Notch-Induced Rat and Human Bone Marrow Stromal Cell Grafts Reduce Ischemic Cell Loss and Ameliorate Behavioral Deficits in Chronic Stroke Animals

Intracerebral Transplantation of Autologous Mesenchymal Stem Cells Improves Functional Recovery in a Rat Model of Chronic Ischemic Stroke

While treatments exist for the acute phase of stroke, there are limited options for patients with chronic infarcts and long-term disability. Allogenic mesenchymal stem cells (alloMSCs) show promise for the treatment of stroke soon after ischemic injury. There is, however, no information on the use of autologous MSCs (autoMSCs), delivered intracerebrally in rats with a chronic infarct. In this study, rats underwent middle cerebral artery occlusion (MCAO) to induce stroke followed by bone marrow aspiration and MSC expansion in a closed bioreactor. Four weeks later, brain MRI was obtained and autoMSCs (1 × 106, 2.5 × 106 or 5 × 106; n = 6 each) were stereotactically injected into the peri-infarct and compared to controls (MCAO only; MCAO + PBS; n = 6-9). Behavior was assessed using the modified neurological severity score (mNSS). For comparison, an additional cohort of MCAO rats were implanted with 2.5 × 106 alloMSCs generated from a healthy rat. All doses of autoMSCs produced significant improvement (54-70%) in sensorimotor function 60 days later. In contrast, alloMSCs improved only 31.7%, similar to that in PBS controls 30%. Quantum dot-labeled auto/alloMSCs were found exclusively at the implantation site throughout the post-transplantation period with no tumor formation on MRI or Ki67 staining of engrafted MSCs. Small differences in stroke volume and no differences in corpus callosum width were observed after MSC treatment. Stroke-induced glial reactivity in the peri-infarct was long-lasting and unabated by auto/alloMSC transplantation. These studies suggest that intracerebral transplantation of autoMSCs as compared to alloMSCs may be a promising treatment in chronic stroke.

Therapeutic effects of intracerebral transplantation of human modified bone marrow-derived stromal cells (SB623) with voluntary and forced exercise in a rat model of ischemic stroke

Ischemic stroke results in significant long-term disability and mortality worldwide. Although existing therapies, such as recombinant tissue plasminogen activator and mechanical thrombectomy, have shown promise, their application is limited by stringent conditions. Mesenchymal stem cell (MSC) transplantation, especially using SB623 cells (modified human bone marrow-derived MSCs), has emerged as a promising alternative, promoting neurogenesis and recovery. This study evaluated the effects of voluntary and forced exercise, alone and in combination with SB623 cell transplantation, on neurological and psychological outcomes in a rat model of ischemic stroke. Male Wistar rats that had undergone middle cerebral artery occlusion (MCAO) were divided into six groups: control, voluntary exercise (V-Ex), forced exercise (F-Ex), SB623 transplantation, SB623 + V-Ex, and SB623 + F-Ex. Voluntary exercise was facilitated using running wheels, while forced exercise was conducted on treadmills. Neurological recovery was assessed using the modified neurological severity score (mNSS). Psychological symptoms were evaluated through the open field test (OFT) and forced swim test (FST), and neurogenesis was assessed via BrdU labeling. Both exercise groups exhibited significant changes in body weight post-MCAO. Both exercises enhanced the treatment effect of SB623 transplantation. The forced exercise showed a stronger treatment effect on ischemic stroke than voluntary exercise alone, and the sole voluntary exercise improved depression-like behavior. The SB623 + F-Ex group demonstrated the greatest improvements in motor function, infarct area reduction, and neurogenesis. The SB623 + V-Ex group was most effective in alleviating depression-like behavior. Future research should optimize these exercise protocols and elucidate the underlying mechanisms to develop tailored rehabilitation strategies for stroke patients.

Clinical state and future directions of stem cell therapy in stroke rehabilitation

Despite substantial advances in the acute management of stroke, it remains a leading cause of adult disability and mortality worldwide. Currently, the reperfusion modalities thrombolysis and thrombectomy benefit only a fraction of patients in the hyperacute phase of ischemic stroke. Thus, with the exception of vagal nerve stimulation combined with intensive physical therapy, there are no approved neuroprotective/neurorestorative therapies for stroke survivors. Stem cell therapy is a promising treatment for stroke patients and has been the focus of an increasing number of clinical trials over the past two decades. We provide a comprehensive overview of stem cell therapies available to stroke patients, focusing on the different types and doses of stem cells, timing and route of administration, patient selection, clinical outcomes, translational challenges, and future directions for the field. Information on ongoing and completed studies was retrieved from ClinicalTrials.gov, PubMed, Google Scholar, ICTRP, and Scopus. Autologous bone marrow-derived mononuclear cells (BMMNCs) are the most used, followed by autologous bone marrow stromal cells. IV therapy is typically applied in acute to subacute phases, while IT or IC routes are utilized in chronic phases. Although early-phase trials (Phase I/II) indicate strong safety and tolerability, definitive clinical effectiveness has yet to be unequivocally proven. Cochrane meta-analyses show NIH Stroke Scale improvements, though studies often have high bias and small sample sizes. Larger randomized, double-blind, placebo-controlled trials are ongoing to refine stem cell transplantation protocols, addressing cell type and source, dosage, timing, patient selection, the potential for combination therapies, and clinical efficacy.

Modified human mesenchymal stromal/stem cells restore cortical excitability after focal ischemic stroke in rats

Allogeneic modified bone marrow-derived human mesenchymal stromal/stem cells (hMSC-SB623 cells) are in clinical development for the treatment of chronic motor deficits after traumatic brain injury and cerebral ischemic stroke. However, their exact mechanisms of action remain unclear. Here, we investigated the effects of this cell therapy on cortical network excitability, brain tissue, and peripheral blood at a chronic stage after ischemic stroke in a rat model. One month after focal cortical ischemic stroke, hMSC-SB623 cells or the vehicle solution were injected into the peri-stroke cortex. Starting one week after treatment, cortical excitability was assessed ex vivo. hMSC-SB623 cell transplants reduced stroke-induced cortical hyperexcitability, restoring cortical excitability to control levels. The histology of brain tissue revealed an increase of factors relevant to neuroregeneration, and synaptic and cellular plasticity. Whole-blood RNA sequencing and serum protein analyses showed that intra-cortical hMSC-SB623 cell transplantation reversed effects of stroke on peripheral blood factors known to be involved in stroke pathophysiology. Our findings demonstrate that intra-cortical transplants of hMSC-SB623 cells correct stroke-induced circuit disruptions even at the chronic stage, suggesting broad usefulness as a therapeutic for neurological conditions with network hyperexcitability. Additionally, the transplanted cells exert far-reaching immunomodulatory effects whose therapeutic impact remains to be explored.

Mesenchymal Stromal Cell Implants for Chronic Motor Deficits After Traumatic Brain Injury: Post Hoc Analysis of a Randomized Trial

BACKGROUND AND OBJECTIVES

Traumatic brain injury (TBI) is frequently characterized by chronic motor deficits. Therefore, this clinical trial assessed whether intracranial implantation of allogeneic modified mesenchymal stromal (SB623) cells can improve chronic motor deficits after TBI.

METHODS

Post hoc analysis of the double-blind, randomized, prospective, surgical sham-controlled, phase 2, STEMTRA clinical trial (June 2016 and March 2019) with 48 weeks of follow-up was conducted. In this international, multicenter clinical trial, eligible participants had moderate-to-severe TBI, were ≥12 months postinjury, and had chronic motor deficits. Participants were randomized in a 1:1:1:1 ratio to stereotactic surgical intracranial implantation of SB623 cells (2.5 × 106, 5.0 × 106, 10 × 106) or surgical sham-controlled procedure. The prespecified primary efficacy end point was significantly greater change from baseline of the Fugl-Meyer Motor Scale (FMMS) score, a measure of motor status, for the SB623 pooled vs control arm at 24 weeks.

RESULTS

A total of 211 participants were screened, 148 were excluded, and 63 underwent randomization, of which 61 (97%; mean age, 34 [SD, 12] years; 43 men [70.5%]) completed the trial. Single participants in the SB623 2.5 × 106 and 5.0 × 106 cell dose groups discontinued before surgery. Safety and efficacy (modified intent-to-treat) were assessed in participants who underwent surgery (N = 61; SB623 = 46, controls = 15). The primary efficacy end point (FMMS) was achieved (least squares mean [SE] SB623: +8.3 [1.4]; 95% CI 5.5-11.2 vs control: +2.3 [2.5]; 95% CI -2.7 to 7.3; p = 0.04), with faster improvement of the FMMS score in SB623-treated groups than in controls at 24 weeks and sustained improvement at 48 weeks. At 48 weeks, improvement of function and activities of daily living (ADL) was greater, but not significantly different in SB623-treated groups vs controls. The incidence of adverse events was equivalent in SB623-treated groups and controls. There were no deaths or withdrawals due to adverse events.

DISCUSSION

Intraparenchymal implantation of SB623 cells was safe and significantly improved motor status at 24 weeks in participants with chronic motor deficits after TBI, with continued improvement of function and ADL at 48 weeks. Cell therapy can modify chronic neurologic deficits after TBI.

TRIAL REGISTRATION INFORMATION

ClinicalTrials.gov Identifier: NCT02416492. Submitted to registry: April 15, 2015. First participant enrolled: July 6, 2016. Available at: classic.clinicaltrials.gov/ct2/show/NCT02416492.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that intracranial implantation of allogeneic stem (SB623) cells in adults with motor deficits from chronic TBI improves motor function at 24 weeks.

Mesenchymal stem cells therapy for chronic ischemic stroke-a systematic review

Stroke represents a significant global health issue, primarily in the form of ischemic stroke. Despite the availability of therapeutic interventions, the recovery from chronic stroke, occurring 3 months post-initial stroke, poses substantial challenges. A promising avenue for post-acute stroke patients is mesenchymal stem cells (MSCs) therapy, which is derived from various sources and is globally recognized as the most utilized and extensively studied stem cell therapy. This systematic review, adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines, aims to synthesize evidence regarding the impact of MSCs therapy on patients with chronic ischemic stroke. Employing an advanced search strategy across databases such as PubMed, PubMed Central, Google Scholar, the Cochrane Central Register of Controlled Trials (CENTRAL), and ClinicalTrial.gov, a total of 70 studies were identified, with 4studies meeting the inclusion criteria. Although positive outcomes were observed in terms of efficacy and safety, certain limitations, such as small sample sizes, study heterogeneity, and the absence of placebo groups, undermine the overall strength of the evidence. It is crucial to address these limitations in future research, highlighting the importance of larger sample sizes, standardized methodologies, and comparative trials to improve the assessment of MSCs' efficacy and safety. Moving forward, key priorities include exploring underlying mechanisms, determining optimal administration modes and dosages, and conducting comparative trials. By addressing these aspects, we can propel MSCs therapies toward greater efficacy, safety, and applicability across diverse patient populations.

An update on stem cell therapy for stroke patients: Where are we now?

With a foundation built upon initial work from the 1980s demonstrating graft viability in cerebral ischemia, stem cell transplantation has shown immense promise in promoting survival, enhancing neuroprotection and inducing neuroregeneration, while mitigating both histological and behavioral deficits that frequently accompany ischemic stroke. These findings have led to a number of clinical trials that have thoroughly supported a strong safety profile for stem cell therapy in patients but have generated variable efficacy. As preclinical evidence continues to expand through the investigation of new cell lines and optimization of stem cell delivery, it remains critical for translational models to adhere to the protocols established through basic scientific research. With the recent shift in approach towards utilization of stem cells as a conjunctive therapy alongside standard thrombolytic treatments, key issues including timing, route of administration, and stem cell type must each be appropriately translated from the laboratory in order to resolve the question of stem cell efficacy for cerebral ischemia that ultimately will enhance therapeutics for stroke patients towards improving quality of life.

Mesenchymal Stem Cells Promote an Increase in Neuronal Oscillation via Glutamate Tonic Release

Mesenchymal stromal cells (MSCs) hold therapeutic potential for neurological disorders, but their impact on neuronal activity remains unclear. We investigated the effects of SB623 cells (Notch-1 intracellular domain-transfected MSCs) and parental MSCs on human induced pluripotent stem cell (iPSC)-derived neurons using multi-electrode arrays. SB623 cells significantly increased neuronal activity and oscillation in a dose-dependent manner, surpassing astrocytes in promoting network bursts. Strikingly, glutamatergic neurons showed a rapid increase in activity and bursts compared to GABAergic neurons, suggesting glutamate release from SB623 cells. We confirmed this by finding high glutamate levels in SB623 cell conditioned medium, which were reduced by glutaminase inhibition. Glutamate release was further implicated by the reduced excitability in co-cultures with astrocytes, known glutamate scavengers. Our findings reveal a novel mechanism for MSCs: promoting neuronal activity and network formation through tonic glutamate release, with potential implications for MSC-based therapies.

Stem Cell Therapy for Repair of the Injured Brain: Five Principles

Cell therapy holds great promise for regenerative treatment of disease. Despite recent breakthroughs in clinical research, applications of cell therapies to the injured brain have not yielded the desired results. We pinpoint current limitations and suggest five principles to advance stem cell therapies for brain regeneration. While we focus on cell therapy for stroke, all principles also apply for other brain diseases.

Mesenchymal stem cells in the treatment of ischemic stroke

Over the past two decades, multiple preclinical studies have shown that transplantation of mesenchymal stem cells leads to a pronounced positive effect in animals with experimental stroke. Based on the promising results of preclinical studies, several clinical trials on the transplantation of mesenchymal stem cells to stroke patients have also been conducted. In this review, we present and analyze the results of completed clinical trials dedicated to the mesenchymal stem cells transplantation in patients with ischemic stroke. According to the obtained results, it can be concluded that transplantation of mesenchymal stem cells is safe and feasible from the economic and biomedical point of view. For the further implementa-tion of this promising approach into the clinical practice, randomized, placebo-controlled, multicenter clinical trials are needed with a large sample of patients and optimized cell transplantation protocols and patient inclusion criteria. In this review we also discuss possi-ble strategies to enhance the effectiveness of cell therapy with the use of mesenchymal stem cells.

Recent advances in tissue repair of the blood-brain barrier after stroke

The selective permeability of the blood-brain barrier (BBB) enables the necessary exchange of substances between the brain parenchyma and circulating blood and is important for the normal functioning of the central nervous system. Ischemic stroke inflicts damage upon the BBB, triggering adverse stroke outcomes such as cerebral edema, hemorrhagic transformation, and aggravated neuroinflammation. Therefore, effective repair of the damaged BBB after stroke and neovascularization that allows for the unique selective transfer of substances from the BBB after stroke is necessary and important for the recovery of brain function. This review focuses on four important therapies that have effects of BBB tissue repair after stroke in the last seven years. Most of these new therapies show increased expression of BBB tight-junction proteins, and some show beneficial results in terms of enhanced pericyte coverage at the injured vessels. This review also briefly outlines three effective classes of approaches and their mechanisms for promoting neoangiogenesis following a stroke.

Effects of the Co-Overexpression of the BCL and BDNF Genes on the Gamma-Aminobutyric Acid-Ergic Differentiation of Wharton's-Jelly-Derived Mesenchymal Stem Cells

One of the problems with using MSCs (mesenchymal stem cells) to treat different neurodegenerative diseases of the central nervous system is their low ability to spontaneously differentiate into functional neurons. The aim of this study was to investigate how the co-overexpression of the BCL and BDNF genes affects the ability of genetically modified MSCs to differentiate into GABA-ergic neurons. A co-overexpression of two genes was performed, one of which, BCL, was supposed to increase the resistance of the cells to the toxic agents in the brain environment. The second one, BDNF, was supposed to direct the cells onto the neuronal differentiation pathway. As a result, the co-overexpression of both BCL2 + BDNF and BCLXL + BDNF caused an increase in the MAP2 gene expression level (a marker of the neuronal pathway) and the SYP gene that is associated with synaptogenesis. In both cases, approximately 18% of the genetically modified and then differentiated cells exhibited the presence of the GAD protein, which is characteristic of GABA-ergic neurons. Despite the presence of GAD, after both modifications, only the BCL2 and BDNF co-overexpression correlated with the ability of the modified cells to release gamma-aminobutyric acid (GABA) after depolarization. Our study identified a novel model of genetically engineered MSCs that can be used as a tool to deliver the antiapoptotic proteins (BCL) and neurotrophic factor (BDNF) directly into the brain microenvironment. Additionally, in the investigated model, the genetically modified MSCs could easily differentiate into functional GABA-ergic neurons and, moreover, due to the secreted BCL and BDNF, promote endogenous neuronal growth and encourage synaptic connections between neurons.

Synergistic therapeutic effects of intracerebral transplantation of human modified bone marrow-derived stromal cells (SB623) and voluntary exercise with running wheel in a rat model of ischemic stroke

BACKGROUND

Mesenchymal stromal cell (MSC) transplantation therapy is a promising therapy for stroke patients. In parallel, rehabilitation with physical exercise could ameliorate stroke-induced neurological impairment. In this study, we aimed to clarify whether combination therapy of intracerebral transplantation of human modified bone marrow-derived MSCs, SB623 cells, and voluntary exercise with running wheel (RW) could exert synergistic therapeutic effects on a rat model of ischemic stroke.

METHODS

Wistar rats received right transient middle cerebral artery occlusion (MCAO). Voluntary exercise (Ex) groups were trained in a cage with RW from day 7 before MCAO. SB623 cells (4.0 × 105 cells/5 μl) were stereotactically injected into the right striatum at day 1 after MCAO. Behavioral tests were performed at day 1, 7, and 14 after MCAO using the modified Neurological Severity Score (mNSS) and cylinder test. Rats were euthanized at day 15 after MCAO for mRNA level evaluation of ischemic infarct area, endogenous neurogenesis, angiogenesis, and expression of brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF). The rats were randomly assigned to one of the four groups: vehicle, Ex, SB623, and SB623 + Ex groups.

RESULTS

SB623 + Ex group achieved significant neurological recovery in mNSS compared to the vehicle group (p < 0.05). The cerebral infarct area of SB623 + Ex group was significantly decreased compared to those in all other groups (p < 0.05). The number of BrdU/Doublecortin (Dcx) double-positive cells in the subventricular zone (SVZ) and the dentate gyrus (DG), the laminin-positive area in the ischemic boundary zone (IBZ), and the mRNA level of BDNF and VEGF in SB623 + Ex group were significantly increased compared to those in all other groups (p < 0.05).

CONCLUSIONS

This study suggests that combination therapy of intracerebral transplantation SB623 cells and voluntary exercise with RW achieves robust neurological recovery and synergistically promotes endogenous neurogenesis and angiogenesis after cerebral ischemia, possibly through a mechanism involving the up-regulation of BDNF and VEGF.

Stem Cell- and Cell-Based Therapies for Ischemic Stroke

Stroke is the second cause of disability worldwide as it is expected to increase its incidence and prevalence. Despite efforts to increase the number of patients eligible for recanalization therapies, a significant proportion of stroke survivors remain permanently disabled. This outcome boosted the search for efficient neurorestorative methods. Stem cells act through multiple pathways: cell replacement, the secretion of growth factors, promoting endogenous reparative pathways, angiogenesis, and the modulation of neuroinflammation. Although neural stem cells are difficult to obtain, pose a series of ethical issues, and require intracerebral delivery, mesenchymal stem cells are less immunogenic, are easy to obtain, and can be transplanted via intravenous, intra-arterial, or intranasal routes. Extracellular vesicles and exosomes have similar actions and are easier to obtain, also allowing for engineering to deliver specific molecules or RNAs and to promote the desired effects. Appropriate timing, dosing, and delivery protocols must be established, and the possibility of tumorigenesis must be settled. Nonetheless, stem cell- and cell-based therapies for stroke have already entered clinical trials. Although safe, the evidence for efficacy is less impressive so far. Hopefully, the STEP guidelines and the SPAN program will improve the success rate. As such, stem cell- and cell-based therapy for ischemic stroke holds great promise.

The role of mesenchymal stem cell transplantation for ischemic stroke and recent research developments

Ischemic stroke is a common cerebrovascular disease that seriously affects human health. However, most patients do not practice self-care and cannot rely on the current clinical treatment for guaranteed functional recovery. Stem cell transplantation is an emerging treatment studied in various central nervous system diseases. More importantly, animal studies show that transplantation of mesenchymal stem cells (MSCs) can alleviate neurological deficits and bring hope to patients suffering from ischemic stroke. This paper reviews the biological characteristics of MSCs and discusses the mechanism and progression of MSC transplantation to provide new therapeutic directions for ischemic stroke.

Transplantation of modified human bone marrow-derived stromal cells affords therapeutic effects on cerebral ischemia in rats

AIMS

SB623 cells are human bone marrow stromal cells transfected with Notch1 intracellular domain. In this study, we examined potential regenerative mechanisms underlying stereotaxic transplantation of SB623 cells in rats with experimental acute ischemic stroke.

METHODS

We prepared control group, empty capsule (EC) group, SB623 cell group (SB623), and encapsulated SB623 cell (eSB623) group. Transient middle cerebral artery occlusion (MCAO) was performed on day 0, and 24 h after MCAO, stroke rats received transplantation into the envisioned ischemic penumbra. Modified neurological severity score (mNSS) was evaluated, and histological evaluations were performed.

RESULTS

In the mNSS, SB623 and eSB623 groups showed significant improvement compared to the other groups. Histological analysis revealed that the infarction area in SB623 and eSB623 groups was reduced. In the eSB623 group, robust cell viability and neurogenesis were detected in the subventricular zone that increased significantly compared to all other groups.

CONCLUSION

SB623 cells with or without encapsulation showed therapeutic effects on ischemic stroke. Encapsulated SB623 cells showed enhanced neurogenesis and increased viability inside the capsules. This study reveals the mechanism of secretory function of transplanted SB623 cells, but not cell-cell interaction as primarily mediating the cells' functional benefits in ischemic stroke.

Muse cells: ushering in a new era of stem cell-based therapy for stroke

Stem cell-based regenerative therapies have recently become promising and advanced for treating stroke. Mesenchymal stem cells (MSCs) and induced pluripotent stem cells (iPSCs) have received the most attention for treating stroke because of the outstanding paracrine function of MSCs and the three-germ-layer differentiation ability of iPSCs. However, the unsatisfactory homing ability, differentiation, integration, and survival time in vivo limit the effectiveness of MSCs in regenerative medicine. The inherent tumorigenic property of iPSCs renders complete differentiation necessary before transplantation, which is complicated and expensive and affects the consistency among cell batches. Multilineage differentiating stress-enduring (Muse) cells are natural pluripotent stem cells in the connective tissues of nearly every organ and thus are considered nontumorigenic. A single Muse cell can differentiate into all three-germ-layer, preferentially migrate to damaged sites after transplantation, survive in hostile environments, and spontaneously differentiate into tissue-compatible cells, all of which can compensate for the shortcomings of MSCs and iPSCs. This review summarizes the recent progress in understanding the biological properties of Muse cells and highlights the differences between Muse cells and other types of stem cells. Finally, we summarized the current research progress on the application of Muse cells on stroke and challenges from bench to bedside.

Ischemic Brain Stroke and Mesenchymal Stem Cells: An Overview of Molecular Mechanisms and Therapeutic Potential

Ischemic brain injury is associated with a high rate of mortality and disability with no effective therapeutic strategy. Recently, a growing number of studies are focusing on mesenchymal stem cell-based therapies for neurodegenerative disorders. However, despite having the promising outcome of preclinical studies, the clinical application of stem cell therapy remained elusive due to little or no progress in clinical trials. The objective of this study was to provide a generalized critique for the role of mesenchymal stem cell therapy in ischemic stroke injury, its underlying mechanisms, and constraints on its preclinical and clinical applications. Thus, we attempted to present an overview of previously published reports to evaluate the progress and provide molecular basis of mesenchymal stem cells (MSCs) therapy and its application in preclinical and clinical settings, which could aid in designing an effective regenerative therapeutic strategy in the future.

Considerations in the Design of Non-Clinical Development Programmes to Support Non-Viral Genetically Modified Mesenchymal Stromal Cell Therapies

Due to their immune suppressive pharmacology, regenerative capacity, and immune privileged status, mesenchymal stromal cells (MSCs) are an attractive cell type to treat a variety of diseases. Genetically engineered MSCs are currently in non-clinical and clinical development for a wide range of applications including the delivery of pro-drugs and therapeutic proteins or modified to enhance their regenerative potential. Unmodified MSCs have been shown to have good safety profiles in clinical development. The introduction of exogenous transgenes introduces possible additional risks that need to be assessed in non-clinical studies prior to initiating clinical studies. The use of ex vivo non-viral genetic modification approaches potentially reduces the risks associated with viral vector transfection approaches, including the potential for cell transformation. This review provides an overview of the regulatory-compliant non-clinical proof-of-concept and safety studies required to take MSC-based gene therapy products from the bench to the clinic.

Cell Therapy for Stroke: A Mechanistic Analysis

Cell therapy has been widely recognized as a promising strategy to enhance recovery in stroke survivors. However, despite an abundance of encouraging preclinical data, successful clinical translation remains elusive. As the field continues to advance, it is important to reexamine prior clinical trials in the context of their intended mechanisms, as this can inform future preclinical and translational efforts. In the present work, we review the major clinical trials of cell therapy for stroke and highlight a mechanistic shift between the earliest studies, which aimed to replace dead and damaged neurons, and later ones that focused on exploiting the various neuromodulatory effects afforded by stem cells. We discuss why both mechanisms are worth pursuing and emphasize the means through which cell replacement can still be achieved.

Cell Therapy for Chronic TBI: Interim Analysis of the Randomized Controlled STEMTRA Trial

OBJECTIVE

To determine whether chronic motor deficits secondary to traumatic brain injury (TBI) can be improved by implantation of allogeneic modified bone marrow-derived mesenchymal stromal/stem cells (SB623).

METHODS

This 6-month interim analysis of the 1-year double-blind, randomized, surgical sham-controlled, phase 2 Stem Cell Therapy for Traumatic Brain Injury (STEMTRA) trial (NCT02416492) evaluated safety and efficacy of the stereotactic intracranial implantation of SB623 in patients with stable chronic motor deficits secondary to TBI. Patients in this multicenter trial (n = 63) underwent randomization in a 1:1:1:1 ratio to 2.5 × 106, 5.0 × 106, or 10 × 106 SB623 cells or control. Safety was assessed in patients who underwent surgery (n = 61), and efficacy was assessed in the modified intent-to-treat population of randomized patients who underwent surgery (n = 61; SB623 = 46, control = 15).

RESULTS

The primary efficacy endpoint of significant improvement from baseline of Fugl-Meyer Motor Scale score at 6 months for SB623-treated patients was achieved. SB623-treated patients improved by (least square [LS] mean) 8.3 (standard error 1.4) vs 2.3 (standard error 2.5) for control at 6 months, the LS mean difference was 6.0 (95% confidence interval 0.3-11.8, p = 0.040). Secondary efficacy endpoints improved from baseline but were not statistically significant vs control at 6 months. There were no dose-limiting toxicities or deaths, and 100% of SB623-treated patients experienced treatment-emergent adverse events vs 93.3% of control patients (p = 0.25).

CONCLUSIONS

SB623 cell implantation appeared to be safe and well tolerated, and patients implanted with SB623 experienced significant improvement from baseline motor status at 6 months compared to controls.

CLINICALTRIALSGOV IDENTIFIER

NCT02416492.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that implantation of SB623 was well tolerated and associated with improvement in motor status.

Revisiting Stem Cell-Based Clinical Trials for Ischemic Stroke

Stroke is the leading cause of serious long-term disability, significantly reducing mobility in almost half of the affected patients aged 65 years and older. There are currently no proven neurorestorative treatments for chronic stroke. To address the complex problem of restoring function in ischemic brain tissue, stem cell transplantation-based therapies have emerged as potential restorative therapies. Aligning with the major cell types found within the ischemic brain, stem-cell-based clinical trials for ischemic stroke have fallen under three broad cell lineages: hematopoietic, mesenchymal, and neural. In this review article, we will discuss the scientific rationale for transplanting cells from each of these lineages and provide an overview of published and ongoing trials using this framework.

Endovascular model of ischemic stroke in swine guided by real-time MRI

Modeling stroke in animals is essential for testing efficacy of new treatments; however, previous neuroprotective therapies, based on systemic delivery in rodents failed, exposing the need for model with improved clinical relevance. The purpose of this study was to develop endovascular approach for inducing ischemia in swine. To achieve that goal, we used intra-arterial administration of thrombin mixed with gadolinium and visualized the occlusion with real-time MRI. Placement of the microcatheter proximally to rete allowed trans-catheter perfusion of the ipsilateral hemisphere as visualized by contrast-enhanced perfusion MR scans. Dynamic T2*w MRI facilitated visualization of thrombin + Gd solution transiting through cerebral vasculature and persistent hyperintensities indicated occlusion. Area of trans-catheter perfusion dynamically quantified on representative slice before and after thrombin administration (22.20 ± 6.31 cm² vs. 13.28 ± 4.71 cm² respectively) indicated significantly reduced perfusion. ADC mapping showed evidence of ischemia as early as 27 min and follow-up T2w scans confirmed ischemic lesion (3.14 ± 1.41 cm²). Animals developed contralateral neurological deficits but were ambulatory. Our study has overcome long lasting challenge of inducing endovascular stroke model in pig. We were able to induce stroke using minimally invasive endovascular approach and observe in real-time formation of the thrombus, blockage of cerebral perfusion and eventually stroke lesion.

Stem Cell Repair of the Microvascular Damage in Stroke

Stroke is a life-threatening disease that leads to mortality, with survivors subjected to long-term disability. Microvascular damage is implicated as a key pathological feature, as well as a therapeutic target for stroke. In this review, we present evidence detailing subacute diaschisis in a focal ischemic stroke rat model with a focus on blood–brain barrier (BBB) integrity and related pathogenic processes in contralateral brain areas. Additionally, we discuss BBB competence in chronic diaschisis in a similar rat stroke model, highlighting the pathological changes in contralateral brain areas that indicate progressive morphological brain disturbances overtime after stroke onset. With diaschisis closely approximating stroke onset and progression, it stands as a treatment of interest for stroke. Indeed, the use of stem cell transplantation for the repair of microvascular damage has been investigated, demonstrating that bone marrow stem cells intravenously transplanted into rats 48 h post-stroke survive and integrate into the microvasculature. Ultrastructural analysis of transplanted stroke brains reveals that microvessels display a near-normal morphology of endothelial cells and their mitochondria. Cell-based therapeutics represent a new mechanism in BBB and microvascular repair for stroke.

From in vitro to in vivo reprogramming for neural transdifferentiation: An approach for CNS tissue remodeling using stem cell technology

Advances in stem cell technology have provided three approaches to address the demanding issue of the treatment of intractable neurological disease. One of the approaches is the screening of compounds attenuating pathological phenotypes in stem-cell based models. A second approach consists of exogenous-targeted cell supplementation to the lesion with stem cell-derived differentiated cells. A third approach involves in vivo direct programming to transdifferentiate endogenous somatic cells and to boost CNS tissue remodeling. In this review, we outline research advances in stem cell technology of direct reprogramming in vitro and in vivo and discuss the future challenge of tissue remodeling by neural transdifferentiation.

Mesenchymal stem cell therapy alleviates the neuroinflammation associated with acquired brain injury

Ischemic stroke and traumatic brain injury (TBI) comprise two particularly prevalent and costly examples of acquired brain injury (ABI). Following stroke or TBI, primary cell death and secondary cell death closely model disease progression and worsen outcomes. Mounting evidence indicates that long‐term neuroinflammation extensively exacerbates the secondary deterioration of brain structure and function. Due to their immunomodulatory and regenerative properties, mesenchymal stem cell transplants have emerged as a promising approach to treating this facet of stroke and TBI pathology. In this review, we summarize the classification of cell death in ABI and discuss the prominent role of inflammation. We then consider the efficacy of bone marrow–derived mesenchymal stem/stromal cell (BM‐MSC) transplantation as a therapy for these injuries. Finally, we examine recent laboratory and clinical studies utilizing transplanted BM‐MSCs as antiinflammatory and neurorestorative treatments for stroke and TBI. Clinical trials of BM‐MSC transplants for stroke and TBI support their promising protective and regenerative properties. Future research is needed to allow for better comparison among trials and to elaborate on the emerging area of cell‐based combination treatments.

Harnessing the anti-inflammatory properties of stem cells for transplant therapy in hemorrhagic stroke

Hemorrhagic stroke is a global health crisis plagued by neuroinflammation in the acute and chronic phases. Neuroinflammation approximates secondary cell death, which in turn robustly contributes to stroke pathology. Both the physiological and behavioral symptoms of stroke correlate with various inflammatory responses in animal and human studies. That slowing the secondary cell death mediated by this inflammation may attenuate stroke pathology presents a novel treatment strategy. To this end, experimental therapies employing stem cell transplants support their potential for neuroprotection and neuroregeneration after hemorrhagic stroke. In this review, we evaluate experiments using different types of stem cell transplants as treatments for stroke-induced neuroinflammation. We also update this emerging area by examining recent preclinical and clinical trials that have deployed these therapies. While further investigations are warranted to solidify their therapeutic profile, the reviewed studies largely posit stem cells as safe and potent biologics for stroke, specifically owing to their mode of action for sequestering neuroinflammation and promoting neuroregenerative processes.

Two-year safety and clinical outcomes in chronic ischemic stroke patients after implantation of modified bone marrow-derived mesenchymal stem cells (SB623): a phase 1/2a study

OBJECTIVE

The aim of this study was to evaluate the safety and clinical outcomes associated with stereotactic surgical implantation of modified bone marrow-derived mesenchymal stem cells (SB623) in patients with stable chronic ischemic stroke.

METHODS

This was a 2-year, open-label, single-arm, phase 1/2a study; the selected patients had chronic motor deficits between 6 and 60 months after nonhemorrhagic stroke. SB623 cells were administered to the target sites surrounding the subcortical stroke region using MRI stereotactic image guidance.

RESULTS

A total of 18 patients were treated with SB623 cells. All experienced at least 1 treatment-emergent adverse event (TEAE). No patients withdrew due to adverse events, and there were no dose-limiting toxicities or deaths. The most frequent TEAE was headache related to the surgical procedure (88.9%). Seven patients experienced 9 serious adverse events, which resolved without sequelae. In 16 patients who completed 24 months of treatment, statistically significant improvements from baseline (mean) at 24 months were reported for the European Stroke Scale (ESS) score, 5.7 (95% CI 1.4-10.1, p < 0.05); National Institutes of Health Stroke Scale (NIHSS) score, -2.1 (95% CI -3.3 to -1.0, p < 0.01), Fugl-Meyer (F-M) total score, 19.4 (95% CI 9.9-29.0, p < 0.01); and F-M motor scale score, 10.4 (95% CI 4.0-16.7, p < 0.01). Measures of efficacy reached plateau by 12 months with no decline thereafter. There were no statistically significant changes in the modified Rankin Scale score. The size of transient lesions detected by T2-weighted FLAIR imaging in the ipsilateral cortex at weeks 1-2 postimplantation significantly correlated with improvement in ESS (0.619, p < 0.05) and NIHSS (-0.735, p < 0.01) scores at 24 months.

CONCLUSIONS

In this completed 2-year phase 1/2a study, implantation of SB623 cells in patients with stable chronic stroke was safe and was accompanied by improvements in clinical outcomes.Clinical trial registration no.: NCT01287936 (clinicaltrials.gov).

Neuroinflammation as a target for treatment of stroke using mesenchymal stem cells and extracellular vesicles

Ischemic stroke is the third cause of death in the developed countries and the main reason of severe disability. Brain ischemia leads to the production of damage-associated molecular patterns (DAMPs) by neurons and glial cells which results in astrocyte and microglia activation, pro-inflammatory cytokines and chemokines production, blood-brain barrier (BBB) disruption, infiltration of leukocytes from the peripheral blood into the infarcted area, and further exacerbation of tissue damage. However, some immune cells such as microglia or monocytes are capable to change their phenotype to anti-inflammatory, produce anti-inflammatory cytokines, and protect injured nervous tissue. In this situation, therapies, which will modulate the immune response after brain ischemia, such as transplantation of mesenchymal stem cells (MSCs) are catching interest. Many experimental studies of ischemic stroke revealed that MSCs are able to modulate immune response and act neuroprotective, through stimulation of neurogenesis, oligodendrogenesis, astrogenesis, and angiogenesis. MSCs may also have an ability to replace injured cells, but the release of paracrine factors directly into the environment or via extracellular vesicles (EVs) seems to play the most pronounced role. EVs are membrane structures containing proteins, lipids, and nucleic acids, and they express similar properties as the cells from which they are derived. However, EVs have lower immunogenicity, do not express the risk of vessel blockage, and have the capacity to cross the blood-brain barrier. Experimental studies of ischemic stroke showed that EVs have immunomodulatory and neuroprotective properties; therefore, they can stimulate neurogenesis and angiogenesis. Up to now, 20 clinical trials with MSC transplantation into patients after stroke were performed, from which two concerned on only hemorrhagic stroke and 13 studied only on ischemic stroke. There is no clinical trial with EV injection into patients after brain ischemia so far, but the case with miR-124-enriched EVs administration is planned and probably there will be more clinical studies with EV transplantation in the near future.

Phase I/II Study of Safety and Preliminary Efficacy of Intravenous Allogeneic Mesenchymal Stem Cells in Chronic Stroke

Background and Purpose- Stroke is a leading cause of long-term disability. Limited treatment options exist for patients with chronic stroke and substantial functional deficits. The current study examined safety and preliminary efficacy estimates of intravenous allogeneic mesenchymal stem cells in this population. Methods- Entry criteria included ischemic stroke >6 months prior and substantial impairment (National Institutes of Health Stroke Scale score ≥6) and disability. Enrollees received a single intravenous dose of allogeneic ischemia-tolerant mesenchymal stem cells. Phase 1 used a dose-escalation design (3 tiers, n=5 each). Phase 2 was an expanded safety cohort. The primary end point was safety over 1-year. Secondary end points examined behavioral change. Results- In phase 1 (n=15), each dose (0.5, 1.0, and 1.5 million cells/kg body weight) was found safe, so phase 2 subjects (n=21) received 1.5 million cells/kg. At baseline, subjects (n=36) averaged 4.2±4.6 years poststroke, age 61.1±10.8 years, National Institutes of Health Stroke Scale score 8 (6.5-10), and Barthel Index 65±29. Two were lost to follow-up, one was withdrawn and 2 died (unrelated to study treatment). Of 15 serious adverse events, none was possibly or probably related to study treatment. Two mild adverse events were possibly related to study treatment, a urinary tract infection and intravenous site irritation. Treatment was safe based on serial exams, electrocardiograms, laboratory tests, and computed tomography scans of chest/abdomen/pelvis. All behavioral end points showed significant gains over the 12-months of follow-up. For example, Barthel Index scores increased by 6.8±11.4 points (mean±SD) at 6-months (P=0.002) and by 10.8±15.5 points at 12-months (P<0.001) post-infusion; the proportion of patients achieving excellent functional outcome (Barthel score ≥95) increased from 11.4% at baseline to 27.3% at 6-months and to 35.5% at 12-months. Conclusions- Intravenous transfusion of allogeneic ischemia-tolerant mesenchymal stem cell in patients with chronic stroke and substantial functional deficits was safe and suggested behavioral gains. These data support proceeding to a randomized, placebo-controlled study of this therapy in this population. Clinical Trial Registration- URL: https://www.clinicaltrials.gov. Unique identifier: NCT01297413.

Neuroprotection by mesenchymal stem cell (MSC) administration is enhanced by local cooling infusion (LCI) in ischemia

OBJECTIVE

The present study aimed to determine if hypothermia augments the neuroprotection conferred by MSC administration by providing a conducive micro-environment.

METHODS

Sprague-Dawley rats were subjected to 1.5 h middle cerebral artery occlusion (MCAO) followed by 6 or 24 h of reperfusion for molecular analyses, as well as 1, 14 and 28 days for brain infarction or functional outcomes. Rats were treated with either MSC (1 × 10⁵), LCI (cold saline, 0.6 ml/min, 5 min) or both. Brain damage was determined by Infarct volume and neurological deficits. Long-term functional outcomes were evaluated using foot-fault and Rota-rod testing. Human neural SHSY5Y cells were investigated in vitro using 2 h oxygen-glucose deprivation (OGD) followed by MSC with or without hypothermia (HT) (34 °C, 4 h). Mitochondrial transfer was assessed by confocal microscope, and cell damage was determined by cell viability, ATP, and ROS level. Protein levels of IL-1β, BAX, Bcl-2, VEGF and Miro1 were measured by Western blot following 6 h and 24 h of reperfusion and reoxygenation.

RESULTS

MSC, LCI, and LCI + MSC significantly reduced infarct volume and deficit scores. Combination therapy of LCI + MSC precipitated better long-term functional outcomes than monotherapy. Upregulation of Miro1 in the combination group increased mitochondrial transfer and lead to a greater increase in neuronal cell viability and ATP, as well as a decrease in ROS. Further, combination therapy significantly decreased expression of IL-1β and BAX while increasing Bcl-2 and VEGF expression.

CONCLUSION

Therapeutic hypothermia upregulated Miro1 and enhanced MSC mitochondrial transfer-mediated neuroprotection in ischemic stroke. Combination of LCI with MSC therapy may facilitate clinical translation of this approach.

Concise Review: Stem Cell Therapy for Stroke Patients: Are We There Yet?

Four decades of preclinical research demonstrating survival, functional integration, and behavioral effects of transplanted stem cells in experimental stroke models have provided ample scientific basis for initiating limited clinical trials of stem cell therapy in stroke patients. Although safety of the grafted cells has been overwhelmingly documented, efficacy has not been forthcoming. Two recently concluded stroke clinical trials on mesenchymal stem cells (MSCs) highlight the importance of strict adherence to the basic science findings of optimal transplant regimen of cell dose, timing, and route of delivery in enhancing the functional outcomes of cell therapy. Echoing the Stem Cell Therapeutics as an Emerging Paradigm for Stroke and Stroke Treatment Academic Industry Roundtable call for an NIH‐guided collaborative consortium of multiple laboratories in testing the safety and efficacy of stem cells and their derivatives, not just as stand‐alone but preferably in combination with approved thrombolytic or thrombectomy, may further increase the likelihood of successful fruition of translating stem cell therapy for stroke clinical application. The laboratory and clinical experience with MSC therapy for stroke may guide the future translational research on stem cell‐based regenerative medicine in neurological disorders. stem cells translational medicine2019;8:983&988

Human parthenogenetic neural stem cell grafts promote multiple regenerative processes in a traumatic brain injury model

International Stem Cell Corporation human parthenogenetic neural stem cells (ISC-hpNSC) have potential therapeutic value for patients suffering from traumatic brain injury (TBI). Here, we demonstrate the behavioral and histological effects of transplanting ISC-hpNSC intracerebrally in an animal model of TBI.

Methods: Sprague-Dawley rats underwent a moderate controlled cortical impact TBI surgery. Transplantation occurred at 72 h post-TBI with functional readouts of behavioral and histological deficits conducted during the subsequent 3-month period after TBI. We characterized locomotor, neurological, and cognitive performance at baseline (before TBI), then on days 0, 1, 7, 14, 30, 60, and 90 (locomotor and neurological), and on days 28-30, 58-60, and 88-90 (cognitive) after TBI. Following completion of behavioral testing at 3 months post-TBI, animals were euthanized by transcardial perfusion and brains harvested to histologically characterize the extent of brain damage. Neuronal survival was revealed by Nissl staining, and stem cell engraftment and host tissue repair mechanisms such as the anti-inflammatory response in peri-TBI lesion areas were examined by immunohistochemical analyses.

Results: We observed that TBI groups given high and moderate doses of ISC-hpNSC had an improved swing bias on an elevated body swing test for motor function, increased scores on forelimb akinesia and paw grasp neurological tests, and committed significantly fewer errors on a radial arm water maze test for cognition. Furthermore, histological analyses indicated that high and moderate doses of stem cells increased the expression of phenotypic markers related to the neural lineage and myelination and decreased reactive gliosis and inflammation in the brain, increased neuronal survival in the peri-impact area of the cortex, and decreased inflammation in the spleen at 90 days post-TBI.

Conclusion: These results provide evidence that high and moderate doses of ISC-hpNSC ameliorate TBI-associated histological alterations and motor, neurological, and cognitive deficits.

Treating childhood traumatic brain injury with autologous stem cell therapy

INTRODUCTION

Neonatal traumatic brain injury (TBI) is a significant cause of developmental disorders. Autologous stem cell therapy may enhance neonatal brain plasticity towards repair of the injured neonatal brain.

AREAS COVERED

The endogenous neonatal anti-inflammatory response can be enhanced through the delivery of anti-inflammatory agents. Stem cell therapy stands as a robust approach for sequestering the inflammation-induced cell death in the injured brain. Here, we discuss the use of umbilical cord blood cells and bone marrow stromal cells for acute and chronic treatment of experimental neonatal TBI. Autologous stem cell transplantation may dampen neuroinflammation. Clinical translation of this stem cell therapy will require identifying the therapeutic window post-injury and harvesting ample supply of transplantable autologous stem cells. Stem cell banking of cryopreserved cells may allow readily available transplantable cells and circumvent the unpredictable nature of neonatal TBI. Harnessing the anti-inflammatory properties of stem cells is key in combating the progressive neurodegeneration after the initial injury.

EXPERT OPINION

Combination treatments, such as with hypothermia, may enhance the therapeutic effects of stem cells. Stem cell therapy has immense potential as a stand-alone or adjunctive therapy for treating neuroinflammation associated with neonatal TBI acutely and for preventing further progression of the injury.

Application of Muse Cell Therapy to Stroke

Stroke is defined as a sudden onset of neurologic deficits arising from cerebrovascular complications. It is the second common cause of death around the world and the major cause of disability. Because brain is an organ with complicated neural networks and neurons are highly differentiated, it has been traditionally considered to possess a limited potential for regeneration. The number of stroke patients is increasing, and stroke represents a serious problem from the viewpoint of the national medical economy. Even with the current sophisticated treatments, more than half of stroke patient survivors remain disabled. Therefore, it is imperative to develop a new treatment for promoting functional recovery and repair of the lost neurological circuit. Multilineage-differentiating stress-enduring (Muse) cells are endogenous non-tumorigenic stem cells with pluripotency. After transplantation, Muse cells recognize the injured site through their specific receptor for damage signal, home preferentially into these tissues and spontaneously differentiate into tissue-compatible cells to replace the lost cells, and repair the tissue, delivering functional and structural regeneration. These properties are desirable for the treatment of strokes and advantageous compared to other stem cell therapies. Here, we describe the current status of stem cell therapies for stroke and future possibilities of Muse cell therapy.

Stem Cell Recipes of Bone Marrow and Fish: Just What the Stroke Doctors Ordered

Stem cell therapy for stroke has advanced from the laboratory to the clinic, but remains as an experimental treatment. Two lines of transplant regimens have emerged, namely the "early bird" peripheral injections in subacute stroke patients and the "late night" direct intracerebral treatments in chronic stroke patients. Autologous bone marrow-derived stem cells, which only required minimal manipulations during graft cell preparation, gained fast-track entry into the clinic, while gene modified stem cells necessitated overcoming more stringent regulatory criteria before they were approved for clinical use. Safety of the stem cell therapy can be declared from these clinical trials, but efficacy warrants further investigations. Here, we offer insights into the translation of cell therapy from the laboratory to the clinic, in the hopes that highlighting the lessons we learned from this experience will guide the optimization of functional outcomes of future clinical trials of stem cell therapy for stroke.

Exogenous stem cells pioneer a biobridge to the advantage of host brain cells following stroke: New insights for clinical applications

Stroke continues to maintain its status as one of the top causes of mortality within the United States. Currently, the only Food and Drug Administration (FDA)-approved drug in place for stroke patients, tissue plasminogen activator (tPA), has a rigid therapeutic window, closing at approximately 4.5 h after stroke onset. Due to this short time frame and other restrictions, such as any condition that increases a patient's risk for hemorrhaging, it has been predicted that <5% of ischemic stroke patients benefit from tPA. Given that rehabilitation therapy remains the only other option for stroke victims, there is a clear unmet clinical need for treatment available for the remaining 95%. While still considered an experimental treatment, the utilization of stem cell therapies for stroke holds consistent promise. Copious preclinical studies report the capacity for transplanted stem cells to rescue the brain parenchyma surrounding the stroke-induced infarct core. At present, the exact mechanisms in which stem cells contribute a robust therapeutic benefit remains unclear. Following stem cell administration, researchers have observed cell replacement, an increase in growth factors, and a reduction in inflammation. With a deeper understanding of the precise mechanism of stem cells, these therapies can be optimized in the clinic to afford the greatest therapeutic benefit. Recent studies have depicted a unique method of endogenous stem cell activation as a result of stem cell therapy. In both traumatic brain injury and stroke models, transplanted mesenchymal stromal cells (MSCs) facilitated a pathway between the neurogenic niches of the brain and the damaged area through extracellular matrix remodeling. The biobridge pioneered by the MSCs was utilized by the endogenous stem cells, and these cells were able to travel to the damaged areas distal to the neurogenic niches, a feat unachievable without prior remodeling. These studies broaden our understanding of stem cell interactions within the injured brain and help to guide both researchers and clinicians in developing an effective stem cell treatment for stroke. This paper is a review article. Referred literature in this paper has been listed in the references section. The datasets supporting the conclusions of this article are available online by searching various databases, including PubMed. Some original points in this article come from the laboratory practice in our research center and the authors’ experiences.

Stem cell therapy for abrogating stroke-induced neuroinflammation and relevant secondary cell death mechanisms

Ischemic stroke is a leading cause of death worldwide. A key secondary cell death mechanism mediating neurological damage following the initial episode of ischemic stroke is the upregulation of endogenous neuroinflammatory processes to levels that destroy hypoxic tissue local to the area of insult, induce apoptosis, and initiate a feedback loop of inflammatory cascades that can expand the region of damage. Stem cell therapy has emerged as an experimental treatment for stroke, and accumulating evidence supports the therapeutic efficacy of stem cells to abrogate stroke-induced inflammation. In this review, we investigate clinically relevant stem cell types, such as hematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs), endothelial progenitor cells (EPCs), very small embryonic-like stem cells (VSELs), neural stem cells (NSCs), extraembryonic stem cells, adipose tissue-derived stem cells, breast milk-derived stem cells, menstrual blood-derived stem cells, dental tissue-derived stem cells, induced pluripotent stem cells (iPSCs), teratocarcinoma-derived Ntera2/D1 neuron-like cells (NT2N), c-mycER(TAM) modified NSCs (CTX0E03), and notch-transfected mesenchymal stromal cells (SB623), comparing their potential efficacy to sequester stroke-induced neuroinflammation and their feasibility as translational clinical cell sources. To this end, we highlight that MSCs, with a proven track record of safety and efficacy as a transplantable cell for hematologic diseases, stand as an attractive cell type that confers superior anti-inflammatory effects in stroke both in vitro and in vivo. That stem cells can mount a robust anti-inflammatory action against stroke complements the regenerative processes of cell replacement and neurotrophic factor secretion conventionally ascribed to cell-based therapy in neurological disorders.

Stem Cell-Induced Biobridges as Possible Tools to Aid Neuroreconstruction after CNS Injury

Notch-induced mesenchymal stromal cells (MSCs) mediate a distinct mechanism of repair after brain injury by forming a biobridge that facilitates biodistribution of host cells from a neurogenic niche to the area of injury. We have observed the biobridge in an area between the subventricular zone and the injured cortex using immunohistochemistry and laser capture. Cells in the biobridge express high levels of extracellular matrix metalloproteinases (MMPs), specifically MMP-9, which co-localized with a trail of MSCs graft. The transplanted stem cells then become almost undetectable, being replaced by newly recruited host cells. This stem cell-paved biobridge provides support for distal migration of host cells from the subventricular zone to the site of injury. Biobridge formation by transplanted stem cells seems to have a fundamental role in initiating endogenous repair processes. Two major stem cell-mediated repair mechanisms have been proposed thus far: direct cell replacement by transplanted grafts and bystander effects through the secretion of trophic factors including fibroblast growth factor 2 (FGF-2), epidermal growth factor (EGF), stem cell factor (SCF), erythropoietin, and brain-derived neurotrophic factor (BDNF) among others. This groundbreaking observation of biobridge formation by transplanted stem cells represents a novel mechanism for stem cell mediated brain repair. Future studies on graft-host interaction will likely establish biobridge formation as a fundamental mechanism underlying therapeutic effects of stem cells and contribute to the scientific pursuit of developing safe and efficient therapies not only for traumatic brain injury but also for other neurological disorders. The aim of this review is to hypothetically extend concepts related to the formation of biobridges in other central nervous system disorders.

Intravenously Transplanted Human Bone Marrow Endothelial Progenitor Cells Engraft Within Brain Capillaries, Preserve Mitochondrial Morphology, and Display Pinocytotic Activity Toward Blood-Brain Barrier Repair in Ischemic Stroke Rats

Stroke is a life-threatening disease with limited therapeutic options. Cell therapy has emerged as an experimental stroke treatment. Blood-brain barrier (BBB) impairment is a key pathological manifestation of ischemic stroke, and barrier repair is an innovative target for neurorestoration in stroke. Here, we evaluated via electron microscopy the ability of transplanted human bone marrow endothelial progenitor cells (hBMEPCs) to repair the BBB in adult Sprague-Dawley rats subjected to transient middle cerebral artery occlusion (tMCAO). β-galactosidase prelabeled hBMEPCs were intravenously transplanted 48 hours post-tMCAO. Ultrastructural analysis of microvessels in nontransplant stroke rats revealed typical BBB pathology. At 5 days post-transplantation with hBMEPCs, stroke rats displayed widespread vascular repair in bilateral striatum and motor cortex, characterized by robust cell engraftment within capillaries. hBMEPC transplanted stroke rats exhibited near normal morphology of endothelial cells (ECs), pericytes, and astrocytes, without detectable perivascular edema. Near normal morphology of mitochondria was also detected in ECs and perivascular astrocytes from transplanted stroke rats. Equally notable, we observed numerous pinocytic vesicles within engrafted cells. Robust engraftment and intricate functionality of transplanted hBMEPCs likely abrogated stroke-altered vasculature. Preserving mitochondria and augmenting pinocytosis in cell-based therapeutics represent a new neurorestorative mechanism in BBB repair for stroke. Stem Cells 2017;35:1246-1258.

Human Muse Cells Reconstruct Neuronal Circuitry in Subacute Lacunar Stroke Model

BACKGROUND AND PURPOSE

Multilineage-differentiating stress-enduring (muse) cells are endogenous nontumorigenic stem cells with pluripotency harvestable as pluripotent marker SSEA-3⁺ cells from the bone marrow from cultured bone marrow-mesenchymal stem cells. After transplantation into neurological disease models, muse cells exert repair effects, but the exact mechanism remains inconclusive.

METHODS

We conducted mechanism-based experiments by transplanting serum/xeno-free cultured-human bone marrow-muse cells into the perilesion brain at 2 weeks after lacunar infarction in immunodeficient mice.

RESULTS

Approximately 28% of initially transplanted muse cells remained in the host brain at 8 weeks, spontaneously differentiated into cells expressing NeuN (≈62%), MAP2 (≈30%), and GST-pi (≈12%). Dextran tracing revealed connections between host neurons and muse cells at the lesioned motor cortex and the anterior horn. Muse cells extended neurites through the ipsilateral pyramidal tract, crossed to contralateral side, and reached to the pyramidal tract in the dorsal funiculus of spinal cord. Muse-transplanted stroke mice displayed significant recovery in cylinder tests, which was reverted by the human-selective diphtheria toxin. At 10 months post-transplantation, human-specific Alu sequence was detected only in the brain but not in other organs, with no evidence of tumor formation.

CONCLUSIONS

Transplantation at the delayed subacute phase showed muse cells differentiated into neural cells, facilitated neural reconstruction, improved functions, and displayed solid safety outcomes over prolonged graft maturation period, indicating their therapeutic potential for lacunar stroke.

Recent Advances in Stem Cell-Based Therapeutics for Stroke

Regenerative medicine for central nervous system disorders, including stroke, has challenged the non-regenerative capacity of the brain. Among the many treatment strategies tailored towards repairing the injured brain, stem cell-based therapeutics have been demonstrated as safe and effective in animal models of stroke, and are being tested in limited clinical trials. We address here key lab-to-clinic translational research that relate to efficacy, safety, and mechanism of action underlying stem cell therapy. Recognizing the multi-pronged cell death processes associated with stroke that will likely require combination therapies, we next discuss potent drugs and novel technologies directed at improving the functional outcomes of stem cell-based therapeutics. We also examine discrepant transplant regimens between preclinical studies and clinical trials, as well as missing appropriate control arm (i.e., stroke subjects undergoing rehabilitation) on which to directly compare the therapeutic benefits of cell therapy. Finally, the bioethics of cell therapy is presented in order to assess its prevailing social status. With preliminary results now being reported from on-going clinical trials of stem cell therapy for stroke, a careful assessment of the true functional benefits of this novel treatment will further direct the future of regenerative medicine for neurological disorders.

Notch signaling in cerebrovascular diseases (Review)

The Notch signaling pathway is a crucial regulator of numerous fundamental cellular processes. Increasing evidence suggests that Notch signaling is involved in inflammation and oxidative stress, and thus in the progress of cerebrovascular diseases. In addition, Notch signaling in cerebrovascular diseases is associated with apoptosis, angiogenesis and the function of blood-brain barrier. Despite the contradictory results obtained to date as to whether Notch signaling is harmful or beneficial, the regulation of Notch signaling may provide a novel strategy for the treatment of cerebrovascular diseases.