Stem Cells in Stroke Treatment: The Promise and the Challenges

Physical therapy exerts sub-additive and suppressive effects on intracerebral neural stem cell implantation in a rat model of stroke

Intracerebral cell therapy (CT) is emerging as a new therapeutic paradigm for stroke. However, the impact of physical therapy (PT) on implanted cells and their ability to promote recovery remains poorly understood. To address this translational issue, a clinical-grade neural stem cell (NSC) line was implanted into peri-infarct tissue using MRI-defined injection sites, two weeks after stroke. PT in the form of aerobic exercise (AE) was administered 5 × per week post-implantation using a paradigm commonly applied in patients with stroke. A combined AE and CT exerted sub-additive therapeutic effects on sensory neglect, whereas AE suppressed CT effects on motor integration and grip strength. Behavioral testing emerged as a potentially major component for task integration. It is expected that this study will guide and inform the incorporation of PT in the design of clinical trials evaluating intraparenchymal NSCs implantation for stroke.

Intravenous Bone Marrow Mononuclear Cells for Acute Ischemic Stroke: Safety, Feasibility, and Effect Size from a Phase I Clinical Trial

Cellular therapy is a promising investigational modality to enhance poststroke recovery. We conducted a single-arm, phase I clinical trial to determine the safety and feasibility of intravenous (IV) administration of autologous bone marrow mononuclear cells (MNCs) after acute ischemic stroke (AIS). Patients with moderate severity of AIS underwent bone marrow harvest followed by IV reinfusion of MNCs within 24-72 hours of onset. A target dose of 10 million cells per kilogram was chosen based on preclinical data. Patients were followed up daily during hospitalization and at 1, 3, 6, 12, and 24 months for incidence of adverse events using laboratory, clinical (12 months), and radiological (24 months) parameters. The trial was powered to detect severe adverse events (SAEs) with incidences of at least 10% and planned to enroll 30 patients. Primary outcomes were study-related SAEs and the proportion of patients successfully completing study intervention. A propensity score-based matched control group was used for the estimation of effect size (ES) for day-90 modified Rankin score (mRS). There were no study-related SAEs and, based on a futility analysis, enrolment was stopped after 25 patients. All patients successfully completed study intervention and most received the target dose. Secondary analysis estimated the ES to be a reduction of 1 point (95% confidence interval: 0.33-1.67) in median day-90 mRS for treated patients as compared with the matched control group. Bone marrow harvest and infusion of MNCs is safe and feasible in patients with AIS. The estimated ES is helpful in designing future randomized controlled trials. Stem Cells 2019;37:1481-1491.

Stem cell-based cell therapy for neuroprotection in stroke: A review

Neurological disorders, such as stroke, are triggered by a loss of neurons and glial cells. Ischemic stroke remains a substantial problem for industrialized countries. Over the previous few decades our understanding about the pathophysiology of stroke has enhanced, nevertheless, more awareness is required to advance the field of stroke recovery. Existing therapies are incapable to adequately relief the disease outcome and are not appropriate to all patients. Meanwhile, the majority of patients continue to show neurological deficits even subsequent effective thrombolysis, recuperative therapies are immediately required that stimulate brain remodeling and repair once stroke damage has happened. Cell therapy is emergent as a hopeful new modality for increasing neurological recovery in ischemic stroke. Numerous types of stem cells from various sources have been identified and their possibility and efficiency for the treatment of stroke have been investigated. Stem cell therapy in patients with stroke using adult stem cells have been first practiced in clinical trials since 15 years ago. Even though stem cells have revealed a hopeful role in ischemic stroke in investigational studies besides early clinical pilot studies, cellular therapy in human is still at a primary stage. In this review, we summarize the types of stem cells, various delivery routes, and clinical application of stem cell-based therapy for stroke treatment.

In vitro studies on space-conforming self-assembling silk hydrogels as a mesenchymal stem cell-support matrix suitable for minimally invasive brain application

Advanced cell therapies require robust delivery materials and silk is a promising contender with a long clinical track record. Our aim was to optimise self-assembling silk hydrogels as a mesenchymal stem cell (MSC)-support matrix that would allow future minimally invasive brain application. We used sonication energy to programme the transition of silk (1-5% w/v) secondary structure from a random coil to a stable β-sheet configuration. This allowed fine tuning of self-assembling silk hydrogels to achieve space conformity in the absence of any silk hydrogel swelling and to support uniform cell distribution as well as cell viability. Embedded cells underwent significant proliferation over 14 days in vitro, with the best proliferation achieved with 2% w/v hydrogels. Embedded MSCs showed significantly better viability in vitro after injection through a 30G needle when the gels were in the pre-gelled versus post-gelled state. Silk hydrogels (4% w/v) with physical characteristics matching brain tissue were visualised in preliminary in vivo experiments to exhibit good space conformity in an ischemic cavity (intraluminal thread middle cerebral artery occlusion model) in adult male Sprague-Dawley rats (n = 3). This study informs on optimal MSC-hydrogel matrix conditions for minimally invasive application as a platform for future experiments targeting brain repair.

Regenerative medicine: Stroke survivor and carer views and motivations towards a proposed stem cell clinical trial using placebo neurosurgery

BACKGROUND

Few studies explore stroke survivor views and motivations towards stem cell therapy (SCT). This qualitative study explores the views and motivations of both stroke survivors and their partners/carers towards a proposed 2-arm Phase III Randomised Controlled Trial (RCT) comparing intracerebral insertion of stem cells with placebo neurosurgery in stroke survivors with disability.

OBJECTIVE

To explore views and motivations towards a proposed 2-arm stem cell trial and identify factors that may impede and enhance participation.

DESIGN

This study adopts a naturalistic design to explore the complexity of this field, employing a participatory action-research approach comprising a specialized Conversation (World) Café form of focus group. Data were collected via 5 Conversation Cafés with stroke survivors (age 40-75) and partners/carers between June and October 2016. Of 66 participants, 53 (31 male, 22 female) were stroke survivors and 13 (6 female, 7 male) were partners/carers. Qualitative data were analysed using a thematic approach.

DISCUSSION AND CONCLUSION

Stroke survivor views and motivations reflect anticipation of the personal and future benefits of regenerative medicine. Partners/carers sought to balance the value of stroke survivor hope with carrying the weight of hope as carer, a conflict burden adding to known caregiver burden. All participants expressed the need for during and post-trial psychological support. This study provides a rare opportunity to explore the prospective views and motivations of stroke survivors and their partners/carers towards a proposed Phase III 2-arm RCT. This adds weight to qualitative evidence exploring capacity, consent, decision making, perceptions of treatment risk and supports required for clinical trial participation.

Clinical trial design for stem cell therapies in stroke: What have we learned?

Stem cells of various sources have been investigated in a series of small, safety and feasibility-focused studies over the past 15 years. Understanding of mechanisms of action has evolved and the trial paradigms have become focused on two different approaches - one being an early subacute delivery of cells to reduce acute tissue injury and modify the tissue environment in a direction favourable to reparative processes (for example by being anti-inflammatory, anti-apoptotic, and encouraging endogenous stem cell mobilisation); the other exploring later delivery of cells during the recovery phase after stroke to modulate the local environment in favour of angiogenesis and neurogenesis. The former approach has generally investigated intravenous or intra-arterial delivery of cells with an expected paracrine mode of action and no expected engraftment within the brain. The latter has explored direct intracerebral implantation adjacent to the infarct. Several relevant trials have been conducted, including two controlled trials of intravenously delivered bone marrow-derived cells in the early subacute stage, and two small single-arm phase 1 trials of intracerebrally implanted cells. The findings of these studies and their implications for future trial design are considered.

Translating G-CSF as an Adjunct Therapy to Stem Cell Transplantation for Stroke

Among recently investigated stroke therapies, stem cell treatment holds great promise by virtue of their putative ability to replace lost cells, promote endogenous neurogenesis,and produce behavioral and functional improvement through their "bystander effects." Translating stem cell in the clinic, however, presents a number of technical difficulties. A strategy suggested to enhance therapeutic utility of stem cells is combination therapy, i.e., co-transplantation of stem cells or adjunct treatment with pharmacological agents and substrates,which is assumed to produce more profound therapeutic benefits by circumventing limitations of individual treatments and facilitating complementary brain repair processes. We previously demonstrated enhanced functional effects of cotreatment with granulocyte-colony stimulating factor (GCSF)and human umbilical cord blood cell (hUCB) transplantation in animal models of traumatic brain injury (TBI). Here,we suggest that the aforementioned combination therapy may also produce synergistic effects in stroke. Accordingly, G-CSF treatment may reduce expression of pro-inflammatory cytokines and enhance neurogenesis rendering a receptive microenvironment for hUCB engraftment. Adjunct treatment of GCSF with hUCB may facilitate stemness maintenance and guide neural lineage commitment of hUCB cells. Moreover, regenerative mechanisms afforded by G-CSF-mobilized endogenous stem cells, secretion of growth factors by hUCB grafts and G-CSF-recruited endothelial progenitor cells(EPCs), as well as the potential graft–host integration that may promote synaptic circuitry re-establishment could altogether produce more pronounced functional improvement in stroked rats subjected to a combination G-CSF treatment and hUCB transplantation. Nevertheless, differences in pathology and repair processes underlying TBI and stroke deserve consideration when testing the effects of combinatorial G-CSF and hUCB cell transplantation for stroke treatment. Further studies are also required to determine the safety and efficacy of this intervention in both preclinical and clinical stroke studies.

[Strategic considerations on the design and choice of animal models for non-clinical investigations of cell-based medicinal products]

For the development of medicinal products animal models are still indispensable to demonstrate efficacy and safety prior to first use in humans. Advanced therapy medicinal products (ATMP), which include cell-based medicinal products (CBMP), differ in their pharmacology and toxicology compared to conventional pharmaceuticals, and thus, require an adapted regime for non-clinical development. Developers are, therefore, challenged to develop particular individual concepts and to reconcile these with regulatory agencies. Guidelines issued by the European Medicines Agency (EMA), the U.S. Food and Drug Administration (FDA) and other sources can provide direction.The published approaches for non-clinical testing of efficacy document that homologous animal models where the therapeutic effect is investigated in a disease-relevant animal model utilizing cells derived from the same species are commonly used. The challenge is that the selected model should reflect the human disease in all critical features and that the cells should be comparable to the investigated human medicinal product in terms of quality and biological activity. This is not achievable in all cases. In these cases, alternative methods may provide supplemental information. To demonstrate the scientific proof-of-concept (PoC), small animal models such as mice or rats are preferred. During the subsequent product development phase, large animal models (i.e. sheep, minipigs, dogs) must be considered, as they may better reflect the anatomical or physiological situation in humans. In addition to efficacy, those models may also be suitable to prove some safety aspects of ATMP (e.g. regarding dose finding, local tolerance, or undesired interactions and effects of the administered cells in the target tissue). In contrast, for evaluation of the two prominent endpoints for characterizing the safety of ATMP (i.e. biodistribution, tumorigenicity) heterologous small animal models, especially immunodeficient mouse strains, are favourable due to their tolerance to the human cell therapy product. The execution of non-clinical studies under the principles of good laboratory practice (GLP) increases the acceptance of the results by authorities and the scientific community.

Concise review: workshop review: understanding and assessing the risks of stem cell-based therapies

The field of stem cell therapeutics is moving ever closer to widespread application in the clinic. However, despite the undoubted potential held by these therapies, the balance between risk and benefit remains difficult to predict. As in any new field, a lack of previous application in man and gaps in the underlying science mean that regulators and investigators continue to look for a balance between minimizing potential risk and ensuring therapies are not needlessly kept from patients. Here, we attempt to identify the important safety issues, assessing the current advances in scientific knowledge and how they may translate to clinical therapeutic strategies in the identification and management of these risks. We also investigate the tools and techniques currently available to researchers during preclinical and clinical development of stem cell products, their utility and limitations, and how these tools may be strategically used in the development of these therapies. We conclude that ensuring safety through cutting-edge science and robust assays, coupled with regular and open discussions between regulators and academic/industrial investigators, is likely to prove the most fruitful route to ensuring the safest possible development of new products.

Considerations for the clinical use of contrast agents for cellular MRI in regenerative medicine

Advances in regenerative medicine are rapidly transforming healthcare. A cornerstone of regenerative medicine is the introduction of cells that were grown or manipulated in vitro. Key questions that arise after these cells are re-introduced are: whether these cells are localized in the appropriate site; whether cells survive; and whether these cells migrate. These questions predominantly relate to the safety of the therapeutic approach (i.e. tumorigenesis), but certain aspects can also influence the efficacy of the therapeutic approach (e.g. site of injection). The European Medicines Agency has indicated that suitable methods for stem cell tracking should be applied where these methods are available. We here discuss the European regulatory framework, as well as the scientific evidence, that should be considered to facilitate the potential clinical implementation of magnetic resonance imaging contrast media to track implanted/injected cells in human studies.

Behavioral and histopathological assessment of adult ischemic rat brains after intracerebral transplantation of NSI-566RSC cell lines

Stroke is a major cause of death and disability, with very limited treatment option. Cell-based therapies have emerged as potential treatments for stroke. Indeed, studies have shown that transplantation of neural stem cells (NSCs) exerts functional benefits in stroke models. However, graft survival and integration with the host remain pressing concerns with cell-based treatments. The current study set out to investigate those very issues using a human NSC line, NSI-566RSC, in a rat model of ischemic stroke induced by transient occlusion of the middle cerebral artery. Seven days after stroke surgery, those animals that showed significant motor and neurological impairments were randomly assigned to receive NSI-566RSC intracerebral transplants at two sites within the striatum at three different doses: group A (0 cells/µl), group B (5,000 cells/µl), group C (10,000 cells/µl), and group D (20,000 cells/µl). Weekly behavioral tests, starting at seven days and continued up to 8 weeks after transplantation, revealed dose-dependent recovery from both motor and neurological deficits in transplanted stroke animals. Eight weeks after cell transplantation, immunohistochemical investigations via hematoxylin and eosin staining revealed infarct size was similar across all groups. To identify the cell graft, and estimate volume, immunohistochemistry was performed using two human-specific antibodies: one to detect all human nuclei (HuNu), and another to detect human neuron-specific enolase (hNSE). Surviving cell grafts were confirmed in 10/10 animals of group B, 9/10 group C, and 9/10 in group D. hNSE and HuNu staining revealed similar graft volume estimates in transplanted stroke animals. hNSE-immunoreactive fibers were also present within the corpus callosum, coursing in parallel with host tracts, suggesting a propensity to follow established neuroanatomical features. Despite absence of reduction in infarct volume, NSI-566RSC transplantation produced behavioral improvements possibly via robust engraftment and neuronal differentiation, supporting the use of this NSC line for stroke therapy.

Altered hMSC functional characteristics in short-term culture and when placed in low oxygen environments: implications for cell retention at physiologic sites

Background: It is very difficult to conserve critical cell characteristics during expansion in culture, particularly those of adult mesenchymal stromal cells (MSCs), whose characteristics can change rapidly even within a short period of expansion. Aim: In this study our aim was to measure cell characteristics that are critical for retention at the injury site after therapeutic delivery. Cells were cultured under conditions typical of current standard best practice. The impact of passage number was assessed and assays were performed in low oxygen (2%) as an in vitro model of physiologic oxygen tension at injury sites. The effect of chemokine preconditioning with SDF1 was also assessed. Materials & methods: Bone marrow mononuclear cells from patients recruited to the REGENERATE Phase II clinical trials, along with MSCs from healthy volunteers subjected to a short period of expansion, were assessed for attachment and migration ability. Using MSCs from healthy donors, the effect of reduced oxygen was also assessed. Results: Short-term expansion resulted in increased cell attachment but decreased rate of migration, whereas attachment and migration of patient-derived bone marrow mononuclear cells was highly heterogeneous. Reduced oxygen impaired MSC attachment but not migration. Finally, SDF1 did not improve any of the responses. Conclusion: The basic functional responses of MSCs required for retention and engraftment alter rapidly even over a relatively short expansion period. This needs careful consideration when expanding cells to achieve clinical quantities for therapy.

Experimental models of brain ischemia: a review of techniques, magnetic resonance imaging, and investigational cell-based therapies

Stroke continues to be a significant cause of death and disability worldwide. Although major advances have been made in the past decades in prevention, treatment, and rehabilitation, enormous challenges remain in the way of translating new therapeutic approaches from bench to bedside. Thrombolysis, while routinely used for ischemic stroke, is only a viable option within a narrow time window. Recently, progress in stem cell biology has opened up avenues to therapeutic strategies aimed at supporting and replacing neural cells in infarcted areas. Realistic experimental animal models are crucial to understand the mechanisms of neuronal survival following ischemic brain injury and to develop therapeutic interventions. Current studies on experimental stroke therapies evaluate the efficiency of neuroprotective agents and cell-based approaches using primarily rodent models of permanent or transient focal cerebral ischemia. In parallel, advancements in imaging techniques permit better mapping of the spatial-temporal evolution of the lesioned cortex and its functional responses. This review provides a condensed conceptual review of the state of the art of this field, from models and magnetic resonance imaging techniques through to stem cell therapies.

Stroke: More than a ‘Brain Attack’

Stroke is a life-altering event that potentially affects stroke survivors, their families, healthcare resources, and society in general. Stroke has often been described as ‘brain attack’, denoting emergency emphasis on the vascular pathology. Consequently, many national and provincial stroke strategies have emphasized vascular care through primary prevention strategies and thrombolysis. Despite being important initiatives, this has resulted in a stroke system that emphasizes the frontloading of stroke care, focusing on the vascular pathology. The advent of thrombolysis therapy has benefited a small proportion of patients while a vast majority are still affected by stroke-related impairments. Management of the vascular elements of stroke is important; however, the impact of rehabilitation on stroke recovery has been relatively undervalued. Stroke care is in need of a revolution toward a more comprehensive and balanced approach. It is anticipated that the major focus of stroke care will include promoting recovery, in line with the growing evidence on stroke rehabilitation interventions. A paradigm shift is necessary to ensure that comprehensive and balanced stroke care which incorporates rehabilitation is taken into account, leading to a stroke care system where patient needs are managed both as a ‘brain attack’ and an ‘injured brain’.

Multiple cell transplantation based on an intraparenchymal approach for patients with chronic phase stroke

Stroke is the third leading cause of death worldwide and a huge perpetrator in adult disability. This pilot clinical study investigates the possible benefits of transplanting multiple cells in chronic stroke. A total of 10 consecutive stroke patients were treated by combination cell transplantation on the basis of an intraparenchymal approach from November 2003 to April 2011. There were six males and four females. Their age ranged from 42 to 87 years, and the course of disease varied from 6 months to 20 years. Six patients suffered cerebral infarction, and four patients suffered a brain hemorrhage. The olfactory ensheathing cells, neural progenitor cells, umbilical cord mesenchymal cells, and Schwann cells were injected through selected routes including intracranial parenchymal implantation, intrathecal implantation, and intravenous administration, respectively. The clinical neurological function was assessed carefully and independently before treatment and during a long-term follow-up using the Clinic Neurologic Impairment Scale and the Barthel index. All patients were followed up successfully from 6 months to 2 years after cell transplantation. Every subject achieved neurological function amelioration including improved speech, muscle strength, muscular tension, balance, pain, and breathing; most patients had an increased Barthel index score and Clinic Neurologic Impairment Scale score. These preliminary results demonstrate the novel strategy of combined multiple cell therapy based on intraparenchymal delivery: it appears to be relatively clinically safe and at least initially beneficial for chronic stroke patients. This manuscript is published as part of the International Association of Neurorestoratology (IANR) supplement issue of Cell Transplantation.

Intranasal treatment of central nervous system dysfunction in humans

One of the most challenging problems facing modern medicine is how to deliver a given drug to a specific target at the exclusion of other regions. For example, a variety of compounds have beneficial effects within the central nervous system (CNS), but unwanted side effects in the periphery. For such compounds, traditional oral or intravenous drug delivery fails to provide benefit without cost. However, intranasal delivery is emerging as a noninvasive option for delivering drugs to the CNS with minimal peripheral exposure. Additionally, this method facilitates the delivery of large and/or charged therapeutics, which fail to effectively cross the blood-brain barrier (BBB). Thus, for a variety of growth factors, hormones, neuropeptides and therapeutics including insulin, oxytocin, orexin, and even stem cells, intranasal delivery is emerging as an efficient method of administration, and represents a promising therapeutic strategy for the treatment of diseases with CNS involvement, such as obesity, Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, depression, anxiety, autism spectrum disorders, seizures, drug addiction, eating disorders, and stroke.

Prospects for stem cell-derived therapy in stroke

The prospects for stem cell-derived therapy in stroke look promising, with a myriad of cell therapy products developed from brain, blood, bone marrow, and adipose tissue in early clinical development. Eight clinical trials have now reported final results, and several are currently registered recruiting patients or pending to start. Products passing the safety hurdle are recruiting patients for large efficacy studies. Besides identifying the most appropriate cell type, other issues to resolve include optimal timing for intervention, optimal delivery route, cell dose, patient selection, relevant clinical endpoints, and monitoring for effectiveness, to advance cell therapy through the hurdles of clinical research. In this chapter, we present the products and strategies used in the current cell therapy trials in ischemic stroke, provide an update on relevant preclinical research, and discuss the vital developments still needed to advance their clinical application as a future therapeutic option.