Changes in cognitive function after neuronal cell transplantation for basal ganglia stroke

Caffeine and Its Neuroprotective Role in Ischemic Events: A Mechanism Dependent on Adenosine Receptors

Ischemia is characterized by a transient, insufficient, or permanent interruption of blood flow to a tissue, which leads to an inadequate glucose and oxygen supply. The nervous tissue is highly active, and it closely depends on glucose and oxygen to satisfy its metabolic demand. Therefore, ischemic conditions promote cell death and lead to a secondary wave of cell damage that progressively spreads to the neighborhood areas, called penumbra. Brain ischemia is one of the main causes of deaths and summed with retinal ischemia comprises one of the principal reasons of disability. Although several studies have been performed to investigate the mechanisms of damage to find protective/preventive interventions, an effective treatment does not exist yet. Adenosine is a well-described neuromodulator in the central nervous system (CNS), and acts through four subtypes of G-protein-coupled receptors. Adenosine receptors, especially A₁ and A_2A receptors, are the main targets of caffeine in daily consumption doses. Accordingly, caffeine has been greatly studied in the context of CNS pathologies. In fact, adenosine system, as well as caffeine, is involved in neuroprotection effects in different pathological situations. Therefore, the present review focuses on the role of adenosine/caffeine in CNS, brain and retina, ischemic events.

Stem Cell Treatment for Ischemic Stroke Recovery

The role of cellular transplantation to promote functional recovery after stroke has been evaluated over the last two decades. Preclinical studies first established the potential for cultured neuronal cells derived from a teratocarcinoma cell line to be tested for safety and efficacy in the treatment of human stroke. In animal models of stroke that caused reproducible learning and motor deficits, injection of neuronal cells resulted in a return of learning behavior, retention time, and motor function. Clinical trials followed. Additional work with cells derived from a bone marrow neuroprogenitor line, fetal cortical stem cells, and other cell sources showed promise in preclinical studies and then these cells were tested in clinical studies. This report reviews the different biological repair approaches using cell implants, discusses clinical trial design and surgical methods, and the current state of research.

Stem cell transplantation for ischemic stroke

BACKGROUND

Stroke is a leading cause of morbidity and mortality worldwide, with very large healthcare and social costs, and a strong demand for alternative therapeutic approaches. Preclinical studies have shown that stem cells transplanted into the brain can lead to functional improvement. However, to date, evidence for the benefits of stem cell transplantation in people with ischemic stroke is lacking. This is the first update of the Cochrane review published in 2010.

OBJECTIVES

To assess the efficacy and safety of stem cell transplantation compared with control in people with ischemic stroke.

SEARCH METHODS

We searched the Cochrane Stroke Group Trials Register (last searched August 2018), CENTRAL (last searched August 2018), MEDLINE (1966 to August 2018), Embase (1980 to August 2018), and BIOSIS (1926 to August 2018). We handsearched potentially relevant conference proceedings, screened reference lists, and searched ongoing trials and research registers (last searched August 2018). We also contacted individuals active in the field and stem cell manufacturers (last contacted August 2018).

SELECTION CRITERIA

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

DATA COLLECTION AND ANALYSIS

Two review authors independently applied the inclusion criteria, assessed trial quality and risk of bias, and extracted data. If needed, we contacted study authors for additional information. We performed random effects meta-analyses when two or more RCTs were available for any outcome. We assessed the certainty of the evidence by using the GRADE approach.

MAIN RESULTS

In this updated review, we included seven completed RCTs with 401 participants. All tested adult human non-neural stem cells; cells were transplanted during the acute, subacute, or chronic phase of ischemic stroke; administered intravenously, intra-arterially, intracerebrally, or into the lumbar subarachnoid space. Follow-up ranged from six months to seven years. Efficacy outcomes were measured with the National Institutes of Health Stroke Scale (NIHSS), modified Rankin Scale (mRS), or Barthel Index (BI). Safety outcomes included case fatality, and were measured at the end of the trial.Overall, stem cell transplantation was associated with a better clinical outcome when measured with the NIHSS (mean difference [MD] -1.49, 95% confidence interval [CI] -2.65 to -0.33; five studies, 319 participants; low-certainty evidence), but not with the mRS (MD -0.42, 95% CI -0.86 to 0.02; six studies, 371 participants; very low-certainty evidence), or the BI (MD 14.09, 95% CI -1.94 to 30.13; three studies, 170 participants; very low-certainty evidence). The studies in favor of stem cell transplantation had, on average, a higher risk of bias, and a sample size of 32 or fewer participants.No significant safety concerns associated with stem cell transplantation were raised with respect to death (risk ratio [RR] 0.66, 95% CI 0.39 to 1.14; six studies, participants; low-certainty evidence).We were not able to perform the sensitivity analysis according to the quality of studies, because all of them were at high risk of bias.

AUTHORS' CONCLUSIONS

Overall, in participants with ischemic stroke, stem cell transplantation was associated with a reduced neurological impairment, but not with a better functional outcome. No obvious safety concerns were raised. However, these conclusions came mostly from small RCTs with high risk of bias, and the certainty of the evidence ranged from low to very low. More well-designed trials are needed.

Human Neural Stem Cells for Ischemic Stroke Treatment

Ischemic stroke is the second most common cause of death worldwide and a major cause of disability. It takes place when the brain does not receive sufficient blood supply due to the blood clot in the vessels or narrowing of vessels' inner space due to accumulation of fat products. Apart from thrombolysis (dissolving of blood clot) and thrombectomy (surgical removal of blood clot or widening of vessel inner area) during the first hours after an ischemic stroke, no effective treatment to improve functional recovery exists in the post-ischemic phase. Due to their narrow therapeutic time window, thrombolysis and thrombectomy are unavailable to more than 80% of stroke patients.Many experimental studies carried out in animal models of stroke have demonstrated that stem cell transplantation may become a new therapeutic strategy in stroke. Transplantation of stem cells of different origin and stage of development has been shown to lead to improvement in experimental models of stroke through several mechanisms including neuronal replacement, modulation of cellular and synaptic plasticity and inflammation, neuroprotection and stimulation of angiogenesis. Several clinical studies and trials based on stem cell delivery in stroke patients are in progress with goal of improvements of functional recovery through mechanisms other than neuronal replacement. These approaches may provide therapeutic benefit, but generation of specific neurons for reconstruction of stroke-injured neural circuitry remains ultimate challenge. For this purpose, neural stem cells could be developed from multiple sources and fated to adopt required neuronal phenotype.

Neurorestorative effect of olfactory ensheathing cells and Schwann cells by intranasal delivery for patients with ischemic stroke: design of a multicenter randomized double-blinded placebo-controlled clinical study

Introduction:

There have been many clinical studies or trials for patients with ischemic stroke by cell therapy, which includes olfactory ensheathing cell (OEC), mononuclear cell, mesenchymal stromal cell, fetal neural cell or products of varying stem cells, etc. Those cells through different transplanting ways have showed moderate neurorestorative effect in patients with ischemic stroke, but majority were not multicenter randomized, double-blinded, placebo-controlled studies or trials. OEC transplantation has shown a more effective to restore neurological damage in central nervous system (CNS). We hypothesize that OEC through intra-olfactory mucosa transplantation can migrate into the ischemic stroke area around and restore neurological deficit caused from this disaster.

Objective of the study:

This is a multicenter, randomized, double-blinded, placebo- controlled 12 month clinical study of OECs and Schwann cells (SCs) for patients with sub-acute ischemic stroke and chronic ischemic stroke, to test which kind of cell has more neurorestorative effect for patients with ischemic stroke relative to placebo.

Design of the study:

This study is involved two groups of patients with sub-acute ischemic stroke and chronic ischemic stroke. Each group enrolls 30 patients. The experimental intervention consists in using OECs and SCs through intra-olfactory mucosa transplantation in participating patients. This will be compared with using placebo (injecting cell culture medium). Participating patients in groups of sub-acute ischemic stroke and chronic ischemic stroke are randomized in natural order to divide into A, B, or C groups and get one of experimental treatment procedures. Patients, operating physicians, and assessing physicians are left unaware of what cells or medium will be injected to participating patients. All patients will be assessed before treatment and after one month, three months, six months, and one year.

Ethics and dissemination:

The clinical study protocol and consent form were approved by Chinese Association of Neurorestoratology and the ethics committees of the hospitals which joined this clinical study. Findings will be published in peer-reviewed journals.

Enhancing Plasticity of the Central Nervous System: Drugs, Stem Cell Therapy, and Neuro-Implants

Stroke represents the first cause of adult acquired disability. Spontaneous recovery, dependent on endogenous neurogenesis, allows for limited recovery in 50% of patients who remain functionally dependent despite physiotherapy. Here, we propose a review of novel drug therapies with strong potential in the clinic. We will also discuss new avenues of stem cell therapy in patients with a cerebral lesion. A promising future for the development of efficient drugs to enhance functional recovery after stroke seems evident. These drugs will have to prove their efficacy also in severely affected patients. The efficacy of stem cell engraftment has been demonstrated but will have to prove its potential in restoring tissue function for the massive brain lesions that are most debilitating. New answers may lay in biomaterials, a steadily growing field. Biomaterials should ideally resemble lesioned brain structures in architecture and must be proven to increase functional reconnections within host tissue before clinical testing.

Cell therapies administered in the chronic phase after stroke: a meta-analysis examining safety and efficacy

Aim: To assess the safety and efficacy of cell therapies for chronic stroke. Methodology: Five databases were searched for treatments administered >90 days post-stroke. Reporting quality, adherence to research guidelines, treatment safety (risk ratios/pooled incidence rates) and neurological/functional efficacy (Hedge’s g) were all evaluated. Results: Twenty-three studies examined 17 treatments. Reporting quality scores were medium to high, but adherence to recommended guidelines was lower. Three treatments resulted in serious adverse events; four improved outcomes more than standard care. However, many studies were under-powered and individual patients varied in their response to some treatments. Conclusion: Preliminary findings suggest that some cell therapies may be relatively safe and effective, but larger double-blinded placebo-controlled studies are needed to establish the long-term risks and benefits.

Clinical imaging in regenerative medicine

In regenerative medicine, clinical imaging is indispensable for characterizing damaged tissue and for measuring the safety and efficacy of therapy. However, the ability to track the fate and function of transplanted cells with current technologies is limited. Exogenous contrast labels such as nanoparticles give a strong signal in the short term but are unreliable long term. Genetically encoded labels are good both short- and long-term in animals, but in the human setting they raise regulatory issues related to the safety of genomic integration and potential immunogenicity of reporter proteins. Imaging studies in brain, heart and islets share a common set of challenges, including developing novel labeling approaches to improve detection thresholds and early delineation of toxicity and function. Key areas for future research include addressing safety concerns associated with genetic labels and developing methods to follow cell survival, differentiation and integration with host tissue. Imaging may bridge the gap between cell therapies and health outcomes by elucidating mechanisms of action through longitudinal monitoring.

Stem cell therapy for acute cerebral injury: what do we know and what will the future bring?

PURPOSE OF REVIEW

The central nervous system has limited capacity for regeneration after acute and chronic injury. An attractive approach to stimulate neural plasticity in the brain is to transplant stem cells in order to restore function. Here, we discuss potential mechanisms of action, current knowledge and future perspectives of clinical stem cell research for stroke and traumatic brain injury.

RECENT FINDINGS

Preclinical data using various models suggest stem cell therapy to be a promising therapeutic avenue. Progress has been made in elucidating the mechanism of action of various cell types used, shifting the hypothesis from neural replacement to enhancing endogenous repair processes. Translation of these findings in clinical trials is currently being pursued with emphasis on both safety as well as efficacy.

SUMMARY

Clinical trials are currently recruiting patients in phase I and II trials to gain more insight in the therapeutic potential of stem cells in acute cerebral injury. A close interplay between results of these clinical trials and more extensive basic research is essential for future trial design, choosing the optimal transplantation strategy and selecting the right patients.

Neural stem/progenitor cell transplantation for cortical visual impairment in neonatal brain injured patients

The purpose of this study was to investigate the clinical efficacy of neural stem/progenitor cell (NS/PC) transplantation to treat severe cortical visual impairment (CVI), a sequela of neonatal brain injury. Fifty-two patients with cerebral injury and CVI were randomly divided into two groups: the treatment group (n = 25, with the median age of 18 months) and the control group (n = 27, with the median age of 19.5 months). The treatment group received intracerebroventricular transplantation of human NS/PCs and rehabilitation training. The control group received rehabilitation only. The visual function was assessed by Holt's method at various time points after transplantation. One in five patients with fundus abnormalities accompanied by blindness regained light perception. The visual functions of 75% of the patients with normal fundus were improved by one level or more in a 2-year follow-up. The median efficacy appeared 60 days posttransplantation. The total effective rate of cell transplantation on visual improvement was 64% (16 patients of 25), among which one blind patient regained light perception, five (31.2%) CVI patients improved by one level, and 10 (62.5%) improved by more than one level. Functional magnetic resonance imaging (fMRI) in a subpopulation of patients showed enhanced signals in the occipital lobe, visual pathway, and apical lobe after transplantation. In the control group, four patients with fundus abnormalities showed no improvement. Nine of 23 CVI patients with normal fundus improved visual function by more than one level. At the 2-year follow-up, no blind patients showed visual improvement. The total effective rate was 33.33% (9 of 27 patients). Among those showing visual improvement in the control group, six patients (66.67%) improved by one level, and three (33.33%) by more than one level. The median efficacy occurred in 365 days. Human NS/PC transplantation is effective to treat patients with severe CVI after neonatal brain injury. Compared with the traditional rehabilitation training, cell transplantation showed not only earlier visual improvement but also higher improvement rates and degrees. This article is published as part of the International Association of Neurorestoratology (IANR) supplement issue of Cell Transplantation.

Devices for cell transplantation into the central nervous system: Design considerations and emerging technologies

Successful use of cell-based therapies for the treatment of neurological diseases is dependent upon effective delivery to the central nervous system (CNS). The CNS poses several challenges to the delivery of cell-based therapeutics, including the blood-brain barrier, anatomic complexity, and regional specificity. Targeted delivery methods are therefore required for the selective treatment of specific CNS regions. In addition, CNS tissues are mechanically and physiologically delicate and even minor injury to normal brain or spinal cord can cause devastating neurological deficits. Targeted delivery methods must therefore minimize tissue trauma. At present, direct injection into brain or spinal cord parenchyma promises to be the most versatile and accurate method of targeted CNS therapeutic delivery. While direct injection methods have already been employed in clinical trials of cell transplantation for a wide variety of neurological diseases, there are many shortcomings with the devices and surgical approaches currently used. Some of these technical limitations may hinder the clinical development of cell transplantation therapies despite validity of the underlying biological mechanisms. In this review, we discuss some of the important technical considerations of CNS injection devices such as targeting accuracy, distribution of infused therapeutic, and overall safety to the patient. We also introduce and discuss an emerging technology - radially branched deployment - that may improve our ability to safely distribute cell-based therapies and other therapeutic agents to the CNS. Finally, we speculate on future technological developments that may further enhance the efficacy of CNS therapeutic delivery.

Radially branched deployment for more efficient cell transplantation at the scale of the human brain

BACKGROUND

In preclinical studies, cell transplantation into the brain has shown great promise for the treatment of a wide range of neurological diseases. However, the use of a straight cannula and syringe for cell delivery to the human brain does not approximate cell distribution achieved in animal studies. This technical deficiency may limit the successful clinical translation of cell transplantation.

OBJECTIVE

To develop a stereotactic device that effectively distributes viable cells to the human brain. Our primary aims were to (1) minimize the number of transcortical penetrations required for transplantation, (2) reduce variability in cell dosing and (3) increase cell survival.

METHODS

We developed a modular cannula system capable of radially branched deployment (RBD) of a cell delivery catheter at variable angles from the longitudinal device axis. We also developed an integrated catheter-plunger system, eliminating the need for a separate syringe delivery mechanism. The RBD prototype was evaluated in vitro and in vivo with subcortical injections into the swine brain. Performance was compared to a 20G straight cannula with dual side ports, a device used in current clinical trials.

RESULTS

RBD enabled therapeutic delivery in a precise 'tree-like' pattern branched from a single initial trajectory, thereby facilitating delivery to a volumetrically large target region. RBD could transplant materials in a radial pattern up to 2.0 cm from the initial penetration tract. The novel integrated catheter-plunger system facilitated manual delivery of small and precise volumes of injection (1.36 ± 0.13 µl per cm of plunger travel). Both dilute and highly concentrated neural precursor cell populations tolerated transit through the device with high viability and unaffected developmental potential. While reflux of infusate along the penetration tract was problematic with the use of the 20G cannula, RBD was resistant to this source of cell dose variability in agarose. RBD enabled radial injections to the swine brain when used with a modern clinical stereotactic system.

CONCLUSIONS

By increasing the total delivery volume through a single transcortical penetration in agarose models, RBD strategy may provide a new approach for cell transplantation to the human brain. Incorporation of RBD or selected aspects of its design into future clinical trials may increase the likelihood of successful translation of cell-based therapy to the human patient.

Effects of neural progenitor cell transplantation in children with severe cerebral palsy

Cerebral palsy (CP) is a chronic nervous system disease that severely damages the physical and developmental health of children. Traditional treatment brings about only improvement of mild to moderate CP, but severe CP still lacks effective interventions. To explore safety and efficacy of using neural progenitor cells (NPCs) to treat CP in children, we performed NPC transplantation in 45 patients with severe CP by injecting NPCs derived from aborted fetal tissue into the lateral ventricle. Gross motor function measures (GMFM), the Peabody Developmental Motor Scale-Fine Motor (PDMS-FM) test, and a unified survey questionnaire designed specifically for children with CP were used to evaluate neurological function of the patients. Motor development was significantly accelerated within the first month after cell transplantation, but the rate of improvement gradually slowed to preoperative levels. However, after 1 year, the developmental level in each functional sphere (gross motor, fine motor, and cognition) of the treatment group was significantly higher compared to the control group. No delayed complications of this therapy were noted. These results suggest that NPC transplantation is a safe and effective therapeutic method for treating children with severe CP.

Potential for Cell-Transplant Therapy with Human Neuronal Precursors to Treat Neuropathic Pain in Models of PNS and CNS Injury: Comparison of hNT2.17 and hNT2.19 Cell Lines

Effective treatment of sensory neuropathies in peripheral neuropathies and spinal cord injury (SCI) is one of the most difficult problems in modern clinical practice. Cell therapy to release antinociceptive agents near the injured spinal cord is a logical next step in the development of treatment modalities. But few clinical trials, especially for chronic pain, have tested the potential of transplant of cells to treat chronic pain. Cell lines derived from the human neuronal NT2 cell line parentage, the hNT2.17 and hNT2.19 lines, which synthesize and release the neurotransmitters gamma-aminobutyric acid (GABA) and serotonin (5HT), respectively, have been used to evaluate the potential of cell-based release of antinociceptive agents near the lumbar dorsal (horn) spinal sensory cell centers to relieve neuropathic pain after PNS (partial nerve and diabetes-related injury) and CNS (spinal cord injury) damage in rat models. Both cell lines transplants potently and permanently reverse behavioral hypersensitivity without inducing tumors or other complications after grafting. Functioning as cellular minipumps for antinociception, human neuronal precursors, like these NT2-derived cell lines, would likely provide a useful adjuvant or replacement for current pharmacological treatments for neuropathic pain.

Injection Parameters Affect Cell Viability and Implant Volumes in Automated Cell Delivery for the Brain

The technique of central nervous system cell implantation can affect the outcome of preclinical or clinical studies. Our goal was to evaluate the impact of various injection parameters that may be of consequence during the delivery of solute-suspended cells. These parameters included ( 1 ) the type and concentration of cells used for implantation, ( 2 ) the rate at which cells are injected (flow rate), ( 3 ) the acceleration of the delivery device, ( 4 ) the period of time between cell loading and injection into the CNS (delay), and ( 5 ) the length and gauge of the needle used to deliver the cells. Neural progenitor cells (NPCs) and bone marrow stromal cells (BMSCs) were injected an automated device. These parameters were assessed in relation to their effect on the volume of cells injected and cell viability. Longer and thinner cannulae and higher cell concentrations were detrimental for cell delivery. Devices and techniques that optimize these parameters should be of benefit.

Neural stem cell-based therapy for ischemic stroke

Stem cell-based approaches for the treatment of stroke have been the subject of intensive research over the past decade. Based on accumulated experimental evidence, stem cell-based therapy is a very promising prospect for the development of a novel treatment to restore stroke-damaged brain and impaired neurological function. Studies performed on experimental animal models of stroke employed a variety of stem cell types from diverse sources and have demonstrated their ability to replace lost neurons and functionally integrate into the brain, modulate inflammation, and stimulate angiogenesis and neurogenesis from an endogenous stem cell pool, most likely through trophic actions. A few clinical trials in stroke patients using stem cell transplantation have been completed or are on-going but the results have not yet proven the effectiveness of the stem cell-based approaches. A joint effort of stroke researchers and clinicians is needed to further optimize treatment protocols using safe and reproducible stem cell sources tested in relevant animal models of stroke and showing substantial neurological recovery of stroke-impaired function.

Cognitive changes after stem cell transplantation in a patient with subcortical stroke

The authors report a case of a 55-year-old Caucasian woman who received autologous bone marrow stem cell transplantation 3 years after a subcortical stroke. She exhibited positive cognitive changes 6 months and 1 year after the surgery without rehabilitation. The blood flow changes, measured with SPECT, were statistical significant in prefrontal areas. During the presurgical neuropsychological assessment, the patient presented a critical speech reduction, reflected in impaired performance in verbal fluency, vocabulary and in each task which required overt verbal response. One year later, she showed improvement in mental flexibility, receptive language, phonological fluency, verbal memory and auditory verbal memory. Positive cognitive changes in verbal and executive functions seem to be contingent on increased blood flow in prefrontal areas. Posterior neuropsychological evaluation 3 and 5 years after transplantation did not show deterioration of the cognitive improvement.

Manual vs automated delivery of cells for transplantation: accuracy, reproducibility, and impact on viability

BACKGROUND

Cellular transplantation holds promise for the management of a variety of neurological disorders. However, there is great variability in cell type, preparation methods, and implantation technique, which are crucial to clinical outcomes.

OBJECTIVE

We compared manual injection with automated injection using a prototype device to determine the possible value of a mechanized delivery system.

METHODS

Neural progenitor cells and bone marrow stromal cells were injected using manual or automated methods. Consistency of injection volumes and cell number and viability were evaluated immediately or 1 day after injection.

RESULTS

When cells were delivered as a series of 3 manual injections from the same syringe, the variation in fluid volume was greater than for single manual injections. Automated delivery of a series of 3 injections resulted in a lower variability in the amount of delivery than manual injection for both cell lines (1.2%-2.6% coefficient of variability for automated delivery vs 4.3%-24.0% for manual delivery). The amount delivered from injection 1 to injection 3 increased significantly with manual injections, whereas the amount injected did not vary over the 3 injections for the automated unit. Cell viability 1 day after injection was typically 30% to 40% of the value immediately after injection for the bone marrow stromal cells and 30% to 70% for the neural progenitor cells. There were no significant differences in viability attributed to the method of injection.

CONCLUSION

The automated delivery device led to enhanced consistency of volumetric cell delivery but did not improve cell viability in the methods tested. Automated techniques could be useful in standardizing reproducible procedures for cell transplantation and improve both preclinical and clinical research.

Chapter 55: neural transplantation

The history of cell transplantation in the nervous system is reviewed in four main sections. The "early era" spans the period from 1890 to 1940, during which the first attempts at cell transplantation in the brain were undertaken. Many contemporary themes were first addressed such as surgical factors to achieve survival of grafted cells and how that should be assessed, immunological factors, use of tumors as a readily viable cell source; and use of the anterior eye chamber as a model transplantation site. However, such studies generally exhibited only low levels of viability or successful implantation. The "middle era" from 1940 to 1970 spans the period when the techniques for viable and reliable cell transplantation using embryonic donor tissues implanted into sites with effective vascularization were first established in brain and neuroendocrine systems in a limited number of specialist centers. However, although sometimes impressive, these results were at variance with the prevailing view that the adult mammalian brain is immutable and resistant to plasticity, growth or regeneration, and were largely ignored. The "modern era," since 1970, began with the pioneering studies that combined cell transplantation with the use of improved histochemical and ultrastructural anatomical techniques to demonstrate selectivity, specificity and regenerative capacity of implanted cells, and the slow acceptance that the adult brain does exhibit considerable potential for plasticity and repair. The last three decades have witnessed the identification of reliable and efficient transplantation technologies combined with progressively refined methods of molecular, cellular, biochemical, physiological and functional analysis. This now enables the ready use of cell transplantation as a powerful novel method within the neuroscience tool-kit, which is being used: to analyze normal organization and function of the nervous system; to reveal the biological mechanisms and principles of neuronal development, regeneration and plasticity; and to study the principles of surgically directed cell therapies for promoting plasticity, replacement and repair in response to injury and disease. The final section reviews recent progress in translating cell transplantation to the clinic for application in Parkinson's and other central nervous system diseases.

Cellular transplantation for the nervous system: impact of time after preparation on cell viability and survival

OBJECT

Cell transplantation has shown promise for the treatment of various neurological disorders, but the factors that influence cell survival and integration following transplantation are poorly understood. In fact, little is known regarding how simple but potentially critical variables, including the method of cellular preparation and administration, might affect transplant success. The goal of the present study was to determine the impact of time between tissue preparation and implantation on cellular viability. Time can vary with cell preparation, delivery to the operating room, and surgical technique. This study was also designed to evaluate the sensitivity of various methods of assessing implant viability.

METHODS

Cell lines of neural progenitor cells and bone marrow stromal cells were generated from healthy adult mice. On the day of experimentation, the cells were collected, suspended in a balanced salt solution, and sequentially assessed for viability for up to 3.5 hours based on their appearance under phase-contrast microscopy, their ability to retain a fluorescent dye, and their attachment to a cultivation surface for 24 hours.

RESULTS

When viability was measured based on the ability of cells to retain a fluorescent dye, there was a decrease in viability of 10-15% each hour. Based on the ability of the cells to attach to a culture surface and grow for 24 hours, viability decreased more rapidly at approximately 20% per hour. In addition, only about one-third of the cells judged viable based on phase-contrast microscopy or acute dye retention were found to be viable based on plating, and only 10% of the cells initially judged as viable were still capable of survival after 3 hours in suspension.

CONCLUSIONS

The authors' results indicate that that there can be significant losses in viability between preparation and implantation and that more sophisticated methods of evaluation, such as the ability of cells to attach to a substrate and grow, may be required to detect decreases in viability. The time between preparation and implantation will be an important factor in clinical trial design.

Stem cell transplantation for ischemic stroke

BACKGROUND

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

OBJECTIVES

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

SEARCH STRATEGY

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

SELECTION CRITERIA

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

DATA COLLECTION AND ANALYSIS

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

MAIN RESULTS

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

AUTHORS' CONCLUSIONS

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

[Cerebral plasticity: from bench to bedside in stroke treatment]

It has long been believed that cerebral lesions were irreversible in the adult human brain. However, the spontaneous improvement in functional outcome observed in the following weeks after cerebral ischemia suggests plasticity phenomenons involving postischemic neuronal network reorganization. Regarding the large prevalence of stroke in industrialized countries, and the few available treatments, the understanding of cerebral plasticity has become an important issue but also a potential source of new therapeutic approaches in stroke. Thus, "constraint induced therapy" and repetitive transcranial magnetic stimulation (rTMS) are based on the concept of local but also remote consequences of the ischemic focal lesion. Cell-therapy is based on the capacity of stem cells to respond to hypoxic signals and adapt their phenotype to the host organ, but above all to release cytokines locally and boost endogeneous repair mechanisms. We could consider to perform in the future a sequential treatment with fibrinolysis, stem cell therapy, repetitive transcranial magnetic stimulation and constraint-induced therapy in the same patient.

Bone marrow-derived mesenchymal stem cells for the treatment of ischemic stroke

Bone marrow-derived mesenchymal stem cells (MSCs) have great potential as therapeutic agents in stroke management, since they are easily accessible and can be rapidly expanded ex vivo for autologous transplantation. Increasing evidence suggests that bone marrow cells migrate throughout the brain and differentiate into neurons and glial cells. Both non-human and human MSCs have been used to treat stroke in murine models with satisfactory results. Several factors, such as transdifferentiation, induction of neurogenesis and angiogenesis, neuroprotection, and activation of endogenous neurorestorative processes, contribute to the benefits of MSCs in the ischemic brain. Many variables, including types of MSCs, cell dose, timing of treatment, route of cell delivery, and characteristics of stroke patients, influence the efficacy of MSC treatment of stroke. Although the first trials of autologous MSC therapy in stroke patients showed promising results, the optimal approach for different clinical settings has yet to be determined. The fundamental properties of MSCs and their potential short-term and long-term toxicities also need to be determined before moving forward to use of these cells in clinical practice.

Stroke repair with cell transplantation: neuronal cells, neuroprogenitor cells, and stem cells

Stroke is a common cause of death and disability. The role of cellular transplantation to promote functional recovery has been explored. Preclinical studies first established the potential for cultured neuronal cells derived from a teratocarcinoma cell line to be tested for safety and efficacy in the treatment of human stroke. In animal models of stroke that caused reproducible learning and motor deficits, injection of neuronal cells resulted in a return of learning behavior retention time and motor function. In this report the authors review several current concepts for cellular repair, discuss important patient selection and surgical technique issues, and discuss plans for future experiments.

Neurogenesis after traumatic brain injury

With the hope of replacing neurons lost in traumatic brain injury (TBI), experimental models are being used to investigate TBI-induced neurogenesis. Although selectively vulnerable to TBI, the neurogenic hippocampus may have the unique ability to replace damaged neurons locally. Injury may also activate signaling pathways that induce neuroblasts from the subventricular zone to migrate to areas of focal cortical damage. Additionally, there is some evidence for local activation of latent neural progenitor cells in the injured neocortex itself. Each of these themes is discussed, with emphasis on the possibility of future therapeutic intervention.

Cell Transplantation for Ischemic Stroke

Cell replacement therapy has been evaluated as a regenerative strategy for patients with fixed neurologic deficits after ischemic stroke. Animal models have identified specific cell lines which lead to regeneration and improvement in behavior and motor function after implantation into areas of ischemic injury. This has led to the development of pilot studies in humans, which have mainly investigated the safety and pilot efficacy of such approaches with promising early results. As research in this area progresses, further prospective trials are necessary not only to demonstrate clinical efficacy but also to understand the mechanisms underlying the early positive experiences, to select appropriate patients for cell replacement therapy, and to elucidate the optimal timing and mode of cell delivery.

Neurogenesis in the adult ischemic brain: generation, migration, survival, and restorative therapy

This article reviews current data on the induction of neurogenesis after stroke in the adult brain. The discussion of neurogenesis is divided into production, migration, and survival of these newly formed cells. For production, the subpopulations and the types of cell division are presented. Discussion of cell migration entails presenting data on both the pathways as well as the molecular targeting of newly formed neural progenitor cells to sites of injury. The role of the vascular and the astrocytic microenvironment in promoting the survival and integration of progenitor cells is also presented. Cell-based and pharmacological therapies designed to restore neurological function that promote neurogenesis are described. These therapies also induce angiogenesis and astrocytic changes that brain tissue, which prime the ischemic brain to foster the survival of the newly formed progenitor cells. Signaling pathways that regulate neurogenesis and angiogenesis are also addressed. This review summarizes recent data on neurogenesis and provides insight into the potential for restorative treatments of stroke.

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

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

Neurotransplantation for patients with subcortical motor stroke: a Phase 2 randomized trial

OBJECT

No definitive treatment exists to restore lost brain function following a stroke. Transplantation of cultured neuronal cells has been shown to be safe and effective in animal models of stroke and safe in a Phase 1 human trial. In the present study the authors tested the usefulness of human neuron transplantation followed by participation in a 2-month stroke rehabilitation program compared with rehabilitation alone in patients with substantial fixed motor deficits associated with a basal ganglia stroke.

METHODS

Human neuronal cells (LBS-Neurons; Layton BioScience, Inc.) were delivered frozen and then thawed and formulated on the morning of surgery. The entry criteria in this randomized, observer-blinded trial of 18 patients included age between 18 and 75 years, completed stroke duration of 1 to 6 years, presence of a fixed motor deficit that was stable for at least 2 months, and no contraindications to stereotactic surgery. Patients were randomized at two centers to receive either 5 or 10 million implanted cells in 25 sites (seven patients per group) followed by participation in a stroke rehabilitation program, or to serve as a nonsurgical control group (rehabilitation only; four patients). The surgical techniques used were the same at both centers. All patients underwent extensive pre- and postoperative motor testing and imaging. Patients received cyclosporine A for 1 week before and 6 months after surgery. The primary efficacy measure was a change in the European Stroke Scale (ESS) motor score at 6 months. Secondary outcomes included Fugl-Meyer, Action Research Arm Test, and Stroke Impact Scale scores, as well as the results of other motor tests. Nine strokes were ischemic in origin and nine were hemorrhagic. All 14 patients who underwent surgery (ages 40-70 years) underwent uncomplicated surgeries. Serial evaluations (maximum duration 24 months) demonstrated no cell-related adverse serological or imaging-defined effects. One patient suffered a single seizure, another had a syncopal event, and in another there was burr-hole drainage of an asymptomatic chronic subdural hematoma. Four of seven patients who received 5 million cells (mean improvement 6.9 points) and two of seven who received 10 million cells had improved ESS scores at 6 months; however, there was no significant change in the ESS motor score in patients who received cell implants (p = 0.756) compared with control or baseline values (p = 0.06). Compared with baseline, wrist movement and hand movement scores recorded on the Fugl-Meyer Stroke Assessment instrument were not improved (p = 0.06). The Action Research Arm Test gross hand-movement scores improved compared with control (p = 0.017) and baseline (p = 0.001) values. On the Stroke Impact Scale, the 6-month daily activities score changed compared with baseline (p = 0.045) but not control (p = 0.056) scores, and the Everyday Memory test score improved in comparison with baseline (p = 0.004) values.

CONCLUSIONS

Human neuronal cells can be produced in culture and implanted stereotactically into the brains of patients with motor deficits due to stroke. Although a measurable improvement was noted in some patients and this translated into improved activities of daily living in some patients as well, this study did not find evidence of a significant benefit in motor function as determined by the primary outcome measure. This experimental trial indicates the safety and feasibility of neuron transplantation for patients with motor stroke.