for cell therapy extends beyond their traditional accessory function in HSC engraftment. MSCs contribute significantly to tissue restructuring and immune functioning, in addition to facilitating durable, long-lasting stem cell engraftment. MSCs are relatively easy to obtain and expand in in vitro cultures, rendering them a prime candidate for genetic manipulations for stem cell therapy. They have the potential to differentiate into multiple lineages such as osteoblasts, adipose tissue, cartilage, tendon, and stromal cells. The role of MSCs for autoimmune disease therapy could thus be based both on immune function modulation and contribution to hematopoiesis. In this review, we examine the biology of MSCs, and their potential for cell therapy of autoimmune disease.