Challenges and translational considerations of mesenchymal stem/stromal cell therapy for Parkinson's disease

The role of mesenchymal stem cells in cancer and prospects for their use in cancer therapeutics

Mesenchymal stem cells (MSCs) are recruited by malignant tumor cells to the tumor microenvironment (TME) and play a crucial role in the initiation and progression of malignant tumors. This role encompasses immune evasion, promotion of angiogenesis, stimulation of cancer cell proliferation, correlation with cancer stem cells, multilineage differentiation within the TME, and development of treatment resistance. Simultaneously, extensive research is exploring the homing effect of MSCs and MSC-derived extracellular vesicles (MSCs-EVs) in tumors, aiming to design them as carriers for antitumor substances. These substances are targeted to deliver antitumor drugs to enhance drug efficacy while reducing drug toxicity. This paper provides a review of the supportive role of MSCs in tumor progression and the associated molecular mechanisms. Additionally, we summarize the latest therapeutic strategies involving engineered MSCs and MSCs-EVs in cancer treatment, including their utilization as carriers for gene therapeutic agents, chemotherapeutics, and oncolytic viruses. We also discuss the distribution and clearance of MSCs and MSCs-EVs upon entry into the body to elucidate the potential of targeted therapies based on MSCs and MSCs-EVs in cancer treatment, along with the challenges they face.

Effects of mesenchymal stem cell on dopaminergic neurons, motor and memory functions in animal models of Parkinson's disease: a systematic review and meta-analysis

ABSTRACT

Parkinson's disease is characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta, and although restoring striatal dopamine levels may improve symptoms, no treatment can cure or reverse the disease itself. Stem cell therapy has a regenerative effect and is being actively studied as a candidate for the treatment of Parkinson's disease. Mesenchymal stem cells are considered a promising option due to fewer ethical concerns, a lower risk of immune rejection, and a lower risk of teratogenicity. We performed a meta-analysis to evaluate the therapeutic effects of mesenchymal stem cells and their derivatives on motor function, memory, and preservation of dopaminergic neurons in a Parkinson's disease animal model. We searched bibliographic databases (PubMed/MEDLINE, Embase, CENTRAL, Scopus, and Web of Science) to identify articles and included only peer-reviewed in vivo interventional animal studies published in any language through June 28, 2023. The study utilized the random-effect model to estimate the 95% confidence intervals (CI) of the standard mean differences (SMD) between the treatment and control groups. We use the systematic review center for laboratory animal experimentation's risk of bias tool and the collaborative approach to meta-analysis and review of animal studies checklist for study quality assessment. A total of 33 studies with data from 840 Parkinson's disease model animals were included in the meta-analysis. Treatment with mesenchymal stem cells significantly improved motor function as assessed by the amphetamine-induced rotational test. Among the stem cell types, the bone marrow MSCs with neurotrophic factor group showed largest effect size (SMD [95% CI] = -6.21 [-9.50 to -2.93], P = 0.0001, I2 = 0.0 %). The stem cell treatment group had significantly more tyrosine hydroxylase positive dopaminergic neurons in the striatum ([95% CI] = 1.04 [0.59 to 1.49], P = 0.0001, I2 = 65.1 %) and substantia nigra (SMD [95% CI] = 1.38 [0.89 to 1.87], P = 0.0001, I2 = 75.3 %), indicating a protective effect on dopaminergic neurons. Subgroup analysis of the amphetamine-induced rotation test showed a significant reduction only in the intracranial-striatum route (SMD [95% CI] = -2.59 [-3.25 to -1.94], P = 0.0001, I2 = 74.4 %). The memory test showed significant improvement only in the intravenous route (SMD [95% CI] = 4.80 [1.84 to 7.76], P = 0.027, I2 = 79.6 %). Mesenchymal stem cells have been shown to positively impact motor function and memory function and protect dopaminergic neurons in preclinical models of Parkinson's disease. Further research is required to determine the optimal stem cell types, modifications, transplanted cell numbers, and delivery methods for these protocols.

Pericyte derivation and transplantation for blood-CNS barrier reconstitution in CNS disorders

Disruption of the blood-central nervous system barrier (BCB) is increasingly recognized as a pathological factor in diseases and trauma of the central nervous system. Despite the neuropathological impact, current treatment modalities do not target the BCB; strategies to reconstitute the impaired BCB have been restricted to nutritional and dietary remedies. As an integral cell type in the neurovascular unit, pericytes are crucial to the development, maintenance, and repair of the BCB. As such, pericytes are well poised as cellular agents for reconstitution of the impaired BCB. Here, we summarize recent revelations regarding the role of BCB disruption in diseases and trauma of the central nervous system and highlight how pericytes are harnessed to provide targeted therapeutic effect in each case. This review will also address how recent advances in pericyte derivation strategies can serve to overcome practical hurdles in the clinical use of pericytes.

Proteomic analysis and functional validation reveal distinct therapeutic capabilities related to priming of mesenchymal stromal/stem cells with IFN-γ and hypoxia: potential implications for their clinical use

Mesenchymal stromal/stem cells (MSCs) are a heterogeneous population of multipotent cells that can be obtained from various tissues, such as dental pulp, adipose tissue, bone marrow and placenta. MSCs have gained importance in the field of regenerative medicine because of their promising role in cell therapy and their regulatory abilities in tissue repair and regeneration. However, a better characterization of these cells and their products is necessary to further potentiate their clinical application. In this study, we used unbiased high-resolution mass spectrometry-based proteomic analysis to investigate the impact of distinct priming strategies, such as hypoxia and IFN-γ treatment, on the composition and therapeutic functionality of the secretome produced by MSCs derived from the amniotic membrane of the human placenta (hAMSCs). Our investigation revealed that both types of priming improved the therapeutic efficacy of hAMSCs, and these improvements were related to the secretion of functional factors present in the conditioned medium (CM) and exosomes (EXOs), which play crucial roles in mediating the paracrine effects of MSCs. In particular, hypoxia was able to induce a pro-angiogenic, innate immune response-activating, and tissue-regenerative hAMSC phenotype, as highlighted by the elevated production of regulatory factors such as VEGFA, PDGFRB, ANGPTL4, ENG, GRO-γ, IL8, and GRO-α. IFN-γ priming, instead, led to an immunosuppressive profile in hAMSCs, as indicated by increased levels of TGFB1, ANXA1, THBS1, HOMER2, GRN, TOLLIP and MCP-1. Functional assays validated the increased angiogenic properties of hypoxic hAMSCs and the enhanced immunosuppressive activity of IFN-γ-treated hAMSCs. This study extends beyond the direct priming effects on hAMSCs, demonstrating that hypoxia and IFN-γ can influence the functional characteristics of hAMSC-derived secretomes, which, in turn, orchestrate the production of functional factors by peripheral blood cells. This research provides valuable insights into the optimization of MSC-based therapies by systematically assessing and comparing the priming type-specific functional features of hAMSCs. These findings highlight new strategies for enhancing the therapeutic efficacy of MSCs, particularly in the context of multifactorial diseases, paving the way for the use of hAMSC-derived products in clinical practice.

Versatile strategies for adult neurogenesis: avenues to repair the injured brain

Brain injuries due to trauma or stroke are major causes of adult death and disability. Unfortunately, few interventions are effective for post-injury repair of brain tissue. After a long debate on whether endogenous neurogenesis actually happens in the adult human brain, there is now substantial evidence to support its occurrence. Although neurogenesis is usually significantly stimulated by injury, the reparative potential of endogenous differentiation from neural stem/progenitor cells is usually insufficient. Alternatively, exogenous stem cell transplantation has shown promising results in animal models, but limitations such as poor long-term survival and inefficient neuronal differentiation make it still challenging for clinical use. Recently, a high focus was placed on glia-to-neuron conversion under single-factor regulation. Despite some inspiring results, the validity of this strategy is still controversial. In this review, we summarize historical findings and recent advances on neurogenesis strategies for neurorepair after brain injury. We also discuss their advantages and drawbacks, as to provide a comprehensive account of their potentials for further studies.

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.

Use of priming strategies to advance the clinical application of mesenchymal stromal/stem cell-based therapy

Mesenchymal stromal/stem cells (MSCs) have garnered significant attention in the field of regenerative medicine due to their remarkable therapeutic potential. MSCs play a pivotal role in maintaining tissue homeostasis and possess diverse functions in tissue repair and recovery in various organs. These cells are characterized by easy accessibility, few ethical concerns, and adaptability to in vitro cultures, making them a valuable resource for cell therapy in several clinical conditions. Over the years, it has been shown that the true therapeutic power of MSCs lies not in cell engraftment and replacement but in their ability to produce critical paracrine factors, including cytokines, growth factors, and exosomes (EXOs), which modulate the tissue microenvironment and facilitate repair and regeneration processes. Consequently, MSC-derived products, such as conditioned media and EXOs, are now being extensively evaluated for their potential medical applications, offering advantages over the long-term use of whole MSCs. However, the efficacy of MSC-based treatments varies in clinical trials due to both intrinsic differences resulting from the choice of diverse cell sources and non-standardized production methods. To address these concerns and to enhance MSC therapeutic potential, researchers have explored many priming strategies, including exposure to inflammatory molecules, hypoxic conditions, and three-dimensional culture techniques. These approaches have optimized MSC secretion of functional factors, empowering them with enhanced immunomodulatory, angiogenic, and regenerative properties tailored to specific medical conditions. In fact, various priming strategies show promise in the treatment of numerous diseases, from immune-related disorders to acute injuries and cancer. Currently, in order to exploit the full therapeutic potential of MSC therapy, the most important challenge is to optimize the modulation of MSCs to obtain adapted cell therapy for specific clinical disorders. In other words, to unlock the complete potential of MSCs in regenerative medicine, it is crucial to identify the most suitable tissue source and develop in vitro manipulation protocols specific to the type of disease being treated.

Unravelling the Parkinson's puzzle, from medications and surgery to stem cells and genes: a comprehensive review of current and future management strategies

Parkinson's disease (PD) is a neurodegenerative disorder, prevalent in the elderly population. Neuropathological hallmarks of PD include loss of dopaminergic cells in the nigro-striatal pathway and deposition of alpha-synuclein protein in the neurons and synaptic terminals, which lead to a complex presentation of motor and non-motor symptoms. This review focuses on various aspects of PD, from clinical diagnosis to currently accepted treatment options, such as pharmacological management through dopamine replacement and surgical techniques such as deep brain stimulation (DBS). The review discusses in detail the potential of emerging stem cell-based therapies and gene therapies to be adopted as a cure, in contrast to the present symptomatic treatment in PD. The potential sources of stem cells for autologous and allogeneic stem cell therapy have been discussed, along with the progress evaluation of pre-clinical and clinical trials. Even though recent techniques hold great potential to improve the lives of PD patients, we present the importance of addressing the safety, efficacy, ethical, cost, and regulatory concerns before scaling them to clinical use.

Novel Therapeutic Opportunities for Neurodegenerative Diseases with Mesenchymal Stem Cells: The Focus on Modulating the Blood-Brain Barrier

Neurodegenerative disorders encompass a broad spectrum of profoundly disabling situations that impact millions of individuals globally. While their underlying causes and pathophysiology display considerable diversity and remain incompletely understood, a mounting body of evidence indicates that the disruption of blood-brain barrier (BBB) permeability, resulting in brain damage and neuroinflammation, is a common feature among them. Consequently, targeting the BBB has emerged as an innovative therapeutic strategy for addressing neurological disorders. Within this review, we not only explore the neuroprotective, neurotrophic, and immunomodulatory benefits of mesenchymal stem cells (MSCs) in combating neurodegeneration but also delve into their recent role in modulating the BBB. We will investigate the cellular and molecular mechanisms through which MSC treatment impacts primary age-related neurological conditions like Alzheimer's disease, Parkinson's disease, and stroke, as well as immune-mediated diseases such as multiple sclerosis. Our focus will center on how MSCs participate in the modulation of cell transporters, matrix remodeling, stabilization of cell-junction components, and restoration of BBB network integrity in these pathological contexts.

Therapeutic Effect of Human Adipocyte-derived Stem Cell-derived Exosomes on a Transgenic Mouse Model of Parkinson's Disease

BACKGROUND/AIM

Stem cell therapy and regenerative medicine are promising for treating Parkinson's disease (PD) not only for the potential for cell replacement but also for the paracrine effect of stem cell secretion, especially proteins and nucleotide-enriched exosomes. This study investigated the neuroprotective effect of exosomes secreted from human adipocyte-derived stem cells (hADSCs) on PD.

MATERIALS AND METHODS

hADSCs were isolated from the visceral fat tissue of individuals without PD who underwent bariatric surgery and were validated using surface markers and differentiation ability. Exosomes were isolated from the culture medium of hADSCs through serial ultracentrifugation and validated. Condensed exosomes were administered intravenously to 12-week-old MitoPark mice, transgenic parkinsonism mouse model with conditional knockout of mitochondrial transcription factor A in dopaminergic neurons, monthly for 3 months. Motor function, gait, and memory were assessed monthly, and immunohistochemical analysis of neuronal and inflammatory markers was performed at the end of the experiments.

RESULTS

The hADSC-derived exosome-treated mice exhibited better motor function in beam walking and gait analyses than did the untreated mice. In the novel object recognition tests, the exosome-treated mice retained better memory function. Immunohistochemical analysis revealed that although exosome treatment did not prevent the loss of dopaminergic neurons in the substantia nigra of mice, it down-regulated microglial activation and neuroinflammation in the midbrain.

CONCLUSION

hADSC-derived exosomes were neuroprotective in this in vivo mouse model of PD, likely because of their anti-inflammatory effect. Use of hADSC-derived exosomes may offer several beneficial effects in stem cell therapy. Since they can also be produced at an industrial level, they are a promising treatment option for PD and other neurodegenerative diseases.

Mesenchymal Stem Cell-Derived Extracellular Vesicles: An Emerging Diagnostic and Therapeutic Biomolecules for Neurodegenerative Disabilities

Mesenchymal stem cells (MSCs) are a type of versatile adult stem cells present in various organs. These cells give rise to extracellular vesicles (EVs) containing a diverse array of biologically active elements, making them a promising approach for therapeutics and diagnostics. This article examines the potential therapeutic applications of MSC-derived EVs in addressing neurodegenerative disorders such as Alzheimer's disease (AD), multiple sclerosis (MS), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD). Furthermore, the present state-of-the-art for MSC-EV-based therapy in AD, HD, PD, ALS, and MS is discussed. Significant progress has been made in understanding the etiology and potential treatments for a range of neurodegenerative diseases (NDs) over the last few decades. The contents of EVs are carried across cells for intercellular contact, which often results in the control of the recipient cell's homeostasis. Since EVs represent the therapeutically beneficial cargo of parent cells and are devoid of many ethical problems connected with cell-based treatments, they offer a viable cell-free therapy alternative for tissue regeneration and repair. Developing innovative EV-dependent medicines has proven difficult due to the lack of standardized procedures in EV extraction processes as well as their pharmacological characteristics and mechanisms of action. However, recent biotechnology and engineering research has greatly enhanced the content and applicability of MSC-EVs.

Different priming strategies improve distinct therapeutic capabilities of mesenchymal stromal/stem cells: Potential implications for their clinical use

Mesenchymal stromal/stem cells (MSCs) have shown significant therapeutic potential, and have therefore been extensively investigated in preclinical studies of regenerative medicine. However, while MSCs have been shown to be safe as a cellular treatment, they have usually been therapeutically ineffective in human diseases. In fact, in many clinical trials it has been shown that MSCs have moderate or poor efficacy. This inefficacy appears to be ascribable primarily to the heterogeneity of MSCs. Recently, specific priming strategies have been used to improve the therapeutic properties of MSCs. In this review, we explore the literature on the principal priming approaches used to enhance the preclinical inefficacy of MSCs. We found that different priming strategies have been used to direct the therapeutic effects of MSCs toward specific pathological processes. Particularly, while hypoxic priming can be used primarily for the treatment of acute diseases, inflammatory cytokines can be used mainly to prime MSCs in order to treat chronic immune-related disorders. The shift in approach from regeneration to inflammation implies, in MSCs, a shift in the production of functional factors that stimulate regenerative or anti-inflammatory pathways. The opportunity to fine-tune the therapeutic properties of MSCs through different priming strategies could conceivably pave the way for optimizing their therapeutic potential.

Harnessing and honing mesenchymal stem/stromal cells for the amelioration of graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation is a deterministic curative procedure for various hematologic disorders and congenital immunodeficiency. Despite its increased use, the mortality rate for patients undergoing this procedure remains high, mainly due to the perceived risk of exacerbating graft-versus-host disease (GVHD). However, even with immunosuppressive agents, some patients still develop GVHD. Advanced mesenchymal stem/stromal cell (MSC) strategies have been proposed to achieve better therapeutic outcomes, given their immunosuppressive potential. However, the efficacy and trial designs have varied among the studies, and some research findings appear contradictory due to the challenges in characterizing the in vivo effects of MSCs. This review aims to provide real insights into this clinical entity, emphasizing diagnostic, and therapeutic considerations and generating pathophysiology hypotheses to identify research avenues. The indications and timing for the clinical application of MSCs are still subject to debate.

Cellular and Molecular Mechanisms Underly the Combined Treatment of Fasudil and Bone Marrow Derived-Neuronal Stem Cells in a Parkinson's Disease Mouse Model

Bone marrow-derived neural stem cells (BM-NSCs) have shed light on novel therapeutic approaches for PD with the potential to halt or even reverse disease progression. Various strategies have been developed to promote therapeutic efficacy via optimizing implanted cells and the microenvironment of transplantation in the central nervous system (CNS). This current study further proved that the combination of fasudil, a Rho-kinase inhibitor, and BM-NSCs exhibited a synergetic effect on restoring neuron loss in the MPTP-PD mice model. It simultaneously unveiled cellular mechanisms underlying synergistic neuron-protection effects of fasudil and BM-NSCs, which included promoting the proliferation, and migration of endogenous NSCs, and contributing to microglia shift into the M2 phenotype. Corresponding molecular mechanisms were observed, including the inhibition of inflammatory responses, the elevation of neurotrophic factors, and the induction of WNT/β-catenin and PI3K/Akt/mTOR signaling pathways. Our study provides evidence for the co-intervention of BM-NSCs and fasudil as a promising therapeutic method with enhanced efficacy in treating neurodegenerative diseases.

Involvement of aquaporin 5 in Sjögren's syndrome

Sjögren's syndrome (SS) is a chronic autoimmune disease with the pathological hallmark of lymphoplasmacytic infiltration of exocrine glands - more specifically salivary and lacrimal glands - resulting in a diminished production of tears and saliva (sicca syndrome). The pathophysiology underscoring the mechanisms of the sicca symptoms in SS has still yet to be unraveled but recent advances have identified a cardinal role of aquaporin-5 (AQP5) as a key player in saliva secretion as well as salivary gland epithelial cell dysregulation. AQP5 expression and localization are significantly altered in salivary glands from patients and mice models of the disease, shedding light on a putative mechanism accounting for diminished salivary flow. Furthermore, aberrant expression and localization of AQP5 protein partners, such as prolactin-inducible protein and ezrin, may account for altered AQP5 localization in salivary glands from patients suffering from SS and are considered as new players in SS development. This review provides an overview of the role of AQP5 in SS salivary gland epithelial cell dysregulation, focusing on its trafficking and protein-protein interactions.

Mechanism of Mesenchymal Stem Cells as a Multitarget Disease- Modifying Therapy for Parkinson's Disease

Parkinson's disease (PD) is one of the most prevalent neurodegenerative disorders, affecting the basal nuclei, causing impairment of motor and cognitive functions. Loss of dopaminergic (DAergic) neurons or their degeneration and the aggregation of Lewy bodies is the hallmark of this disease. The medications used to treat PD relieve the symptoms and maintain quality of life, but currently, there is no cure. There is a need for the development of therapies that can cease or perhaps reverse neurodegeneration effectively. With the rapid advancements in cell replacement therapy techniques, medical professionals are trying to find a cure by which restoration of dopamine neurotransmitters can occur. Researchers have started focusing on cell-based therapies using mesenchymal stem cells (MSCs) due to their abundance in the body, the ability of proliferation, and immunomodulation. Here we review the MSC-based treatment in Parkinson's disease and the various mechanisms it repairs DAergic neurons in parkinsonian patients.

Nanowired Delivery of Mesenchymal Stem Cells with Antioxidant Compound H-290/51 Reduces Exacerbation of Methamphetamine Neurotoxicity in Hot Environment

Military personnel are often exposed to hot environments either for combat operations or peacekeeping missions. Hot environment is a severe stressful situation leading to profound hyperthermia, fatigue and neurological impairments. To avoid stressful environment, some people frequently use methamphetamine (METH) or other psychostimulants to feel comfortable under adverse situations. Our studies show that heat stress alone induces breakdown of the blood-brain barrier (BBB) and edema formation associated with reduced cerebral blood flow (CBF). On the other hand, METH alone induces hyperthermia and neurotoxicity. These effects of METH are exacerbated at high ambient temperatures as seen with greater breakdown of the BBB and brain pathology. Thus, a combination of METH use at hot environment may further enhance the brain damage-associated behavioral dysfunctions. METH is well known to induce severe oxidative stress leading to brain pathology. In this investigation, METH intoxication at hot environment was examined on brain pathology and to explore suitable strategies to induce neuroprotection. Accordingly, TiO₂-nanowired delivery of H-290/51 (150 mg/kg, i.p.), a potent chain-breaking antioxidant in combination with mesenchymal stem cells (MSCs), is investigated in attenuating METH-induced brain damage at hot environment in model experiments. Our results show that nanodelivery of H-290/51 with MSCs significantly enhanced CBF and reduced BBB breakdown, edema formation and brain pathology following METH exposure at hot environment. These observations are the first to point out that METH exacerbated brain pathology at hot environment probably due to enhanced oxidative stress, and MSCs attenuate these adverse effects, not reported earlier.

Alzheimer's and Parkinson's disease therapies in the clinic

Alzheimer's disease (AD) and Parkinson's disease (PD) are the most prevalent neurodegenerative diseases, affecting millions and costing billions each year in the United States alone. Despite tremendous progress in developing therapeutics that manage the symptoms of these two diseases, the scientific community has yet to develop a treatment that effectively slows down, inhibits, or cures neurodegeneration. To gain a better understanding of the current therapeutic frontier for the treatment of AD and PD, we provide a review on past and present therapeutic strategies for these two major neurodegenerative disorders in the clinical trial process. We briefly recap currently US Food and Drug Administration-approved therapies, and then explore trends in clinical trials across the variables of therapy mechanism of disease intervention, administration route, use of delivery vehicle, and outcome measures, across the clinical phases over time for "Drug" and "Biologic" therapeutics. We then present the success rate of past clinical trials and analyze the intersections in therapeutic approaches for AD and PD, revealing the shift in clinical trials away from therapies targeting neurotransmitter systems that provide symptomatic relief, and towards anti-aggregation, anti-inflammatory, anti-oxidant, and regeneration strategies that aim to inhibit the root causes of disease progression. We also highlight the evolving distribution of the types of "Biologic" therapies investigated, and the slowly increasing yet still severe under-utilization of delivery vehicles for AD and PD therapeutics. We then briefly discuss novel preclinical strategies for treating AD and PD. Overall, this review aims to provide a succinct overview of the clinical landscape of AD and PD therapies to better understand the field's therapeutic strategy in the past and the field's evolution in approach to the present, to better inform how to effectively treat AD and PD in the future.

Co-administration of Nanowired DL-3-n-Butylphthalide (DL-NBP) Together with Mesenchymal Stem Cells, Monoclonal Antibodies to Alpha Synuclein and TDP-43 (TAR DNA-Binding Protein 43) Enhance Superior Neuroprotection in Parkinson's Disease Following Concussive Head Injury

dl-3-n-butylphthalide (dl-NBP) is one of the potent antioxidant compounds that induces profound neuroprotection in stroke and traumatic brain injury. Our previous studies show that dl-NBP reduces brain pathology in Parkinson's disease (PD) following its nanowired delivery together with mesenchymal stem cells (MSCs) exacerbated by concussive head injury (CHI). CHI alone elevates alpha synuclein (ASNC) in brain or cerebrospinal fluid (CSF) associated with elevated TAR DNA-binding protein 43 (TDP-43). TDP-43 protein is also responsible for the pathologies of PD. Thus, it is likely that exacerbation of brain pathology in PD following brain injury may be thwarted using nanowired delivery of monoclonal antibodies (mAb) to ASNC and/or TDP-43. In this review, the co-administration of dl-NBP with MSCs and mAb to ASNC and/or TDP-43 using nanowired delivery in PD and CHI-induced brain pathology is discussed based on our own investigations. Our observations show that co-administration of TiO2 nanowired dl-NBP with MSCs and mAb to ASNC with TDP-43 induced superior neuroprotection in CHI induced exacerbation of brain pathology in PD, not reported earlier.

Mesenchymal stem cell therapy for neurological disorders: The light or the dark side of the force?

Neurological disorders are recognized as major causes of death and disability worldwide. Because of this, they represent one of the largest public health challenges. With awareness of the massive burden associated with these disorders, came the recognition that treatment options were disproportionately scarce and, oftentimes, ineffective. To address these problems, modern research is increasingly looking into novel, more effective methods to treat neurological patients; one of which is cell-based therapies. In this review, we present a critical analysis of the features, challenges, and prospects of one of the stem cell types that can be employed to treat numerous neurological disorders-mesenchymal stem cells (MSCs). Despite the fact that several studies have already established the safety of MSC-based treatment approaches, there are still some reservations within the field regarding their immunocompatibility, heterogeneity, stemness stability, and a range of adverse effects-one of which is their tumor-promoting ability. We additionally examine MSCs' mechanisms of action with respect to in vitro and in vivo research as well as detail the findings of past and ongoing clinical trials for Parkinson's and Alzheimer's disease, ischemic stroke, glioblastoma multiforme, and multiple sclerosis. Finally, this review discusses prospects for MSC-based therapeutics in the form of biomaterials, as well as the use of electromagnetic fields to enhance MSCs' proliferation and differentiation into neuronal cells.

Emerging Perspectives on Gene Therapy Delivery for Neurodegenerative and Neuromuscular Disorders

Neurodegenerative disorders (NDDs), such as Alzheimer's disease (AD) and Parkinson's Disease (PD), are a group of heterogeneous diseases that mainly affect central nervous system (CNS) functions. A subset of NDDs exhibit CNS dysfunction and muscle degeneration, as observed in Gangliosidosis 1 (GM1) and late stages of PD. Neuromuscular disorders (NMDs) are a group of diseases in which patients show primary progressive muscle weaknesses, including Duchenne Muscular Dystrophy (DMD), Pompe disease, and Spinal Muscular Atrophy (SMA). NDDs and NMDs typically have a genetic component, which affects the physiological functioning of critical cellular processes, leading to pathogenesis. Currently, there is no cure or efficient treatment for most of these diseases. More than 200 clinical trials have been completed or are currently underway in order to establish safety, tolerability, and efficacy of promising gene therapy approaches. Thus, gene therapy-based therapeutics, including viral or non-viral delivery, are very appealing for the treatment of NDDs and NMDs. In particular, adeno-associated viral vectors (AAV) are an attractive option for gene therapy for NDDs and NMDs. However, limitations have been identified after systemic delivery, including the suboptimal capacity of these therapies to traverse the blood-brain barrier (BBB), degradation of the particles during the delivery, high reactivity of the patient's immune system during the treatment, and the potential need for redosing. To circumvent these limitations, several preclinical and clinical studies have suggested intrathecal (IT) delivery to target the CNS and peripheral organs via cerebrospinal fluid (CSF). CSF administration can vastly improve the delivery of small molecules and drugs to the brain and spinal cord as compared to systemic delivery. Here, we review AAV biology and vector design elements, different therapeutic routes of administration, and highlight CSF delivery as an attractive route of administration. We discuss the different aspects of neuromuscular and neurodegenerative diseases, such as pathogenesis, the landscape of mutations, and the biological processes associated with the disease. We also describe the hallmarks of NDDs and NMDs as well as discuss current therapeutic approaches and clinical progress in viral and non-viral gene therapy and enzyme replacement strategies for those diseases.

Breakthrough of extracellular vesicles in pathogenesis, diagnosis and treatment of osteoarthritis

Osteoarthritis (OA) is a highly prevalent whole-joint disease that causes disability and pain and affects a patient's quality of life. However, currently, there is a lack of effective early diagnosis and treatment. Although stem cells can promote cartilage repair and treat OA, problems such as immune rejection and tumorigenicity persist. Extracellular vesicles (EVs) can transmit genetic information from donor cells and mediate intercellular communication, which is considered a functional paracrine factor of stem cells. Increasing evidences suggest that EVs may play an essential and complex role in the pathogenesis, diagnosis, and treatment of OA. Here, we introduced the role of EVs in OA progression by influencing inflammation, metabolism, and aging. Next, we discussed EVs from the blood, synovial fluid, and joint-related cells for diagnosis. Moreover, we outlined the potential of modified and unmodified EVs and their combination with biomaterials for OA therapy. Finally, we discuss the deficiencies and put forward the prospects and challenges related to the application of EVs in the field of OA.

Stem cell-based therapy for human diseases

Recent advancements in stem cell technology open a new door for patients suffering from diseases and disorders that have yet to be treated. Stem cell-based therapy, including human pluripotent stem cells (hPSCs) and multipotent mesenchymal stem cells (MSCs), has recently emerged as a key player in regenerative medicine. hPSCs are defined as self-renewable cell types conferring the ability to differentiate into various cellular phenotypes of the human body, including three germ layers. MSCs are multipotent progenitor cells possessing self-renewal ability (limited in vitro) and differentiation potential into mesenchymal lineages, according to the International Society for Cell and Gene Therapy (ISCT). This review provides an update on recent clinical applications using either hPSCs or MSCs derived from bone marrow (BM), adipose tissue (AT), or the umbilical cord (UC) for the treatment of human diseases, including neurological disorders, pulmonary dysfunctions, metabolic/endocrine-related diseases, reproductive disorders, skin burns, and cardiovascular conditions. Moreover, we discuss our own clinical trial experiences on targeted therapies using MSCs in a clinical setting, and we propose and discuss the MSC tissue origin concept and how MSC origin may contribute to the role of MSCs in downstream applications, with the ultimate objective of facilitating translational research in regenerative medicine into clinical applications. The mechanisms discussed here support the proposed hypothesis that BM-MSCs are potentially good candidates for brain and spinal cord injury treatment, AT-MSCs are potentially good candidates for reproductive disorder treatment and skin regeneration, and UC-MSCs are potentially good candidates for pulmonary disease and acute respiratory distress syndrome treatment.

Noncovalent functionalization of carbon nanotubes as a scaffold for tissue engineering

Tissue engineering is one of the hot topics in recent research that needs special requirements. It depends on the development of scaffolds that allow tissue formation with certain characteristics, carbon nanotubes (CNTs)-collagen composite attracted the attention of the researchers with this respect. However, CNTs suffer from low water dispersibility, which hampered their utilization. Therefore, we aim to functionalize CNTs non-covalently with pyrene moiety using an appropriate hydrophilic linker derivatized from polyethylene glycol (PEG) terminated with hydroxyl or carboxyl group to disperse them in water. The functionalization of the CNTs is successfully confirmed by TEM, absorption spectroscopy, TGA, and zeta potential analysis. 3T3 cells-based engineered connective tissues (ECTs) are generated with different concentrations of the functionalized CNTs (f-CNTs). These tissues show a significant enhancement in electrical conductivity at a concentration of 0.025%, however, the cell viability is reduced by about 10 to 20%. All ECTs containing f-CNTs show a significant reduction in tissue fibrosis and matrix porosity relative to the control tissues. Taken together, the developed constructs show great potential for further in vivo studies as engineered tissue.

Therapeutic Mesenchymal Stem/Stromal Cells: Value, Challenges and Optimization

Cellular therapy aims to replace damaged resident cells by restoring cellular and molecular environments suitable for tissue repair and regeneration. Among several candidates, mesenchymal stem/stromal cells (MSCs) represent a critical component of stromal niches known to be involved in tissue homeostasis. In vitro, MSCs appear as fibroblast-like plastic adherent cells regardless of the tissue source. The therapeutic value of MSCs is being explored in several conditions, including immunological, inflammatory and degenerative diseases, as well as cancer. An improved understanding of their origin and function would facilitate their clinical use. The stemness of MSCs is still debated and requires further study. Several terms have been used to designate MSCs, although consensual nomenclature has yet to be determined. The presence of distinct markers may facilitate the identification and isolation of specific subpopulations of MSCs. Regarding their therapeutic properties, the mechanisms underlying their immune and trophic effects imply the secretion of various mediators rather than direct cellular contact. These mediators can be packaged in extracellular vesicles, thus paving the way to exploit therapeutic cell-free products derived from MSCs. Of importance, the function of MSCs and their secretome are significantly sensitive to their environment. Several features, such as culture conditions, delivery method, therapeutic dose and the immunobiology of MSCs, may influence their clinical outcomes. In this review, we will summarize recent findings related to MSC properties. We will also discuss the main preclinical and clinical challenges that may influence the therapeutic value of MSCs and discuss some optimization strategies.

Human Umbilical Cord Mesenchymal Stem Cells Improve Locomotor Function in Parkinson’s Disease Mouse Model Through Regulating Intestinal Microorganisms

Parkinson’s disease (PD) is a progressive neurological disorder characterized by loss of neurons that synthesize dopamine, and subsequent impaired movement. Umbilical cord mesenchymal stem cells (UC-MSCs) exerted neuroprotection effects in a rodent model of PD. However, the mechanism underlying UC-MSC-generated neuroprotection was not fully elucidated. In the present study, we found that intranasal administration of UC-MSCs significantly alleviated locomotor deficits and rescued dopaminergic neurons by inhibiting neuroinflammation in a PD mouse model induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, a toxic agent which selectively destroys nigrostriatal neurons but does not affect dopaminergic neurons elsewhere). Furthermore, UC-MSC treatment altered gut microbiota composition characterized by decreased phylum Proteobacteria, class Gammaproteobacteria, family Enterobacteriaceae, and genus Escherichia-Shigella. In addition, the neurotransmitter dopamine in the striatum and 5-hydroxytryptamine in the colon were also modulated by UC-MSCs. Meanwhile, UC-MSCs significantly maintained intestinal goblet cells, which secrete mucus as a mechanical barrier against pathogens. Furthermore, UC-MSCs alleviate the level of TNF-α and IL-6 as well as the conversion of NF-κB expression in the colon, indicating that inflammatory responses were blocked by UC-MSCs. PICRUSt showed that some pathways including bacterial invasion of epithelial cells, fluorobenzoate degradation, and pathogenic Escherichia coli infection were significantly reversed by UC-MSCs. These data suggest that the beneficial effects were detected following UC-MSC intranasal transplantation in MPTP-treated mice. There is a possible neuroprotective role of UC-MSCs in MPTP-induced PD mice by cross talk between the brain and gut.

Multifactoriality of Parkinson's Disease as Explored Through Human Neural Stem Cells and Their Transplantation in Middle-Aged Parkinsonian Mice

Parkinson's disease (PD) is an age-associated neurodegenerative disorder for which there is currently no cure. Cell replacement therapy is a potential treatment for PD; however, this therapy has more clinically beneficial outcomes in younger patients with less advanced PD. In this study, hVM1 clone 32 cells, a line of human neural stem cells, were characterized and subsequently transplanted in middle-aged Parkinsonian mice in order to examine cell replacement therapy as a treatment for PD. In vitro analyses revealed that these cells express standard dopamine-centered markers as well as others associated with mitochondrial and peroxisome function, as well as glucose and lipid metabolism. Four months after the transplantation of the hVM1 clone 32 cells, striatal expression of tyrosine hydroxylase was minimally reduced in all Parkinsonian mice but that of dopamine transporter was decreased to a greater extent in buffer compared to cell-treated mice. Behavioral tests showed marked differences between experimental groups, and cell transplant improved hyperactivity and gait alterations, while in the striatum, astroglial populations were increased in all groups due to age and a higher amount of microglia were found in Parkinsonian mice. In the motor cortex, nonphosphorylated neurofilament heavy was increased in all Parkinsonian mice. Overall, these findings demonstrate that hVM1 clone 32 cell transplant prevented motor and non-motor impairments and that PD is a complex disorder with many influencing factors, thus reinforcing the idea of novel targets for PD treatment that tend to be focused on dopamine and nigrostriatal damage.

Changes in the Transcriptome Profiles of Human Amnion-Derived Mesenchymal Stromal/Stem Cells Induced by Three-Dimensional Culture: A Potential Priming Strategy to Improve Their Properties

Mesenchymal stromal/stem cells (MSCs) are believed to function in vivo as a homeostatic tool that shows therapeutic properties for tissue repair/regeneration. Conventionally, these cells are expanded in two-dimensional (2D) cultures, and, in that case, MSCs undergo genotypic/phenotypic changes resulting in a loss of their therapeutic capabilities. Moreover, several clinical trials using MSCs have shown controversial results with moderate/insufficient therapeutic responses. Different priming methods were tested to improve MSC effects, and three-dimensional (3D) culturing techniques were also examined. MSC spheroids display increased therapeutic properties, and, in this context, it is crucial to understand molecular changes underlying spheroid generation. To address these limitations, we performed RNA-seq on human amnion-derived MSCs (hAMSCs) cultured in both 2D and 3D conditions and examined the transcriptome changes associated with hAMSC spheroid formation. We found a large number of 3D culture-sensitive genes and identified selected genes related to 3D hAMSC therapeutic effects. In particular, we observed that these genes can regulate proliferation/differentiation, as well as immunomodulatory and angiogenic processes. We validated RNA-seq results by qRT-PCR and methylome analysis and investigation of secreted factors. Overall, our results showed that hAMSC spheroid culture represents a promising approach to cell-based therapy that could significantly impact hAMSC application in the field of regenerative medicine.

Stalling SARS-CoV2 infection with stem cells: can regenerating perinatal tissue mesenchymal stem cells offer a multi-tiered therapeutic approach to COVID-19?

The emergence of COVID-19 has created a major health crisis across the globe. Invasion of SARS-CoV-2 into the lungs causes acute respiratory distress syndrome (ARDS) that result in the damage of lung alveolar epithelial cells. Currently, there is no standard treatment available to treat the disease and the resultant lung scarring is irreversible even after recovery. This has prompted researchers across the globe to focus on developing new therapeutics and vaccines for the treatment and prevention of COVID-19. Mesenchymal stem cells (MSCs) have emerged as an efficient drug screening platform and MSC-derived organoids has found applications in disease modeling and drug discovery. Perinatal tissue derived MSC based cell therapies have been explored in the treatment of various disease conditions including ARDS because of their enhanced regenerative and immunomodulatory properties. The multi-utility properties of MSCs have been described in this review wherein we discuss the potential use of MSC-derived lung organoids in screening of novel therapeutic compounds for COVID-19 and also in disease modeling to better understand the pathogenesis of the disease. This article also summarizes the rationale behind the development of MSC-based cell- and cell-free therapies and vaccines for COVID-19 with a focus on the current progress in this area. With the pandemic raging, an important necessity is to develop novel treatment strategies which will not only alleviate the disease symptoms but also avoid any off-target effects which could further increase post infection sequelae. Naturally occurring mesenchymal stem cells could be the magic bullet which fulfil these criteria.

Steps Toward Standardized In Vitro Assessment of Immunomodulatory Equine Mesenchymal Stromal Cells Before Clinical Application

Inflammation-associated disorders are significant causes of morbidity in horses. Equine single-donor mesenchymal stromal cells (sdMSCs) hold promise as cell-therapy candidates due to their secretory nonprogenitor functions. This has been demonstrated by mononuclear cell suppression assays (MSAs) showing that sdMSCs are blood mononuclear cell (BMC) suppressive in vitro. sdMSCs derived from umbilical cord blood are of clinical interest due to their ease of procurement, multipotency, and immunomodulatory ability. Due to the inherent donor-to-donor heterogeneity of MSCs, the development of robust and easily deployable methods of potency assessment is critical for improving MSCs' predictability in treating inflammatory diseases. This study focuses on the development of robust in vitro potency assays and the assessment of potential sdMSC therapeutic end products generated from pooled sdMSCs (pMSCs). We hypothesized that, compared to MSA using only one donor, MSA using pooled BMCs (pBMCs) is a more robust sdMSC potency assay due to reduced donor BMC heterogeneity. pBMCs were generated by pooling equine BMCs isolated from peripheral blood of five donors in equal ratios. pBMCs were labeled with carboxyfluorescein succinimidyl ester (CFSE) and stored in liquid nitrogen until use. Similarly, pooling sdMSCs from multiple equine donors in equal ratios generated pMSCs. sdMSC cultures were assessed with pBMCs in MSA using Bromodeoxyuridine ELISA and CFSE. Proliferation assessment of BMCs from individual donors revealed varied responses to concanavalin A (ConA) stimulation. MSA using BMCs from single donors further demonstrated BMC donor variability. Utilizing this assay, we have also found that the immunosuppressive potencies of pMSCs are at least equal, if not more, than the calculated mean of individual cultures. MSA based on pBMCs provides a consistent and reproducible equine sdMSC potency assay. This knowledge could be used in production monitoring of cellular potency and as release criteria before clinical use.

Recent advances in stem cell therapy for neurodegenerative disease: Three dimensional tracing and its emerging use

Neurodegenerative disease is a brain disorder caused by the loss of structure and function of neurons that lowers the quality of human life. Apart from the limited potential for endogenous regeneration, stem cell-based therapies hold considerable promise for maintaining homeostatic tissue regeneration and enhancing plasticity. Despite many studies, there remains insufficient evidence for stem cell tracing and its correlation with endogenous neural cells in brain tissue with three-dimensional structures. Recent advancements in tissue optical clearing techniques have been developed to overcome the existing shortcomings of cross-sectional tissue analysis in thick and complex tissues. This review focuses on recent progress of stem cell treatments to improve neurodegenerative disease, and introduces tissue optical clearing techniques that can implement a three-dimensional image as a proof of concept. This review provides a more comprehensive understanding of stem cell tracing that will play an important role in evaluating therapeutic efficacy and cellular interrelationship for regeneration in neurodegenerative diseases.

Dose-dependent effect of mesenchymal stromal cells co-grafted with dopaminergic neurons in a Parkinson's disease rat model

A major limiting factor for cell therapy in Parkinson's disease is the poor survival and reinnervation capacity of grafted dopaminergic neurons, independently of the cell source. Mesenchymal stromal cells (MSCs) have high capability to regulate the local environment through the release of trophic, antiapoptotic and immunomodulatory factors. In this work, we investigated whether co-grafting of MSCs could improve the survival and reinnervation ability of dopaminergic precursors transplanted in animal models of Parkinson's disease. Rats with total unilateral dopaminergic denervation were grafted with a cell suspension of rat dopaminergic precursors (500,000 cells) with or without a high (200,000 cells) or low (25,000 cells) number of MSCs. Eight weeks after grafting, rats were tested for motor behaviour and sacrificed for histological analysis. Our results showed that the survival of dopaminergic neurons and graft-derived striatal dopaminergic innervation was higher in rats that received co-grafts containing a low number of MSCs than in non-co-grafted controls. However, the survival of dopaminergic neurons and graft-derived dopaminergic reinnervation was lower in rats receiving co-grafts with high number of MSCs than in non-co-grafted controls. In conclusion, co-grafting with MSCs or MSCs-derived products may constitute a useful strategy to improve dopaminergic graft survival and function. However, a tight control of MSCs density or levels of MSCs-derived products is necessary.

Leber's hereditary optic neuropathy: Current approaches and future perspectives on Mesenchymal stem cell-mediated rescue

Leber's Hereditary Optic Neuropathy (LHON) is an inherited optic nerve disorder. It is a mitochondrially inherited disease due to point mutation in the MT-ND1, MT-ND4, and MT-ND6 genes of mitochondrial DNA (mtDNA) coding for complex I subunit proteins. These mutations affect the assembly of the mitochondrial complex I and hence the electron transport chain leading to mitochondrial dysfunction and oxidative damage. Optic nerve cells like retinal ganglion cells (RGCs) are more sensitive to mitochondrial loss and oxidative damage which results in the progressive degeneration of RGCs at the axonal region of the optic nerve leading to bilateral vision loss. Currently, gene therapy using Adeno-associated viral vector (AAV) is widely studied for the therapeutics application in LHON. Our review highlights the application of cell-based therapy for LHON. Mesenchymal stem cells (MSCs) are known to rescue cells from the pre-apoptotic stage by transferring healthy mitochondria through tunneling nanotubes (TNT) for cellular oxidative function. Empowering the transfer of healthy mitochondria using MSCs may replace the mitochondria with pathogenic mutation and possibly benefit the cells from progressive damage. This review discusses the ongoing research in LHON and mitochondrial transfer mechanisms to explore its scope in inherited optic neuropathy.

Reelin Alleviates Mesenchymal Stem Cell Senescence and Reduces Pathological α-Synuclein Expression in an In Vitro Model of Parkinson's Disease

Parkinson's disease (PD) is one of the most common neurodegenerative diseases. The mechanisms underlying PD remain to be fully elucidated, and research into treatments for this condition is ongoing. Recent advances in genetic research have shed light on the mechanisms underlying PD. In this study, we used PD and control mesenchymal stem cells (MSCs) obtained from adipose tissues to confirm the differences between groups at the cellular and molecular levels. The results revealed that in PD MSCs, cell viability was clearly lower, and the rate of cell senescence was higher compared to the controls. Next, to compare the gene expression in PD and control cells, transcriptome analysis was performed. Genes in pathways, including extracellular matrix (ECM) receptor interaction, P53 signaling, and focal adhesion, were down-regulated in PD. Among genes related to ECM receptor interaction, RELN gene expression was markedly decreased in PD cells; however, after being treated with recombinant Reelin protein, a significant increase in cell viability and a decrease in α-Synuclein aggregation and cell senescence were observed. In conclusion, Reelin affects PD by positively influencing the cell characteristics. Our findings will facilitate research into new treatments for PD.

Recent trends in stem cell-based therapies and applications of artificial intelligence in regenerative medicine

Stem cells are undifferentiated cells that can self-renew and differentiate into diverse types of mature and functional cells while maintaining their original identity. This profound potential of stem cells has been thoroughly investigated for its significance in regenerative medicine and has laid the foundation for cell-based therapies. Regenerative medicine is rapidly progressing in healthcare with the prospect of repair and restoration of specific organs or tissue injuries or chronic disease conditions where the body’s regenerative process is not sufficient to heal. In this review, the recent advances in stem cell-based therapies in regenerative medicine are discussed, emphasizing mesenchymal stem cell-based therapies as these cells have been extensively studied for clinical use. Recent applications of artificial intelligence algorithms in stem cell-based therapies, their limitation, and future prospects are highlighted.

Bringing Advanced Therapies for Parkinson's Disease to the Clinic: An Analysis of Ethical Issues

Advanced therapies for Parkinson’s disease (PD) constitute a broad range of treatments, each presenting specific ethical challenges. Some of these therapies are established and in clinical use, like device-aided therapies, and others, based on advanced therapeutic medicinal products (ATMPs), are still in early stage of clinical trials. This paper focuses on some common ethical issues arising in these two categories of advanced therapies, especially challenges arising when advanced therapies are proposed to PD patients in the form of advanced care, under a clinical trial, or, in case of ATMPs, under the “hospital exemption” rule. The ethical issues covered here relate mainly to ensuring informed consent in these different contexts, to the stakeholder role of patient’s non-professional caretakers, such as family, and to patient safety in treatments under “hospital exemption”. To illustrate the points discussed in connection with “hospital exemption” rule, the example of the EU has been chosen. This paper does not claim completeness of ethical issues raised by bringing advanced therapies for PD to the clinic, but rather presents examples of ethical challenges in this context.

Different kinds of stem cells in the development of SARS-CoV-2 treatments

On February 11, 2020, the World Health Organization officially announced the coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), as an emerging recent pandemic illness, which currently has approximately taken the life of two million persons in more than 200 countries. Medical, clinical, and scientific efforts have focused on searching for new prevention and treatment strategies. Regenerative medicine and tissue engineering focused on using stem cells (SCs) have become a promising tool, and the regenerative and immunoregulatory capabilities of mesenchymal SCs (MSCs) and their exosomes have been demonstrated. Moreover, it has been essential to establishing models to reproduce the viral life cycle and mimic the pathology of COVID-19 to understand the virus's behavior. The fields of pluripotent SCs (PSCs), induced PSCs (iPSCs), and artificial iPSCs have been used for this purpose in the development of infection models or organoids. Nevertheless, some inconveniences have been declared in SC use; for example, it has been reported that SARS-CoV-2 enters human cells through the angiotensin-converting enzyme 2 receptor, which is highly expressed in MSCs, so it is important to continue investigating the employment of SCs in COVID-19, taking into consideration their advantages and disadvantages. In this review, we expose the use of different kinds of SCs and their derivatives for studying the SARS-CoV-2 behavior and develop treatments to counter COVID-19.

Interaction Between Mesenchymal Stem Cells and Retinal Degenerative Microenvironment

Retinal degenerative diseases (RDDs) are a group of diseases contributing to irreversible vision loss with yet limited therapies. Stem cell-based therapy is a promising novel therapeutic approach in RDD treatment. Mesenchymal stromal/stem cells (MSCs) have emerged as a leading cell source due to their neurotrophic and immunomodulatory capabilities, limited ethical concerns, and low risk of tumor formation. Several pre-clinical studies have shown that MSCs have the potential to delay retinal degeneration, and recent clinical trials have demonstrated promising safety profiles for the application of MSCs in retinal disease. However, some of the clinical-stage MSC therapies have been unable to meet primary efficacy end points, and severe side effects were reported in some retinal “stem cell” clinics. In this review, we provide an update of the interaction between MSCs and the RDD microenvironment and discuss how to balance the therapeutic potential and safety concerns of MSCs' ocular application.

Therapeutic Properties of Mesenchymal Stromal/Stem Cells: The Need of Cell Priming for Cell-Free Therapies in Regenerative Medicine

Mesenchymal stromal/stem cells (MSCs) are multipotent adult stem cells that support homeostasis during tissue regeneration. In the last decade, cell therapies based on the use of MSCs have emerged as a promising strategy in the field of regenerative medicine. Although these cells possess robust therapeutic properties that can be applied in the treatment of different diseases, variables in preclinical and clinical trials lead to inconsistent outcomes. MSC therapeutic effects result from the secretion of bioactive molecules affected by either local microenvironment or MSC culture conditions. Hence, MSC paracrine action is currently being explored in several clinical settings either using a conditioned medium (CM) or MSC-derived exosomes (EXOs), where these products modulate tissue responses in different types of injuries. In this scenario, MSC paracrine mechanisms provide a promising framework for enhancing MSC therapeutic benefits, where the composition of secretome can be modulated by priming of the MSCs. In this review, we examine the literature on the priming of MSCs as a tool to enhance their therapeutic properties applicable to the main processes involved in tissue regeneration, including the reduction of fibrosis, the immunomodulation, the stimulation of angiogenesis, and the stimulation of resident progenitor cells, thereby providing new insights for the therapeutic use of MSCs-derived products.