Effects of cool storage on survival and function of intrastriatal ventral mesencephalic grafts

SUPT4H1-edited stem cell therapy rescues neuronal dysfunction in a mouse model for Huntington's disease

Huntington’s disease (HD) is a severe inherited neurological disorder caused by a CAG repeat expansion in the huntingtin gene (HTT), leading to the accumulation of mutant huntingtin with polyglutamine repeats. Despite its severity, there is no cure for this debilitating disease. HTT lowering strategies, including antisense oligonucleotides (ASO) showed promising results very recently. Attempts to develop stem cell-based therapeutics have shown efficacy in preclinical HD models. Using an HD patient’s autologous cells, which have genetic defects, may hamper therapeutic efficacy due to mutant HTT. Pretreating these cells to reduce mutant HTT expression and transcription may improve the transplanted cells’ therapeutic efficacy. To investigate this, we targeted the SUPT4H1 gene that selectively supports the transcription of long trinucleotide repeats. Transplanting SUPT4H1-edited HD-induced pluripotent stem cell-derived neural precursor cells (iPSC-NPCs) into the YAC128 HD transgenic mouse model improved motor function compared to unedited HD iPSC-NPCs. Immunohistochemical analysis revealed reduced mutant HTT expression without compensating wild-type HTT expression. Further, SUPT4H1 editing increased neuronal and decreased reactive astrocyte differentiation in HD iPSC-NPCs compared to the unedited HD iPSC-NPCs. This suggests that ex vivo editing of SUPT4H1 can reduce mutant HTT expression and provide a therapeutic gene editing strategy for autologous stem cell transplantation in HD.

Gene and Cell-Based Therapies for Parkinson's Disease: Where Are We?

Parkinson's disease (PD) is a neurodegenerative disorder that carries large health and socioeconomic burdens. Current therapies for PD are ultimately inadequate, both in terms of symptom control and in modification of disease progression. Deep brain stimulation and infusion therapies are the current mainstay for treatment of motor complications of advanced disease, but these have very significant drawbacks and offer no element of disease modification. In fact, there are currently no agents that are established to modify the course of the disease in clinical use for PD. Gene and cell therapies for PD are now being trialled in the clinic. These treatments are diverse and may have a range of niches in the management of PD. They hold great promise for improved treatment of symptoms as well as possibly slowing progression of the disease in the right patient group. Here, we review the current state of the art for these therapies and look to future strategies in this fast-moving field.

The Effect of Hypothermic and Cryogenic Preservation on Engineered Neural Tissue

This study explored different approaches to preserve engineered neural tissue (EngNT), a stabilized, cellular collagen hydrogel containing columns of aligned Schwann cells for nervous system repair. The ability to preserve EngNT without disrupting cellular and extracellular components and structures is important for clinical translation and commercialization. Stabilized cellular gels and EngNT constructs were preserved under various conditions and cell survival assessed using live/dead microscopy and metabolic assay. Optimal survival was recorded in hypothermic (4°C) conditions for 2–3 days using Hibernate^®-A media and, for longer-term cryogenic storage (liquid nitrogen), using a mixture of 60% Dulbecco's modified Eagle's medium, 30% fetal bovine serum, and 10% dimethyl sulfoxide. Functionality and structure of preserved EngNT were assessed in coculture with dorsal root ganglion neurons, which indicated that alignment of Schwann cells and the ability of EngNT to support and guide neuronal regeneration were not disrupted. The identification of conditions that preserve EngNT will inform development of storage and transport methodologies to support clinical and commercial translation of this technology and other therapies based on cellular hydrogels.

Historical perspective of cell transplantation in Parkinson’s disease

Cell grafting has been considered a therapeutic approach for Parkinson’s disease (PD) since the 1980s. The classical motor symptoms of PD are caused by the loss of dopaminergic neurons in the substantia nigra pars compacta, leading to a decrement in dopamine release in the striatum. Consequently, the therapy of cell-transplantation for PD consists in grafting dopamine-producing cells directly into the brain to reestablish dopamine levels. Different cell sources have been shown to induce functional benefits on both animal models of PD and human patients. However, the observed motor improvements are highly variable between individual subjects, and the sources of this variability are not fully understood. The purpose of this review is to provide a general overview of the pioneering studies done in animal models of PD that established the basis for the first clinical trials in humans, and compare these with the latest findings to identify the most relevant aspects that remain unanswered to date. The main focus of the discussions presented here will be on the mechanisms associated with the survival and functionality of the transplants. These include the role of the dopamine released by the grafts and the capacity of the grafted cells to extend fibers and to integrate into the motor circuit. The complete understanding of these aspects will require extensive research on basic aspects of molecular and cellular physiology, together with neuronal network function, in order to uncover the real potential of cell grafting for treating PD.

Foetal Cell Transplantation for Parkinson's Disease: Focus on Graft-Induced Dyskinesia

Transplantation of dopamine- (DA-) rich foetal ventral mesencephalic cells emerged as a promising therapy for Parkinson's disease (PD), as it allowed significant improvement of motor symptoms in several PD patients in open-label studies. However, double-blind clinical trials have been largely disappointing. The general agreement in the field is that the lack of standardization of tissue collection and preparation, together with the absence of postsurgical immunosuppression, played a key role in the failure of these studies. Moreover, a further complication that emerged in previous studies is the appearance of the so-called graft-induced dyskinesia (GID), in a subset of grafted patients, which resembles dyskinesia induced by L-DOPA but in the absence of medication. Preclinical evidence pointed to the serotonin neurons as possible players in the appearance of GID. In agreement, clinical investigations have shown that grafted tissue may contain a large number of serotonin neurons, in the order of half of the DA cells; moreover, the serotonin 5-HT1A receptor agonist buspirone has been found to produce significant dampening of GID in grafted patients. In this paper, we will review the recent preclinical and clinical studies focusing on cell transplantation for PD and on the mechanisms underlying GID.

The A9 dopamine neuron component in grafts of ventral mesencephalon is an important determinant for recovery of motor function in a rat model of Parkinson's disease

Grafts of foetal ventral mesencephalon, used in cell replacement therapy for Parkinson’s disease, are known to contain a mix of dopamine neuronal subtypes including the A9 neurons of the substantia nigra and the A10 neurons of the ventral tegmental area. However, the relative importance of these subtypes for functional repair of the brain affected by Parkinson’s disease has not been studied thoroughly. Here, we report results from a series of grafting experiments where the anatomical and functional properties of grafts either selectively lacking in A9 neurons, or with a typical A9/A10 composition were compared. The results show that the A9 component of intrastriatal grafts is of critical importance for recovery in tests on motor performance, in a rodent model of Parkinson’s disease. Analysis at the histological level indicates that this is likely to be due to the unique ability of A9 neurons to innervate and functionally activate their target structure, the dorsolateral region of the host striatum. The findings highlight dopamine neuronal subtype composition as a potentially important parameter to monitor in order to understand the variable nature of functional outcome better in transplantation studies. Furthermore, the results have interesting implications for current efforts in this field to generate well-characterized and standardized preparations of transplantable dopamine neuronal progenitors from stem cells.

Cell therapy in Huntington's disease

Huntington's disease is an autosomal dominant genetic disease, which results in progressive neuronal degeneration in the neostriatum and neocortex, and associated functional impairments in motor, cognitive, and psychiatric domains. Although the genetic mutation is identified, involving an abnormal CAG expansion within the htt gene on chromosome 4, the mechanism by which this leads to neuronal cell death and the question of why striatal neurones are targeted both remain unknown. Thus, in addition to the search for molecular and genetic strategies to inhibit development of the disease, we still need to identify effective strategies for cellular repair in affected individuals. Aspects of the human neuropathology can be well modeled by excitotoxic or metabolic lesions in experimental animals, and in transgenic mice carrying the htt mutation, providing the basis for testing alternative therapeutic strategies. The rationale and efficacy of alternative cell therapies are reviewed, including transplantation repair with embryonic striatal tissues, expansion and differentiation of striatal-like cells from stem cells, and in vivo and ex vivo gene therapy for delivery of neuroprotective growth factor molecules. Pilot and experimental clinical trials of several approaches are now also underway, and the alternative strategies are compared.

Prospects for the treatment of Parkinson's disease using neurotrophic factors

Parkinson's disease (PD) is a debilitating neurodegenerative condition that is characterised by a progressive loss of dopaminergic neurones of the substantia nigra pars compacta (SNpc) and the presence of alpha-synuclein cytoplasmic inclusions (Lewy bodies). Cardinal symptoms include tremor, bradykinesia, and rigidity, although cognitive and autonomic disturbances are not uncommon. Pharmacological treatment targeting the dopaminergic network is relatively effective at ameliorating these symptoms, especially in the early stages of the disease, but none of these therapies are curative and they generate their own problems. As dopaminergic neuronal death in PD occurs in a gradual manner, it is amenable to treatments that can either protect remaining dopaminergic neurones or prevent death of those neurones that have begun to die. Use of neurotrophic factors is a potential candidate, as various factors have been shown to increase dopaminergic neuronal survival in culture and promote survival and axonal growth in animal models of PD. Glial cell line-derived neurotrophic factor (GDNF) is currently the most effective substance that has been intensively studied and shown to have a specific 'dopaminotrophic' effect. This review will therefore focus on studies that have investigated GDNF and discuss the potential for neurotrophic factor treatment in PD.

Generation of dopaminergic neurons in the adult brain from mesencephalic precursor cells labeled with a nestin-GFP transgene

Mesencephalic precursor cells may one day provide dopaminergic neurons for the treatment of Parkinson's disease. However, the generation of dopaminergic neurons from mesencephalic precursors has been difficult to follow, partly because an appropriate means for recognizing mesencephalic ventricular zone precursors has not been available. To visualize and isolate mesencephalic precursor cells from a mixed population, we used transgenic mice and rats carrying green fluorescent protein (GFP) cDNA under the control of the nestin enhancer. nestin-driven GFP was detected in the mesencephalic ventricular zone, and it colocalized with specific markers for neural precursor cells. In addition, data from flow-cytometry indicated that Prominin/CD133, a cell-surface marker for ventricular zone cells, was expressed specifically in these GFP-positive (GFP(+)) cells. After sorting by fluorescence-activated cell sorting, the GFP(+) cells proliferated in vitro and expressed precursor cell markers but not neuronal markers. Using clonogenic sphere formation assays, we showed that this sorted population was enriched in multipotent precursor cells that could differentiate into both neurons and glia. Importantly, many neurons generated from nestin-GFP-sorted mesencephalic precursors developed a dopaminergic phenotype in vitro. Finally, nestin-GFP(+) cells were transplanted into the striatum of a rat model of Parkinson's disease. Bromodeoxyuridine-tyrosine hydroxylase double-labeling revealed that the transplanted cells generated new dopaminergic neurons within the host striatum. The implanted cells were able to restore dopaminergic function in the host striatum, as assessed by a behavioral measure: recovery from amphetamine-induced rotation. Together, these findings indicate that precursor cells harvested from the embryonic ventral mesencephalon can generate dopaminergic neurons able to restore function to the chemically denervated adult striatum.

Discordant neural tissue xenografts survive longer in immunoglobulin deficient mice

BACKGROUND

The immune response against discordant xenografts in the brain is incompletely understood and remains a major obstacle for future clinical applications of xenogeneic neural tissue transplants in neurodegenerative disorders. To determine the role of antibodies in the rejection process, we compared graft survival and immune reactions between immunoglobulin deficient (IgKO) and normal mice.

METHODS

A cell suspension of embryonic porcine ventral mesencephalon was injected into the striatum of adult normal and IgKO mice. Graft sizes and number of infiltrating CD4- and CD8-positive lymphocytes were determined by stereological methods at 4 days and 2, 4, and 6 weeks after the transplants. Microglial accumulation was determined using the optical densitometrical method. Intraparenchymal deposition of IgG was investigated at 4 days and 2 weeks.

RESULTS

The majority of IgKO mice had surviving grafts for up to 4 weeks, whereas survival was minimal in control mice beyond 4 days. Graft sizes differed significantly between IgKO and control mice at 2 weeks (P<0.01, Kruskal Wallis ANOVA, followed by Mann Whitney test). The majority of infiltrating lymphocytes were CD4-positive in control mice but CD8-positive in IgKO mice. Microglial accumulation was strong around surviving grafts in IgKO mice at 4 weeks. Prominent staining of IgG, diffuse in the transplanted hemisphere and specific on grafted neurons, was found in control mice.

CONCLUSIONS

Our results suggest that immunoglobulins play an initiating role in rejection of discordant neural xenografts. After a prolonged graft survival of approximately 4 weeks, a cellular response with a large proportion CD8-positive cells leads to rejection in IgKO mice.

Fetal tissue transplantation [correction of transplanation] in Parkinson's disease

Since the first successful attempts in 1990, human embryonic tissue transplantation has attracted the attention of multiple investigators and clinicians as a serious candidate therapy for Parkinson's disease. Although over two hundred patients have undergone the procedure, multiple issues and questions remain unresolved. We will address this topic emphasizing the recent advances in the technical aspects of the transplantation procedure in light of the limited animal and clinical experience available.

Basic neural transplantation techniques. I. Dissociated cell suspension grafts of embryonic ventral mesencephalon in the adult rat brain

Lesions and grafts in the nigrostriatal dopamine system in rats is widely used as a model of degeneration and regeneration in the CNS, and the development for alternative strategies for treatment in Parkinson's disease. The methods of preparing a dissociated cell suspension of embryonic rat substantia nigra and its transplantation into the brain of adult rats are described. This is the first of a series of methodological reports on the basic methodology and refinements of neural transplantation techniques in the mammalian central nervous system.

Cryopreservation, survival and function of intrastriatal fetal mesencephalic grafts in a rat model of Parkinson's disease

In the present study we quantitatively assessed to what extent freeze-storage at liquid nitrogen temperature influences the survival and function of fetal mesencephalic grafts in the dopamine-depleted rat striatum. Ventral mesencephalic (VM) tissue was dissected from rat fetuses and stored overnight in a preservative medium at 4 degrees C (hibernation). It was grafted intrastriatally either as a fresh cell suspension or was frozen as tissue fragments or as a cell suspension after stepwise incubation in ascending concentrations of dimethyl-sulphoxide. Following a cryopreservation interval of 80 days in liquid nitrogen, the frozen samples were rapidly thawed, rinsed, and grafted. Cellular viabilities of graft cell suspensions, as assessed by ethidium bromide/acridine orange staining, were decreased from 90% in fresh tissue to 38-35% in frozen and thawed tissue. Amphetamine-induced turning behavior at 6 weeks post-grafting was significantly attenuated in hosts that had received fresh grafts or grafts that were frozen as tissue fragments. Tyrosine hydroxylase-(TH-) immunocytochemistry of recipient brains revealed significant decreases in TH-positive graft cell numbers in rats grafted with cryopreserved tissue (38-42% of fresh tissue). Moreover, the dye exclusion viability of thawed VM tissue was found to accurately predict the subsequent graft survival. There was no difference with respect to graft cell numbers between the two freezing methods employed, though block storage seems to be more simple from a practical point of view.(ABSTRACT TRUNCATED AT 250 WORDS)