Preclinical quality, safety, and efficacy of a human embryonic stem cell-derived product for the treatment of Parkinson's disease, STEM-PD

Functional recovery through the plastic adaptation of organoid grafts in cortical tissue

The lack of effective therapeutic options for patients suffering from neurological impairments related to acquired brain damage requires novel translational strategies, among which transplantation of neural tissue is receiving strong attention. One of the most recent developments involves the implantation of brain organoid models, derived from embryonic or induced pluripotent stem cells, into damaged rodent cortices. While this approach is gaining popularity, the extent of graft integration within the host tissue remains poorly understood. This review aims to examine whether xenotransplanting organoids into cortical tissue induces functional recovery and plastic adaptation to the damaged implantation sites. Physiological indications of grafted organoid plasticity and integration into the host included viability, corticogenesis, vascularisation, growth, and the development of area-specific morphological identities. The functional integration into host neural circuitry has been probed by tracing of axonal projection growth according to implantation sites, but also through observations of spontaneous, stimulus evoked, and selectively tuned activity of grafted neurons. Finally, some studies also investigated whether the engraftment procedure facilitated behavioural recovery in tasks requiring motor, memory, or reward-seeking functions. Overall, organoid grafts show signs of progressive anatomical, functional, and behaviourally-relevant integration within the damaged host cortices. Yet, further investigation is necessary before this transplantation approach can be actually translated into a robust method to achieve functional restoration in patients suffering from brain damage.

CD200-based cell sorting results in homogeneous transplantable striatal neuroblasts for human cell therapy for Huntington's disease

Neurodegenerative diseases are characterized by selective loss of neurons. Cell replacement therapies are the most promising therapeutic strategies to restore the neuronal functions lost during these neurodegenerative processes. However, cell replacement-based clinical trials for Huntington's (HD) and Parkinson's diseases (PD) failed due to the large heterogeneity of the samples. Here, we identify CD200 as a cell surface marker for human striatal neuroblasts (NBs) using massively parallel single-cell RNA sequencing. Next, we set up a CD200-based immunomagnetic sorting pipeline that allows high-yield enrichment of human striatal NBs from in vitro differentiation of human pluripotent stem cells (hPSCs). We also show that sorted CD200-positive cells are striatal projection neuron (SPN)-committed NBs which survive upon intra-striatal transplantation in adult mice with no evidence of graft overgrowth in vivo. In conclusion, we implemented a new CD200 cell selection strategy that reduces the heterogeneity and batch-to-batch variation and potentially decreases the teratogenic risk of hPSC-based cell therapy for neurodegenerative diseases.

Mechanical Forces Guide Axon Growth through the Nigrostriatal Pathway in an Organotypic Model

Reconstructing the nigrostriatal pathway is one of the major challenges in cell replacement therapies for Parkinson's disease due to the lack of enabling technologies capable of guiding the reinnervation of dopaminergic precursors transplanted into the substantia nigra toward the striatum. This paper examines nano-pulling, as a technology to enable the remote manipulation of axonal growth. Specifically, an organotypic model consisting of co-cultures of the substantia nigra and the striatum is developed to demonstrate that when cortical neural progenitors are transplanted into the substantia nigra, nano-pulling can guide and enhance the elongation of neural projections toward the striatum. To provide additional evidence, induced pluripotent stem cell-derived dopaminergic progenitor neurospheres are generated and it is shown that nano-pulling can induce guided growth and promote the maturation of their neural processes. Altogether, this study demonstrates the potential of nano-pulling as an emerging technique to promote directed reinnervation within the central nervous system.

The TransEuro open-label trial of human fetal ventral mesencephalic transplantation in patients with moderate Parkinson's disease

Transplantation of human fetal ventral mesencephalic tissue in individuals with Parkinson's disease has yielded clinical benefits but also side effects, such as graft-induced dyskinesias. The open-label TransEuro trial ( NCT01898390 ) was designed to determine whether this approach could be further developed into a clinically useful treatment. Owing to poor availability of human fetal ventral mesencephalic tissue, only 11 individuals were grafted at two centers using the same tissue preparation protocol but different implantation devices. No overall clinical effect was seen for the primary endpoint 3 years after grafting. No major graft-induced dyskinesias were seen, but we observed differences in outcome related to transplant device and/or site. Mean dopamine uptake improved at 18 months in seven individuals according to [18F]fluorodopa positron emission tomography imaging but was restored to near-normal levels in only one individual. Our findings highlight the need for a stem cell source of dopamine neurons for potential Parkinson's disease cell therapy and provide critical insights into how such clinical studies should be approached.

A cloaked human stem-cell-derived neural graft capable of functional integration and immune evasion in rodent models

Human pluripotent stem cell (hPSC)-derived therapies are a realistic possibility for numerous disorders, including Parkinson's disease. While generating replacement neurons is achievable, immunosuppressive drug challenges, to prevent rejection, remain. Here we adopted a hPSC line (termed H1-FS-8IM), engineered to overexpress 8 immunomodulatory transgenes, to enable transplant immune evasion. In co-cultures, H1-FS-8IM PSC-derived midbrain neurons evaded rejection by T lymphocytes, natural killer cells, macrophages, and dendritic cells. In humanized mice, allogeneic H1-FS-8IM neural grafts evaded rejection, while control hPSC-derived neural grafts evoked activation of human immune cells, elevated inflammatory cytokines in blood and cerebrospinal fluid, and caused spleen and lymph node enlargement. H1-FS-8IM neural grafts retained functionality, reversing motor deficits in Parkinsonian rats. Additional incorporation of a suicide gene into the H1-FS-8IM hPSC line enabled proliferative cell elimination within grafts. Findings demonstrate feasibility of generating a population-wide applicable, safe, off-the-shelf cell product, suitable for treating diseases for which cell-based therapies are a viable option.

Phase I trial of hES cell-derived dopaminergic neurons for Parkinson's disease

Parkinson's disease is a progressive neurodegenerative condition with a considerable health and economic burden1. It is characterized by the loss of midbrain dopaminergic neurons and a diminished response to symptomatic medical or surgical therapy as the disease progresses2. Cell therapy aims to replenish lost dopaminergic neurons and their striatal projections by intrastriatal grafting. Here, we report the results of an open-label phase I clinical trial (NCT04802733) of an investigational cryopreserved, off-the-shelf dopaminergic neuron progenitor cell product (bemdaneprocel) derived from human embryonic stem (hES) cells and grafted bilaterally into the putamen of patients with Parkinson's disease. Twelve patients were enrolled sequentially in two cohorts-a low-dose (0.9 million cells, n = 5) and a high-dose (2.7 million cells, n = 7) cohort-and all of the participants received one year of immunosuppression. The trial achieved its primary objectives of safety and tolerability one year after transplantation, with no adverse events related to the cell product. At 18 months after grafting, putaminal 18Fluoro-DOPA positron emission tomography uptake increased, indicating graft survival. Secondary and exploratory clinical outcomes showed improvement or stability, including improvement in the Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS) Part III OFF scores by an average of 23 points in the high-dose cohort. There were no graft-induced dyskinesias. These data demonstrate safety and support future definitive clinical studies.

Current Applications of Human Pluripotent Stem Cells in Neuroscience Research and Cell Transplantation Therapy for Neurological Disorders

Many neurological diseases involving tissue damage cannot be treated with drug-based approaches, and the inaccessibility of human brain samples further hampers the study of these diseases. Human pluripotent stem cells (PSCs), including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), provide an excellent model for studying neural development and function. PSCs can be differentiated into various neural cell types, providing a renewal source of functional human brain cells. Therefore, PSC-derived neural cells are increasingly used for multiple applications, including neurodevelopmental and neurotoxicological studies, neurological disease modeling, drug screening, and regenerative medicine. In addition, the neural cells generated from patient iPSCs can be used to study patient-specific disease signatures and progression. With the recent advances in genome editing technologies, it is possible to remove the disease-related mutations in the patient iPSCs to generate corrected iPSCs. The corrected iPSCs can differentiate into neural cells with normal physiological functions, which can be used for autologous transplantation. This review highlights the current progress in using PSCs to understand the fundamental principles of human neurodevelopment and dissect the molecular mechanisms of neurological diseases. This knowledge can be applied to develop better drugs and explore cell therapy options. We also discuss the basic requirements for developing cell transplantation therapies for neurological disorders and the current status of the ongoing clinical trials.

Phase I/II trial of iPS-cell-derived dopaminergic cells for Parkinson's disease

Parkinson's disease is caused by the loss of dopamine neurons, causing motor symptoms. Initial cell therapies using fetal tissues showed promise but had complications and ethical concerns1-5. Pluripotent stem (PS) cells emerged as a promising alternative for developing safe and effective treatments6. In this phase I/II trial at Kyoto University Hospital, seven patients (ages 50-69) received bilateral transplantation of dopaminergic progenitors derived from induced PS (iPS) cells. Primary outcomes focused on safety and adverse events, while secondary outcomes assessed motor symptom changes and dopamine production for 24 months. There were no serious adverse events, with 73 mild to moderate events. Patients' anti-parkinsonian medication doses were maintained unless therapeutic adjustments were required, resulting in increased dyskinesia. Magnetic resonance imaging showed no graft overgrowth. Among six patients subjected to efficacy evaluation, four showed improvements in the Movement Disorder Society Unified Parkinson's Disease Rating Scale part III OFF score, and five showed improvements in the ON scores. The average changes of all six patients were 9.5 (20.4%) and 4.3 points (35.7%) for the OFF and ON scores, respectively. Hoehn-Yahr stages improved in four patients. Fluorine-18-L-dihydroxyphenylalanine (18F-DOPA) influx rate constant (Ki) values in the putamen increased by 44.7%, with higher increases in the high-dose group. Other measures showed minimal changes. This trial (jRCT2090220384) demonstrated that allogeneic iPS-cell-derived dopaminergic progenitors survived, produced dopamine and did not form tumours, therefore suggesting safety and potential clinical benefits for Parkinson's disease.

Chimeric brain models: Unlocking insights into human neural development, aging, diseases, and cell therapies

Human-rodent chimeric brain models serve as a unique platform for investigating the pathophysiology of human cells within a living brain environment. These models are established by transplanting human tissue- or human pluripotent stem cell (hPSC)-derived macroglial, microglial, or neuronal lineage cells, as well as cerebral organoids, into the brains of host animals. This approach has opened new avenues for exploring human brain development, disease mechanisms, and regenerative processes. Here, we highlight recent advancements in using chimeric models to study human neural development, aging, and disease. Additionally, we explore the potential applications of these models for studying human glial cell-replacement therapies, studying in vivo human glial-to-neuron reprogramming, and harnessing single-cell omics and advanced functional assays to uncover detailed insights into human neurobiology. Finally, we discuss strategies to enhance the precision and translational relevance of these models, expanding their impact in stem cell and neuroscience research.

An immunomodulatory encapsulation system to deliver human iPSC-derived dopaminergic neuron progenitors for Parkinson's disease treatment

Parkinson's disease is a neurodegenerative condition associated with the progressive loss of dopaminergic neurons. This leads to neurological impairments with heightening severity and is globally increasing in prevalence due to population ageing. Cell transplantation has demonstrated significant promise in altering the disease course in the clinic, and stem cell-derived grafts are being investigated. Current clinical protocols involve systemic immunosuppression to prevent graft rejection, which could potentially be avoided by encapsulating the therapeutic cells in a locally immunosuppressive biomaterial matrix before delivery. Here we report the progression of an immunomodulatory encapsulation system employing ultrapure alginate hydrogel beads alongside tacrolimus-loaded microparticles in the encapsulation of dopaminergic neuron progenitors derived from human induced pluripotent stem cells (hiPSCs). The hiPSC-derived progenitors were characterised and displayed robust viability after encapsulation within alginate beads, producing dopamine as they matured in vitro. The encapsulation system effectively reduced T cell activation (3-fold) and protected progenitors from cytotoxicity in vitro. The alginate bead diameter was optimised using microfluidics to yield spherical and monodisperse hydrogels with a median size of 215.6 ± 0.5 μm, suitable for delivery to the brain through a surgical cannula. This technology has the potential to advance cell transplantation by locally protecting grafts from the host immune system.

Cell-based regenerative and rejuvenation strategies for treating neurodegenerative diseases

Neurodegenerative diseases including Alzheimer's and Parkinson's disease are age-related disorders which severely impact quality of life and impose significant societal burdens. Cellular senescence is a critical factor in these disorders, contributing to their onset and progression by promoting permanent cell cycle arrest and reducing cellular function, affecting various types of cells in brain. Recent advancements in regenerative medicine have highlighted "R3" strategies-rejuvenation, regeneration, and replacement-as promising therapeutic approaches for neurodegeneration. This review aims to critically analyze the role of cellular senescence in neurodegenerative diseases and organizes therapeutic approaches within the R3 regenerative medicine paradigm. Specifically, we examine stem cell therapy, direct lineage reprogramming, and partial reprogramming in the context of R3, emphasizing how these interventions mitigate cellular senescence and counteracting aging-related neurodegeneration. Ultimately, this review seeks to provide insights into the complex interplay between cellular senescence and neurodegeneration while highlighting the promise of cell-based regenerative strategies to address these debilitating conditions.

Advances in clinical translation of stem cell-based therapy in neurological diseases

Stem cell-based therapies have raised considerable interest to develop regenerative treatment for neurological disorders with high disability. In this review, we focus on recent preclinical and clinical evidence of stem cell therapy in the treatment of degenerative neurological diseases and discuss different cell types, delivery routes and biodistribution of stem cell therapy. In addition, recent advances of mechanistic insights of stem cell therapy, including functional replacement by exogenous cells, immunomodulation and paracrine effects of stem cell therapies are also demonstrated. Finally, we also highlight the adjunction approaches that has been implemented to augment their reparative function, survival and migration to target specific tissue, including stem cell preconditioning, genetical engineering, co-transplantation and combined therapy.

Incretin-based therapeutics for the treatment of neurodegenerative diseases

Neurodegenerative diseases (NDDs) represent a heterogeneous group of disorders characterized by progressive neuronal loss, which results in significant deficits in memory, cognition, motor skills, and sensory functions. As the prevalence of NDDs rises, there is an urgent unmet need for effective therapies. Current drug development approaches primarily target single pathological features of the disease, which could explain the limited efficacy observed in late-stage clinical trials. Originally developed for the treatment of obesity and diabetes, incretin-based therapies, particularly long-acting GLP-1 receptor (GLP-1R) agonists and GLP-1R-gastric inhibitory polypeptide receptor (GIPR) dual agonists, are emerging as promising treatments for NDDs. Despite limited conclusive preclinical evidence, their pleiotropic ability to reduce neuroinflammation, enhance neuronal energy metabolism and promote synaptic plasticity positions them as potential disease-modifying NDD interventions. In anticipation of results from larger clinical trials, continued advances in next-generation incretin mimetics offer the potential for improved brain access and enhanced neuroprotection, paving the way for incretin-based therapies as a future cornerstone in the management of NDDs.

Sox9 and nuclear factor I transcription factors regulate the timing of neurogenesis and ependymal maturation in dopamine progenitors

Correct timing of neurogenesis is crucial for generating the correct number and subtypes of glia and neurons in the embryo, and for preventing tumours and stem cell depletion in the adults. Here, we analyse how the midbrain dopamine (mDA) neuron progenitors transition into cell cycle arrest (G0) and begin to mature into ependymal cells. Comparison of mDA progenitors from different embryonic stages revealed upregulation of the genes encoding Sox9 and nuclear factor I transcription factors during development. Their conditional inactivation in the early embryonic midbrain led to delayed G0 entry and ependymal maturation in the entire midbrain ventricular zone, reduced gliogenesis and increased generation of neurons, including mDA neurons. In contrast, their inactivation in late embryogenesis did not result in mitotic re-entry, suggesting that these factors are necessary for G0 induction, but not for its maintenance. Our characterisation of adult ependymal cells by single-cell RNA sequencing and histology show that mDA-progenitor-derived cells retain several progenitor features but also secrete neuropeptides and contact neighbouring cells and blood vessels, indicating that these cells may form part of the circumventricular organ system.

Patterning effects of FGF17 and cAMP on generation of dopaminergic progenitors for cell replacement therapy in Parkinson's disease

Cell replacement therapies using human pluripotent stem cell-derived ventral midbrain (VM) dopaminergic (DA) progenitors are currently in clinical trials for treatment of Parkinson's disease (PD). Recapitulating developmental patterning cues, such as fibroblast growth factor 8 (FGF8), secreted at the midbrain-hindbrain boundary (MHB), is critical for the in vitro production of authentic VM DA progenitors. Here, we explored the application of alternative MHB-secreted FGF-family members, FGF17 and FGF18, for VM DA progenitor patterning. We show that while FGF17 and FGF18 both recapitulated VM DA progenitor patterning events, FGF17 induced expression of key VM DA progenitor markers at higher levels than FGF8 and transplanted FGF17-patterned progenitors fully reversed motor deficits in a rat PD model. Early activation of the cAMP pathway mimicked FGF17-induced patterning, although strong cAMP activation came at the expense of EN1 expression. In summary, we identified FGF17 as a promising alternative FGF candidate for robust VM DA progenitor patterning.

Pre-clinical safety and efficacy of human induced pluripotent stem cell-derived products for autologous cell therapy in Parkinson's disease

Human induced pluripotent stem cell (hiPSC)-derived midbrain dopaminergic cells (mDACs) represent a promising source for autologous cell therapy in Parkinson's disease (PD), but standardized regulatory criteria are essential for clinical translation. In this pre-clinical study, we generated multiple clinical-grade hiPSC lines from freshly biopsied fibroblasts of four sporadic PD patients using episomal reprogramming and differentiated them into mDACs using a refined 21-day protocol. Rigorous evaluations included whole-genome/exome sequencing, RNA sequencing, and in vivo studies, including a 39-week Good Laboratory Practice-compliant mouse safety study. While mDACs from all lines met safety criteria, mDACs from one patient failed to improve rodent behavioral outcomes, underscoring inter-individual variability. Importantly, in vitro assessments did not reliably predict in vivo efficacy, identifying dopaminergic fiber density as a key efficacy criterion. These findings support comprehensive quality control guidelines for autologous cell therapy and pave the way for a clinical trial with eight sporadic PD patients, scheduled to commence in 2025.

Advancements in PROTAC-based therapies for neurodegenerative diseases

Neurodegenerative diseases are characterized by impairments in movement and cognitive functions. These disorders are frequently associated with the accumulation of misfolded protein aggregates, which present significant challenges for treatment with conventional small-molecule inhibitors. While FDA-approved amyloid-beta-directed antibodies, such as Lecanemab, have recently shown clinical success in modifying disease progression, there are currently no treatments capable of curing neurodegenerative diseases. Emerging technologies like proteolysis-targeting chimeras (PROTACs) offer additional promise by targeting disease-causing proteins for degradation, potentially opening new therapeutic avenues. Recent experiments have demonstrated that PROTACs can specifically target and degrade pathogenic proteins associated with neurodegenerative diseases, thereby offering potential therapeutic avenues. This review discusses the latest advances in employing PROTACs for treating neurodegenerative diseases and delves into the associated challenges and opportunities. Our goal is to provide researchers in drug development with new insights on creating novel PROTACs for therapeutic applications.

Stem Cell-Based Approaches in Parkinson's Disease Research

Parkinson's disease (PD) is a neurodegenerative condition characterized by the loss of midbrain dopaminergic neurons, leading to motor symptoms. While current treatments provide limited relief, they don't alter disease progression. Stem cell technology, involving patient-specific stem cell-derived neurons, offers a promising avenue for research and personalized regenerative therapies. This article reviews the potential of stem cell-based research in PD, summarizing ongoing efforts, their limitations, and introducing innovative research models. The integration of stem cell technology and advanced models promises to enhance our understanding and treatment strategies for PD.

Age-Related Neurodegenerative Diseases: A Stem Cell's Perspective

Neurodegenerative diseases encompass a number of very heterogeneous disorders, primarily characterized by neuronal loss and a concomitant decline in neurological function. Examples of this type of clinical condition are Alzheimer's Disease, Parkinson's Disease, Huntington's Disease and Amyotrophic Lateral Sclerosis. Age has been identified as a major risk in the etiology of these disorders, which explains their increased incidence in developed countries. Unfortunately, despite continued and intensive efforts, no cure has yet been found for any of these diseases; reliable markers that allow for an early diagnosis of the disease and the identification of key molecular events leading to disease onset and progression are lacking. Altered adult neurogenesis appears to precede the appearance of severe symptoms. Given the scarcity of human samples and the considerable differences with model species, increasingly complex human stem-cell-based models are being developed. These are shedding light on the molecular alterations that contribute to disease development, facilitating the identification of new clinical targets and providing a screening platform for the testing of candidate drugs. Moreover, the secretome and other promising features of these cell types are being explored, to use them as replacement cells of high plasticity or as co-adjuvant therapy in combinatorial treatments.

Mapping the global clinical landscape of stem cell therapies for neurological diseases from 1998 to 2023: an analysis based on the Trialtrove database

Stem cell therapies have in many respects revolutionized the way we explore and treat neurological diseases. Characterizing past and ongoing clinical trials using stem cells for neurological diseases will provide important insights for academia, industry and government. Based on the Trialtrove database, we retrospectively analyzed 530 clinical trials initiated by the end of 2023.

iPSC-based cell replacement therapy: from basic research to clinical application

The advancement of induced pluripotent stem cell (iPSC) technology has revolutionized regenerative medicine, enabling breakthroughs in disease modeling, drug discovery, and cell replacement therapies. This review examines the progression of iPSC-based regenerative medicine, focusing on cell replacement therapy and mechanisms like the Replacement Effect, which is crucial for long-term tissue regeneration. Using Parkinson's disease as a key example, it discusses the induction of midbrain dopaminergic neurons from iPSCs and the importance of precise signaling for safety and efficacy. By demonstrating the integration and safety of these cells, animal studies have paved the way for clinical trials. This review highlights the need for strategic collaboration among stakeholders-regulatory authorities, research and medical staff, and industry-to ensure successful clinical applications. iPSC technology's ongoing evolution holds significant promise for broader therapeutic applications and improved patient outcomes.

Regenerating Locus Coeruleus-Norepinephrine (LC-NE) Function: A Novel Approach for Neurodegenerative Diseases

Pathological changes in the locus coeruleus-norepinephrine (LC-NE) neurons, the major source of norepinephrine (NE, also known as noradrenaline) in the brain, are evident during the early stages of neurodegenerative diseases (ND). Research on both human and animal models have highlighted the therapeutic potential of targeting the LC-NE system to mitigate the progression of ND and alleviate associated psychiatric symptoms. However, the early and widespread degeneration of the LC-NE system presents a significant challenge for direct intervention in ND. Recent advances in regenerative cell therapy offer promising new strategies for ND treatment. The regeneration of LC-NE from pluripotent stem cells (PSCs) could significantly broaden the scope of LC-NE-based therapies for ND. In this review, we delve into the fundamental background and physiological functions of LC-NE. Additionally, we systematically examine the evidence and role of the LC-NE system in the neuropathology of ND and psychiatric diseases over recent years. Notably, we focus on the significance of PSCs-derived LC-NE and its potential impact on ND therapy. A deeper understanding and further investigation into the regeneration of LC-NE function could pave the way for practical and effective treatments for ND.

Enhanced yield and subtype identity of hPSC-derived midbrain dopamine neuron by modulation of WNT and FGF18 signaling

While clinical trials are ongoing using human pluripotent stem cell-derived midbrain dopamine (mDA) neuron precursor grafts in Parkinson's disease (PD), current protocols to derive mDA neurons remain suboptimal. In particular, the yield of TH+ mDA neurons after in vivo grafting and the expression of some mDA neuron and subtype-specific markers can be further improved. For example, characterization of mDA grafts by single cell transcriptomics has yielded only a small proportion of mDA neurons and a considerable fraction of contaminating cell populations. Here we present an optimized mDA neuron differentiation strategy that builds on our clinical grade ("Boost") protocol but includes the addition of FGF18 and IWP2 treatment ("Boost+") at the mDA neurogenesis stage. We demonstrate that Boost+ mDA neurons show higher expression of EN1, PITX3 and ALDH1A1. Improvements in both mDA neurons yield and transcriptional similarity to primary mDA neurons is observed both in vitro and in grafts. Furthermore, grafts are enriched in authentic A9 mDA neurons by single nucSeq. Functional studies in vitro demonstrate increased dopamine production and release and improved electrophysiological properties. In vivo analyses show increased percentages of TH+ mDA neurons resulting in efficient rescue of amphetamine induced rotation behavior in the 6-OHDA rat model and rescue of some motor deficits in non-drug induced assays, including the ladder rung assay that is not improved by Boost mDA neurons. The Boost+ conditions present an optimized protocol with advantages for disease modeling and mDA neuron grafting paradigms.

Reconceptualizing Endothelial-to-mesenchymal transition in atherosclerosis: Signaling pathways and prospective targeting strategies

BACKGROUND

The modification of endothelial cells (ECs) biological function under pathogenic conditions leads to the expression of mesenchymal stromal cells (MSCs) markers, defined as endothelial-to-mesenchymal transition (EndMT). Invisible in onset and slow in progression, atherosclerosis (AS) is a potential contributor to various atherosclerotic cardiovascular diseases (ASCVD). By triggering AS, EndMT, the "initiator" of AS, induces the progression of ASCVD such as coronary atherosclerotic heart disease (CHD) and ischemic cerebrovascular disease (ICD), with serious clinical complications such as myocardial infarction (MI) and stroke. In-depth research of the pathomechanisms of EndMT and identification of potential targeted therapeutic strategies hold considerable research value for the prevention and treatment of ASCVD-associated with delayed EndMT. Although previous studies have progressively unraveled the complexity of EndMT and its pathogenicity triggered by alterations in vascular microenvironmental factors, systematic descriptions of the most recent pathogenic roles of EndMT in the progression of AS, targeted therapeutic strategies, and their future research directions are scarce.

AIM OF REVIEW

We aim to provide new researchers with comprehensive knowledge of EndMT in AS. We exhaustively review the latest research advancements in the field and provide a theoretical basis for investigating EndMT, a biological process with sophisticated mechanisms.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review summarized that altered hemodynamics with microenvironmental crosstalk consisting of inflammatory responses or glycolysis, oxidative stress, lactate or acetyl-CoA (Ac-CoA), fatty acid oxidation (FAO), intracellular iron overload, and transcription factors, including ELK1 and STAT3, modulate the EndMT and affect AS progression. In addition, we provide new paradigms for the development of promising therapeutic agents against these disease-causing processes and indicate promising directions and challenges that need to be addressed to elucidate the EndMT process.

Pluripotent stem-cell-derived therapies in clinical trial: A 2025 update

Since the first derivation of human pluripotent stem cells (hPSCs) 27 years ago, technologies to control their differentiation and manufacturing have advanced immensely, enabling increasing numbers of clinical trials with hPSC-derived products. Here, we revew the landscape of interventional hPSC trials worldwide, highlighting available data on clinical safety and efficacy. As of December 2024, we identify 116 clinical trials with regulatory approval, testing 83 hPSC products. The majority of trials are targeting eye, central nervous system, and cancer. To date, more than 1,200 patients have been dosed with hPSC products, accumulating to >1011 clinically administered cells, so far showing no generalizable safety concerns.

Enhancements in Parkinson's Disease Management: Leveraging Levodopa Optimization and Surgical Breakthroughs

Parkinson's disease (PD) is a complex neurological condition caused due to inheritance, environment, and behavior among various other parameters. The onset, diagnosis, course of therapy, and future of PD are thoroughly examined in this comprehensive review. This review also presents insights into pathogenic mechanisms of reactive microgliosis, Lewy bodies, and their functions in the evolution of PD. It addresses interaction complexity with genetic mutations, especially in genes such as UCH-L1, parkin, and α-synuclein, which illuminates changes in the manner dopaminergic cells handle proteins and use proteases. This raises the improved outcomes and life quality for those with PD. Potential treatments for severe PD include new surgical methods like Deep Brain Stimulation (DBS). Further, exploration of non-motor manifestations, such as cognitive impairment, autonomic dysfunction, and others, is covered in this review article. These symptoms have a significant impact on patients' quality of life. Furthermore, one of the emerging therapeutic routes that are being investigated is neuroprotective medicines that aim to prevent the aggregation of α-synuclein and interventions that modify the progression of diseases. The review concludes by stressing the dynamic nature of PD research and the potential game-changing impact of precision medicines on current approaches to therapy.

Age-dependent regenerative mechanisms in the brain

Repairing the adult mammalian brain represents one of the greatest clinical challenges in medicine. Injury to the adult brain often results in substantial loss of neural tissue and permanent functional impairment. In contrast with the adult, during development, the mammalian brain exhibits a remarkable capacity to replace lost cells. A plethora of cell-intrinsic and extrinsic factors regulate the age-dependent loss of regenerative potential in the brain. As the developmental window closes, neural stem cells undergo epigenetic changes, limiting their proliferation and differentiation capacities, whereas, changes in the brain microenvironment pose additional challenges opposing regeneration, including inflammation and gliosis. Therefore, studying the regenerative mechanisms during development and identifying what impairs them with age may provide key insights into how to stimulate regeneration in the brain. Here, we will discuss how the mammalian brain engages regenerative mechanisms upon injury or neuron loss. Moreover, we will describe the age-dependent changes that affect these processes. We will conclude by discussing potential therapeutic approaches to overcome the age-dependent regenerative decline and stimulate regeneration.

The history and status of dopamine cell therapies for Parkinson's disease

Parkinson's disease (PD) is characterized by the loss of the dopaminergic nigrostriatal pathway which has led to the successful development of drug therapies that replace or stimulate this network pharmacologically. Although these drugs work well in the early stages of the disease, over time they produce side effects along with less consistent clinical benefits to the person with Parkinson's (PwP). As such there has been much interest in repairing this pathway using transplants of dopamine neurons. This work which began 50 years ago this September is still ongoing and has now moved to first in human trials using human pluripotent stem cell-derived dopaminergic neurons. The results of these trials are eagerly awaited although proof of principle data has already come from trials using human fetal midbrain dopamine cell transplants. This data has shown that developing dopamine cells when transplanted in the brain of a PwP can survive long term with clinical benefits lasting decades and with restoration of normal dopaminergic innervation in the grafted striatum. In this article, we discuss the history of this field and how this has now led us to the recent stem cell trials for PwP.

TARGET-seq: Linking single-cell transcriptomics of human dopaminergic neurons with their target specificity

Dopaminergic (DA) neurons exhibit significant diversity characterized by differences in morphology, anatomical location, axonal projection pattern, and selective vulnerability to disease. More recently, scRNAseq has been used to map DA neuron diversity at the level of gene expression. These studies have revealed a higher than expected molecular diversity in both mouse and human DA neurons. However, whether different molecular expression profiles correlate with specific functions of different DA neurons or with their classical division into mesolimbic (A10) and nigrostriatal (A9) neurons, remains to be determined. To address this, we have developed an approach termed TARGET-seq (Tagging projections by AAV-mediated RetroGrade Enrichment of Transcriptomes) that links the transcriptional profile of the DA neurons with their innervation of specific target structures in the forebrain. Leveraging this technology, we identify molecularly distinct subclusters of human DA neurons with a clear link between transcriptome and axonal target-specificity, offering the possibility to infer neuroanatomical-based classification to molecular identity and target-specific connectivity. We subsequently used this dataset to identify candidate transcription factors along DA developmental trajectories that may control subtype identity, thus providing broad avenues that can be further explored in the design of next-generation A9 and A10 enriched DA-neurons for drug screening or A9 enriched DA cells for clinical stem cell-based therapies.

The Abnormal Proliferation of Midbrain Dopamine Cells From Human Pluripotent Stem Cells Is Induced by Exposure to the Tumor Microenvironment

AIMS

Tumorigenicity is a significant concern in stem cell-based therapies. However, traditional tumorigenicity tests using animal models often produce inaccurate results. Consequently, a more sensitive method for assessing tumorigenicity is required. This study aimed to enhance sensitivity by exposing functional progenitors derived from human pluripotent stem cells (hPSCs) to the tumor microenvironment (TME) in vitro before transplantation, potentially making them more prone to abnormal proliferation or tumorigenicity.

METHODS

Midbrain dopamine (mDA) cells derived from hPSCs were exposed to the TME by coculturing with medulloblastoma. The cellular characteristics of these cocultured mDA cells were evaluated both in vitro and in vivo, and the mechanisms underlying the observed alterations were investigated.

RESULTS

Our findings demonstrated increased proliferation of cocultured mDA cells both in vitro and in vivo. Moreover, these proliferating cells showed a higher expression of Ki67 and SOX1, suggesting abnormal proliferation. The observed abnormal proliferation in cocultured mDA cells was attributed to the hyperactivation of proliferation-related genes, the JAK/STAT3 pathway, and cytokine stimulation.

CONCLUSION

This study indicates that exposing functional progenitors to the TME in vitro before transplantation can induce abnormal proliferation, thereby increasing the sensitivity of tumorigenicity tests.

A tumorigenicity evaluation platform for cell therapies based on brain organoids

BACKGROUND

Tumorigenicity represents a critical challenge in stem cell-based therapies requiring rigorous monitoring. Conventional approaches for tumorigenicity evaluation are based on animal models and have numerous limitations. Brain organoids, which recapitulate the structural and functional complexity of the human brain, have been widely used in neuroscience research. However, the capacity of brain organoids for tumorigenicity evaluation needs to be further elucidated.

METHODS

A cerebral organoid model produced from human pluripotent stem cells (hPSCs) was employed. Meanwhile, to enhance the detection sensitivity for potential tumorigenic cells, we created a glioblastoma-like organoid (GBM organoid) model from TP53-/-/PTEN-/- hPSCs to provide a tumor microenvironment for injected cells. Midbrain dopamine (mDA) cells from human embryonic stem cells were utilized as a cell therapy product. mDA cells, hPSCs, mDA cells spiked with hPSCs, and immature mDA cells were then injected into the brain organoids and NOD SCID mice. The injected cells within the brain organoids were characterized, and compared with those injected in vivo to evaluate the capability of the brain organoids for tumorigenicity evaluation. Single-cell RNA sequencing was performed to identify the differential gene expression between the cerebral organoids and the GBM organoids.

RESULTS

Both cerebral organoids and GBM organoids supported maturation of the injected mDA cells. The hPSCs and immature mDA cells injected in the GBM organoids showed a significantly higher proliferative capacity than those injected in the cerebral organoids and in NOD SCID mice. Furthermore, the spiked hPSCs were detectable in both the cerebral organoids and the GBM organoids. Notably, the GBM organoids demonstrated a superior capacity to enhance proliferation and pluripotency of spiked hPSCs compared to the cerebral organoids and the mouse model. Kyoto Encyclopedia of Genes and Genomes analysis revealed upregulation of tumor-related metabolic pathways and cytokines in the GBM organoids, suggesting that these factors underlie the high detection sensitivity for tumorigenicity evaluation.

CONCLUSIONS

Our findings suggest that brain organoids could represent a novel and effective platform for evaluating the tumorigenic risk in stem cell-based therapies. Notably, the GBM organoids offer a superior platform that could complement or potentially replace traditional animal-based models for tumorigenicity evaluation.

Lineage tracing of stem cell-derived dopamine grafts in a Parkinson's model reveals shared origin of all graft-derived cells

Stem cell therapies for Parkinson's disease are at an exciting time of development, and several clinical trials have recently been initiated. Human pluripotent stem cells are differentiated into transplantable dopamine (DA) progenitors which are proliferative at the time of grafting and undergo terminal differentiation and maturation in vivo. While the progenitors are homogeneous at the time of transplantation, they give rise to heterogeneous grafts composed not only of therapeutic DA neurons but also of other mature cell types. The mechanisms for graft diversification are unclear. We used single-nucleus RNA-seq and ATAC-seq to profile DA progenitors before transplantation combined with molecular barcode-based tracing to determine origin and shared lineages of the mature cell types in the grafts. Our data demonstrate that astrocytes, vascular leptomeningeal cells, and DA neurons are the main component of the DAergic grafts, originating from a common progenitor that is tripotent at the time of transplantation.

Cell therapy for neurological disorders

Cell therapies for neurological disorders are entering the clinic and present unique challenges and opportunities compared with conventional medicines. They have the potential to replace damaged nervous tissue and integrate into the brain or spinal cord to produce functional effects for the lifetime of the patient, which could revolutionize the way clinicians treat debilitating neurological disorders. The major challenge has been cell sourcing, which historically relied mainly on fetal brain tissue. This has largely been overcome with the advent of pluripotent stem cell technology and the ability to make almost any cell of the nervous system at scale. Furthermore, advances in gene editing now allow the generation of genetically modified cells that could perform better and evade the immune system. With all the remarkable new approaches to treat neurological disorders, we take a critical look at the state of current clinical trials and how challenges may be overcome with the evolving technology and innovation occurring in the stem cell field.

Ready-to-use iPSC-derived microglia progenitors for the treatment of CNS disease in mouse models of neuropathic mucopolysaccharidoses

Mucopolysaccharidoses are inherited metabolic disorders caused by the deficiency in lysosomal enzymes required to break down glycosaminoglycans. Accumulation of glycosaminoglycans leads to progressive, systemic degenerative disease. The central nervous system is particularly affected, resulting in developmental delays, neurological regression, and early mortality. Current treatments fail to adequately address neurological defects. Here we explore the potential of human induced pluripotent stem cell (hiPSC)-derived microglia progenitors as a one-time, allogeneic off-the-shelf cell therapy for several mucopolysaccharidoses (MPS). We show that hiPSC-derived microglia progenitors, possessing normal levels of lysosomal enzymes, can deliver functional enzymes into four subtypes of MPS knockout cell lines through mannose-6-phosphate receptor-mediated endocytosis in vitro. Additionally, our findings indicate that a single administration of hiPSC-derived microglia progenitors can reduce toxic glycosaminoglycan accumulation and prevent behavioral deficits in two different animal models of MPS. Durable efficacy is observed for eight months after transplantation. These results suggest a potential avenue for treating MPS with hiPSC-derived microglia progenitors.

Cryogel microcarriers loaded with glial cell line-derived neurotrophic factor enhance the engraftment of primary dopaminergic neurons in a rat model of Parkinson's disease

Objective.Cryogel microcarriers made of poly(ethylene glycol) diacrylate and 3-sulfopropyl acrylate have the potential to act as delivery vehicles for long-term retention of neurotrophic factors (NTFs) in the brain. In addition, they can potentially enhance stem cell-derived dopaminergic (DAergic) cell replacement strategies for Parkinson's disease (PD), by addressing the limitations of variable survival and poor differentiation of the transplanted precursors due to neurotrophic deprivation post-transplantation in the brain. In this context, to develop a proof-of-concept, the aim of this study was to determine the efficacy of glial cell line-derived NTF (GDNF)-loaded cryogel microcarriers by assessing their impact on the survival of, and reinnervation by, primary DAergic grafts after intra-striatal delivery in Parkinsonian rat brains.Approach.Rat embryonic day 14 ventral midbrain cells were transplanted into the 6-hydroxydopamine-lesioned striatum either alone, or with GDNF, or with unloaded cryogel microcarriers, or with GDNF-loaded cryogel microcarriers.Post-mortem, GDNF and tyrosine hydroxylase immunostaining were used to identify retention of the delivered GDNF within the implanted cryogel microcarriers, and to identify the transplanted DAergic neuronal cell bodies and fibres in the brains, respectively.Main results.We found an intact presence of GDNF-stained cryogel microcarriers in graft sites, indicating their ability for long-term retention of the delivered GDNF up to 4 weeks in the brain. This resulted in an enhanced survival (1.9-fold) of, and striatal reinnervation (density & volume) by, the grafted DAergic neurons, in addition to an enhanced sprouting of fibres within graft sites.Significance.This data provides an important proof-of-principle for the beneficial effects of neurotrophin-loaded cryogel microcarriers on engraftment of cells in the context of cell replacement therapy in PD. For clinical translation, further studies will be needed to assess the impact of cryogel microcarriers on the survival and differentiation of stem cell-derived DAergic precursors in Parkinsonian rat brains.

Advancing Parkinson's disease treatment: cell replacement therapy with neurons derived from pluripotent stem cells

The motor symptoms of Parkinson's disease (PD) are caused by the progressive loss of dopamine neurons from the substantia nigra. There are currently no treatments that can slow or reverse the neurodegeneration. To restore the lost neurons, international groups have initiated clinical trials using human embryonic or induced pluripotent stem cells (PSCs) to derive dopamine neuron precursors that are used as transplants to replace the lost neurons. Proof-of-principle experiments in the 1980s and 1990s showed that grafts of fetal ventral mesencephalon, which contains the precursors of the substantial nigra, could, under rare circumstances, reverse symptoms of the disease. Improvements in PSC technology and genomics have inspired researchers to design clinical trials using PSC-derived dopamine neuron precursors as cell replacement therapy for PD. We focus here on 4 such first-in-human clinical trials that have begun in the US, Europe, and Japan. We provide an overview of the sources of PSCs and the methods used to generate cells for transplantation. We discuss pros and cons of strategies for allogeneic, immune-matched, and autologous approaches and novel methods for overcoming rejection by the immune system. We consider challenges for safety and efficacy of the cells for durable engraftment, focusing on the genomics-based quality control methods to assure that the cells will not become cancerous. Finally, since clinical trials like these have never been undertaken before, we comment on the value of cooperation among rivals to contribute to advancements that will finally provide relief for the millions suffering from the symptoms of PD.

Bioreactor-produced iPSCs-derived dopaminergic neuron-containing neural microtissues innervate and normalize rotational bias in a dose-dependent manner in a Parkinson rat model

A breadth of preclinical studies now support the rationale of pluripotent stem cell-derived cell replacement therapies to alleviate motor symptoms in Parkinsonian patients. Replacement of the primary dysfunctional cell population in the disease, i.e. the A9 dopaminergic neurons, is the major focus of these therapies. To achieve this, most therapeutical approaches involve grafting single-cell suspensions of DA progenitors. However, most cells die during the transplantation process, as cells face anoïkis. One potential solution to address this challenge is to graft solid preparations, i.e. adopting a 3D format. Cryopreserving such a format remains a major hurdle and is not exempt from causing delays in the time to effect, as observed with cryopreserved single-cell DA progenitors. Here, we used a high-throughput cell-encapsulation technology coupled with bioreactors to provide a 3D culture environment enabling the directed differentiation of hiPSCs into neural microtissues. The proper patterning of these neural microtissues into a midbrain identity was confirmed using orthogonal methods, including qPCR, RNAseq, flow cytometry and immunofluorescent microscopy. The efficacy of the neural microtissues was demonstrated in a dose-dependent manner using a Parkinsonian rat model. The survival of the cells was confirmed by post-mortem histological analysis, characterised by the presence of human dopaminergic neurons projecting into the host striatum. The work reported here is the first bioproduction of a cell therapy for Parkinson's disease in a scalable bioreactor, leading to a full behavioural recovery 16 weeks after transplantation using cryopreserved 3D format.

Organoids and chimeras: the hopeful fusion transforming traumatic brain injury research

Research in the field of traumatic brain injury has until now heavily relied on the use of animal models to identify potential therapeutic approaches. However, a long series of failed clinical trials has brought many scientists to question the translational reliability of pre-clinical results obtained in animals. The search for an alternative to conventional models that better replicate human pathology in traumatic brain injury is thus of the utmost importance for the field. Recently, orthotopic xenotransplantation of human brain organoids into living animal models has been achieved. This review summarizes the existing literature on this new method, focusing on its potential applications in preclinical research, both in the context of cell replacement therapy and disease modelling. Given the obvious advantages of this approach to study human pathologies in an in vivo context, we here critically review its current limitations while considering its possible applications in traumatic brain injury research.

Past, present, and future of cell replacement therapy for parkinson's disease: a novel emphasis on host immune responses

Parkinson's disease (PD) stands as the second most common neurodegenerative disorder after Alzheimer's disease, and its prevalence continues to rise with the aging global population. Central to the pathophysiology of PD is the specific degeneration of midbrain dopamine neurons (mDANs) in the substantia nigra. Consequently, cell replacement therapy (CRT) has emerged as a promising treatment approach, initially supported by various open-label clinical studies employing fetal ventral mesencephalic (fVM) cells. Despite the initial favorable results, fVM cell therapy has intrinsic and logistical limitations that hinder its transition to a standard treatment for PD. Recent efforts in the field of cell therapy have shifted its focus towards the utilization of human pluripotent stem cells, including human embryonic stem cells and induced pluripotent stem cells, to surmount existing challenges. However, regardless of the transplantable cell sources (e.g., xenogeneic, allogeneic, or autologous), the poor and variable survival of implanted dopamine cells remains a major obstacle. Emerging evidence highlights the pivotal role of host immune responses following transplantation in influencing the survival of implanted mDANs, underscoring an important area for further research. In this comprehensive review, building upon insights derived from previous fVM transplantation studies, we delve into the functional ramifications of host immune responses on the survival and efficacy of grafted dopamine cells. Furthermore, we explore potential strategic approaches to modulate the host immune response, ultimately aiming for optimal outcomes in future clinical applications of CRT for PD.

Stem cell therapeutics and gene therapy for neurologic disorders

Rapid advances in biological knowledge and technological innovation have greatly advanced the fields of stem cell and gene therapies to combat a broad spectrum of neurologic disorders. Researchers are currently exploring a variety of stem cell types (e.g., embryonic, progenitor, induced pluripotent) and various transplantation strategies, each with its own advantages and drawbacks. Similarly, various gene modification techniques (zinc finger, TALENs, CRISPR-Cas9) are employed with various delivery vectors to modify underlying genetic contributors to neurologic disorders. While these two individual fields continue to blaze new trails, it is the combination of these technologies which enables genetically engineered stem cells and vastly increases investigational and therapeutic opportunities. The capability to culture and expand stem cells outside the body, along with their potential to correct genetic abnormalities in patient-derived cells or enhance cells with extra gene products, unleashes the full biological potential for innovative, multifaceted approaches to treat complex neurological disorders. In this review, we provide an overview of stem cell and gene therapies in the context of neurologic disorders, highlighting recent advances and current shortcomings, and discuss prospects for future therapies in clinical settings.

Pre-clinical evaluation of clinically relevant iPS cell derived neuroepithelial stem cells as an off-the-shelf cell therapy for spinal cord injury

Preclinical transplantations using human neuroepithelial stem (NES) cells in spinal cord injury models have exhibited promising results and demonstrated cell integration and functional improvement in transplanted animals. Previous studies have relied on the generation of research grade cell lines in continuous culture. Using fresh cells presents logistic hurdles for clinical transition regarding time and resources for maintaining high quality standards. In this study, we generated a good manufacturing practice (GMP) compliant human iPS cell line in GMP clean rooms alongside a research grade iPS cell line which was produced using standardized protocols with GMP compliant chemicals. These two iPS cell lines were differentiated into human NES cells, from which six batches of cell therapy doses were produced. The doses were cryopreserved, thawed on demand and grafted in a rat spinal cord injury model. Our findings demonstrate that NES cells can be directly grafted post-thaw with high cell viability, maintaining their cell identity and differentiation capacity. This opens the possibility of manufacturing off-the-shelf cell therapy products. Moreover, our manufacturing process yields stable cell doses with minimal batch-to-batch variability, characterized by consistent expression of identity markers as well as similar viability of cells across the two iPS cell lines. These cryopreserved cell doses exhibit sustained viability, functionality, and quality for at least 2 years. Our results provide proof of concept that cryopreserved NES cells present a viable alternative to transplanting freshly cultured cells in future cell therapies and exemplify a platform from which cell formulation can be optimized and facilitate the transition to clinical trials.

C. Tsang I. Exploring stem cell frontiers: definitions, challenges, and perspectives for regenerative medicine

Each year, the European Summer School on Stem Cell Biology and Regenerative Medicine (SCSS) attracts early-career researchers and actively practicing clinicians who specialise in stem cell and regenerative biology. The 16th edition of this influential course took place from 12th to 19th September 2023 on the charming Greek island of Spetses. Focusing on important concepts and recent advances in stem cells, the distinguished faculty included experts spanning the spectrum from fundamental research to clinical trials to market-approved therapies. Alongside an academically intensive programme that bridges the various contexts of stem cell research, delegates were encouraged to critically address relevant questions in stem cell biology and medicine, including broader societal implications. Here, we present a comprehensive overview and key highlights from the SCSS 2023.

Advancements in Human Embryonic Stem Cell Research: Clinical Applications and Ethical Issues

BACKGROUND

The development and use of human embryonic stem cells (hESCs) in regenerative medicine have been revolutionary, offering significant advancements in treating various diseases. These pluripotent cells, derived from early human embryos, are central to modern biomedical research. However, their application is mired in ethical and regulatory complexities related to the use of human embryos.

METHOD

This review utilized key databases such as ClinicalTrials.gov, EU Clinical Trials Register, PubMed, and Google Scholar to gather recent clinical trials and studies involving hESCs. The focus was on their clinical application in regenerative medicine, emphasizing clinical trials and research directly involving hESCs.

RESULTS

Preclinical studies and clinical trials in various areas like ophthalmology, neurology, endocrinology, and reproductive medicine have demonstrated the versatility of hESCs in regenerative medicine. These studies underscore the potential of hESCs in treating a wide array of conditions. However, the field faces ethical and regulatory challenges, with significant variations in policies and perspectives across different countries.

CONCLUSION

The potential of hESCs in regenerative medicine is immense, offering new avenues for treating previously incurable diseases. However, navigating the ethical, legal, and regulatory landscapes is crucial for the continued advancement and responsible application of hESC research in the medical field. Considering both scientific potential and ethical implications, a balanced approach is essential for successfully integrating hESCs into clinical practice.

Clinical translation of pluripotent stem cell-based therapies: successes and challenges

The translational stem cell research field has progressed immensely in the past decade. Development and refinement of differentiation protocols now allows the generation of a range of cell types, such as pancreatic β-cells and dopaminergic neurons, from human pluripotent stem cells (hPSCs) in an efficient and good manufacturing practice-compliant fashion. This has led to the initiation of several clinical trials using hPSC-derived cells to replace lost or dysfunctional cells, demonstrating evidence of both safety and efficacy. Here, we highlight successes from some of the hPSC-based trials reporting early signs of efficacy and discuss common challenges in clinical translation of cell therapies.

Focused ultrasound gene delivery for the treatment of neurological disorders

The transformative potential of gene therapy has been demonstrated in humans. However, there is an unmet need for non-invasive targeted gene delivery and regulation in the treatment of brain disorders. Transcranial focused ultrasound (FUS) has gained tremendous momentum to address these challenges. FUS non-invasively modulates brain cells and their environment, and is a powerful tool to facilitate gene delivery across the blood-brain barrier (BBB) with millimeter precision and promptly regulate transgene expression. This review highlights technical aspects of FUS-mediated gene therapies for the central nervous system (CNS) and lessons learned from discoveries in other organs. Understanding the possibilities and remaining obstacles of FUS-mediated gene therapy will be necessary to harness remarkable technologies and create life-changing treatments for neurological disorders.

Preparation of Viable Human Neurites for Neurobiological and Neurodegeneration Studies

Few models allow the study of neurite damage in the human central nervous system. We used here dopaminergic LUHMES neurons to establish a culture system that allows for (i) the observation of highly enriched neurites, (ii) the preparation of the neurite fraction for biochemical studies, and (iii) the measurement of neurite markers and metabolites after axotomy. LUHMES-based spheroids, plated in culture dishes, extended neurites of several thousand µm length, while all somata remained aggregated. These cultures allowed an easy microscopic observation of live or fixed neurites. Neurite-only cultures (NOC) were produced by cutting out the still-aggregated somata. The potential application of such cultures was exemplified by determinations of their protein and RNA contents. For instance, the mitochondrial TOM20 protein was highly abundant, while nuclear histone H3 was absent. Similarly, mitochondrial-encoded RNAs were found at relatively high levels, while the mRNA for a histone or the neuronal nuclear marker NeuN (RBFOX3) were relatively depleted in NOC. Another potential use of NOC is the study of neurite degeneration. For this purpose, an algorithm to quantify neurite integrity was developed. Using this tool, we found that the addition of nicotinamide drastically reduced neurite degeneration. Also, the chelation of Ca2+ in NOC delayed the degeneration, while inhibitors of calpains had no effect. Thus, NOC proved to be suitable for biochemical analysis and for studying degeneration processes after a defined cut injury.

Development of a Smart Wireless Multisensor Platform for an Optogenetic Brain Implant

Implantable cell replacement therapies promise to completely restore the function of neural structures, possibly changing how we currently perceive the onset of neurodegenerative diseases. One of the major clinical hurdles for the routine implementation of stem cell therapies is poor cell retention and survival, demanding the need to better understand these mechanisms while providing precise and scalable approaches to monitor these cell-based therapies in both pre-clinical and clinical scenarios. This poses significant multidisciplinary challenges regarding planning, defining the methodology and requirements, prototyping and different stages of testing. Aiming toward an optogenetic neural stem cell implant controlled by a smart wireless electronic frontend, we show how an iterative development methodology coupled with a modular design philosophy can mitigate some of these challenges. In this study, we present a miniaturized, wireless-controlled, modular multisensor platform with fully interfaced electronics featuring three different modules: an impedance analyzer, a potentiostat and an optical stimulator. We show the application of the platform for electrical impedance spectroscopy-based cell monitoring, optical stimulation to induce dopamine release from optogenetically modified neurons and a potentiostat for cyclic voltammetry and amperometric detection of dopamine release. The multisensor platform is designed to be used as an opto-electric headstage for future in vivo animal experiments.

Preclinical and dose-ranging assessment of hESC-derived dopaminergic progenitors for a clinical trial on Parkinson's disease

Human embryonic stem cell (hESC)-derived midbrain dopaminergic (mDA) cell transplantation is a promising therapeutic strategy for Parkinson's disease (PD). Here, we present the derivation of high-purity mDA progenitors from clinical-grade hESCs on a large scale under rigorous good manufacturing practice (GMP) conditions. We also assessed the toxicity, biodistribution, and tumorigenicity of these cells in immunodeficient rats in good laboratory practice (GLP)-compliant facilities. Various doses of mDA progenitors were transplanted into hemi-parkinsonian rats, and a significant dose-dependent behavioral improvement was observed with a minimal effective dose range of 5,000-10,000 mDA progenitor cells. These results provided insights into determining a low cell dosage (3.15 million cells) for human clinical trials. Based on these results, approval for a phase 1/2a clinical trial for PD cell therapy was obtained from the Ministry of Food and Drug Safety in Korea, and a clinical trial for treating patients with PD has commenced.