Cell therapies for Parkinson's disease: how far have we come?

The therapeutic use of clonal neural stem cells in experimental Parkinson´s disease

BACKGROUND

Parkinson´s disease (PD), the second most common neurodegenerative disease in the world, is characterized by the death or impairment of dopaminergic neurons (DAn) in the substantia nigra pars compacta and dopamine depletion in the striatum. Currently, there is no cure for PD, and treatments only help to reduce the symptoms of the disease, and do not repair or replace the DAn damaged or lost in PD. Cell replacement therapy (CRT) seeks to relieve both pathological and symptomatic PD manifestations and has been shown to have beneficial effects in experimental PD models as well as in PD patients, but an apt cell line to be used in the treatment of PD has yet to be established. The purpose of this study was to examine the effects of the transplantation of hVM1 clone 32 cells, a bankable line of human neural stem cells (hNSCs), in a PD mouse model at four months post-transplant.

METHODS

Adult (five month-old) C57BL/6JRccHsd male mice were injected with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and subsequently transplanted with hVM1 clone 32 cells, or buffer, in the left striatum. Four months post-transplant, behavioral effects were explored using the open field and paw print tests, and histological analyses were performed.

RESULTS

Transplantation of hVM1 clone 32 cells rescued dopaminergic nigrostriatal populations in adult Parkinsonian mice. Motor and neurological deterioration were observed in buffer-treated mice, the latter of which had a tendency to improve in hNSC-transplanted mice. Detection of mast cell migration to the superficial cervical lymph nodes in cell-transplanted mice denoted a peripheral effect. Transplantation of hNSCs also rescued neuroblast neurogenesis in the subgranular zone, which was correlated with dopaminergic recovery and is indicative of local recovery mechanisms.

CONCLUSIONS

In this proof-of-concept study, the transplantation of hVM1 clone 32 cells provided neuroprotection in adult Parkinsonian mice by restoring the dopaminergic nigrostriatal pathway and hippocampal neurogenesis, demonstrating the efficacy of cell replacement therapy as a treatment for PD.

A bioengineered artificial interstitium supports long-term islet xenograft survival in nonhuman primates without immunosuppression

Cell-based therapies hold promise for many chronic conditions; however, the continued need for immunosuppression along with challenges in replacing cells to improve durability or retrieving cells for safety are major obstacles. We subcutaneously implanted a device engineered to exploit the innate transcapillary hydrostatic and colloid osmotic pressure generating ultrafiltrate to mimic interstitium. Long-term stable accumulation of ultrafiltrate was achieved in both rodents and nonhuman primates (NHPs) that was chemically similar to serum and achieved capillary blood oxygen concentration. The majority of adult pig islet grafts transplanted in non-immunosuppressed NHPs resulted in xenograft survival >100 days. Stable cytokine levels, normal neutrophil to lymphocyte ratio, and a lack of immune cell infiltration demonstrated successful immunoprotection and averted typical systemic changes related to xenograft transplant, especially inflammation. This approach eliminates the need for immunosuppression and permits percutaneous access for loading, reloading, biopsy, and recovery to de-risk the use of "unlimited" xenogeneic cell sources to realize widespread clinical translation of cell-based therapies.

Embryoid Body Cells from Human Embryonic Stem Cells Overexpressing Dopaminergic Transcription Factors Survive and Initiate Neurogenesis via Neural Rosettes in the Substantia Nigra

Transplantation of immature dopaminergic neurons or neural precursors derived from embryonic stem cells (ESCs) into the substantia nigra pars compacta (SNpc) is a potential therapeutic approach for functional restitution of the nigrostriatal pathway in Parkinson's disease (PD). However, further studies are needed to understand the effects of the local microenvironment on the transplanted cells to improve survival and specific differentiation in situ. We have previously reported that the adult SNpc sustains a neurogenic microenvironment. Non-neuralized embryoid body cells (EBCs) from mouse ESCs (mESCs) overexpressing the dopaminergic transcription factor Lmx1a gave rise to many tyrosine hydroxylase (Th⁺) cells in the intact and damaged adult SNpc, although only for a short-term period. Here, we extended our study by transplanting EBCs from genetically engineered naive human ESC (hESC), overexpressing the dopaminergic transcription factors LMX1A, FOXA2, and OTX2 (hESC-LFO), in the SNpc. Unexpectedly, no graft survival was observed in wild-type hESC EBCs transplants, whereas hESC-LFO EBCs showed viability in the SNpc. Interestingly, neural rosettes, a developmental hallmark of neuroepithelial tissue, emerged at 7- and 15-days post-transplantation (dpt) from the hESC-LFO EBCs. Neural rosettes expressed specification dopaminergic markers (Lmx1a, Otx2), which gave rise to several Th⁺ cells at 30 dpt. Our results suggest that the SNpc enables the robust initiation of neural differentiation of transplanted human EBCs prompted to differentiate toward the midbrain dopaminergic phenotype.

Long-Term Evaluation of Intranigral Transplantation of Human iPSC-Derived Dopamine Neurons in a Parkinson's Disease Mouse Model

Parkinson's disease (PD) is a neurodegenerative disorder associated with loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc). One strategy for treating PD is transplantation of DA neuroblasts. Significant advances have been made in generating midbrain DA neurons from human pluripotent stem cells. Before these cells can be routinely used in clinical trials, extensive preclinical safety studies are required. One of the main issues to be addressed is the long-term therapeutic effectiveness of these cells. In most transplantation studies using human cells, the maturation of DA neurons has been analyzed over a relatively short period not exceeding 6 months. In present study, we generated midbrain DA neurons from human induced pluripotent stem cells (hiPSCs) and grafted these neurons into the SNpc in an animal model of PD. Graft survival and maturation were analyzed from 1 to 12 months post-transplantation (mpt). We observed long-term survival and functionality of the grafted neurons. However, at 12 mpt, we observed a decrease in the proportion of SNpc DA neuron subtype compared with that at 6 mpt. In addition, at 12 mpt, grafts still contained immature neurons. Our results suggest that longer-term evaluation of the maturation of neurons derived from human stem cells is mandatory for the safe application of cell therapy for PD.

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.

Understanding cell culture dynamics: a tool for defining protocol parameters for improved processes and efficient manufacturing using human embryonic stem cells

Standardization is crucial when culturing cells including human embryonic stem cells (hESCs) which are valuable for therapy development and disease modeling. Inherent issues regarding reproducibility of protocols are problematic as they hinder translation to good manufacturing practice (GMP), thus reducing clinical efficacy and uptake. Pluripotent cultures require standardization to ensure that input material is consistent prior to differentiation, as inconsistency of input cells creates end-product variation. To improve protocols, developers first must understand the cells they are working with and their related culture dynamics. This innovative work highlights key conditions required for optimized and cost-effective bioprocesses compared to generic protocols typically implemented. This entailed investigating conditions affecting growth, metabolism, and phenotype dynamics to ensure cell quality is appropriate for use. Results revealed critical process parameters (CPPs) including feeding regime and seeding density impact critical quality attributes (CQAs) including specific metabolic rate (SMR) and specific growth rate (SGR). This implied that process understanding, and control is essential to maintain key cell characteristics, reduce process variation and retain CQAs. Examination of cell dynamics and CPPs permitted the formation of a defined protocol for culturing H9 hESCs. The authors recommend that H9 seeding densities of 20,000 cells/cm2, four-day cultures or three-day cultures following a recovery passage from cryopreservation and 100% medium exchange after 48 hours are optimal. These parameters gave ~SGR of 0.018 hour-1 ± 1.5x10-3 over three days and cell viabilities ≥95%±0.4, while producing cells which highly expressed pluripotent and proliferation markers, Oct3/4 (>99% positive) and Ki-67 (>99% positive).

Toward Functional Restoration of the Central Nervous System: A Review of Translational Neuroscience Principles

Injury to the central nervous system (CNS) can leave patients with devastating neurological deficits that may permanently impair independence and diminish quality of life. Recent insights into how the CNS responds to injury and reacts to critically timed interventions are being translated into clinical applications that have the capacity to drastically improve outcomes for patients suffering from permanent neurological deficits due to spinal cord injury, stroke, or other CNS disorders. The translation of such knowledge into practical and impactful treatments involves the strategic collaboration between neurosurgeons, clinicians, therapists, scientists, and industry. Therefore, a common understanding of key neuroscientific principles is crucial. Conceptually, current approaches to CNS revitalization can be divided by scale into macroscopic (systems-circuitry) and microscopic (cellular-molecular). Here we review both emerging and well-established tenets that are being utilized to enhance CNS recovery on both levels, and we explore the role of neurosurgeons in developing therapies moving forward. Key principles include plasticity-driven functional recovery, cellular signaling mechanisms in axonal sprouting, critical timing for recovery after injury, and mechanisms of action underlying cellular replacement strategies. We then discuss integrative approaches aimed at synergizing interventions across scales, and we make recommendations for the basis of future clinical trial design. Ultimately, we argue that strategic modulation of microscopic cellular behavior within a macroscopic framework of functional circuitry re-establishment should provide the foundation for most neural restoration strategies, and the early involvement of neurosurgeons in the process will be crucial to successful clinical translation.

From protocol to product: ventral midbrain dopaminergic neuron differentiation for the treatment of Parkinson's disease

Current cell therapy product limitations include the need for in-depth product understanding to ensure product potency, safety and purity. New technologies require development and validation to address issues of production scale-up to meet clinical need; assays are required for process control, validation and release. Prior to clinical realization, an understanding of production processes is required to implement process changes that are essential for process control. Identification of key parameters forms the basis of process tolerances, allowing for validated, adaptive manufacturing processes. This enables greater process control and yield while withstanding regulatory scrutiny. This report summaries key milestones in specifically for ventral midbrain dopaminergic neuroprogenitor differentiation and key translational considerations and recommendations to enable successful, robust and reproducible current cell therapy product-manufacturing.

Transcription Factor Levels after Forward Programming of Human Pluripotent Stem Cells with GATA1, FLI1, and TAL1 Determine Megakaryocyte versus Erythroid Cell Fate Decision

The production of blood cells and their precursors from human pluripotent stem cells (hPSCs) in vitro has the potential to make a significant impact upon healthcare provision. We demonstrate that the forward programming of hPSCs through overexpression of GATA1, FLI1, and TAL1 leads to the production of a population of progenitors that can differentiate into megakaryocyte or erythroblasts. Using “rainbow” lentiviral vectors to quantify individual transgene expression in single cells, we demonstrate that the cell fate decision toward an erythroblast or megakaryocyte is dictated by the level of FLI1 expression and is independent of culture conditions. Early FLI1 expression is critical to confer proliferative potential to programmed cells while its subsequent silencing or maintenance dictates an erythroid or megakaryocytic fate, respectively. These committed progenitors subsequently expand and mature into megakaryocytes or erythroblasts in response to thrombopoietin or erythropoietin. Our results reveal molecular mechanisms underlying hPSC forward programming and novel opportunities for application to transfusion medicine.

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Overexpression of GATA1, TAL1, and FLI1 in hPSCS produces megakaryocytes and erythroblasts

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Lineage fate is an early event independent of cytokines but dictated by FLI1 transgene

Guggulsterone-releasing microspheres direct the differentiation of human induced pluripotent stem cells into neural phenotypes

Parkinson's disease (PD), a common neurodegenerative disorder, results from the loss of motor function when dopaminergic neurons (DNs) in the brain selectively degenerate. While pluripotent stem cells (PSCs) show promise for generating replacement neurons, current protocols for generating terminally differentiated DNs require a complicated cocktail of factors. Recent work demonstrated that a naturally occurring steroid called guggulsterone effectively differentiated PSCs into DNs, simplifying this process. In this study, we encapsulated guggulsterone into novel poly-ε-caprolactone-based microspheres and characterized its release profile over 44 d in vitro, demonstrating we can control its release over time. These guggulsterone-releasing microspheres were also successfully incorporated in human induced pluripotent stem cell-derived cellular aggregates under feeder-free and xeno-free conditions and cultured for 20 d to determine their effect on differentiation. All cultures stained positive for the early neuronal marker TUJ1 and guggulsterone microsphere-incorporated aggregates did not adversely affect neurite length and branching. Guggulsterone microsphere incorporated aggregates exhibited the highest levels of TUJ1 expression as well as high Olig 2 expression, an inhibitor of the STAT3 astrogenesis pathway previously known as a target for guggulsterone in cancer treatment. Together, this study represents an important first step towards engineered neural tissues consisting of guggulsterone microspheres and PSCs for generating DNs that could eventually be evaluated in a pre-clinical model of PD.

PARKIN overexpression in human mesenchymal stromal cells from Wharton's jelly suppresses 6-hydroxydopamine-induced apoptosis: Potential therapeutic strategy in Parkinson's disease

BACKGROUND AIMS

Stem cell transplantation is an excellent option for regenerative or replacement therapy. However, deleterious microenvironmental and endogenous factors (e.g., oxidative stress) compromise ongoing graft survival and longevity. Therefore, (transient or stable) genetically modified cells may be reasonably thought to resist oxidative stress-induced damage. Genetic engineering of mesenchymal stromal cells (MSCs) obtained from Wharton's jelly tissue may offer some therapeutic potential. PARKIN is a multifunctional ubiquitin ligase able to protect dopaminergic cells against stress-related signaling. We, therefore, evaluated the effect of the neurotoxicant 6-hydroxydopamine (6-OHDA) on regulated cell death signaling in MSCs and investigated whether overexpression of PARKIN in MSCs was capable of modulating the effect of 6-OHDA.

METHODS

We transiently transfected Wharton's jelly-derived MSCs with an mCherry-PARKIN vector using the Lipofectamine LTX method. Naïve MSCs and MSCs overexpressing PARKIN were exposed to increasing concentrations of 6-OHDA. We used light and fluorescence microscopy, flow cytometry, immunocytochemistry staining, in-cell Western and Western blot analysis.

RESULTS

After 12-24 h of 6-OHDA exposure, we detected dichlorofluorescein (DCF)-positive cells (80%) indicative of reactive oxygen species (H2O2) production, reduced cell viability (40-50%), decreased mitochondrial membrane potential (ΔΨm, ~35-45%), DNA fragmentation (18-30%), and G1-arrested cell cycle in the MSCs. 6-OHDA exposure increased the expression of the transcription factor c-JUN, increased the expression of the mitochondria maintenance Phosphatase and tensin homologue-induced putative kinase 1 (PINK1) protein and increased the expression of pro-apoptotic PUMA, caspase-3 and apoptosis-inducing factor (AIF). 6-OHDA exposure also significantly augmented the oxidation of the oxidative stress sensor, DJ-1. Overexpression of PARKIN in MSCs not only significantly reduced the expression of cell death and oxidative stress markers but also significantly reduced DCF-positive cells (~50% reduction).

DISCUSSION

6-OHDA induced apoptosis in MSCs via generation of H2O2, activation of c-JUN and PUMA, mitochondrial depolarization and nuclei fragmentation. Our findings suggest that PARKIN protects MSCs against 6-OHDA toxicity by partly interacting with H2O2, reducing the expression of c-JUN, PUMA, AIF and caspase-3, and maintaining the mitochondrial ΔΨm.

Interleukin-6-Mediated Induced Pluripotent Stem Cell (iPSC)-Derived Neural Differentiation

In an aging society with an increasing threat to higher brain cognitive functions due to dementia, it becomes imperative to identify new molecular remedies for supporting adult neurogenesis. Interleukin-6 (IL-6) is a promising cytokine that can support neurogenesis under conditions of neurodegeneration, and neuron replacement is eventually possible due to its agonistic acting soluble receptor sIL-6R. Here, we report that activation of the IL-6-signal transducer and activator of transcription 3 (STAT3) axis is neurogenic and has potential therapeutic applications for the treatment of neurodegenerative diseases such as Parkinson's disease (PD).

Neural grafting for Parkinson's disease: challenges and prospects

Parkinson's disease (PD) is a neurodegenerative condition which causes a characteristic movement disorder secondary to loss of dopaminergic neurons in the substanitia nigra. The motor disorder responds well to dopamine-replacement therapies, though these result in significant adverse effects due to non-physiological release of dopamine in the striatum, and off-target effects. Cell-based regenerative treatments offer a potential means for targeted replacement of dopamine, in a physiological manner. Dopaminergic neurons for cell-based therapies can be obtained from several sources. Fetal ventral mesencephalon tissue contains dopaminergic neuron progenitors, and has been transplanted into the striatum of PD patients with good results in a number of cases. However, the ethical implications and logistical challenges of using fetal tissue mean that fetal ventral mesencephalon is unlikely to be used in a widespread clinical setting. Induced pluripotent stem cells can be used to generate dopaminergic neurons for transplantation, providing a source of autologous tissue for grafting. This approach means that challenges associated with allografts, such as the potential for immune rejection, can be circumvented. However, the associated cost and difficulty in producing a standardized product from different cell lines means that, at present, this approach is not commercially viable as a cell-based therapy. Dopaminergic neurons derived from embryonic stem cells offer the most promising basis for a cell-based therapy for Parkinson's disease, with trials due to commence in the next few years. Though there are ethical considerations to take into account when using embryonic tissue, the possibility of producing a standardized, optimized cell product means that this approach can be both effective, and commercially viable.