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

Early Changes in Porcine Larynges Following Injection of Motor-Endplate Expressing Muscle Cells for the Treatment of Unilateral Vocal Fold Paralysis

OBJECTIVES

No curative injectable therapy exists for unilateral vocal fold paralysis. Herein, we explore the early implications of muscle-derived motor-endplate expressing cells (MEEs) for injectable vocal fold medialization after recurrent laryngeal nerve (RLN) injury.

METHODS

Yucatan minipigs underwent right RLN transection (without repair) and muscle biopsies. Autologous muscle progenitor cells were isolated, cultured, differentiated, and induced to form MEEs. Three weeks after the injury, MEEs or saline were injected into the paralyzed right vocal fold. Outcomes including evoked laryngeal electromyography (LEMG), laryngeal adductor pressure, and acoustic vocalization data were analyzed up to 7 weeks post-injury. Harvested porcine larynges were examined for volume, gene expression, and histology.

RESULTS

MEE injections were tolerated well, with all pigs demonstrating continued weight gain. Blinded analysis of videolaryngoscopy post-injection revealed infraglottic fullness, and no inflammatory changes. Four weeks after injection, LEMG revealed on average higher right distal RLN activity retention in MEE pigs. MEE-injected pigs on average had vocalization durations, frequencies, and intensities higher than saline pigs. Post-mortem, the MEE-injected larynges revealed statistically greater volume on quantitative 3D ultrasound, and statistically increased expression of neurotrophic factors (BDNF, NGF, NTF3, NTF4, NTN1) on quantitative PCR.

CONCLUSIONS

Minimally invasive MEE injection appears to establish an early molecular and microenvironmental framework to encourage innate RLN regeneration. Longer follow-up is needed to determine if early findings will translate into functional contraction.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:272-282, 2024.

Dopaminergic Cell Replacement for Parkinson's Disease: Addressing the Intracranial Delivery Hurdle

Parkinson's disease (PD) is an increasingly prevalent neurological disorder, affecting more than 8.5 million individuals worldwide. α-Synucleinopathy in PD is considered to cause dopaminergic neuronal loss in the substantia nigra, resulting in characteristic motor dysfunction that is the target for current medical and surgical therapies. Standard treatment for PD has remained unchanged for several decades and does not alter disease progression. Furthermore, symptomatic therapies for PD are limited by issues surrounding long-term efficacy and side effects. Cell replacement therapy (CRT) presents an alternative approach that has the potential to restore striatal dopaminergic input and ameliorate debilitating motor symptoms in PD. Despite promising pre-clinical data, CRT has demonstrated mixed success clinically. Recent advances in graft biology have renewed interest in the field, resulting in several worldwide ongoing clinical trials. However, factors surrounding the effective neurosurgical delivery of cell grafts have remained under-studied, despite their significant potential to influence therapeutic outcomes. Here, we focus on the key neurosurgical factors to consider for the clinical translation of CRT. We review the instruments that have been used for cell graft delivery, highlighting current features and limitations, while discussing how future devices could address these challenges. Finally, we review other novel developments that may enhance graft accessibility, delivery, and efficacy. Challenges surrounding neurosurgical delivery may critically contribute to the success of CRT, so it is crucial that we address these issues to ensure that CRT does not falter at the final hurdle.

Preclinical research studies for treating severe muscular injuries: focus on tissue-engineered strategies

Severe skeletal muscle injuries are a lifelong trauma with limited medical solutions. Significant progress has been made in developing in vitro surrogates for treating such trauma. However, more attention is needed when translating these approaches to the clinic. In this review, we survey the potential of tissue-engineered surrogates in promoting muscle healing, by critically analyzing data from recent preclinical models. The therapeutic advantages provided by a combination of different biomaterials, cell types, and biochemical mediators are discussed. Current therapies on muscle healing are also summarized, emphasizing their main advantages and drawbacks. We also discuss previous and ongoing clinical trials as well as highlighting future directions for the field.

Potential disease-modifying therapies for Huntington's disease: lessons learned and future opportunities

Huntington's disease is the most frequent autosomal dominant neurodegenerative disorder; however, no disease-modifying interventions are available for patients with this disease. The molecular pathogenesis of Huntington's disease is complex, with toxicity that arises from full-length expanded huntingtin and N-terminal fragments of huntingtin, which are both prone to misfolding due to proteolysis; aberrant intron-1 splicing of the HTT gene; and somatic expansion of the CAG repeat in the HTT gene. Potential interventions for Huntington's disease include therapies targeting huntingtin DNA and RNA, clearance of huntingtin protein, DNA repair pathways, and other treatment strategies targeting inflammation and cell replacement. The early termination of trials of the antisense oligonucleotide tominersen suggest that it is time to reflect on lessons learned, where the field stands now, and the challenges and opportunities for the future.

Toward Generalizable Trajectory Planning for Human Intracerebral Trials and Therapy

<b><i>Introduction:</i></b> Stereotactic neurosurgical techniques are increasingly used to deliver biologics, such as cells and viruses, although standardized procedures are necessary to ensure consistency and reproducibility. <b><i>Objective:</i></b> We provide an instructional guide to help plan for complex image-guided trajectories; this may be of particular benefit to surgeons new to biologic trials and companies planning such trials. <b><i>Methods:</i></b> We show how nuclei can be segmented and multiple trajectories with multiple injection points can be created through a single or multiple burr hole(s) based on preoperative images. Screenshots similar to those shown in this article can be used for planning purposes and for quality control in clinical trials. <b><i>Results:</i></b> This method enables the precise definition of 3-D target structures, such as the putamen, and efficient planning trajectories for biologic injections. The technique is generalizable and largely independent of procedural format, and thus can be integrated with frame-based or frameless platforms to streamline reproducible therapeutic delivery. <b><i>Conclusions:</i></b> We describe an easy-to-use and generalizable protocol for intracerebral trajectory planning for stereotactic delivery of biologics. Although we highlight intracerebral stem cell delivery to the putamen using a frame-based stereotactic delivery system, similar strategies may be employed for different brain nuclei using different platforms. We anticipate this will inform future advanced and fully automated neurosurgical procedures to help unify the field and decrease inherent variability seen with manual trajectory planning.

Do foetal transplant studies continue to be justified in Huntington's disease?

Early CNS transplantation studies used foetal derived cell products to provide a foundation of evidence for functional recovery in preclinical studies and early clinical trials. However, it was soon recognised that the practical limitations of foetal tissue make it unsuitable for widespread clinical use. Considerable effort has since been directed towards producing target cell phenotypes from pluripotent stem cells (PSCs) instead, and there now exist several publications detailing the differentiation and characterisation of PSC-derived products relevant for transplantation in Huntington's disease (HD). In light of this progress, we ask if foetal tissue transplantation continues to be justified in HD research. We argue that (i) the extent to which accurately differentiated target cells can presently be produced from PSCs is still unclear, currently making them undesirable for studying wider CNS transplantation issues; (ii) foetal derived cells remain a valuable tool in preclinical research for advancing our understanding of which products produce functional striatal grafts and as a reference to further improve PSC-derived products; and (iii) until PSC-derived products are ready for human trials, it is important to continue using foetal cells to gather clinical evidence that transplantation is a viable option in HD and to use this opportunity to optimise practical parameters (such as trial design, clinical practices, and delivery strategies) to pave the way for future PSC-derived products.

Delivery strategies for cell-based therapies in the brain: overcoming multiple barriers

Cell-based therapies to the brain are promising for the treatment of multiple brain disorders including neurodegeneration and cancers. In order to access the brain parenchyma, there are multiple physiological barriers that must be overcome depending on the route of delivery. Specifically, the blood-brain barrier has been a major difficulty in drug delivery for decades, and it still presents a challenge for the delivery of therapeutic cells. Other barriers, including the blood-cerebrospinal fluid barrier and lymphatic-brain barrier, are less explored, but may offer specific challenges or opportunities for therapeutic delivery. Here we discuss the barriers to the brain and the strategies currently in place to deliver cell-based therapies, including engineered T cells, dendritic cells, and stem cells, to treat diseases. With a particular focus on cancers, we also highlight the current ongoing clinical trials that use cell-based therapies to treat disease, many of which show promise at treating some of the deadliest illnesses.

Advanced Materials to Enhance Central Nervous System Tissue Modeling and Cell Therapy

The progressively deeper understanding of mechanisms underlying stem cell fate decisions has enabled parallel advances in basic biology-such as the generation of organoid models that can further one's basic understanding of human development and disease-and in clinical translation-including stem cell based therapies to treat human disease. Both of these applications rely on tight control of the stem cell microenvironment to properly modulate cell fate, and materials that can be engineered to interface with cells in a controlled and tunable manner have therefore emerged as valuable tools for guiding stem cell growth and differentiation. With a focus on the central nervous system (CNS), a broad range of material solutions that have been engineered to overcome various hurdles in constructing advanced organoid models and developing effective stem cell therapeutics is reviewed. Finally, regulatory aspects of combined material-cell approaches for CNS therapies are considered.

Columnar Injection for Intracerebral Cell Therapy

BACKGROUND

Surgical implantation of cellular grafts into the brain is of increasing importance, as stem cell-based therapies for Parkinson and other diseases continue to develop. The effect of grafting technique on development and survival of the graft has received less attention. Rate and method of graft delivery may impact the cell viability and success of these therapies. Understanding the final location of the graft with respect to the intended target location is also critical.

OBJECTIVE

To describe a "columnar injection" technique designed to reduce damage to host tissue and result in a column of graft material with greater surface area to volume ratio than traditional injection techniques.

METHODS

Using a clinically relevant model system of human embryonic stem cell-derived dopaminergic progenitors injected into athymic rat host brain, we describe a novel device that allows separate control of syringe barrel and plunger, permitting precise deposition of the contents into the cannula tract during withdrawal. Controls consist of contralateral injection using traditional techniques. Graft histology was examined at graft maturity.

RESULTS

Bolus grafts were centered on the injection tract but were largely proximal to the "target" location. These grafts displayed a conspicuous peripheral distribution of cells, particularly of mature dopaminergic neurons. In contrast, column injections remained centered at the intended target, contained more evenly distributed cells, and had significantly more mature dopaminergic neurons.

CONCLUSION

We suggest that this columnar injection technique may allow better engraftment and development of intracerebral grafts, enhancing outcomes of cell therapy, compared to fixed-point injection techniques.

Technical note: accuracy and precision in stereotactic stem cell transplantation

BACKGROUND

While multiple trials have employed stereotactic stem cell transplantation, injection techniques have received little critical attention. Precise cell delivery is critical for certain applications, particularly when targeting deep nuclei.

METHODS

Ten patients with a history of ischemic stroke underwent CT-guided stem cell transplantation. Cells were delivered along 3 tracts adjacent to the infarcted area. Intraoperative air deposits and postoperative T2-weighted MRI fluid signals were mapped in relation to calculated targets.

RESULTS

The deepest air deposit was found 4.5 ± 1.0 mm (mean ± 2 SEM) from target. The apex of the T2-hyperintense tract was found 2.8 ± 0.8 mm from target. On average, air pockets were found anterior (1.2 ± 1.1 mm, p = 0.04) and superior (2.4 ± 1.0 mm, p < 0.001) to the target; no directional bias was noted for the apex of the T2-hyperintense tract. Location and distribution of air deposits were variable and were affected by the relationship of cannula trajectory to stroke cavity.

CONCLUSIONS

Precise stereotactic cell transplantation is a little-studied technical challenge. Reflux of cell suspension and air, and the structure of the injection tract affect delivery of cell suspensions. Intraoperative CT allows assessment of delivery and potential trajectory correction.

Modern Concepts in Regenerative Therapy for Ischemic Stroke: From Stem Cells for Promoting Angiogenesis to 3D-Bioprinted Scaffolds Customized via Carotid Shear Stress Analysis

Ischemic stroke is associated with a tremendous economic and societal burden, and only a few therapies are currently available for the treatment of this devastating disease. The main therapeutic approaches used nowadays for the treatment of ischemic brain injury aim to achieve reperfusion, neuroprotection and neurorecovery. Therapeutic angiogenesis also seems to represent a promising tool to improve the prognosis of cerebral ischemia. This review aims to present the modern concepts and the current status of regenerative therapy for ischemic stroke and discuss the main results of major clinical trials addressing the effectiveness of stem cell therapy for achieving neuroregeneration in ischemic stroke. At the same time, as a glimpse into the future, this article describes modern concepts for stroke prevention, such as the implantation of bioprinted scaffolds seeded with stem cells, whose 3D geometry is customized according to carotid shear stress.

Minimally Invasive and Regenerative Therapeutics

Advances in biomaterial synthesis and fabrication, stem cell biology, bioimaging, microsurgery procedures, and microscale technologies have made minimally invasive therapeutics a viable tool in regenerative medicine. Therapeutics, herein defined as cells, biomaterials, biomolecules, and their combinations, can be delivered in a minimally invasive way to regenerate different tissues in the body, such as bone, cartilage, pancreas, cardiac, skeletal muscle, liver, skin, and neural tissues. Sophisticated methods of tracking, sensing, and stimulation of therapeutics in vivo using nano-biomaterials and soft bioelectronic devices provide great opportunities to further develop minimally invasive and regenerative therapeutics (MIRET). In general, minimally invasive delivery methods offer high yield with low risk of complications and reduced costs compared to conventional delivery methods. Here, minimally invasive approaches for delivering regenerative therapeutics into the body are reviewed. The use of MIRET to treat different tissues and organs is described. Although some clinical trials have been performed using MIRET, it is hoped that such therapeutics find wider applications to treat patients. Finally, some future perspective and challenges for this emerging field are highlighted.

Preclinical development of an automated injection device for intradermal delivery of a cell-based therapy

Current methods for intradermal delivery of therapeutic products in clinical use include manual injection via the Mantoux technique and the use of injection devices, primarily developed for the delivery of vaccines and small molecules. A novel automated injection device is presented specifically designed for accurate delivery of multiple doses of product through a number of adjustable injection parameters, including injection depth, dose volume and needle insertion speed. The device was originally conceived for the delivery of a cell-based therapy to patients with skin wounds caused by epidermolysis bullosa. A series of preclinical studies was conducted (i) to evaluate the performance of the pre-production model (PreCTCDV01) and optimise the final design, (ii) to confirm that a cell therapy product can be effectively delivered through the injection system and (iii) to test whether the device can be safely and effectively operated by potential end-users. Results from these studies confirmed that the device is able to consistently deliver repeated doses of a liquid to the intradermal layer in an ex vivo skin model. In addition, the device can support delivery of a cell therapy product through a customised microbore tubing without compromising cell viability. Finally, the device was shown to be safe and easy to use as evidenced by usability testing. The clinical device has since been granted European market access and plans for clinical use are currently underway. The device is expected to find use in the emerging area of cell therapies and a broad spectrum of traditional parenteral drug delivery applications.

Bioengineered cellular and cell membrane-derived vehicles for actively targeted drug delivery: So near and yet so far

Cellular carriers for drug delivery are attractive alternatives to synthetic nanoparticles owing to their innate homing/targeting abilities. Here, we review molecular interactions involved in the homing of Mesenchymal stem cells (MSCs) and other cell types to understand the process of designing and engineering highly efficient, actively targeting cellular vehicles. In addition, we comprehensively discuss various genetic and non-genetic strategies and propose futuristic approaches of engineering MSC homing using micro/nanotechnology and high throughput small molecule screening. Most of the targeting abilities of a cell come from its plasma membrane, thus, efforts to harness cell membranes as drug delivery vehicles are gaining importance and are highlighted here. We also recognize and report the lack of detailed characterization of cell membranes in terms of safety, structural integrity, targeting functionality, and drug transport. Finally, we provide insights on future development of bioengineered cellular and cell membrane-derived vesicles for successful clinical translation.

Ex vivo biomechanical characterization of syringe-needle ejections for intracerebral cell delivery

Intracerebral implantation of cell suspensions is finding its clinical translation with encouraging results in patients with stroke. However, the survival of cells in the brain remains poor. Although the biological potential of neural stem cells (NSCs) is widely documented, the biomechanical effects of delivering cells through a syringe-needle remain poorly understood. We here detailed the biomechanical forces (pressure, shear stress) that cells are exposed to during ejection through different sized needles (20G, 26G, 32G) and syringes (10, 50, 250 µL) at relevant flow rates (1, 5, 10 µL/min). A comparison of 3 vehicles, Phosphate Buffered Saline (PBS), Hypothermosol (HTS), and Pluronic, indicated that less viscous vehicles are favorable for suspension with a high cell volume fraction to minimize sedimentation. Higher suspension viscosity was associated with greater shear stress. Higher flow rates with viscous vehicle, such as HTS reduced viability by ~10% and also produced more apoptotic cells (28%). At 5 µL/min ejection using a 26G needle increased neuronal differentiation for PBS and HTS suspensions. These results reveal the biological impact of biomechanical forces in the cell delivery process. Appropriate engineering strategies can be considered to mitigate these effects to ensure the efficacious translation of this promising therapy.

Translational considerations in injectable cell-based therapeutics for neurological applications: concepts, progress and challenges

Significant progress has been made during the past decade towards the clinical adoption of cell-based therapeutics. However, existing cell-delivery approaches have shown limited success, with numerous studies showing fewer than 5% of injected cells persisting at the site of injection within days of transplantation. Although consideration is being increasingly given to clinical trial design, little emphasis has been given to tools and protocols used to administer cells. The different behaviours of various cell types, dosing accuracy, precise delivery, and cell retention and viability post-injection are some of the obstacles facing clinical translation. For efficient injectable cell transplantation, accurate characterisation of cellular health post-injection and the development of standardised administration protocols are required. This review provides an overview of the challenges facing effective delivery of cell therapies, examines key studies that have been carried out to investigate injectable cell delivery, and outlines opportunities for translating these findings into more effective cell-therapy interventions.

Magnetic Resonance Imaging of Ferumoxytol-Labeled Human Mesenchymal Stem Cells in the Mouse Brain

The success of stem cell therapy is highly dependent on accurate delivery of stem cells to the target site of interest. Possible ways to track the distribution of MSCs in vivo include the use of reporter genes or nanoparticles. The U.S. Food and Drug Administration (FDA) has approved ferumoxytol (Feraheme® [USA], Rienso® [UK]) as a treatment for iron deficiency anemia. Ferumoxytol is an ultrasmall superparamagnetic iron oxide nanoparticle (USPIO) that has recently been used to track the fate of transplanted cells using magnetic resonance imaging (MRI). The major objectives of this study were to demonstrate the feasibility of labeling hUCB-MSCs with ferumoxytol and to observe, through MRI, the engraftment of ferumoxytol-labeled human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) delivered via stereotactic injection into the hippocampi of a transgenic mouse model of familial Alzheimer's disease (5XFAD). Ferumoxytol had no toxic effects on the viability or stemness of hUCB-MSCs when assessed in vitro. Through MRI, hypointense signals were discernible at the site where ferumoxytol-labeled human MSCs were injected. Iron-positive areas were also observed in the engrafted hippocampi. The results from this study support the use of nanoparticle labeling to monitor transplanted MSCs in real time as a follow-up for AD stem cell therapy in the clinical field.

Direct brain infusion can be enhanced with focused ultrasound and microbubbles

The delivery of most therapeutic agents is rendered ineffective for the treatment of brain diseases due to the presence of the blood-brain barrier (BBB). The goal of this study was to investigate the effect of pre-infusion focused ultrasound (FUS) and microbubbles on the distribution of direct brain infusion in vivo. A single-element FUS transducer was used in all sonications, which were carried out immediately prior to direct infusion procedures. Mice received direct infusion of either Gadolinium-labeled albumin (Gd-albumin, 74 kDa) or adeno-associated virus (AAV, ∼4 MDa). The volumes of Gd-albumin at 30 min were deemed comparable ( P = 0.334) between the direct infusion (DI)-only group and the FUS + DI group. At 120 min, the FUS + DI group showed significantly higher contrast-enhanced volume (9.76 ± 0.74 mm³) than the DI-only group (7.14 ± 0.34 mm³). For mice infused with AAV, the total volume of transduction was estimated as GFP-positive regions and FUS + DI group demonstrated significantly higher ( P = 0.017) transduction efficiency in vivo. In conclusion, enhanced bio-distribution of directly infused agents was observed when the targeted region was pre-conditioned with FUS and microbubbles. Focused ultrasound has the potential, as an adjuvant technique, to significantly enhance direct brain infusion and achieve the desired therapeutic outcomes.

Non-Viral Nucleic Acid Delivery Strategies to the Central Nervous System

With an increased prevalence and understanding of central nervous system (CNS) injuries and neurological disorders, nucleic acid therapies are gaining promise as a way to regenerate lost neurons or halt disease progression. While more viral vectors have been used clinically as tools for gene delivery, non-viral vectors are gaining interest due to lower safety concerns and the ability to deliver all types of nucleic acids. Nevertheless, there are still a number of barriers to nucleic acid delivery. In this focused review, we explore the in vivo challenges hindering non-viral nucleic acid delivery to the CNS and the strategies and vehicles used to overcome them. Advantages and disadvantages of different routes of administration including: systemic injection, cerebrospinal fluid injection, intraparenchymal injection and peripheral administration are discussed. Non-viral vehicles and treatment strategies that have overcome delivery barriers and demonstrated in vivo gene transfer to the CNS are presented. These approaches can be used as guidelines in developing synthetic gene delivery vectors for CNS applications and will ultimately bring non-viral vectors closer to clinical application.

The Dark Side of the Force - Constraints and Complications of Cell Therapies for Stroke

Cell therapies are increasingly recognized as a promising option to augment the limited therapeutic arsenal available to fight ischemic stroke. During the last two decades, cumulating preclinical evidence has indicated a substantial efficacy for most cell treatment paradigms and first clinical trials are currently underway to assess safety and feasibility in patients. However, the strong and still unmet demand for novel stroke treatment options and exciting findings reported from experimental studies may have drawn our attention away from potential side effects related to cell therapies and the ways by which they are commonly applied. This review summarizes common and less frequent adverse events that have been discovered in preclinical and clinical investigations assessing cell therapies for stroke. Such adverse events range from immunological and neoplastic complications over seizures to cell clotting and cell-induced embolism. It also describes potential complications of clinically applicable administration procedures, detrimental interactions between therapeutic cells, and the pathophysiological environment that they are placed into, as well as problems related to cell manufacturing. Virtually each therapeutic intervention comes at a certain risk for complications. Side effects do therefore not generally compromise the value of cell treatments for stroke, but underestimating such complications might severely limit therapeutic safety and efficacy of cell treatment protocols currently under development. On the other hand, a better understanding will provide opportunities to further improve existing therapeutic strategies and might help to define those circumstances, under which an optimal effect can be realized. Hence, the review eventually discusses strategies and recommendations allowing us to prevent or at least balance potential complications in order to ensure the maximum therapeutic benefit at minimum risk for stroke patients.

Effective Eradication of Glioblastoma Stem Cells by Local Application of an AC133/CD133-Specific T-cell-Engaging Antibody and CD8 T Cells

Cancer stem cells (CSC) drive tumorigenesis and contribute to genotoxic therapy resistance, diffuse infiltrative invasion, and immunosuppression, which are key factors for the incurability of glioblastoma multiforme (GBM). The AC133 epitope of CD133 is an important CSC marker for GBM and other tumor entities. Here, we report the development and preclinical evaluation of a recombinant AC133×CD3 bispecific antibody (bsAb) that redirects human polyclonal T cells to AC133(+) GBM stem cells (GBM-SC), inducing their strong targeted lysis. This novel bsAb prevented the outgrowth of AC133-positive subcutaneous GBM xenografts. Moreover, upon intracerebral infusion along with the local application of human CD8(+) T cells, it exhibited potent activity in prophylactic and treatment models of orthotopic GBM-SC-derived invasive brain tumors. In contrast, normal hematopoietic stem cells, some of which are AC133-positive, were virtually unaffected at bsAb concentrations effective against GBM-SCs and retained their colony-forming abilities. In conclusion, our data demonstrate the high activity of this new bsAb against patient-derived AC133-positive GBM-SCs in models of local therapy of highly invasive GBM.

Transplantation of stem cell-derived astrocytes for the treatment of amyotrophic lateral sclerosis and spinal cord injury

Neglected for years, astrocytes are now recognized to fulfill and support many, if not all, homeostatic functions of the healthy central nervous system (CNS). During neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and spinal cord injury (SCI), astrocytes in the vicinity of degenerating areas undergo both morphological and functional changes that might compromise their intrinsic properties. Evidence from human and animal studies show that deficient astrocyte functions or loss-of-astrocytes largely contribute to increased susceptibility to cell death for neurons, oligodendrocytes and axons during ALS and SCI disease progression. Despite exciting advances in experimental CNS repair, most of current approaches that are translated into clinical trials focus on the replacement or support of spinal neurons through stem cell transplantation, while none focus on the specific replacement of astroglial populations. Knowing the important functions carried out by astrocytes in the CNS, astrocyte replacement-based therapies might be a promising approach to alleviate overall astrocyte dysfunction, deliver neurotrophic support to degenerating spinal tissue and stimulate endogenous CNS repair abilities. Enclosed in this review, we gathered experimental evidence that argue in favor of astrocyte transplantation during ALS and SCI. Based on their intrinsic properties and according to the cell type transplanted, astrocyte precursors or stem cell-derived astrocytes promote axonal growth, support mechanisms and cells involved in myelination, are able to modulate the host immune response, deliver neurotrophic factors and provide protective molecules against oxidative or excitotoxic insults, amongst many possible benefits. Embryonic or adult stem cells can even be genetically engineered in order to deliver missing gene products and therefore maximize the chance of neuroprotection and functional recovery. However, before broad clinical translation, further preclinical data on safety, reliability and therapeutic efficiency should be collected. Although several technical challenges need to be overcome, we discuss the major hurdles that have already been met or solved by targeting the astrocyte population in experimental ALS and SCI models and we discuss avenues for future directions based on latest molecular findings regarding astrocyte biology.

Interventional magnetic resonance imaging-guided cell transplantation into the brain with radially branched deployment

Intracerebral cell transplantation is being pursued as a treatment for many neurological diseases, and effective cell delivery is critical for clinical success. To facilitate intracerebral cell transplantation at the scale and complexity of the human brain, we developed a platform technology that enables radially branched deployment (RBD) of cells to multiple target locations at variable radial distances and depths along the initial brain penetration tract with real-time interventional magnetic resonance image (iMRI) guidance. iMRI-guided RBD functioned as an "add-on" to standard neurosurgical and imaging workflows, and procedures were performed in a commonly available clinical MRI scanner. Multiple deposits of super paramagnetic iron oxide beads were safely delivered to the striatum of live swine, and distribution to the entire putamen was achieved via a single cannula insertion in human cadaveric heads. Human embryonic stem cell-derived dopaminergic neurons were biocompatible with the iMRI-guided RBD platform and successfully delivered with iMRI guidance into the swine striatum. Thus, iMRI-guided RBD overcomes some of the technical limitations inherent to the use of straight cannulas and standard stereotactic targeting. This platform technology could have a major impact on the clinical translation of a wide range of cell therapeutics for the treatment of many neurological diseases.

Proceedings: cell therapies for Parkinson's disease from discovery to clinic

In March 2013, the California Institute for Regenerative Medicine, in collaboration with the NIH Center for Regenerative Medicine, held a 2-day workshop on cell therapies for Parkinson's disease (PD), with the goals of reviewing the state of stem cell research for the treatment of PD and discussing and refining the approach and the appropriate patient populations in which to plan and conduct new clinical trials using stem cell-based therapies for PD. Workshop participants identified priorities for research, development, and funding; discussed existing resources and initiatives; and outlined a path to the clinic for a stem cell-based therapy for PD. A consensus emerged among participants that the development of cell replacement therapies for PD using stem cell-derived products could potentially offer substantial benefits to patients. As with all stem cell-based therapeutic approaches, however, there are many issues yet to be resolved regarding the safety, efficacy, and methodology of transplanting cell therapies into patients. Workshop participants agreed that designing an effective stem cell-based therapy for PD will require further research and development in several key areas. This paper summarizes the meeting.

Use of genetically modified mesenchymal stem cells to treat neurodegenerative diseases

The transplantation of mesenchymal stem cells (MSCs) for treating neurodegenerative disorders has received growing attention recently because these cells are readily available, easily expanded in culture, and when transplanted, survive for relatively long periods of time. Given that such transplants have been shown to be safe in a variety of applications, in addition to recent findings that MSCs have useful immunomodulatory and chemotactic properties, the use of these cells as vehicles for delivering or producing beneficial proteins for therapeutic purposes has been the focus of several labs. In our lab, the use of genetic modified MSCs to release neurotrophic factors for the treatment of neurodegenerative diseases is of particular interest. Specifically, glial cell-derived neurotrophic factor (GDNF), nerve growth factor (NGF), and brain derived neurotrophic factor (BDNF) have been recognized as therapeutic trophic factors for Parkinson's, Alzheimer's and Huntington's diseases, respectively. The aim of this literature review is to provide insights into: (1) the inherent properties of MSCs as a platform for neurotrophic factor delivery; (2) the molecular tools available for genetic manipulation of MSCs; (3) the rationale for utilizing various neurotrophic factors for particular neurodegenerative diseases; and (4) the clinical challenges of utilizing genetically modified MSCs.