Are Stem Cell-Based Therapies for Parkinson's Disease Ready for the Clinic in 2016?

Novel Gene Therapy Approaches for Targeting Neurodegenerative Disorders: Focusing on Delivering Neurotrophic Genes

Neurodegenerative illnesses (NDDs) like Alzheimer's, Parkinson's, amyotrophic lateral sclerosis, spinal muscular atrophy, and Huntington's disease have demonstrated considerable potential for gene therapy as a viable therapeutic intervention. NDDs are marked by the decline of neurons, resulting in changes in both behavior and pathology within the body. Strikingly, only symptomatic management is available without a cure for the NDDs. There is an unmet need for a permanent therapeutic approach. Many studies have been going on to target the newer therapeutic molecular targets for NDDs including gene-based therapy. Gene therapy has the potential to provide therapeutic benefits to a large number of patients with NDDs by offering mechanisms including neuroprotection, neuro-restoration, and rectification of pathogenic pathways. Gene therapy is a medical approach that aims to modify the biological characteristics of living cells by controlling the expression of specific genes in certain neurological disorders. Despite being the most complex and well-protected organ in the human body, there is clinical evidence to show that it is possible to specifically target the central nervous system (CNS). This provides hope for the prospective application of gene therapy in treating NDDs in the future. There are several advanced techniques available for using viral or non-viral vectors to deliver the therapeutic gene to the afflicted region. Neurotrophic factors (NTF) in the brain are crucial for the development, differentiation, and survival of neurons in the CNS, making them important in the context of various neurological illnesses. Gene delivery of NTF has the potential to be used as a therapeutic approach for the treatment of neurological problems in the brain. This review primarily focuses on the methodologies employed for delivering the genes of different NTFs to treat neurological disorders. These techniques are currently being explored as a viable therapeutic approach for neurodegenerative diseases. The article exclusively addresses gene delivery approaches and does not cover additional therapy strategies for NDDs. Gene therapy offers a promising alternative treatment for NDDs by stimulating neuronal growth instead of solely relying on symptom relief from drugs and their associated adverse effects. It can serve as a long-lasting and advantageous treatment choice for the management of NDDs. The likelihood of developing NDDs increases with age as a result of neuronal degradation in the brain. Gene therapy is an optimal approach for promoting neuronal growth through the introduction of nerve growth factor genes.

Can pluripotent/multipotent stem cells reverse Parkinson's disease progression?

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by continuous and selective degeneration or death of dopamine neurons in the midbrain, leading to dysfunction of the nigrostriatal neural circuits. Current clinical treatments for PD include drug treatment and surgery, which provide short-term relief of symptoms but are associated with many side effects and cannot reverse the progression of PD. Pluripotent/multipotent stem cells possess a self-renewal capacity and the potential to differentiate into dopaminergic neurons. Transplantation of pluripotent/multipotent stem cells or dopaminergic neurons derived from these cells is a promising strategy for the complete repair of damaged neural circuits in PD. This article reviews and summarizes the current preclinical/clinical treatments for PD, their efficacies, and the advantages/disadvantages of various stem cells, including pluripotent and multipotent stem cells, to provide a detailed overview of how these cells can be applied in the treatment of PD, as well as the challenges and bottlenecks that need to be overcome in future translational studies.

Perinatal Tissue-Derived Stem Cells: An Emerging Therapeutic Strategy for Challenging Neurodegenerative Diseases

Over the past 20 years, stem cell therapy has been considered a promising option for treating numerous disorders, in particular, neurodegenerative disorders. Stem cells exert neuroprotective and neurodegenerative benefits through different mechanisms, such as the secretion of neurotrophic factors, cell replacement, the activation of endogenous stem cells, and decreased neuroinflammation. Several sources of stem cells have been proposed for transplantation and the restoration of damaged tissue. Over recent decades, intensive research has focused on gestational stem cells considered a novel resource for cell transplantation therapy. The present review provides an update on the recent preclinical/clinical applications of gestational stem cells for the treatment of protein-misfolding diseases including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD) and amyotrophic lateral sclerosis (ALS). However, further studies should be encouraged to translate this promising therapeutic approach into the clinical setting.

Emerging Therapeutic Strategies for Parkinson’s Disease and Future Prospects: A 2021 Update

Parkinson’s disease (PD) is a neurodegenerative disorder pathologically distinguished by degeneration of dopaminergic neurons in the substantia nigra pars compacta. Muscle rigidity, tremor, and bradykinesia are all clinical motor hallmarks of PD. Several pathways have been implicated in PD etiology, including mitochondrial dysfunction, impaired protein clearance, and neuroinflammation, but how these factors interact remains incompletely understood. Although many breakthroughs in PD therapy have been accomplished, there is currently no cure for PD, only trials to alleviate the related motor symptoms. To reduce or stop the clinical progression and mobility impairment, a disease-modifying approach that can directly target the etiology rather than offering symptomatic alleviation remains a major unmet clinical need in the management of PD. In this review, we briefly introduce current treatments and pathophysiology of PD. In addition, we address the novel innovative therapeutic targets for PD therapy, including α-synuclein, autophagy, neurodegeneration, neuroinflammation, and others. Several immunomodulatory approaches and stem cell research currently in clinical trials with PD patients are also discussed. Moreover, preclinical studies and clinical trials evaluating the efficacy of novel and repurposed therapeutic agents and their pragmatic applications with encouraging outcomes are summarized. Finally, molecular biomarkers under active investigation are presented as potentially valuable tools for early PD diagnosis.

An alginate-based encapsulation system for delivery of therapeutic cells to the CNS

Treatment options for neurodegenerative conditions such as Parkinson's disease have included the delivery of cells which release dopamine or neurotrophic factors to the brain. Here, we report the development of a novel approach for protecting cells after implantation into the central nervous system (CNS), by developing dual-layer alginate beads that encapsulate therapeutic cells and release an immunomodulatory compound in a sustained manner. An optimal alginate formulation was selected with a view to providing a sustained physical barrier between engrafted cells and host tissue, enabling exchange of small molecules while blocking components of the host immune response. In addition, a potent immunosuppressant, FK506, was incorporated into the outer layer of alginate beads using electrosprayed poly-ε-caprolactone core–shell nanoparticles with prolonged release profiles. The stiffness, porosity, stability and ability of the alginate beads to support and protect encapsulated SH-SY5Y cells was demonstrated, and the release profile of FK506 and its effect on T-cell proliferation in vitro was characterized. Collectively, our results indicate this multi-layer encapsulation technology has the potential to be suitable for use in CNS cell delivery, to protect implanted cells from host immune responses whilst providing permeability to nutrients and released therapeutic molecules.

Novel composite cell encapsulation system: dual-layer, micro-scale beads maintain cell survival while releasing immunomodulatory FK506 in a sustained manner. This biotechnology platform could be applicable for treatment of CNS and other disorders.

Therapeutic Potential of Astrocyte Transplantation

Cell transplantation is an attractive treatment strategy for a variety of brain disorders, as it promises to replenish lost functions and rejuvenate the brain. In particular, transplantation of astrocytes has come into light recently as a therapy for amyotrophic lateral sclerosis (ALS); moreover, grafting of astrocytes also showed positive results in models of other conditions ranging from neurodegenerative diseases of older age to traumatic injury and stroke. Despite clear differences in etiology, disorders such as ALS, Parkinson's, Alzheimer's, and Huntington's diseases, as well as traumatic injury and stroke, converge on a number of underlying astrocytic abnormalities, which include inflammatory changes, mitochondrial damage, calcium signaling disturbance, hemichannel opening, and loss of glutamate transporters. In this review, we examine these convergent pathways leading to astrocyte dysfunction, and explore the existing evidence for a therapeutic potential of transplantation of healthy astrocytes in various models. Existing literature presents a wide variety of methods to generate astrocytes, or relevant precursor cells, for subsequent transplantation, while described outcomes of this type of treatment also differ between studies. We take technical differences between methodologies into account to understand the variability of therapeutic benefits, or lack thereof, at a deeper level. We conclude by discussing some key requirements of an astrocyte graft that would be most suitable for clinical applications.

Therapeutic potentials of human microfluidic encapsulated conjunctival mesenchymal stem cells on the rat model of Parkinson's disease

BACKGROUND AND AIM

Parkinson's disease (PD) is a progressive neurodegenerative disorder caused by the destruction of the dopaminergic neurons in the nigrostriatal pathway, leading to motor-behavioral complications. Cell therapy has been proposed as a promising approach for PD treatment using various cellular sources. Despite a few disadvantages mesenchymal stem cells (MSCs) represent, they have more auspicious effects for PD cell therapy. The present study aimed to evaluate a new source of MSCs isolated from human Conjunctiva (CJ-MSCs) impact on PD complications for the first time.

MATERIALS AND METHODS

Parkinson's was induced by stereotactic injection of 6-hydroxydopamine (6-OHDA) into the right medial forebrain bundle (MFB). An apomorphine-induced rotation test was used to confirm the model establishment. After PD model confirmation, green fluorescent protein (GFP) labeled CJ-MSCs and induced CJ-MSCs (microfluidic encapsulated and non-capsulated) were transplanted into the rats' right striatum. Then Rotation, Rotarod, and Open-field tests were performed to evaluate the behavioral assessment. Additionally, the immunohistochemistry technique was used for identifying tyrosine hydroxylase (TH).

RESULTS

According to the obtained data, the cell transplantation caused a reduction in the rats' rotation number and improved locomotion compared to the control group. The previous results were also more pronounced in induced and microfluidic encapsulated cells compared to other cells. Rats recipient CJ-MSCs also have represented more TH-expressed GFP-labeled cell numbers in the striatum than the control group.

CONCLUSION

It can be concluded that CJ-MSCs therapy can have protective effects against PD complications and nerve induction of cells due to their ability to express dopamine. On the other hand, CJ-MSCs microencapsulating leads to enhance even more protective effect of CJ-MSCs. However, confirmation of this hypothesis requires further studies and investigation of these cells' possible mechanisms of action.

Human Pluripotent Stem-Cell-Derived Models as a Missing Link in Drug Discovery and Development

Human pluripotent stem cells (hPSCs), including human embryonic stem cells (hESCs) and human-induced pluripotent stem cells (hiPSCs), have the potential to accelerate the drug discovery and development process. In this review, by analyzing each stage of the drug discovery and development process, we identified the active role of hPSC-derived in vitro models in phenotypic screening, target-based screening, target validation, toxicology evaluation, precision medicine, clinical trial in a dish, and post-clinical studies. Patient-derived or genome-edited PSCs can generate valid in vitro models for dissecting disease mechanisms, discovering novel drug targets, screening drug candidates, and preclinically and post-clinically evaluating drug safety and efficacy. With the advances in modern biotechnologies and developmental biology, hPSC-derived in vitro models will hopefully improve the cost-effectiveness and the success rate of drug discovery and development.

Recent developments in the treatment of Parkinson's Disease

Parkinson's disease (PD) is a common neurodegenerative disease typified by a movement disorder consisting of bradykinesia, rest tremor, rigidity, and postural instability. Treatment options for PD are limited, with most of the current approaches based on restoration of dopaminergic tone in the striatum. However, these do not alter disease course and do not treat the non-dopamine-dependent features of PD such as freezing of gait, cognitive impairment, and other non-motor features of the disorder, which often have the greatest impact on quality of life. As understanding of PD pathogenesis grows, novel therapeutic avenues are emerging. These include treatments that aim to control the symptoms of PD without the problematic side effects seen with currently available treatments and those that are aimed towards slowing pathology, reducing neuronal loss, and attenuating disease course. In this latter regard, there has been much interest in drug repurposing (the use of established drugs for a new indication), with many drugs being reported to affect PD-relevant intracellular processes. This approach offers an expedited route to the clinic, given that pharmacokinetic and safety data are potentially already available. In terms of better symptomatic therapies that are also regenerative, gene therapies and cell-based treatments are beginning to enter clinical trials, and developments in other neurosurgical strategies such as more nuanced deep brain stimulation approaches mean that the landscape of PD treatment is likely to evolve considerably over the coming years. In this review, we provide an overview of the novel therapeutic approaches that are close to, or are already in, clinical trials.

Cell Therapies for Spinal Cord Injury: Trends and Challenges of Current Clinical Trials

Cell therapies have the potential to revolutionize the treatment of spinal cord injury. Basic research has progressed significantly in recent years, with a plethora of cell types now reaching early-phase human clinical trials, offering new strategies to repair the spinal cord. However, despite initial enthusiasm for preclinical and early-phase clinical trials, there has been a notable hiatus in the translation of cell therapies to routine clinical practice. Here, we review cell therapies that have reached clinical trials for spinal cord injury, providing a snapshot of all registered human trials and a summary of all published studies. Of registered trials, the majority have used autologous cells and approximately a third have been government funded, a third industry sponsored, and a third funded by university or healthcare systems. A total of 37 cell therapy trials have been published, primarily using stem cells, although a smaller number have used Schwann cells or olfactory ensheathing cells. Significant challenges remain for cell therapy trials in this area, including achieving stringent regulatory standards, ensuring appropriately powered efficacy trials, and establishing sustainable long-term funding. However, cell therapies hold great promise for human spinal cord repair and future trials must continue to capitalize on the exciting developments emerging from preclinical studies.

Restoring Function to Dopaminergic Neurons: Progress in the Development of Cell-Based Therapies for Parkinson's Disease

There is escalating interest in cell-based therapies to restore lost dopamine inputs in Parkinson's disease. This is based upon the rationale that implanting dopamine progenitors into the striatum can potentially improve dopamine-responsive motor symptoms. A rich body of data describing clinical trials of previous cell transplantation exists. These have included multiple cell sources for transplantation including allogeneic (human embryonic mesencephalic tissue, retinal pigment epithelial cells) and autologous (carotid body, adrenal medullary tissue) cells, as well as xenotransplantation. However, there are multiple limitations related to these cell sources, including availability of adequate numbers of cells for transplant, heterogeneity within cells transplanted, imprecisely defined mechanisms of action, and poor cell survival after transplantation in some cases. Nonetheless, evidence has accrued from a subset of trials to support the rationale for such a regenerative approach. Recent rapid advances in stem cell technology may now overcome these prior limitations. For example, dopamine neuron precursor cells for transplant can be generated from induced pluripotent cells and human embryonic stem cells. The benefits of these innovative approaches include: the possibility of scalability; a high degree of quality control; and improved understanding of mechanisms of action with rigorous preclinical testing. In this review, we focus on the potential for cell-based therapies in Parkinson's disease to restore the function of dopaminergic neurons, we critically review previous attempts to harness such strategies, we discuss potential benefits and predicted limitations, and we address how previous roadblocks may be overcome to bring a cell-based approach to the clinic.

Promissory and protective imaginaries of regenerative medicine: Expectations work and scenario maintenance of disease research charities in the United Kingdom

This article draws upon recent scholarship on technoscientific imaginaries and the sociology of technology expectations to reveal the mediating roles played by a number of disease-focused research charities in the United Kingdom. We examine the expectations they deal with about regenerative medicine research, and how they develop strategies to support and 'protect' potential medical scenarios for new therapies for dread diseases. In so doing, we develop and detail a concept of scenario maintenance to denote the strategic discursive and practical work of preserving stakeholders' faith in specific disease research pathways in the face of obstacles. Semi-structured in-depth interviews (N = 10) of research managers at nine research charities were qualitatively analysed, alongside a variety of charities' documentary data. Our analysis yielded three themes: managing and moderating media expectations; specifying expectations about disease-specific appropriateness of regenerative medicine; and maintaining scenarios of possible pathways for future success taking challenges into account.

Stimulation of L-type calcium channels increases tyrosine hydroxylase and dopamine in ventral midbrain cells induced from somatic cells

Making high‐quality dopamine (DA)‐producing cells for basic biological or small molecule screening studies is critical for the development of novel therapeutics for disorders of the ventral midbrain. Currently, many ventral midbrain assays have low signal‐to‐noise ratio due to low levels of cellular DA and the rate‐limiting enzyme of DA synthesis, tyrosine hydroxylase (TH), hampering discovery efforts. Using intensively characterized ventral midbrain cells derived from human skin, which demonstrate calcium pacemaking activity and classical electrophysiological properties, we show that an L‐type calcium agonist can significantly increase TH protein levels and DA content and release. Live calcium imaging suggests that it is the immediate influx of calcium occurring simultaneously in all cells that drives this effect. Genome‐wide expression profiling suggests that L‐type calcium channel stimulation has a significant effect on specific genes related to DA synthesis and affects expression of L‐type calcium receptor subunits from the CACNA1 and CACNA2D families. Together, our findings provide an advance in the ability to increase DA and TH levels to improve the accuracy of disease modeling and small molecule screening for disorders of the ventral midbrain, including Parkinson's disease.

Strategies for the Treatment of Parkinson's Disease: Beyond Dopamine

Parkinson’s disease (PD) is the second-leading cause of dementia and is characterized by a progressive loss of dopaminergic neurons in the substantia nigra alongside the presence of intraneuronal α-synuclein-positive inclusions. Therapies to date have been directed to the restoration of the dopaminergic system, and the prevention of dopaminergic neuronal cell death in the midbrain. This review discusses the physiological mechanisms involved in PD as well as new and prospective therapies for the disease. The current data suggest that prevention or early treatment of PD may be the most effective therapeutic strategy. New advances in the understanding of the underlying mechanisms of PD predict the development of more personalized and integral therapies in the years to come. Thus, the development of more reliable biomarkers at asymptomatic stages of the disease, and the use of genetic profiling of patients will surely permit a more effective treatment of PD.

GDNF-expressing macrophages restore motor functions at a severe late-stage, and produce long-term neuroprotective effects at an early-stage of Parkinson's disease in transgenic Parkin Q311X(A) mice

There is an unmet medical need in the area of Parkinson's disease (PD) to develop novel therapeutic approaches that can stop and reverse the underlying mechanisms responsible for the neuronal death. We previously demonstrated that systemically administered autologous macrophages transfected ex vivo to produce glial cell line-derived neurotrophic factor (GDNF) readily migrate to the mouse brain with acute toxin-induced neuroinflammation and ameliorate neurodegeneration in PD mouse models. We hypothesized that the high level of cytokines due to inflammatory process attracted GDNF-expressing macrophages and ensured targeted drug delivery to the PD brain. Herein, we validated a therapeutic potential of GDNF-transfected macrophages in a transgenic Parkin Q311X(A) mice with slow progression and mild brain inflammation. Systemic administration of GDNF-macrophages at a severe late stage of the disease leaded to a near complete restoration of motor functions in Parkin Q311X(A) mice and improved brain tissue integrity with healthy neuronal morphology. Furthermore, intravenous injections of GDNF-macrophages at an early stage of disease resulted in potent sustained therapeutic effects in PD mice for more than a year after the treatment. Importantly, multiple lines of evidence for therapeutic efficacy were observed including: diminished neuroinflammation and α-synuclein aggregation, increased survival of dopaminergic neurons, and improved locomotor functions. In summary, GDNF-transfected macrophages represent a promising therapeutic strategy for PD at both late- and early-stages of the disease.

Cannabinoid Actions on Neural Stem Cells: Implications for Pathophysiology

With the increase of life expectancy, neurodegenerative disorders are becoming not only a health but also a social burden worldwide. However, due to the multitude of pathophysiological disease states, current treatments fail to meet the desired outcomes. Therefore, there is a need for new therapeutic strategies focusing on more integrated, personalized and effective approaches. The prospect of using neural stem cells (NSC) as regenerative therapies is very promising, however several issues still need to be addressed. In particular, the potential actions of pharmacological agents used to modulate NSC activity are highly relevant. With the ongoing discussion of cannabinoid usage for medical purposes and reports drawing attention to the effects of cannabinoids on NSC regulation, there is an enormous, and yet, uncovered potential for cannabinoids as treatment options for several neurological disorders, specifically when combined with stem cell therapy. In this manuscript, we review in detail how cannabinoids act as potent regulators of NSC biology and their potential to modulate several neurogenic features in the context of pathophysiology.

The Genomic Health of Human Pluripotent Stem Cells: Genomic Instability and the Consequences on Nuclear Organization

Human pluripotent stem cells (hPSCs) are increasingly used for cell-based regenerative therapies worldwide, with embryonic and induced pluripotent stem cells as potential treatments for debilitating and chronic conditions, such as age-related macular degeneration, Parkinson's disease, spinal cord injuries, and type 1 diabetes. However, with the level of genomic anomalies stem cells generate in culture, their safety may be in question. Specifically, hPSCs frequently acquire chromosomal abnormalities, often with gains or losses of whole chromosomes. This review discusses how important it is to efficiently and sensitively detect hPSC aneuploidies, to understand how these aneuploidies arise, consider the consequences for the cell, and indeed the individual to whom aneuploid cells may be administered.

Evidence-Based Evaluation of the Ethics of Sham Surgery for Parkinson's Disease

The stated purpose of sham or placebo surgery is to enable the implementation of surgical placebo-controlled trials (SPTs) for evaluating the safety and efficacy of surgical interventions. Exposing the participants to the burdens and harms of sham surgery has been justified on the grounds of the absolute necessity for controlling large placebo effects and observer bias, assumed to be associated with surgical procedures. In the present review, we argue that evidence obtained from SPTs of cellular therapies for the treatment of Parkinson's disease (PD) has failed to demonstrate either large and consistent placebo effects or decisive methodological advantages for relying on sham surgical controls. We outline several alternative assessment strategies and designs available to establish the efficacy of cellular therapies. It is concluded that the evidence evaluated in the present analysis indicated that use of sham surgery in the context of developing novel surgical procedures for PD is not necessary, and therefore, unethical under a utilitarian model.

Differentiation of adult human mesenchymal stem cells into dopaminergic neurons

The striatal dopamine (DA) deficiency is known as the main cause of the clinical picture of Parkinson’s disease (PD). The disease is a progressive degeneration of dopaminergic neurons in the striatum. The treatment of PD is based on compensation for the brain’s supply of DA lost by drug therapy, deep brain stimulation, surgery, gene and cell therapies. Clinical studies have focused on the utility of stem cell-based therapies in PD. Embryonic and mesenchymal stem cells (MSCs) are widely used. Recently, human adipose derived stem cells (hADSCs) have been considered as a suitable source of tissue for this purpose. In this project, hADSCs differentiated into dopaminergic neurons and the specificity of the cell preparations was examined. Human adipose tissues were collected from healthy volunteers undergoing liposuction and hADSCs were isolated by collagenase-based enzymatic method. Flow cytometry was performed using the surface cluster of differentiation (CD) markers to confirm the cell typical properties. Then hADSCs were differentiated to dopaminergic neurons in neurobasal medium in the presence of differentiation factors and confirmed by immunocytochemistry via neuronal and dopaminergic markers. The isolated hADSCs were cultured and identified by the expression of MSCs surface markers including CD90, and CD44. These cells did not express hematopoietic surface markers such as CD45 and CD14. Differentiated cells express neuronal marker NeuN and dopaminergic marker tyrosine hydroxylase (TH). It is concluded that hADSCs can be easily taken from the patient’s own body and differentiated into dopaminergic cells having a lower risk of transplant rejection.

Pluripotent Stem Cells for Modelling and Cell Therapy of Parkinson's Disease

Studying pathogenesis of neurodegenerative diseases, including Parkinson's disease (PD), requires adequate disease models. The available patient's material is limited to biological fluids and post mortem brain samples. Disease modeling and drug screening can be done in animal models, although this approach has its own limitations, since laboratory animals do not suffer from many neurodegenerative diseases, including PD. The use of neurons obtained by targeted differentiation from induced pluripotent stem cells (iPSCs) with known genetic mutations, as well as from carriers of sporadic forms of the disease, will allow to elucidate new components of the molecular mechanisms of neurodegeneration. Such neuronal cultures can also serve as unique models for testing neuroprotective compounds and monitoring neurodegenerative changes against a background of various therapeutic interventions. In the future, dopaminergic neurons differentiated from iPSCs can be used for cell therapy of PD.

How to design preclinical studies in nanomedicine and cell therapy to maximize the prospects of clinical translation

The clinical translation of promising products, technologies and interventions from the disciplines of nanomedicine and cell therapy has been slow and inefficient. In part, translation has been hampered by suboptimal research practices that propagate biases and hinder reproducibility. These include the publication of small and underpowered preclinical studies, suboptimal study design (in particular, biased allocation of experimental groups, experimenter bias and lack of necessary controls), the use of uncharacterized or poorly characterized materials, poor understanding of the relevant biology and mechanisms, poor use of statistics, large between-model heterogeneity, absence of replication, lack of interdisciplinarity, poor scientific training in study design and methods, a culture that does not incentivize transparency and sharing, poor or selective reporting, misaligned incentives and rewards, high costs of materials and protocols, and complexity of the developed products, technologies and interventions. In this Perspective, we discuss special manifestations of these problems in nanomedicine and in cell therapy, and describe mitigating strategies. Progress on reducing bias and enhancing reproducibility early on ought to enhance the translational potential of biomedical findings and technologies.

Accomplishments and challenges in stem cell imaging in vivo

Stem cell therapies have demonstrated promising preclinical results, but very few applications have reached the clinic owing to safety and efficacy concerns. Translation would benefit greatly if stem cell survival, distribution and function could be assessed in vivo post-transplantation, particularly in patients. Advances in molecular imaging have led to extraordinary progress, with several strategies being deployed to understand the fate of stem cells in vivo using magnetic resonance, scintigraphy, PET, ultrasound and optical imaging. Here, we review the recent advances, challenges and future perspectives and opportunities in stem cell tracking and functional assessment, as well as the advantages and challenges of each imaging approach.

Human Trials of Stem Cell-Derived Dopamine Neurons for Parkinson's Disease: Dawn of a New Era

Stem cell-based therapies for Parkinson's disease are moving into a new and exciting era, with several groups pursuing clinical trials with pluripotent stem cell (PSC)-derived dopamine neurons. As many groups have ongoing or completed GMP-level cell manufacturing, we highlight key clinical translation considerations from our recent fourth GForce-PD meeting.

Are We There Yet? How and When Specific Biotechnologies Will Improve Human Health

Patient X: A 67-year-old Caucasian man slips on a patch of ice. He has abrasions to his hands and has sustained significant damage to his hip. At the emergency room, he informs clinicians he takes atorvastatin, metformin, and glimepiride to treat hypertension and Type 2 Diabetes Mellitus (T2DM). X-rays reveal a fractured hip, which will require total hip replacement surgery.

Pluripotent stem cell-based therapy for Parkinson's disease: Current status and future prospects

Parkinson's disease (PD) is one of the most common neurodegenerative disorders, which affects about 0.3% of the general population. As the population in the developed world ages, this creates an escalating burden on society both in economic terms and in quality of life for these patients and for the families that support them. Although currently available pharmacological or surgical treatments may significantly improve the quality of life of many patients with PD, these are symptomatic treatments that do not slow or stop the progressive course of the disease. Because motor impairments in PD largely result from loss of midbrain dopamine neurons in the substantia nigra pars compacta, PD has long been considered to be one of the most promising target diseases for cell-based therapy. Indeed, numerous clinical and preclinical studies using fetal cell transplantation have provided proof of concept that cell replacement therapy may be a viable therapeutic approach for PD. However, the use of human fetal cells as a standardized therapeutic regimen has been fraught with fundamental ethical, practical, and clinical issues, prompting scientists to explore alternative cell sources. Based on groundbreaking establishments of human embryonic stem cells and induced pluripotent stem cells, these human pluripotent stem cells have been the subject of extensive research, leading to tremendous advancement in our understanding of these novel classes of stem cells and promising great potential for regenerative medicine. In this review, we discuss the prospects and challenges of human pluripotent stem cell-based cell therapy for PD.

Why has adult hippocampal neurogenesis had so little impact on psychiatry?

Hippocampal neurogenesis continues throughout adult life and potentially plays a crucial role in mood and cognitive disorders. We summarise the preclinical insights and potential translational steps that could be taken to investigate the role and importance of this phenomenon in disease and health in humans. Declaration of interest None.

Assessing the Efficacy of Cell Transplantation for Parkinson's Disease: A Patient-Centered Approach

BACKGROUND

Evidence from a growing number of preclinical studies indicate that recently discovered stem cell lines may be translated into viable cellular therapies for people with Parkinson's disease.

OBJECTIVES

In a brief but critical review, we examine the use of primary and secondary outcome measures currently used to evaluate the efficacy of cellular therapies.

METHODS

The current practice of relying on a single primary outcome measure does not appear to provide the evidence required for demonstrating the robust, life-changing recovery anticipated with the successful implementation of cellular therapies.

RESULTS

We propose a 360-degree assessment protocol, which includes co-primary and composite outcome measures to provide accurate and comprehensive evidence of treatment efficacy, from the perspectives of both the researchers and the patients.

Indications and prospects of neural transplantation for chronic neurological diseases

PURPOSE OF REVIEW

The replacement of damaged cells in the central nervous system (CNS) affected by degenerative disorders represents an attractive therapeutic strategy. The advent of stem cell technology may offer the possibility of generating a large number of renewable, specifically differentiated cells to potentially cure large cohorts of patients. In this review, we discuss current knowledge and issues involved in neural cell transplantation. The most important preclinical and clinical results of cellular transplantation applied to Parkinson's, Huntington's disease and amyotrophic lateral sclerosis will be summarized.

RECENT FINDINGS

Cellular transplantation is emerging as a possible therapy for a variety of incurable neurological disorders. The disorders that will primarily take advantage from neural stem cell grafting are those involving a well defined cell population in a restricted area of the CNS. Several clinical trials have been initiated to assess safety and efficacy of different stem cell-derived products, and promising results have been obtained for disorders such as Parkinson's disease. However, several scientific questions remain unanswered. Among these, the impact of the immunological interaction between host and graft in the particular environment of the CNS still requires additional investigations.

SUMMARY

Several chronic neurological disorders appear to be amenable to cell regenerative therapies. However, safety, efficacy and immunological issues will need to be carefully evaluated beforehand.

Cell Therapy for Parkinson's Disease

Cell therapy for Parkinson's disease (PD) began in 1979 with the transplantation of fetal rat dopamine-containing neurons that improved motor abnormalities in the PD rat model with good survival of grafts and axonal outgrowth. Thirty years have passed since the 2 clinical trials using cell transplantation for PD patients were first reported. Recently, cell therapy is expected to develop as a realistic treatment option for PD patients owing to the advancement of biotechnology represented by pluripotent stem cells. Medication using levodopa, surgery including deep brain stimulation, and rehabilitation have all been established as current therapeutic strategies. Strong therapeutic effects have been demonstrated by these treatment methods, but they have been unable to stop the progression of the disease. Fortunately, cell therapy might be a key for true neurorestoration. This review article describes the historical development of cell therapy for PD, the current status of cell therapy, and the future direction of this treatment method.

Stem cells and stroke-how glowing neurons illuminate new paths

A reliable method of cell tracing is essential in evaluating potential therapeutic procedures based on stem cell transplantation. Here we present data collected using neural stem cells isolated from a transgenic mouse line Thy1-YFP. When transplanted into a stroke affected brain these cells give rise to neurons that express a fluorescent signal which can be used for their detection and tracing. Observed processes were compared with those taking place during normal embryonic neurogenesis as well as during in vitro differentiation. Since the same neurogenic patterns were observed, we confirm that neural stem cell transplantation fits well into the paradigm of neuronal birth and differentiation.

Preparation, characterization, and banking of clinical-grade cells for neural transplantation: Scale up, fingerprinting, and genomic stability of stem cell lines

Parkinson's disease is a complex and progressive neurodegenerative condition that is characterized by the severe loss of midbrain dopaminergic (mDA) neurons, which innervate the striatum. Cell transplantation therapies to rebuild this dopaminergic network have been attempted for over 30 years. The most promising outcomes were observed when human fetal mesencephalic tissue was used as the source of cells for transplantation. However, reliance on terminations for a Parkinson's therapy presents significant logistical and ethical hurdles. An alternative source of transplantable mDA neurons is urgently needed, and the solution may come from human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs). Protocols to differentiate hESCs/iPSCs toward mDA neurons are now robust and efficient, and upon grafting the cells rescue preclinical animal models of Parkinson's disease. The challenge now is to apply Good Manufacturing Practice (GMP) to the academic discoveries and protocols to produce clinical-grade transplantable mDA cells. Major technical and logistical considerations include (i) source of hESC or iPSC line, (ii) GMP compliance of the differentiation protocol and all reagents, (iii) characterization of the cell product in terms of identity, safety, and efficacy, (iv) characterization of genomic state and stability, and (v) banking of a transplantation-ready cell product. Approaches and solutions to these challenges are reviewed here.

Parkinson disease

Parkinson disease is the second-most common neurodegenerative disorder that affects 2-3% of the population ≥65 years of age. Neuronal loss in the substantia nigra, which causes striatal dopamine deficiency, and intracellular inclusions containing aggregates of α-synuclein are the neuropathological hallmarks of Parkinson disease. Multiple other cell types throughout the central and peripheral autonomic nervous system are also involved, probably from early disease onwards. Although clinical diagnosis relies on the presence of bradykinesia and other cardinal motor features, Parkinson disease is associated with many non-motor symptoms that add to overall disability. The underlying molecular pathogenesis involves multiple pathways and mechanisms: α-synuclein proteostasis, mitochondrial function, oxidative stress, calcium homeostasis, axonal transport and neuroinflammation. Recent research into diagnostic biomarkers has taken advantage of neuroimaging in which several modalities, including PET, single-photon emission CT (SPECT) and novel MRI techniques, have been shown to aid early and differential diagnosis. Treatment of Parkinson disease is anchored on pharmacological substitution of striatal dopamine, in addition to non-dopaminergic approaches to address both motor and non-motor symptoms and deep brain stimulation for those developing intractable L-DOPA-related motor complications. Experimental therapies have tried to restore striatal dopamine by gene-based and cell-based approaches, and most recently, aggregation and cellular transport of α-synuclein have become therapeutic targets. One of the greatest current challenges is to identify markers for prodromal disease stages, which would allow novel disease-modifying therapies to be started earlier.

Bringing Neural Cell Therapies to the Clinic: Past and Future Strategies

Cell replacement therapy in the nervous system has a rich history, with ∼40 years of research and ∼30 years of clinical experience. There is compelling evidence that appropriate cells can integrate and function in the dysfunctioning human nervous system, but the clinical results are mixed in practice. A number of factors conspire to vary patient outcome: the indication, cell source, patient selection, and team performing transplantation are all variables that can affect efficacy. Most early clinical trials have used fetal cells, a limited cell source that resists scale and standardization. Direct fetal cell transplantation creates significant challenges to commercialization that is the ultimate goal of an effective cell therapy. One approach to help scale and standardize fetal cell preparations is the expansion of neural cells in vitro. Expansion is achieved by transformation or through the application of mitogens before cryopreservation. Recently, neural cells derived from pluripotent stem cells have provided a scalable alternative. Pluripotent stem cells are desirable for manufacturing but present alternative concerns and manufacturing obstacles. All cell sources require robust and reproducible manufacturing to make nervous system cell replacement therapy an option for patients. Here, we discuss the challenges and opportunities for cell replacement in the nervous system. In this review, we give an overview of completed and ongoing neural cell transplantation clinical trials, and we discuss the challenges and opportunities for future cell replacement trials with a particular focus on pluripotent stem cell-derived therapies.

GFORCE-PD still going strong in 2016

In 2014, a new initiative was undertaken by groups working on plans for the transplantation of stem-cell-based derived dopaminergic neurons for treating Parkinson’s disease patients. This GForce-PD group held its annual meeting on 18–19 April 2016 in Chicago at Rush University to discuss their progress and the challenges that the translation of this experimental therapy still faces. Over 2 days, the key issues were discussed around the cell lines that will be used, the differentiation protocols, preclinical testing, GMP-adaptation, and cell manufacturing to allow first in human clinical trials, which are anticipated to start in 2017–2018. GForce-PD members also discussed how they can improve outreach and be of better service to the Parkinson's disease (PD) community and help them to make the best possible decisions when pursuing stem cell treatments.

Protein aggregation, misfolding and consequential human neurodegenerative diseases

Proteins are major components of the biological functions in a cell. Biology demands that a protein must fold into its stable three-dimensional structure to become functional. In an unfavorable cellular environment, protein may get misfolded resulting in its aggregation. These conformational disorders are directly related to the tissue damage resulting in cellular dysfunction giving rise to different diseases. This way, several neurodegenerative diseases such as Alzheimer, Parkinson Huntington diseases and amyotrophic lateral sclerosis are caused. Misfolding of the protein is prevented by innate molecular chaperones of different classes. It is envisaged that work on this line is likely to translate the knowledge into the development of possible strategies for early diagnosis and efficient management of such related human diseases. The present review deals with the human neurodegenerative diseases caused due to the protein misfolding highlighting pathomechanisms and therapeutic intervention.

Surgical Treatment of Levodopa-induced Dyskinesia in Parkinson's Disease

The treatment of motor manifestations of Parkinson's disease (PD) is essentially a trade-off between adequate relief of motor symptoms and prevention and control of motor complications, particularly levodopa-induced dyskinesia (LID). Progression of PD is paralleled by a progressive difficulty in achieving the balance. Functional neurosurgical procedures provide sustained relief of LID in carefully selected patients when further tailoring of medical therapy fails to achieve this goal. Though deep brain stimulation (DBS) has superseded lesioning surgeries, pallidotomy still has a role in those patients in whom DBS is not feasible for financial or other reasons.

Regenerative Medicine: Advances from Developmental to Degenerative Diseases

Chronic tissue and organ failure caused by an injury, disease, ageing or congenital defects represents some of the most complex therapeutic challenges and poses a significant financial healthcare burden. Regenerative medicine strategies aim to fulfil the unmet clinical need by restoring the normal tissue function either through stimulating the endogenous tissue repair or by using transplantation strategies to replace the missing or defective cells. Stem cells represent an essential pillar of regenerative medicine efforts as they provide a source of progenitors or differentiated cells for use in cell replacement therapies. Whilst significant leaps have been made in controlling the stem cell fates and differentiating them to cell types of interest, transitioning bespoke cellular products from an academic environment to off-the-shelf clinical treatments brings about a whole new set of challenges which encompass manufacturing, regulatory and funding issues. Notwithstanding the need to resolve such issues before cell replacement therapies can benefit global healthcare, mounting progress in the field has highlighted regenerative medicine as a realistic prospect for treating some of the previously incurable conditions.