Cell transplantation therapy for stroke

Human umbilical mesenchymal stem cells promote recovery after ischemic stroke

BACKGROUND AND PURPOSE

Stroke is a cerebrovascular defect that leads to many adverse neurological complications. Current pharmacological treatments for stroke remain unclear in their effectiveness, whereas stem cell transplantation shows considerable promise. Previously, we have shown that human umbilical mesenchymal stem cells (HUMSCs) can differentiate into neurons in neuronal-conditioned medium. Here we evaluate the therapeutic potential of HUMSC transplantation for ischemic stroke in rats.

METHODS

Focal cerebral ischemia was produced by middle cerebral artery occlusion and reperfusion. The HUMSCs treated with neuronal-conditioned medium or not treated were transplanted into the ischemic cortex 24 hours after surgery.

RESULTS

Histology and MRI revealed that rats implanted with HUMSCs treated with neuronal-conditioned medium or not treated exhibited a trend toward less infarct volume and significantly less atrophy compared with the control group, which received no HUMSCs. Moreover, rats receiving HUMSCs showed significant improvements in motor function, greater metabolic activity of cortical neurons, and better revascularization in the infarct cortex. Implanted HUMSCs, treated or not treated, survived in the infarct cortex for at least 36 days and released neuroprotective and growth-associated cytokines, including brain-derived neurotrophic factor, platelet-derived growth factor-AA, basic fibroblast growth factor, angiopoietin-2, CXCL-16, neutrophil-activating protein-2, and vascular endothelial growth factor receptor-3.

CONCLUSIONS

Our results demonstrate the therapeutic benefits of HUMSC transplantation for ischemic stroke, likely due to the ability of the cells to produce growth-promoting factors. Thus, HUMSC transplantation may be an effective therapy in the future.

Combined transplantation of bone marrow stromal cell-derived neural progenitor cells with a collagen sponge and basic fibroblast growth factor releasing microspheres enhances recovery after cerebral ischemia in rats

Bone marrow stromal cells (MSCs) are a useful source of cells because of their abundant supply and few associated ethical problems. We have previously reported that neural progenitor cells (NS-MSCs) can be effectively induced from MSCs and differentiate into neurons to contribute to functional recovery when transplanted into the rat stroke model. In this study, we attempted to enhance the therapeutic effects of NS-MSCs with a collagen sponge and basic fibroblast growth factor (bFGF) releasing microspheres. NS-MSCs were generated from MSCs by transfection of Notch-1 intracellular domain followed by culturing the cells in a free-floating culture system. The resulting NS-MSCs were transplanted into the rats with induced brain ischemia by using collagen sponges as scaffolds for transplanted cells, and with bFGF incorporated into gelatin microspheres to aid neovascularization around the transplanted region and proliferation of neural stem cells/neural progenitor cells. In culture, NS-MSCs successfully formed spheres containing cells highly expressing neural progenitor markers. Cell survival, neovascularization, and proliferation of host neural stem cells/neural progenitor cells were improved in animals that received NS-MSCs together with these biomaterials. Behavioral analysis also revealed significant functional recovery. These observations demonstrate that transplantation of NS-MSCs in combination with a collagen sponge and bFGF releasing microspheres significantly improves histological and functional recovery in the rat stroke model. When used with these biomaterials, NS-MSCs would be a promising cell source for treating stroke and neurodegenerative diseases.

Stem and progenitor cells for neurological repair: minor issues, major hurdles, and exciting opportunities for paracrine-based therapeutics

The transplantation of cultured stem and progenitor cells is a key element in the rapidly growing field of regenerative medicine. Based on their ability to rescue and/or repair injured tissue and partially restore organ function, multiple types of stem/progenitor cells have already entered into clinical trials. However, despite several decades of intense research, the goal to apply culture-expanded stem/progenitor cells in a manner that can effectively replace cells after injury has yet to be realized. Many sources of potentially useful cells are available, but something is clearly missing. In addition, recent studies suggest that paracrine effects of secreted or released factors are responsible for most of the benefits observed after cell transplantation, rather than direct cell replacement. These data call into question the need for cell transplantation for many types of therapy, in particular for acute injuries such as myocardial infarction and stroke. In this review, we examine current progress in the area of cell transplantation and minor issues and major hurdles regarding the clinical application of different cell types. We discuss the "paracrine hypothesis" for the action of transplanted stem/progenitor cells as an opportunity to identify defined combinations of biomolecules to rescue and/or repair tissues after injury. Although many of the concepts in this review will apply to multiple injury/repair systems, we will focus primarily on stem/progenitor cell-based treatments for neurological disorders and stroke.

Intra-arterial injection of neural stem cells using a microneedle technique does not cause microembolic strokes

Intra-arterial (IA) injection represents an experimental avenue for minimally invasive delivery of stem cells to the injured brain. It has however been reported that IA injection of stem cells carries the risk of reduction in cerebral blood flow (CBF) and microstrokes. Here we evaluate the safety of IA neural progenitor cell (NPC) delivery to the brain. Cerebral blood flow of rats was monitored during IA injection of single cell suspensions of NPCs after stroke. Animals received 1 × 10(6) NPCs either injected via a microneedle (microneedle group) into the patent common carotid artery (CCA) or via a catheter into the proximally ligated CCA (catheter group). Controls included saline-only injections and cell injections into non-stroked sham animals. Cerebral blood flow in the microneedle group remained at baseline, whereas in the catheter group a persistent (15 minutes) decrease to 78% of baseline occurred (P<0.001). In non-stroked controls, NPCs injected via the catheter method resulted in higher levels of Iba-1-positive inflammatory cells (P=0.003), higher numbers of degenerating neurons as seen in Fluoro-Jade C staining (P<0.0001) and ischemic changes on diffusion weighted imaging. With an appropriate technique, reduction in CBF and microstrokes do not occur with IA transplantation of NPCs.

Autologous bone marrow stromal cell transplantation for central nervous system disorders - recent progress and perspective for clinical application

There is increasing evidence that the transplanted BMSC significantly promote functional recovery after CNS damage in the animal models of various kinds of CNS disorders, including cerebral infarct, traumatic brain injury and spinal cord injury. However, there are several shortages of information when considering clinical application of BMSC transplantation for patients with CNS disorders. In this review, therefore, we discuss what we should clarify to establish cell transplantation therapy as the scientifically proven entity in clinical situation and describe our recent works for this purpose. The BMSC have the ability to alter their gene expression profile and phenotype in response to the surrounding circumstances and to protect the neurons by producing some neurotrophic factors. They also promote neurite extension and rebuild the neural circuits in the injured CNS. The BMSC can be expanded in vitro using the animal serum-free medium. Pharmacological modulation may accelerate the in vitro proliferation of the BMSC. Using in vivo optical imaging technique, the transplanted BMSC can non-invasively be tracked in the living animals for at least 8 weeks after transplantation. It is urgent issues to develop clinical imaging technique to track the transplanted cells in the CNS and evaluate the therapeutic significance of BMSC transplantation in order to establish it as a definite therapeutic strategy in clinical situation in the future.

Stem cell therapy for neurological disorders

Stem cells have long been in focus as potential therapy or even cure for a whole myriad of diseases. Many neurodegenerative disorders, both acute and chronic, are characterized by irreversible neuronal damage and loss, and only a few efficient treatment options exist. In contrast to many other tissues, the potential of self-regeneration of the central nervous system is highly limited. There is hope that stem cells could replace the damaged neuronal and glial cells, and provide biological and functional restoration based on their properties of self renewal and the ability to give rise to different cells. In recent years, the promising results of research on animal models has led to the establishment of the first clinical trials; although no clear evidence of therapeutic benefit for any of the conditions have been ascertained. Here we give a review of the current strategies of stem-cell based therapy for some of the more common neurological disorders, discussing the progress and current challenges, and giving an overview of future perspectives.

In vivo imaging of embryonic stem cell therapy

Embryonic stem cells (ESCs) have the most pluripotent potential of any stem cell. These cells, isolated from the inner cell mass of the blastocyst, are "pluripotent," meaning that they can give rise to all cell types within the developing embryo. As a result, ESCs have been regarded as a leading candidate source for novel regenerative medicine therapies and have been used to derive diverse cell populations, including myocardial and endothelial cells. However, before they can be safely applied clinically, it is important to understand the in vivo behavior of ESCs and their derivatives. In vivo analysis of ESC-derived cells remains critically important to define how these cells may function in novel regenerative medicine therapies. In this review, we describe several available imaging modalities for assessing cell engraftment and discuss their strengths and limitations. We also analyze the applications of these modalities in assessing the utility of ESCs in regenerative medicine therapies.

Cell-based therapy for stroke

Current treatments for stroke, such as the use of thrombolytic agents, are often limited by a narrow therapeutic time window. However, the regeneration of the brain after damage is still active days even weeks after stroke occurs, which might provide a second window for treatment. Cell-based therapy can be categorized into two strategies. One is transplantation of exogenous cells into the injured brain to replace the lost cells or support the remaining cells. The other strategy is to enhance the proliferation, differentiation, migration of endogenous stem or progenitor cells. Recent development in adult stem cell research and advancement in the induction of pluripotent stem cells from somatic adult cells provide a tremendous opportunity for transplantation therapy. Understanding the mechanisms and regulations involved in the endogenous neurogenesis will also help develop novel therapeutic interventions to promote neurogenesis and functional recovery in stroke. This review describes up-to-date progresses in cell-based therapy for the treatment of stroke.

Stem cell transplantation for ischemic stroke

BACKGROUND

Studies in animal models of ischemic stroke have shown that stem cells transplanted into the brain can lead to functional improvement. However, to date, evidence for the benefits of stem cell transplantation in ischemic stroke patients is lacking.

OBJECTIVES

To assess the efficacy and safety of stem cell transplantation compared with conventional treatments in patients with ischemic stroke.

SEARCH STRATEGY

We searched the Cochrane Stroke Group Trials Register (last searched February 2010), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2009, Issue 3), MEDLINE (1966 to August 2008), EMBASE (1980 to August 2008), Science Citation Index (1900 to August 2008), and BIOSIS (1926 to August 2008). We handsearched potentially relevant conference proceedings, screened reference lists, and searched ongoing trials and research registers (last searched November 2008). We also contacted individuals active in the field and stem cell manufacturers (last contacted December 2008).

SELECTION CRITERIA

We included randomized controlled trials (RCTs) recruiting patients with ischemic stroke, in any phase of the disease, and an ischemic lesion confirmed by computerized tomography or magnetic resonance imaging scan. We included all types of stem cell transplantation regardless of cell source (autograft, allograft, or xenograft; embryonic, fetal, or adult; from brain or other tissues), route of cell administration (systemic or local), and dosage. The primary outcome was efficacy (assessed as combined functional outcome or disability and dependency) at longer follow-up (minimum six months). Secondary outcomes included post-procedure safety outcomes (death, worsening of neurological deficit, infections and neoplastic transformation).

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and assessed trial quality. We contacted study authors for additional information.

MAIN RESULTS

We identified three very small RCTs. Two are still awaiting classification because only subgroups of patients could be included in this meta-analysis and additional unpublished data are needed. The third trial randomized 30 patients to intravenous transplantation of autologous mesenchymal stem cell (10 participants) or reference group (20 participants) (five participants, initially randomized to the intervention group, refused the treatment and were allocated to the reference group) and found a statistically non-significant functional improvement in treated patients at longer follow-up. No adverse cell-related events were reported.

AUTHORS' CONCLUSIONS

No large trials of stem cell transplantation have been performed in ischemic stroke patients and it is too early to know whether this intervention can improve functional outcome. Large, well-designed trials are needed.

Changes in Host Blood Factors and Brain Glia Accompanying the Functional Recovery after Systemic Administration of Bone Marrow Stem Cells in Ischemic Stroke Rats

In this study, we examined the effects of systemic administration of rat or human bone marrow stromal stem cells (MSC) at early and later times following middle cerebral artery occlusion (MCAO) on blood cytokines/growth factors, brain glia, and motor behavior in rats. Rats were tail vein injected with rat (r) and human (h) MSCs at 1 or 7 days post-MCAO. In some rats ( N = 4) MSCs isolated from transgenic GFP rats were used to track the migration of cells peripherally and centrally at 2.5 and 28 days. Motor behavior was assessed using the modified Neurological Severity Score/climbing test at various time points before and after MCAO and transplantation. Prior to sacrifice at 1, 7, or 28 days post-MCAO, blood serum was collected for cytokine array analysis. Brains were analyzed for markers of activated microglia (CD11) and reactive astrocytes (GFAP). Administration of either allogeneic (rMSCs) or xenogeneic (hMSCs) stem cells produced a significant recovery of motor behavior after MCAO, with cells delivered at 1 day having greater effect than those at 7 days. Correlated with recovery was an amplification in activated microglia, reactive astrocytes, and new blood vessels in the infarct region, resulting in greater preservation in brain integrity. Concomitantly, expression of blood cytokines/chemokines (IL-13, MMP2, MIP) and growth factors/receptors (VEGF, neuropilin, EPOR, TROY, NGFR, RAGE) were modified following MSC administration. Because only rare GFP-labeled MSCs were observed in the brain, these effects did not depend on the central incorporation of stem cells. The early systemic administration of allogeneic or xenogeneic MSCs soon after experimental stroke produces a structural/functional recovery in the brain which is correlated with an increase in activated brain glia and changes in circulating cytokines and growth factors. Stem cells therefore induce an important neuroprotective and/or regenerative response in the host organism.

Biodistribution of neural stem cells after intravascular therapy for hypoxic-ischemia

BACKGROUND AND PURPOSE

Intravascular transplantation of neural stem cells represents a minimally invasive therapeutic approach for the treatment of central nervous system diseases. The cellular biodistribution after intravascular injection needs to be analyzed to determine the ideal delivery modality. We studied the biodistribution and efficiency of targeted central nervous system delivery comparing intravenous and intra-arterial (IA) administration of neural stem cells after brain ischemia.

METHODS

Mouse neural stem cells were transduced with a firefly luciferase reporter gene for bioluminescence imaging (BLI). Hypoxic-ischemia was induced in adult mice and reporter neural stem cells were transplanted IA or intravenous at 24 hours after brain ischemia. In vivo BLI was used to track transplanted cells up to 2 weeks after transplantation and ex vivo BLI was used to determine single organ biodistribution.

RESULTS

Immediately after transplantation, BLI signal from the brain was 12 times higher in IA versus intravenous injected animals (P<0.0001). After IA injection, 69% of the total luciferase activity arose from the brain early after transplantation and 93% at 1 week. After intravenous injection, 94% of the BLI signal was detected in the lungs (P=0.004) followed by an overall 94% signal loss at 1 week, indicating lack of cell survival outside the brain. Ex vivo single organ analysis showed a significantly higher BLI signal in the brain than in the lungs, liver, and kidneys at 1 week (P<0.0001) and 2 weeks in IA (P=0.007).

CONCLUSIONS

IA transplantation results in superior delivery and sustained presence of neural stem cells in the ischemic brain in comparison to intravenous infusion.

Induction of neuro-protective/regenerative genes in stem cells infiltrating post-ischemic brain tissue

BACKGROUND

Although the therapeutic potential of bone marrow-derived stromal stem cells (BMSC) has been demonstrated in different experimental models of ischemic stroke, it remains unclear how stem cells (SC) induce neuroprotection following stroke. In this study, we describe a novel method for isolating BMSC that infiltrate postischemic brain tissue and use this method to identify the genes that are persistently activated or depressed in BMSC that infiltrate brain tissue following ischemic stroke.

METHODS

Ischemic strokes were induced in C57BL/6 mice by middle cerebral artery occlusion for 1 h, followed by reperfusion. BMSC were isolated from H-2 Kb-tsA58 (immortomouse) mice, and were administered (i.v.) 24 h after reperfusion. At the peak of therapeutic improvement (14 days after the ischemic insult), infarcted brain tissue was isolated, and the BMSC were isolated by culturing at 33 degrees C. Microarray analysis and RT-PCR were performed to compare differential gene expression between naïve and infiltrating BMSC populations.

RESULTS

Z-scoring revealed dramatic differences in the expression of extracellular genes between naïve and infiltrating BMSC. Pair-wise analysis detected 80 extracellular factor genes that were up-regulated (>/= 2 fold, P < 0.05, Benjamini-Hochberg correction) between naïve and infiltrated BMSC. Although several anticipated neuroregenerative, nerve guidance and angiogenic factor (e.g., bFGF, bone morphogenetic protein, angiopoietins, neural growth factor) genes exhibited an increased expression, a remarkable induction of genes for nerve guidance survival (e.g., cytokine receptor-like factor 1, glypican 1, Dickkopf homolog 2, osteopontin) was also noted.

CONCLUSIONS

BMSC infiltrating the post-ischemic brain exhibit persistent epigenetic changes in gene expression for numerous extracellular genes, compared to their naïve counterparts. These genes are relevant to the neuroprotection, regeneration and angiogenesis previously described following stem cell therapy in animal models of ischemic stroke.

New endovascular method for transvascular exit of arteries and veins: developed in simulator, in rat and in rabbit with full clinical integration

BACKGROUND

Endovascular technique has benefits vis-a-vis surgical access to organs with less accessible anatomical locations. To minimize surgical risk we propose a novel endovascular technique, to create parenchymal access through endovascular methods.

METHODOLOGY/PRINCIPAL FINDINGS

We have developed, manufactured and tested an endovascular catheter with a depth limiting collar and a penetrating tip that is used to perforate vessels, thereby creating a working channel to the extra-vascular space. Computer simulations and subsequent interventions have been performed ex vivo and in vivo in both small and large animals by testing different prototypes. All tests were designed for testing extravascular hemostasis and absence of thrombo-embolic complications when exiting the vessels from the inside to the extra vascular space. We have deposited prototypes after intervention in vascular walls over a period of 14 days in rat with no impairment on blood flow and no signs of thrombo-embolic complications upon re-exploration (n = 7). We have also incorporated the catheter system with clinically available systems both in an ex vivo simulator setting and in a full scale clinical angiographical setting in rabbit were no bleeding (0%) in any of the interventions performed (n = 40). To prevent hemorrhage during termination of the procedure, a hollow electrolysis detachment-zone leaves the distal tip in the vessel-wall after the intervention. This has also been tested with absolute hemostasis in large animals (n = 6).

CONCLUSIONS/SIGNIFICANCE

We have developed and tested a new system for transvascular tissue access in simulations, ex vivo and in vivo in small and large animals, integrating it with standard clinical catheters and angiographical environment, with absolute hemostasis and without thromboembolic complications. In a clinical setting for stem cell transplantation, local substance administration or tissue sampling, the benefit should be greatest in organs that are difficult or high-risk to access with other techniques, such as the pancreas, the central nervous system (CNS) and the heart.

Hydrogel matrix to support stem cell survival after brain transplantation in stroke

Stroke is a leading cause of adult disability. Stem/progenitor cell transplantation improves recovery after stroke in rodent models. These studies have 2 main limitations to clinical translation. First, most of the cells in stem/progenitor transplants die after brain transplantation. Second, intraparenchymal approaches target transplants to normal brain adjacent to the stroke, which is the site of the most extensive natural recovery in humans. Transplantation may damage this tissue. The stroke cavity provides an ideal target for transplantation because it is a compartmentalized region of necrosis, can accept a high volume transplant without tissue damage, and lies directly adjacent to the most plastic brain area in stroke. However, direct transplantation into the stroke cavity has caused massive death in the transplant. To overcome these limitations, the authors tested stem/progenitor transplants within a specific biopolymer hydrogel matrix to create a favorable environment for transplantation into the infarct cavity after stroke, and they tested this in comparison to stem cell injection without hydrogel support. A biopolymer hydrogel composed of cross-linked hyaluronan and heparin sulfate significantly promoted the survival of 2 different neural progenitor cell lines in vitro in conditions of stress and in vivo into the infarct cavity. Quantitative analysis of the transplant and surrounding tissue indicates diminished inflammatory infiltration of the graft with the hydrogel transplant. This result indicates that altering the local environment in stem cell transplantation enhances survival and diminishes cell stress. Stem cell transplantation into the infarct cavity within a pro-survival hydrogel matrix may provide a translational therapy for stroke recovery.

Menstrual blood cells display stem cell-like phenotypic markers and exert neuroprotection following transplantation in experimental stroke

Cell therapy remains an experimental treatment for neurological disorders. A major obstacle in pursuing the clinical application of this therapy is finding the optimal cell type that will allow benefit to a large patient population with minimal complications. A cell type that is a complete match of the transplant recipient appears as an optimal scenario. Here, we report that menstrual blood may be an important source of autologous stem cells. Immunocytochemical assays of cultured menstrual blood reveal that they express embryonic-like stem cell phenotypic markers (Oct4, SSEA, Nanog), and when grown in appropriate conditioned media, express neuronal phenotypic markers (Nestin, MAP2). In order to test the therapeutic potential of these cells, we used the in vitro stroke model of oxygen glucose deprivation (OGD) and found that OGD-exposed primary rat neurons that were co-cultured with menstrual blood-derived stem cells or exposed to the media collected from cultured menstrual blood exhibited significantly reduced cell death. Trophic factors, such as VEGF, BDNF, and NT-3, were up-regulated in the media of OGD-exposed cultured menstrual blood-derived stem cells. Transplantation of menstrual blood-derived stem cells, either intracerebrally or intravenously and without immunosuppression, after experimentally induced ischemic stroke in adult rats also significantly reduced behavioral and histological impairments compared to vehicle-infused rats. Menstrual blood-derived cells exemplify a source of "individually tailored" donor cells that completely match the transplant recipient, at least in women. The present neurostructural and behavioral benefits afforded by transplanted menstrual blood-derived cells support their use as a stem cell source for cell therapy in stroke.

Non-haematological uses of cord blood stem cells

Embryonic stem (ES) cell therapies are often promoted as the optimal stem cell source for regenerative medicine applications because of their ability to develop into any tissue in the body. Unfortunately, ES cell applications are currently limited by ethical, political, biological and regulatory hurdles. However, multipotent non-ES cells are available in large numbers in umbilical cord blood (CB). CB stem cells are capable of giving rise to hematopoietic, epithelial, endothelial and neural tissues both in vitro and in vivo. Thus, CB stem cells are amenable to treat a wide variety of diseases including cardiovascular, ophthalmic, orthopaedic, neurological and endocrine diseases. In addition, the recent use of CB in several regenerative medicine clinical studies has demonstrated its pluripotent nature. Here we review the latest developments in the use of CB in regenerative medicine. Examples of these usages include cerebral palsy and type I diabetes. The numbers of individuals affected with each of these diseases are estimated at 10 000 infants diagnosed with cerebral palsy annually and 15 000 youths diagnosed with type 1 diabetes annually. A summary of the initial results from such clinical studies using autologous cord blood stem cells will be presented.

Advances in cord blood transplants in adults

Umbilical cord blood is an acceptable source of hematopoietic stem cells for patients with malignant diseases but has limitations in its use. In this review, we will discuss these limitations and the recent advances in cord blood transplants that may enable cord blood to become more widely available as an alternative stem cell source for adults for the treatment of malignant diseases and for use in regenerative medicine.

Intracarotid administration of human bone marrow mononuclear cells in rat photothrombotic ischemia

Background

Increasing evidence suggests that cell therapy improves functional recovery in experimental models of stroke and myocardial infarction. So far only small pilot trials tested the effects of cell therapy in stroke patients, whereas large clinical trials were conducted in patients with ischemic heart disease. To investigate the therapeutic benefit of cell therapy to improve the recovery after stroke, we determined the efficacy of bone marrow derived mononuclear cells, which were shown to improve the recovery in experimental and clinical acute myocardial infarction studies, in a rat stroke model.

Methods

Adult male Wistar rats were randomly assigned to receive either five million human bone marrow mononuclear cells (hBMC) or placebo intraarterially 3 days after photothrombotic ischemia. For immunosuppression the animals received daily injections of cyclosporine throughout the experiment, commencing 24 hours before the cell transplantation. A battery of behavioral tests was performed before and up to 4 weeks after ischemia.

Results

Body temperature and body weight revealed no difference between groups. Neurological deficits measured by the Rotarod test, the adhesive-removal test and the cylinder test were not improved by hBMC transplantation compared to placebo.

Conclusions

This study demonstrates that hBMC do not improve functional recovery when transplanted intraaterially 3 days after the onset of focal cerebral ischemia. A possible reason for the failed neurological improvement after cell therapy might be the delayed treatment initiation compared to other experimental stroke studies that showed efficacy of bone marrow mononuclear cells.

Transplantation of placenta-derived mesenchymal stromal cells upon experimental stroke in rats

The beneficial effects of bone marrow-derived mesenchymal stromal cell (MSC) administration following experimental stroke have already been described. Despite several promising characteristics, placenta-derived MSC have not been used in models of focal ischemia. The aim of the current study is to investigate the impact of intravenously transplanted placenta-derived MSC on post-stroke recovery. Permanent occlusion of the middle cerebral artery was induced in spontaneously hypertensive rats. MSC were obtained from the human maternal or fetal placenta and intravenously administered after 24 h (single transplantation) or after 8 h and 24 h (dual transplantation). Sensorimotor deficits were quantified for 60 days using the beam walk test and the modified Neurological Severity Score system. Infarct volume was determined in vivo by means of magnetic resonance imaging on days 1, 8, 29 and 60. Astroglial reactivity was semiquantitatively ascertained within a small and a broad region adjacent to the lesion border. The double infusion of placental MSC was superior to single transplantation in the functional tests. However, a significant difference to the control group in all outcome parameters was observed only for maternally derived MSC. These findings suggest that placental tissue constitutes a promising source for experimental stroke therapies.

In vitro neural differentiation of human embryonic stem cells using a low-density mouse embryonic fibroblast feeder protocol

Human embryonic stem cells (hESCs) have the capacity to self-renew and to differentiate into all components of the embryonic germ layers (ectoderm, mesoderm, endoderm) and subsequently all cell types that comprise human tissues. HESCs can potentially provide an extraordinary source of cells for tissue engineering and great insight into early embryonic development. Much attention has been given to the possibility that hESCs and their derivatives may someday play major roles in the study of the development, disease therapeutics, and repair of injuries to the central and peripheral nervous systems. This tantalizing promise will be realized only when we understand fundamental biological questions about stem cell growth and development into distinct tissue types. In vitro, differentiation of hESCs into neurons proceeds as a multistep process that in many ways recapitulates development of embryonic neurons. We have found in vitro conditions that promote differentiation of stem cells into neuronal precursor or neuronal progenitor cells. Specifically, we have investigated the ability of two federally approved hESC lines, HSF-6 and H7, to form embryonic and mature neuronal cells in culture. Undifferentiated hESCs stain positively for markers of undifferentiated/pluripotent hESCs including surface glycoproteins, SSEA-3 and 4, and transcription factors Oct-3/4 and Nanog. Using reduced numbers of mouse embryonic fibroblasts as feeder substrates, these markers of pluripotency are lost quickly and replaced by primarily neuroglial phenotypes with only a few cells representing other embryonic germ layer types remaining. Within the first 2 weeks of co-culture with reduced MEFs, the undifferentiated hESCs show progression from neuroectodermal to neural stem cell to maturing and migrating neurons to mature neurons in a stepwise fashion that is dependent on both the type of hESCs and the density of MEFs. In this chapter, we provide the methods for culturing pluripotent hESCs and MEFs, differentiating hESCs using reduced density MEFs, and phenotypic analyses of this culture system.

Two-component protein-engineered physical hydrogels for cell encapsulation

Current protocols to encapsulate cells within physical hydrogels require substantial changes in environmental conditions (pH, temperature, or ionic strength) to initiate gelation. These conditions can be detrimental to cells and are often difficult to reproduce, therefore complicating their use in clinical settings. We report the development of a two-component, molecular-recognition gelation strategy that enables cell encapsulation without environmental triggers. Instead, the two components, which contain multiple repeats of WW and proline-rich peptide domains, undergo a sol-gel phase transition upon simple mixing and hetero-assembly of the peptide domains. We term these materials mixing-induced, two-component hydrogels. Our results demonstrate use of the WW and proline-rich domains in protein-engineered materials and expand the library of peptides successfully designed into engineered proteins. Because both of these association domains are normally found intracellularly, their molecular recognition is not disrupted by the presence of additional biomolecules in the extracellular milieu, thereby enabling reproducible encapsulation of multiple cell types, including PC-12 neuronal-like cells, human umbilical vein endothelial cells, and murine adult neural stem cells. Precise variations in the molecular-level design of the two components including (i) the frequency of repeated association domains per chain and (ii) the association energy between domains enable tailoring of the hydrogel viscoelasticity to achieve plateau shear moduli ranging from approximately 9 to 50 Pa. Because of the transient physical crosslinks that form between association domains, these hydrogels are shear-thinning, injectable, and self-healing. Neural stem cells encapsulated in the hydrogels form stable three-dimensional cultures that continue to self-renew, differentiate, and sprout extended neurites.

Generation of functional neural artificial tissue from human umbilical cord blood stem cells

Stem cell-based regenerative neurology is an emerging concept for treatment of diseases of central nervous system. Among variety of proposed procedures, one of the most promising is refilling of cystic cavities of injured brain parenchyma with artificial neural tissue. Recent studies revealed that after allogenic transplantation in rodents these tissue-engineered entities were shown efficient in repair of hypoxic/ischemic brain injury. Human umbilical cord blood (HUCB) was recognized to be an efficient and noncontroversial source of neural stem cells (NSC). The main purpose of this study was to generate HUCB-derived neural artificial tissue and investigate their functional properties. Neural organoids formed on human-originated biodegradable scaffolds within 3 weeks and resembled niche structure where immature stem cells (Oct4+ and Sox2+) and proliferating neuroblasts (Nestin+, GFAP+, and Ki67+) were present. Such aggregates were placed on multi-electrode chips and differentiated toward mature neurons (TUJ1+ and MAP2+). These three-dimensional aggregates in contrast to two-dimensional cultures formed functional circuits and generated spontaneous field/action potentials. Our results indicate that three-dimensional environment facilitates maturation of HUCB-derived NSC what should be considered regarding regenerative medicine application.

Human dental pulp stem cells with highly angiogenic and neurogenic potential for possible use in pulp regeneration

Dental caries is a common public health problem, causing early loss of dental pulp and resultant tooth loss. Dental pulp has important functions to sustain teeth providing nutrient and oxygen supply, innervation, reactionary/reparative dentin formation and immune response. Regeneration of pulp is an unmet need in endodontic therapy, and angiogenesis/vasculogenesis and neurogenesis are critical for pulp regeneration. Permanent and deciduous pulp tissue is easily available from teeth after extraction without ethical issues and has potential for clinical use. In this review, we introduce some stem cell subfractions, CD31(-)/CD146(-) SP cells and CD105(+) cells with high angiogenic and neurogenic potential, derived from human adult dental pulp tissue. Potential utility of these cells is addressed as a source of cells for treatment of cerebral and limb ischemia and pulp inflammation complete with angiogenesis and vasculogenesis.

Plasticity during stroke recovery: from synapse to behaviour

Reductions in blood flow to the brain of sufficient duration and extent lead to stroke, which results in damage to neuronal networks and the impairment of sensation, movement or cognition. Evidence from animal models suggests that a time-limited window of neuroplasticity opens following a stroke, during which the greatest gains in recovery occur. Plasticity mechanisms include activity-dependent rewiring and synapse strengthening. The challenge for improving stroke recovery is to understand how to optimally engage and modify surviving neuronal networks, to provide new response strategies that compensate for tissue lost to injury.

Migration and homing of bone-marrow mononuclear cells in chronic ischemic stroke after intra-arterial injection

Cell-based treatments have been considered a promising therapy for neurological diseases. However, currently there are no clinically available methods to monitor whether the transplanted cells reach and remain in the brain. In this study we investigated the feasibility of detecting the distribution and homing of autologous bone-marrow mononuclear cells (BMMCs) labeled with Technetium-99 m ((99m)Tc) in a cell-based therapy clinical study for chronic ischemic stroke. Six male patients (ages 24-65 years) with ischemic cerebral infarcts within the middle cerebral artery (MCA) between 59 and 82 days were included. Cell dose ranged from 1.25x10(8) to 5x10(8). Approximately 2x10(7) cells were labeled with (99m)Tc and intra-arterially delivered together with the unlabeled cells via a catheter navigated to the MCA. None of the patients showed any complications on the 120-day follow-up. Whole body scintigraphies indicated cell homing in the brain of all patients at 2 h, while the remaining uptake was mainly distributed to liver, lungs, spleen, kidneys and bladder. Moreover, quantification of uptake in Single-Photon Emission Computed Tomography (SPECT) at 2 h showed preferential accumulation of radioactivity in the hemisphere affected by the ischemic infarct in all patients. However, at 24 h homing could only distinguished in the brains of 2 patients, while in all patients uptake was still seen in the other organs. Taken together, these results indicate that labeling of BMMCs with (99m)Tc is a safe and feasible technique that allows monitoring the migration and engraftment of intra-arterially transplanted cells for at least 24 h.

Optimizing the success of cell transplantation therapy for stroke

Stem cell transplantation has evolved as a promising experimental treatment approach for stroke. In this review, we address the major hurdles for successful translation from basic research into clinical applications and discuss possible strategies to overcome these issues. We summarize the results from present pre-clinical and clinical studies and focus on specific areas of current controversy and research: (i) the therapeutic time window for cell transplantation; (ii) the selection of patients likely to benefit from such a therapy; (iii) the optimal route of cell delivery to the ischemic brain; (iv) the most suitable cell types and sources; (v) the potential mechanisms of functional recovery after cell transplantation; and (vi) the development of imaging techniques to monitor cell therapy.

Future of cord blood for non-oncology uses

For the last 5 years cord blood (CB) has been under intense experimental investigation in in vitro differentiation models and in preclinical animal models ranging from bone to muscle regeneration, cardiovascular diseases including myocardial and peripheral arterial disease, stroke and Parkinson's disease. On the basis of its biological advantages, CB can be an ideal source for tissue regeneration. However, in the hype of the so-called 'plasticity', many cell types have been characterized either on cell surface Ag expression alone or by RNA expression only, and without detailed characterization of genetic pathways; frequently, cells are defined without analysis of cellular function in vitro and in vivo, and the definition of the lineage of origin and cells have not been defined in preclinical studies. Here, we explore not only the most consistent data with regard to differentiation of CB cells in vitro and in vivo, but also show technical limitations, such as why in contrast to cell populations isolated from fresh CB, cryopreserved CB is not the ideal source for tissue regeneration. By taking advantage of numerous CB units discarded due to lack of sufficient hematopoietic cells for clinical transplantation, new concepts to produce off-the-shelf products are presented as well.

Intravenous administration of 99mTc-HMPAO-labeled human mesenchymal stem cells after stroke: in vivo imaging and biodistribution

Human mesenchymal stem cells (hMSC) are a promising source for cell therapy after stroke. To deliver these cells, an IV injection appears safer than a local graft. We aimed to assess the whole-body biodistribution of IV-injected (99m)Tc-HMPAO-labeled hMSC in normal rats (n = 9) and following a right middle cerebral artery occlusion (MCAo, n = 9). Whole-body nuclear imaging, isolated organ counting (at 2 and 20 h after injection) and histology were performed. A higher activity was observed in the right damaged hemisphere of the MCAo group [6.5 +/- 0.9 x 10(-3) % of injected dose (ID)/g] than in the control group (3.6 +/- 1.2 x 10(-3) %ID/g), 20 h after injection. In MCAo rats, right hemisphere activity was higher than that observed in the contralateral hemisphere at 2 h after injection (11.6 +/- 2.8 vs. 9.8 +/- 1.7 x 10(-3) %ID/g). Following an initial hMSC lung accumulation, there was a decrease in pulmonary activity from 2 to 20 h after injection in both groups. The spleen was the only organ in which activity increased between 2 and 20 h. The presence of hMSC was documented in the spleen, liver, lung, and brain following histology. IV-injected hMSC are transiently trapped in the lungs, can be sequestered in the spleen, and are predominantly eliminated by kidneys. After 20 h, more hMSC are found in the ischemic lesion than into the undamaged cerebral tissue. IV delivery of hMSC could be the initial route for a clinical trial of tolerance.

Committed neural progenitor cells derived from genetically modified bone marrow stromal cells ameliorate deficits in a rat model of stroke

Bone marrow stromal cells (MSCs) are an excellent source of cells for treating a variety of central nervous system diseases. In this study, we report the efficient induction of committed neural progenitor cells from rat and human MSCs (NS-MSCs) by introduction of cells with the intracellular domain of Notch-1 followed by growth in the free-floating culture system. NS-MSCs successfully formed spheres, in which cells highly expressed the neural precursor cell markers. The commitment of spheres to neural lineage cells was confirmed by their successful differentiation into neuronal cells when exposed to a differentiation medium. To determine the therapeutic potential of NS-MSCs, cells were transplanted into the cortex and striatum in a rat model of focal cerebral ischemia. The survival, distribution, and integration of NS-MSCs in the host brain were very high, and at day 100, grafted NS-MSCs were positive for dopaminergic, glutamatergic, and gamma-amino butyric acid(GABA)ergic neuronal markers. They extended long neurites for nearly 6.3 mm and many of these expressed synaptophysin. Significant behavioral recovery was also observed in limb-placing and water-maze tests. These suggest a high potential for this MSC approach in the replenishment of neural cells for stroke and for a wide range of neurodegenerative conditions that require various types of neural cells.

Cerebral transplantation of encapsulated mesenchymal stem cells improves cellular pathology after experimental traumatic brain injury

PURPOSE

"Naked" human mesenchymal stem cells (MSC) are neuro-protective in experimental brain injury (TBI). In a controlled cortical impact (CCI) rat model, we investigated whether encapsulated MSC (eMSC) act similarly, and whether efficacy is augmented using cells transfected to produce the neuro-protective substance glucagon-like peptide-1 (GLP-1).

METHODS

Thirty two Sprague-Dawley rats were randomized to five groups: controls (no CCI), CCI-only, CCI+eMSC, CCI+GLP-1 eMSC, and CCI+empty capsules. On day 14, cisternal cerebro-spinal fluid (CSF) was sampled for measurement of GLP-1 concentration. Brains were immuno-histochemically assessed using specific antibody staining for NeuN, MAP-2 and GFAP. In another nine healthy rats, in vitro.

RESULTS

GLP-1 production rates were measured from cells explanted after 2, 7 and 14 days. GLP-1 production rate in transfected cells, before implantation, was 7.03 fmol/capsule/h. Cells were still secreting GLP-1 at a rate of 3.68+/-0.49, 2.85+/-0.45 and 3.53+/-0.55 after 2, 7 and 14 days, respectively. In both of the stem cell treated CCI groups, hippocampal cell loss was reduced, along with an attenuation of cortical neuronal and glial abnormalities, as measured by MAP-2 and GFAP expression. The effects were more pronounced in animals treated with GLP-1 secreting eMSC. This group displayed an increased CSF level of GLP-1 (17.3+/-3.4pM).

CONCLUSIONS

Hippocampal neuronal cell loss, and cortical glial and neuronal cyto-skeletal abnormalities, after CCI are reduced following transplantation of encapsulated eMSC. These effects were augmented by GLP-1 transfected eMSC.

The neural stem cell line CTX0E03 promotes behavioral recovery and endogenous neurogenesis after experimental stroke in a dose-dependent fashion

BACKGROUND

This study investigated behavioral recovery in rats following implanting increasing doses of CTX0E03 cells into the putamen ipsilateral to the stroke damage. Postmortem histological analysis investigated possible mechanisms of behavioral recovery.

METHODS

. At 4 weeks after middle cerebral artery occlusion (MCAO), rats were treated with 4500, 45,000, or 450,000 CTX0E03 cells or vehicle implanted into the putamen with testing on a battery of tasks preocclusion and postocclusion. Histological examination of brains included assessment of lesion volumes, implant cell survival and differentiation, changes to host brain matrix, angiogenesis, and neurogenesis using immunohistochemical methods.

RESULTS

. Statistically significant dose-related recovery in sensorimotor function deficits (bilateral asymmetry test [BAT; P < .0002] in the mid- and high-dose groups and rotameter test after amphetamine exposure [P < .05] in the high-dose group) was found in the CTX0E03 cell implanted groups compared to the vehicle group. In-life functional improvements correlated with cell dose, though did not correlate with survival of CTX0E03 cells measured at postmortem. Surviving CTX0E03 cells differentiated into oligodendroglial and endothelial phenotypes. MCAO-induced reduction of neurogenesis in the subventricular zone (SVZ) was partially restored to that observed in sham operated controls. No adverse CTX0E03 cell-related effects were observed during in-life observations or on tissue histology.

CONCLUSIONS

. This study found that the implantation of CTX0E03 human neural stem cells in rats after MCAO stroke promoted significant behavioral recovery depending on cell dose. The authors propose a paracrine trophic mechanism, which is triggered early after CTX0E03 cell implantation, and which in turn targets restoration of neurogenesis in the SVZ of MCAO rats.

Delayed post-ischaemic neuroprotection following systemic neural stem cell transplantation involves multiple mechanisms

Recent evidence suggests that neural stem/precursor cells (NPCs) promote recovery in animal models with delayed neuronal death via a number of indirect bystander effects. A comprehensive knowledge of how transplanted NPCs exert their therapeutic effects is still lacking. Here, we investigated the effects of a delayed transplantation of adult syngenic NPCs--injected intravenously 72 h after transient middle cerebral artery occlusion--on neurological recovery, histopathology and gene expression. NPC-transplanted mice showed a significantly improved recovery from 18 days post-transplantation (dpt) onwards, which persisted throughout the study. A small percentage of injected NPCs accumulated in the brain, integrating mainly in the infarct boundary zone, where most of the NPCs remained undifferentiated up to 30 dpt. Histopathological analysis revealed a hitherto unreported very delayed neuroprotective effect of NPCs, becoming evident at 10 and 30 dpt. Tissue survival was associated with downregulation of markers of inflammation, glial scar formation and neuronal apoptotic death at both mRNA and protein levels. Our data highlight the relevance of very delayed degenerative processes in the stroke brain that are intimately associated with inflammatory and glial responses. These processes may efficaciously be antagonized by (stem) cell-based strategies at time-points far beyond established therapeutic windows for pharmacological neuroprotection.

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.

The potential of PET/MR for brain imaging

INTRODUCTION

The completion of an integrated PET/MR prototype system for brain imaging is the latest step in the evolution of positron emission tomography. Early images with this new imaging system demonstrate that high-resolution multiparametric studies can be combined without significant loss of performance of either imaging modality.

OBJECTIVE

This new technology will make fusion of morphological and biological information much easier, yield real-time assessment of complementary variables and will provide dynamic information for kinetic modelling. Simultaneous acquisition of various metabolic and functional parameters may open new insights into the organization of the brain and its changes in disease.

DISCUSSION

A new field may open up for molecular and cellular imaging, where new targets--e.g. angiogenesis, gene transfer, function and migration of transplanted cells--can be imaged in the morphological context and within a functional environment. This application might have a special impact on the translation of treatment concepts from experimental models into clinical application. If the added value of the hybrid system for diagnosis and treatment monitoring is established, a cost-effective PET/MR combination might attain wider clinical application.

Functional engraftment of the medial ganglionic eminence cells in experimental stroke model

Currently there are no effective treatments targeting residual anatomical and behavioral deficits resulting from stroke. Evidence suggests that cell transplantation therapy may enhance functional recovery after stroke through multiple mechanisms. We used a syngeneic model of neural transplantation to explore graft-host communications that enhance cellular engraftment.The medial ganglionic eminence (MGE) cells were derived from 15-day-old transgenic rat embryos carrying green fluorescent protein (GFP), a marker, to easily track the transplanted cells. Adult rats were subjected to transient intraluminal occlusion of the medial cerebral artery. Two weeks after stroke, the grafts were deposited into four sites, along the rostro-caudal axis and medially to the stroke in the penumbra zone. Control groups included vehicle and fibroblast transplants. Animals were subjected to motor behavioral tests at 4 week posttransplant survival time. Morphological analysis demonstrated that the grafted MGE cells differentiated into multiple neuronal subtypes, established synaptic contact with host cells, increased the expression of synaptic markers, and enhanced axonal reorganization in the injured area. Initial patch-clamp recording demonstrated that the MGE cells received postsynaptic currents from host cells. Behavioral analysis showed reduced motor deficits in the rotarod and elevated body swing tests. These findings suggest that graft-host interactions influence the fate of grafted neural precursors and that functional recovery could be mediated by neurotrophic support, new synaptic circuit elaboration, and enhancement of the stroke-induced neuroplasticity.

Systemic delivery of umbilical cord blood cells for stroke therapy: a review

PURPOSE

This review paper summarizes relevant studies, discusses potential mechanisms of transplanted cell-mediated neuroprotection, and builds a case for the need to establish outcome parameters that are critical for transplantation success. In particular, we outline the advantages and disadvantages of systemic delivery of human umbilical cord blood (HUCB) cells in the field of cellular transplantation for treating ischemic stroke.

METHODS

A MEDLINE/PubMed systematic search of published articles in peer-reviewed journals over the last 25 years was performed focusing on the theme of HUCB as donor graft source for transplantation therapy in neurological disorders with emphasis on stroke.

RESULTS

Ischemic stroke remains a leading cause of human death and disability. Although stroke survivors may gain spontaneous partial functional recovery, they often suffer from sensory-motor dysfunction, behavioral/neurological alterations, and various degrees of paralysis. Currently, limited clinical intervention is available to prevent ischemic damage and restore lost function in stroke victims. Stem cells from fetal tissues, bone marrow, and HUCB has emerged in the last few years as a potential cell transplant cell source for ischemic stroke, because of their capability to differentiate into multiple cell types and the possibility that they may provide trophic support for cell survival, tissue repair, and functional recovery.

CONCLUSION

A growing number of studies highlight the potential of systemic delivery of HUCB cells as a novel therapeutic approach for stroke. However, additional preclinical studies are warranted to reveal the optimal HUCB transplant regimen that is safe and efficacious prior to proceeding to large-scale clinical application of these cells for stroke therapy.

Neuroprotective effects of mesenchymal stem cells derived from human embryonic stem cells in transient focal cerebral ischemia in rats

Embryonic mesenchymal stem cells (eMSCs) were first derived from human embryonic stem cells (hESCs) overexpressing green fluorescence protein (GFP). They expressed CD29, CD44, CD73, CD105, CD166 and nestin, but not CD34, CD45, CD106 SSEA-4 or Oct3/4. Twenty million eMSCs in 1 mL of phosphate-buffered saline (PBS) were injected into the femoral veins of spontaneously hypertensive rats after transient middle cerebral artery occlusion. The migration and differentiation of the eMSCs in the ischemic brain were analyzed. The results revealed that eMSCs migrated to the infarction region and differentiated into neurons, which were positive for beta-tubulin III, microtubule-associated protein 2 (MAP2), HuC, neurofilament and human nuclear antibody, and to vascular endothelial cells, which were positive for von Willebrand factor (vWF). The transplanted cells survived in the infarction region for at least 4 weeks. Adhesive removal function significantly improved in the first week after cell transplantation, and rotarod motor function significantly improved starting from the second week. The infarction volume in the eMSC group was significantly smaller than that in the PBS control group at 4 weeks after infusion. The results of this study show that when administered intravenously, eMSCs differentiated into neuronal and endothelial cells, reduced the infarction volume, and improved behavioral functional outcome significantly in transient focal cerebral ischemia.

MRI tracking of intravenously transplanted human neural stem cells in rat focal ischemia model

The present study investigated the ability of 1.5 T clinical magnetic resonance imaging (MRI) to detect ferumoxides- labeled human neural stem cells (NSCs) that had been intravenously (i.v.) injected into a rat model of focal cerebral ischemia. To detect transplanted cells, hNSCs were labeled with ferumoxide then followed by bromodeoxyuridine (BrdU) prior to transplantation. In the rat ischemia-human NSC group, human NSCs (4 x 10(6)cells in 5 ml PBS) were injected via tail vein 24 h after middle cerebral artery occlusion (MCAo), and the brains of the rats were scanned using a 1.5 T MRI unit over a period of 4 weeks (1 day before MCAo, then 1 and 3 days after cell injection, and weekly thereafter). In histologic sections, transplanted cells were identified by Prussian blue and anti-BrdU fluorescence staining. Regions with hypointense signals on T2-weighted and 3D gradient echo MR images corresponded with areas stained by Prussian blue, which suggested the presence of superparamagnetic iron oxide (SPIO) nanoparticles within the engrafted cells. Hypointense areas on MR images were observed in peri-infarct areas 3 days after cell injection. The findings indicate that 1.5 T MRI has sufficient sensitivity to track engrafted stem cells in vivo.

Positron Emission Tomography Imaging of Poststroke Angiogenesis

Background and Purpose— Vascular endothelial growth factor (VEGF) and VEGF receptors (VEGFRs) play important roles during neurovascular repair after stroke. In this study, we imaged VEGFR expression with positron emission tomography (PET) to noninvasively analyze poststroke angiogenesis.

Methods— Female Sprague-Dawley rats after distal middle cerebral artery occlusion surgery were subjected to weekly MRI, 18 F-FDG PET, and 64 Cu-DOTA-VEGF 121 PET scans. Several control experiments were performed to confirm the VEGFR specificity of 64 Cu-DOTA-VEGF 121 uptake in the stroke border zone. VEGFR, BrdU, lectin staining, and 125 I-VEGF 165 autoradiography on stroke brain tissue slices were performed to validate the in vivo findings.

Results— T2-weighed MRI correlated with the “cold spot” on 18 F-FDG PET for rats undergoing distal middle cerebral artery occlusion surgery. The 64 Cu-DOTA-VEGF 121 uptake in the stroke border zone peaked at ≈10 days after surgery, indicating neovascularization as confirmed by histology (VEGFR-2, BrdU, and lectin staining). VEGFR specificity of 64 Cu-DOTA-VEGF 121 uptake was confirmed by significantly lower uptake of 64 Cu-DOTA-VEGF mutant in vivo and intense 125 I-VEGF 165 uptake ex vivo in the stroke border zone. No appreciable uptake of 64 Cu-DOTA-VEGF 121 was observed in the brain of sham-operated rats.

Conclusions— For the first time to our knowledge, we successfully evaluated the VEGFR expression kinetics noninvasively in a rat stroke model. In vivo imaging of VEGFR expression could become a significant clinical tool to plan and monitor therapies aimed at improving poststroke angiogenesis.

Potential of adult neural stem cells in stroke therapy

Despite state-of-the-art therapy, clinical outcome after stroke remains poor, with many patients left permanently disabled and dependent on care. Stem cell therapy has evolved as a promising new therapeutic avenue for the treatment of stroke in experimental studies, and recent clinical trials have proven its feasibility and safety in patients. Replacement of damaged cells and restoration of function can be accomplished by transplantation of different cell types, such as embryonic, fetal or adult stem cells, human fetal tissue and genetically engineered cell lines. Adult neural stem cells offer the advantage of avoiding the ethical problems associated with embryonic or fetal stem cells and can be harvested as autologous grafts from the individual patients. Furthermore, stimulation of endogenous adult stem cell-mediated repair mechanisms in the brain might offer new avenues for stroke therapy without the necessity of transplantation. However, important scientific issues need to be addressed to advance our understanding of the molecular mechanisms underlying the critical steps in cell-based repair to allow the introduction of these experimental techniques into clinical practice. This review describes up-to-date experimental concepts using adult neural stem cells for the treatment of stroke.

Biological approaches to ischemic tissue repair: gene- and cell-based strategies

Gene therapy is a potential therapeutic strategy for treatment of ischemic vascular diseases; however, the clinical application of gene therapy has met some anticipated challenges. Recent randomized, controlled trials suggest that patients with cardiovascular disease may also benefit from cell-based therapies, and the optimal treatment regimen may combine both approaches to take advantage of potential synergy between the underlying therapeutic mechanisms. This review discusses recent research into both gene and cell therapy and considers the potential application of a combined treatment approach for cardiovascular and cerebrovascular ischemic diseases.