Clinical observations after neural transplantation in Parkinson's disease

Myocyte enhancer factor 2C as a neurogenic and antiapoptotic transcription factor in murine embryonic stem cells

Cell-based therapies require a reliable source of cells that can be easily grown, undergo directed differentiation, and remain viable after transplantation. Here, we generated stably transformed murine ES (embryonic stem) cells that express a constitutively active form of myocyte enhancer factor 2C (MEF2CA). MEF2C has been implicated as a calcium-dependent transcription factor that enhances survival and affects synapse formation of neurons as well as differentiation of cardiomyocytes. We now report that expression of MEF2CA, both in vitro and in vivo, under regulation of the nestin enhancer effectively produces "neuronal" progenitor cells that differentiate into a virtually pure population of neurons. Histological, electrophysiological, and behavioral analyses demonstrate that MEF2C-directed neuronal progenitor cells transplanted into a mouse model of cerebral ischemia can successfully differentiate into functioning neurons and ameliorate stroke-induced behavioral deficits.

Effects on differentiation of embryonic ventral midbrain progenitors by Lmx1a, Msx1, Ngn2, and Pitx3

Neurons derived from neural stem cells could potentially be used for cell therapy in neurodegenerative disorders, such as Parkinson's disease. To achieve controlled differentiation of neural stem cells, we expressed transcription factors involved in the development of midbrain dopaminergic neurons in rat and human neural progenitors. Using retroviral-mediated transgene delivery, we overexpressed Lmx1a (LIM homeobox transcription factor 1, alpha), Msx1 (msh homeobox homolog 1), Ngn2 (neurogenin 2), or Pitx3 (paired-like homeodomain transcription factor 3) in neurospheres derived from embryonic day 14.5 rat ventral mesencephalic progenitors. We also expressed either Lmx1a or Msx1 in the human embryonic midbrain-derived progenitor cell line NGC-407. Rat cells transduced with Ngn2 exited the cell cycle and expressed the neuronal marker microtubule-associated protein 2 and catecholamine-neuron protein vesicular monoamine transporter 2. Interestingly, Pitx3 downregulated the expression of SOX2 (SRY-box containing gene 2) and Nestin, altered cell morphology, but never induced neuronal or glial differentiation. Ngn2 exhibited a strong neuron-inducing effect. In contrast, few Lmx1a-transduced cells matured into neurons, and Msx1 overexpression promoted oligodendrogenesis rather than neuronal differentiation. Importantly, none of these four genes, alone or in combination, enhanced differentiation of rat neural stem cells into dopaminergic neurons. Notably, the overexpression of Lmx1a, but not Msx1, in human neural progenitors increased the yield of tyrosine hydroxylase-immunoreactive cells by threefold. Together, we demonstrate that induced overexpression of transcription factor genes has profound and specific effects on the differentiation of rat and human midbrain progenitors, although few dopamine neurons are generated.

Stem cells and neurodegenerative diseases

Neurodegenerative diseases are characterized by the neurodegenerative changes or apoptosis of neurons involved in networks, which are important to specific physiological functions. With the development of old-aging society, the incidence of neurodegenerative diseases is on the increase. However, it is difficult to diagnose for most of neurodegenerative diseases. At present, there are too few effective therapies. Advances in stem cell biology have raised the hope and possibility for the therapy of neurodegenerative diseases. Recently, stem cells have been widely attempted to treat neurodegenerative diseases of animal model. Here we review the progress and prospects of various stem cells, including embryonic stem cells, mesenchymal stem cell and neural stem cells and so on, for the treatments of neurodegenerative diseases, such as Parkinson's disease, Alzheimer's disease, Huntington' disease and Amyotrophic lateral sclerosis/Lou Gehrig's disease.

Transplantation of neural stem cells into the traumatized brain induces lymphocyte infiltration

OBJECTIVE

This study examined the lymphocyte infiltration induced by neural stem cell grafts in the traumatized brain.

METHODS

Sixty Sprague-Dawley rats were assigned randomly to transplantation (n = 30) or control (n = 30) groups, and each rat was subjected to brain contusion. The neural stem cells derived from Wistar rats were transplanted into the lesion of the transplantation group, and saline was injected instead into the controls. Local lymphocyte infiltration was studied using haematoxylin and eosin staining, immunohistochemistry and flow cytometry. The immunogenicity of neural stem cells was evaluated using MHC-I expression.

RESULTS

About 6.57 +/- 0.44% of the neural stem cells expressed MHC-I. In the transplantation group, histological examination and immunohistochemistry revealed significant lymphocyte infiltration in the contusion. The ratio of CD4(+) lymphocytes to total cells in the lesions was 13.28 +/- 1.60% in the transplantation group and 0.41 +/- 0.12% in the controls (p < 0.01). Likewise, the ratio of CD8(+) lymphocytes to total cells was 5.11 +/- 1.03% in the transplantation group and 0.57 +/- 0.26% in the controls (p < 0.01).

CONCLUSIONS

Neural stem cells possess immunogenicity and can induce lymphocyte infiltration when transplanted into a traumatised brain. Our findings imply that immunosuppressive treatment is necessary following neural stem cell transplantation.

Noninvasive cell tracking

Cell-based therapies may gain future importance in defeating different kinds of diseases, including cancer, immunological disorders, neurodegenerative diseases, cardiac infarction and stroke. In this context, the noninvasive localization of the transplanted cells and the monitoring of their migration can facilitate basic research on the underlying mechanism and improve clinical translation. In this chapter, different ways to label and track cells in vivo are described. The oldest and only clinically established method is leukocyte scintigraphy, which enables a (semi)quantitative assessment of cell assemblies and, thus, the localization of inflammation foci. Noninvasive imaging of fewer or even single cells succeeds with MRI after labeling of the cells with (ultrasmall) superparamagentic iron oxide particles (SPIO and USPIO). However, in order to gain an acceptable signal-to-noise ratio, at a sufficiently high spatial resolution of the MR sequence to visualize a small amount of cells, experimental MR scanners working at high magnetic fields are usually required. Nevertheless, feasibility of clinical translation has been achieved by showing the localization of USPIO-labeled dendritic cells in cervical lymph nodes of patients by clinical MRI.Cell-tracking approaches using optical methods are important for preclinical research. Here, cells are labeled either with fluorescent dyes or quantum dots, or transfected with plasmids coding for fluorescent proteins such as green fluorescent protein (GFP) or red fluorescent protein (RFP). The advantage of the latter approach is that the label does not get lost during cell division and, thus, makes imaging of proliferating transplanted cells (e.g., tumor cells) possible. In summary, there are several promising options for noninvasive cell tracking, which have different strengths and limitations that should be considered when planning cell-tracking experiments.

GDNF delivery for Parkinson's disease

The mainstays of Parkinson's disease (PD) treatment remain symptomatic, including initial dopamine replacement and subsequent deep brain stimulation, however, neither of these approaches is neuroprotective. Neurotrophic factors - proteins that activate cell signalling pathways regulating neuronal survival, differentiation, growth and regeneration - represent an alternative for treating dopaminergic neurons in PD but are difficult to administer clinically because they do not pass through the blood-brain barrier. Glial cell line-derived neurotrophic factor (GDNF) has potent neurotrophic effects particularly but not exclusively on dopaminergic neurons; in animal models of PD, it has consistently demonstrated both neuroprotective and neuroregenerative effects when provided continuously, either by means of a viral vector or through continuous infusion either into the cerebral ventricles (ICV) or directly into the denervated putamen. This led to a human PD study in which GDNF was administered by monthly bolus intracerebroventricular injections, however, no clinical benefit resulted, probably because of the limited penetration to the target brain areas, and instead significant side effects occurred. In an open-label study of continuous intraputamenal GDNF infusion in five patients (one unilaterally and four bilaterally), we reported excellent tolerance, few side effects and clinical benefit evident within three months of the commencement of treatment. The clinical improvement was sustained and progressive, and by 24-months patients demonstrated a 57 and 63% improvement in their off-medication motor and activities of daily living UPDRS subscores, respectively, with clear benefit in dyskinesias. The benefit was associated with a significant increase in putamenal 18F-dopa uptake on positron emission tomography (PET), and in one patient coming to autopsy after 43 months of unilateral infusion there was evident increased tyrosine hydroxylase immunopositive nerve fibres in the infused putamen. A second open trial in 10 patients using unilateral intraputamenal GDNF infusions has also demonstrated a greater than 30% bilateral benefit in both on- and off-medication scores at 24 weeks. Based on our 6-month results, a randomized controlled clinical trial was conducted to confirm the open-label results, however, GDNF infusion over 6-months did not confer the predetermined level of clinical benefit to patients with PD despite increased 18F-dopa uptake surrounding the catheter tip. It is possible that technical differences between this trial and the positive open label studies contributed to this negative outcome.

Stem-cell-based strategies for the treatment of Parkinson's disease

BACKGROUND

Cell transplantation to replace lost neurons in neurodegenerative diseases such as Parkinson's disease (PD) offers a hopeful prospect for many patients. Previously, fetal grafts have been shown to survive, integrate and induce functional recovery in PD patients. However, limited tissue availability has haltered the widespread use of this therapy and begs the demand for alternative tissue sources. In this regard, stem cells may constitute one such source.

OBJECTIVE/METHODS

In this review we outline various types of stem cells currently available and provide an overview of their possible application for PD. We address not only the obvious possibility of using stem cells in cell replacement therapy but also the benefits of stem cell lines in drug discovery.

RESULTS/CONCLUSION

Stem cells carrying reporters or mutations in genes linked to familial PD are likely to contribute to the identification of new drug targets and subsequent development of new drugs for PD. Thus, stem cells are, and will be more so in the future, invaluable tools in the quest for new therapies against neurodegenerative diseases such as PD.

Differential effects on forelimb grasping behavior induced by fetal dopaminergic grafts in hemiparkinsonian rats

Skilled forelimb movements depend on an intact dopaminergic (DA) neurotransmission and are substantially impaired in the unilateral rat model of Parkinson's disease. It has remained unclear, however, to what extent reaching and grasping movements can be influenced by intrastriatal transplantation of fetal DA neurons. Here an extensive behavioral assessment of skilled forelimb movement patterns in hemiparkinsonian and DA-grafted rats was carried out. Good DA graft survival was accompanied by a compensation of drug-induced rotational asymmetries. Interestingly, skilled forelimb use was significantly improved in transplanted animals as compared to lesion-only animals in the staircase test. Qualitative analysis of single forelimb reaching movement components revealed dissociable patterns of graft effects: while some movement components in grafted animals improved, others remained unchanged or even deteriorated. These findings provide novel insights into the complex interactions of graft-derived restoration of DA neurotransmission and skilled forelimb behavior.

Cell transplantation for Huntington's disease

Cell transplantation for Huntington's disease has developed over the last decade to clinical application in pilot trials in the USA, France and the UK. Although the procedures are feasible, and under appropriate conditions safe, evidence for efficacy is still limited, which has led to some calls that further development should be discontinued. We review the background of striatal cell transplantation in experimental animal models of Huntington's disease and the rationale for applying similar strategies in the human disease, and we survey the present status of the preliminary studies that have so far been undertaken in patients. When we consider the variety of parameters and principles that remain poorly defined -- such as the optimal source, age, dissection, preparation, implantation, immunoprotection and assessment protocols -- it is not surprising that clinical efficacy is still unreliable. However, since these protocols are all tractable to experimental refinement, we consider that the potential for cell transplantation in Huntington's disease is greater than has yet been realised, and remains a therapeutic strategy worthy of investigation and pursuit.

"NeuroStem Chip": a novel highly specialized tool to study neural differentiation pathways in human stem cells

Background

Human stem cells are viewed as a possible source of neurons for a cell-based therapy of neurodegenerative disorders, such as Parkinson's disease. Several protocols that generate different types of neurons from human stem cells (hSCs) have been developed. Nevertheless, the cellular mechanisms that underlie the development of neurons in vitro as they are subjected to the specific differentiation protocols are often poorly understood.

Results

We have designed a focused DNA (oligonucleotide-based) large-scale microarray platform (named "NeuroStem Chip") and used it to study gene expression patterns in hSCs as they differentiate into neurons. We have selected genes that are relevant to cells (i) being stem cells, (ii) becoming neurons, and (iii) being neurons. The NeuroStem Chip has over 1,300 pre-selected gene targets and multiple controls spotted in quadruplicates (~46,000 spots total). In this study, we present the NeuroStem Chip in detail and describe the special advantages it offers to the fields of experimental neurology and stem cell biology. To illustrate the utility of NeuroStem Chip platform, we have characterized an undifferentiated population of pluripotent human embryonic stem cells (hESCs, cell line SA02). In addition, we have performed a comparative gene expression analysis of those cells versus a heterogeneous population of hESC-derived cells committed towards neuronal/dopaminergic differentiation pathway by co-culturing with PA6 stromal cells for 16 days and containing a few tyrosine hydroxylase-positive dopaminergic neurons.

Conclusion

We characterized the gene expression profiles of undifferentiated and dopaminergic lineage-committed hESC-derived cells using a highly focused custom microarray platform (NeuroStem Chip) that can become an important research tool in human stem cell biology. We propose that the areas of application for NeuroStem microarray platform could be the following: (i) characterization of the expression of established, pre-selected gene targets in hSC lines, including newly derived ones, (ii) longitudinal quality control for maintained hSC populations, (iii) following gene expression changes during differentiation under defined cell culture conditions, and (iv) confirming the success of differentiation into specific neuronal subtypes.

Culturing of glial and neuronal cells on polysialic acid

Although peripheral nerves exhibit regeneration capacities after transection injuries, the success of nerve repair depends crucially on the length of the gap. In addition to autologous nerve grafting as the conventional neurosurgical treatment to overcome long gaps, alternative strategies are needed. Numerous experimental studies have been undertaken to find the optimal material for production of artificial prostheses, which can be introduced as conduits between the nerve stumps. The current study follows the aim to establish polysialic acid (polySia), a homopolymer of alpha2,8-linked sialic acid residues, as a novel, biocompatible, and bioresorbable material for nerve tissue engineering. As a first step towards this goal, protocols for efficient coating of cell culture dishes with soluble polySia were established. In addition, primary nerve cells which are candidates for reconstructive therapies, including neonatal and adult Schwann cells, neural progenitor cells, spinal ganglionic neurons and motoneurons were cultured on polySia substrates. Cultures were evaluated with regard to cell survival and cell proliferation capacities. polySia turned out to be stable under cell culture conditions, and induced degradable and degradation products had no negative effects on cell cultures. Furthermore, polySia revealed its compatibility for several cell types derived from rat embryonic, postnatal and adult nervous tissue when used as a substrate.

Applications of Clinical Dopamine Imaging

Recent technologic advances make it increasingly possible to image neurotransmitter systems in living human brain, The dopamine system has been most intensively studied owing to its involvement in several brain disorders such as Parkinson's disease and Huntington's disease, as well as psychiatric disorders such as schizophrenia, depression, and compulsive behavioral disorders of multiple types. A variety of aspects of dopamine receptor density, function, and dopaminergic terminal status can now be assessed using the minimally invasive neuroimaging techniques of positron emission tomography and single-photon emission computed tomography. Although these techniques are currently used most often in the context of research, clinical applications are rapidly emerging.

The role of growth/differentiation factor 5 (GDF5) in the induction and survival of midbrain dopaminergic neurones: relevance to Parkinson's disease treatment

Growth/differentiation factor-5 (GDF5) is a member of the transforming growth factor-beta superfamily which has potent effects on dopaminergic neurones in vitro and in vivo. GDF5 is under investigation as a potential therapeutic agent for Parkinson's disease (PD), which is caused by the progressive degeneration of dopaminergic neurones projecting from the substantia nigra (SN) to the striatum. In the rat ventral mesencephalon (VM; the developing SN), GDF5 expression peaks at embryonic day 14, the time at which dopaminergic neurones undergo terminal differentiation. Addition of GDF5 protein to cultures of embryonic rat VM increases the survival and improves the morphology of dopaminergic neurones in these cultures. GDF5 treatment also increases the number of cells which adopt a dopaminergic phenotype in cultures of VM progenitor cells. Intracerebral administration of GDF5 has potent neuroprotective and restorative effects on the nigrostriatal pathway in animal models of PD. Furthermore, addition of GDF5 protein to embryonic rat dopaminergic neuronal transplants improves their survival and function in a rat model of PD. Thus, GDF5 has potential applications to PD therapy as a dopaminergic neuroprotective agent and as a factor that may induce a dopaminergic neuronal fate in unrestricted progenitor cells.

Nucleofection is the most efficient nonviral transfection method for neuronal stem cells derived from ventral mesencephali with no changes in cell composition or dopaminergic fate

Neuronal progenitor cells (NPCs) play an important role in potential regenerative therapeutic strategies for neurodegenerative diseases, such as Parkinson disease. However, survival of transplanted cells is, as yet, limited, and the identification of grafted cells in situ remains difficult. The use of NPCs could be more effective with regard to a better survival and maturation when transfected with one or more neurotrophic factors. Therefore, we investigated the possibility of transfecting mesencephalic neuronal progenitors with different constructs carrying neurotrophic factors or the expression reporters enhanced green fluorescence protein (EGFP) and red fluorescent protein (DsRed). Different techniques for transfection were compared, and the highest transfection rate of up to 47% was achieved by nucleofection. Mesencephalic neuronal progenitors survived the transfection procedure; 6 hours after transfection, viability was approximately 40%, and the transfected cells differentiated into, for example, tyrosine hydroxylase-positive neurons. Within the group of transfected cells, many progenitors and several neurons were found. To provide the progenitor cells with a neurotrophic factor, different isoforms of fibroblast growth factor-2 were introduced. To follow the behavior of the transfected cells in vitro, functional tests such as the cell viability assay (water-soluble tetrazolium salt assay [WST-1]) and the cell proliferation assay (5-bromo-2'-deoxyuridine-enzyme-linked immunosorbent assay) were performed. In addition, these transfected NPCs were viable after transplantation, expressed tyrosine hydroxylase in vivo, and could easily be detected within the host striatum because of their EGFP expression. This study shows that genetic modification of neural progenitors could provide attractive perspectives for new therapeutic concepts in neurodegenerative diseases.

Heterogeneous Dopamine Neurochemistry in the Striatum: The Fountain-Drain Matrix

In contrast to the relatively high attention paid to the structural heterogeneity of striatal dopamine (DA) innervation, little attention has been focused on the possible striatal heterogeneity for release and uptake of DA. By using amperometric methods, we found striatal regions showing a DA decrease during the medial forebrain bundle stimulation (drain areas) near to other zones that showed an increase in DA concentration (fountain areas). Both areas were intermixed to form a tridimensional matrix to regulate DA concentration throughout the striatum (fountain-drain matrix). The response to electrical stimuli of different amplitudes and durations and to different drugs (alpha-methyl-l-tyrosine, cocaine, gamma-butyrolactone, and haloperidol) suggests that regional differences for both DA release/DA uptake and DA cell firing autoregulation are behind the striatal fountain-drain matrix. The high diversity of DA activity observed in the striatum is a new framework for analyzing experimental and clinical phenomena.

Estimating the value of novel interventions for Parkinson's disease: an early decision-making model with application to dopamine cell replacement

A long-term cost-effectiveness model for early decision-making and estimation of outcomes of novel therapeutic procedures for Parkinson's disease (PD) was developed based on the Hoehn and Yahr (HY) stages of PD. Results provided support for model validity. Model application to a future dopamine cell replacement therapy indicated long-term cost offsets and gains in quality-adjusted life years (QALYs) in early onset PD (HY III-IV), as compared to standard drug therapy. The maximum price premium (i.e., profit or compensation for developmental costs) for the intervention to remain cost-effective was estimated to euro12000-64000 according to cost-per-QALY thresholds of euro38000-70000 and depending on whether all or only medical direct costs are considered. The study illustrates the value of early health economic modeling and the described model shows promise as a means to estimate outcomes and aid decision-making regarding novel interventions for PD.

Dopaminergic properties and function after grafting of attached neural precursor cultures

Generation of dopaminergic (DA) neurons from multipotent embryonic progenitors represents a promising therapeutical strategy for Parkinson's disease (PD). Aim of the present study was the establishment of enhanced cell culture conditions, which optimize the use of midbrain progenitor cells in animal models of PD. In addition, the progenitor cells were characterized during expansion and differentiation according to morphological and electrophysiological criteria and compared to primary tissue. Here, we report that CNS precursors can be expanded in vitro up to 40-fold and afterwards be efficiently differentiated into DA neurons. After 4-5 days under differentiation conditions, more than 70% of the neurons were TH+, equivalent to 30% of the total cell population. Calcium imaging revealed the presence of calcium-permeable AMPA receptors in the differentiated precursors which are capable to contribute to many developmental processes. The overall survival rate, degree of reinnervation and the behavioral performance after transplantation of 4 days in-vitro-differentiated cells were similar to results after direct grafting of E14 ventral mesencephalic cells, whereas after shorter or longer differentiation periods, respectively, less effects were achieved. Compared to the amount of in-vitro-generated DA neurons, the survival rate was only 0.8%, indicating that these cells are very vulnerable. Our results suggest that expanded and differentiated DA precursors from attached cultures can survive microtransplantation and integrate within the striatum in terms of behavioral recovery. However, there is only a short time window during in vitro differentiation, in which enough cells are already differentiated towards a DA phenotype and simultaneously not too mature for implantation. However, additional factors and/or genetical manipulation of these expanded progenitors will be required to increase their in vivo survival in order to improve both the ethical and the technical outlook for the use of fetal tissue in clinical transplantation.

Long-term assessment of striatal dopamine transporters in parkinsonian patients with intrastriatal embryonic mesencephalic grafts

PURPOSE

Single-photon emission computed tomography (SPECT) of striatal dopamine transporters (DAT) has been used to demonstrate presynaptic dopaminergic dysfunction and to monitor the progression of Parkinson's disease. In parkinsonian patients who were implanted with embryonic mesencephalic tissue in the striatum, positron emission tomography (PET) has shown an increase in striatal [(18)F]dopa uptake as an indicator of graft survival and striatal reinnervation. The aim of this study was to investigate two patients who had undergone bilateral intrastriatal transplantation of human embryonic mesencephalic tissue using SPECT and the (123)I-labelled DAT ligand N-(3-iodopropen-2-yl)-2beta-carbomethoxy-3beta-(4-chlorophenyl) tropane (IPT).

METHODS

Two patients were subjected to [(123)I]IPT SPECT according to a standardised protocol prospectively and repeatedly up to 8 years after transplantation.

RESULTS

From baseline to year 3 after transplantation, mean striatal DAT availability increased by a mean of 61% (93% and 29% in patients 1 and 2, respectively). It then remained relatively stable up to 8 years in patient 2, but increased further by another 77% of baseline values in patient 1. Clinically, both patients experienced a moderate improvement in motor performance but developed moderate (patient 2) to severe (patient 1) off-medication dyskinesias.

CONCLUSION

Our data indicate that DAT imaging using IPT and SPECT can be used to demonstrate graft survival following dopaminergic tissue implantation. Because SPECT with DAT ligands is widely available in the routine clinical setting, this methodology may be a useful alternative to [(18)F]dopa PET for repeated scanning of grafted parkinsonian patients. The relevance of the long-term increase in DAT binding for the development of off-medication dyskinesias remains to be elucidated further.

Stem cell therapy for human brain disorders

Transplantation of stem cells or their derivatives, and mobilization of endogenous stem cells in the adult brain, have been proposed as future therapies for various brain disorders such as Parkinson's disease and stroke. In support, recent progress shows that neurons suitable for transplantation can be generated from stem cells in culture, and that the adult brain produces new neurons from its own stem cells in response to injury. However, from a clinical perspective, the development of stem cell-based therapies for brain diseases is still at an early stage. Many basic issues remain to be solved and we need to move forward with caution and avoid scientifically ill-founded trials in patients. We do not know the best stem cell source, and research on embryonic stem cells and stem cells from embryonic or adult brain or from other tissues should therefore be performed in parallel. We need to understand how to control stem cell proliferation and differentiation into specific cell types, induce their integration into neural networks, and optimize the functional recovery in animal models closely resembling the human disease. All these scientific efforts are clearly justified because, for the first time, there is now real hope that we in the future can offer patients with currently intractable diseases effective cell-based treatments to restore brain function.

Continuous exposure to glial cell line-derived neurotrophic factor to mature dopaminergic transplants impairs the graft’s ability to improve spontaneous motor behavior in parkinsonian rats

Functional recovery following intrastriatal transplantation of fetal dopaminergic neurons in animal models of Parkinson's disease is, at least in part, dependent on the number of surviving dopaminergic neurons and the degree of graft-derived dopaminergic reinnervation of the host striatum. In the present study, we analyzed whether continuous exposure of glial cell line-derived neurotrophic factor (GDNF) to mature dopaminergic grafts could further boost the functional outcome of widespread intrastriatal dopaminergic grafts. Rats with dopamine-denervating lesions received multiple intrastriatal transplants of fetal dopaminergic cells and graft-induced behavioral effects were analyzed in drug-induced and spontaneous motor behaviors. At three months after grafting, animals received intrastriatal injections of recombinant lentiviral vectors encoding for either human GDNF or the green fluorescent protein. Continuous exposure of GDNF to the grafts did not boost the functional recovery beyond what was observed in the control animals. Rather, in some of the spontaneous motor behaviors, animals in the GDNF-group showed deterioration as compared with control animals, and this negative effect of GDNF was associated with a down-regulation of the tyrosine hydroxylase enzyme. Based on these and our earlier results, we propose that intrastriatal administration of GDNF at the time of or shortly after grafting is highly effective in initially promoting the cell survival and fiber outgrowth from the grafts. However, once the grafts are mature, GDNF's ability to boost dopaminergic neurotransmission follows the same dynamics as for the native nigral dopaminergic neurons, which appears to be dependent on the concentration of GDNF. Since rather low doses of glial cell line-derived neurotrophic factor at nanogram levels appear to saturate these effects, it may be critical to adjust GDNF levels using tightly regulated gene expression systems.

Generation of graftable dopaminergic neuron progenitors from mouse ES cells by a combination of coculture and neurosphere methods

Parkinson's disease is characterized by a loss of midbrain dopamine (DA) neurons and is generally viewed as a potential target for stem cell therapy. Although several studies have reported the generation of postmitotic DA neurons from embryonic stem (ES) cells, it is unknown whether the proliferative progenitors of DA neurons can be isolated in vitro. To investigate this possibility, we have developed a combined approach in which ES cells are cocultured with PA6 stromal cells to expose them to stromal cell-derived inducing activity (SDIA) and are then cultured as neurospheres. Mouse ES cell colonies were detached from PA6 feeder cells after 8 days of SDIA treatment and then expanded as spheres for another 4 days in serum-free medium supplemented with fibroblast growth factor-2. The spheres exhibited neural stem cell characteristics and contained few DA neurons at this stage of culture. After being induced to differentiate on polyornithine/laminin-coated dishes for 7 days, these spheres generated DA neurons in vitro at a relatively low frequency. Intriguingly, addition of PA6 cell conditioned medium to the sphere culture medium significantly increased the percentage of DA neurons to 25-30% of the total number of neurons. Transplantation of conditioned medium-treated day 4 spheres, which contained DA neuron progenitors, into the mouse striatum resulted in the generation of a significant number of graft-derived DA neurons. These findings suggest that progenitors of DA neurons are generated and can proliferate in ES cell-derived neurospheres induced by serial SDIA and PA6 conditioned medium treatment.

Olfactory ensheathing glial co-grafts improve functional recovery in rats with 6-OHDA lesions

Olfactory ensheathing cells (OEC) transplanted to the site of a spinal cord injury can promote axonal sparing/regeneration and functional recovery. The purpose of this study was to investigate if OEC enhance the effects of grafted dopamine-neuron-rich ventral mesencephalic tissue (VM) in a rodent model of Parkinson's disease. We co-grafted VM with either OEC or astrocytes derived from the same olfactory bulbs as the OEC to rats with a unilateral 6-hydroxydopamine lesion of the nigrostriatal system. Co-grafting fetal VM with OEC, but not with astrocytes enhanced dopamine cell survival, striatal reinnervation and functional recovery of amphetamine- and apomorphine-induced rotational behaviour compared with grafting embryonic VM alone. Grafting OEC or astrocytes alone had no effects. Intriguingly, only in the presence of OEC co-grafts, did dopamine neurons extend strikingly long neurites that reached peripheral striatal compartments. Comparable results were observed in a co-culture system where OEC promoted dopamine cell survival and neurite elongation through a mechanism involving both releasable factors and direct contact. Cell type analysis of fetal VM grafts suggested that dopamine neurons of the substantia nigra rather than of the ventral tegmental area were increased in the presence of OEC co-grafts. We conclude that the addition of OEC enhances efficacy of grafted immature dopamine neurons in a rat Parkinson's disease model.

Factors affecting the clinical outcome after neural transplantation in Parkinson's disease

Intrastriatal grafts of embryonic mesencephalic tissue can survive in the brains of patients with Parkinson's disease, but the degree of symptomatic relief is highly variable and some cases develop troublesome dyskinesias. Here we explored, using clinical assessment and 18F-dopa and 11C-raclopride PET, factors which may influence the functional outcome after transplantation. We observed increased 18F-dopa uptake in the grafted putamen, signifying continued survival of the transplanted dopaminergic neurons, in parallel with a progressive reduction of 18F-dopa uptake in non-grafted regions for the whole patient group. The patients with the best functional outcome after transplantation exhibited no dopaminergic denervation in areas outside the grafted areas either preoperatively or at 1 or 2 years post-operatively. In contrast, patients with no or modest clinical benefit showed reduction of 18F-dopa in ventral striatum prior to or following transplantation, which may have limited graft-induced improvement. We obtained no evidence that dyskinesias were caused by abnormal dopamine (DA) release from the grafts. As has been observed for intrinsic dopaminergic neurons, there was a significant correlation between 18F-dopa uptake and methamphetamine-induced change of 11C-raclopride binding (as a measure of DA release) in the putamen containing the graft. Furthermore, we observed no correlation between 11C-raclopride binding in anterior, posterior or entire putamen under basal conditions or after methamphetamine, and dyskinesia severity scores in the contralateral side of the body. Withdrawal of immunosuppression at 29 months after transplantation caused no reduction of 18F-dopa uptake or worsening of UPDRS motor score, indicating continued survival and function of the graft. However, patients showed increased dyskinesia scores, which might have been caused either by growth of the graft or worsening of a low-grade inflammation around the graft. These findings indicate that poor outcome after transplantation is associated with progressive dopaminergic denervation in areas outside the grafts, a process which may have started already before surgery. Also, that the development of dyskinesias after transplantation is not associated with excessive DA release from the grafts. Finally, our data provide evidence that long-term immunosuppression can be withdrawn without interfering with graft survival or the motor recovery induced by transplantation.

Cell therapy in Parkinson's disease

The clinical studies with intrastriatal transplants of fetal mesencephalic tissue in Parkinson's disease (PD) patients have provided proof-of-principle for the cell replacement strategy in this disorder. The grafted dopaminergic neurons can reinnervate the denervated striatum, restore regulated dopamine (DA) release and movement-related frontal cortical activation, and give rise to significant symptomatic relief. In the most successful cases, patients have been able to withdraw L-dopa treatment after transplantation and resume an independent life. However, there are currently several problems linked to the use of fetal tissue: 1) lack of sufficient amounts of tissue for transplantation in a large number of patients, 2) variability of functional outcome with some patients showing major improvement and others modest if any clinical benefit, and 3) occurrence of troublesome dyskinesias in a significant proportion of patients after transplantation. Thus, neural transplantation is still at an experimental stage in PD. For the development of a clinically useful cell therapy, we need to define better criteria for patient selection and how graft placement should be optimized in each patient. We also need to explore in more detail the importance for functional outcome of the dissection and cellular composition of the graft tissue as well as of immunological mechanisms. Strategies to prevent the development of dyskinesias after grafting have to be developed. Finally, we need to generate large numbers of viable DA neurons in preparations that are standardized and quality controlled. The stem cell technology may provide a virtually unlimited source of DA neurons, but several scientific issues need to be addressed before stem cell-based therapies can be tested in PD patients.

Immune problems in central nervous system cell therapy

Transplantation of cells and tissues to the mammalian brain and CNS has revived the interest in the immunological status of brain and its response to grafted tissue. The previously held view that the brain was an absolute "immunologically privileged site" allowing indefinite survival without rejection of grafts of cells has proven to be wrong. Thus, the brain should be regarded as a site where immune responses can occur, albeit in a modified form, and under certain circumstances these are as vigorous as those seen in other peripheral sites. Clinical cell transplant trials have now been performed in Parkinson's disease, Huntington's disease, demyelinating diseases, retinal disorders, stroke, epilepsy, and even deafness, and normally are designed as cell replacement strategies, although implantation of genetically modified cells for supplementation of growth factors has also been tried. In addition, some disorders of the CNS for which cell therapies are being considered have an immunological basis, such as multiple sclerosis, which further complicates the situation. Embryonic neural tissue allografted into the CNS of animals and patients with neurodegenerative conditions survives, makes and receives synapses, and ameliorates behavioral deficits. The use of aborted human tissue is logistically and ethically complicated, which has lead to the search for alternative sources of cells, including xenogeneic tissue, genetically modified cells, and stem cells, all of which can and will induce some level of immune reaction. We review some of the immunological factors involved in transplantation of cells to CNS.

Factors involved in the determination of the neurotransmitter phenotype of developing neurons of the CNS: Applications in cell replacement treatment for Parkinson's disease

The developmental stages involved in the conversion of stem cells to fully functional neurons of specific neurotransmitter phenotype are complex and not fully understood. Over the past decade many studies have been published that demonstrate that in vitro manipulation of the epigenetic environment of the stem cells allows experimental control of final neuronal phenotypic choice. This review presents the evidence for the involvement of a number of endogenous neurobiochemicals, which have been reported to potently influence DAergic (and other neurotransmitter) phenotype expression in vitro. They act at different stages on the pathway to neurotransmitter phenotype determination, and in different ways. Many are better known for their involvement in other aspects of development, and in other biochemical roles. Their proper place, and precise roles, in neurotransmitter phenotype determination in vivo will no doubt be determined in the future. Meanwhile, considerable medical benefits are offered from producing large, long-term, viable cryostores of self-regenerating multipotential neural precursor cells (i.e., brain stem cells), which can be used for cell replacement therapies in the treatment of degenerative brain diseases, such as Parkinson's disease.

Increased fiber outgrowth from xeno-transplanted human embryonic dopaminergic neurons with co-implants of polymer-encapsulated genetically modified cells releasing glial cell line-derived neurotrophic factor

We investigated whether a continuous supply of glial cell line-derived neurotrophic factor (GDNF) via encapsulated genetically modified cells can promote survival and fiber outgrowth from xenotransplanted human dopaminergic neurons. Cells genetically engineered to continuously secrete GDNF were confined in hollow fiber-based macrocapsules. Each hemiparkinsonian rat received either a single C2C12-hGDNF capsule (n=8) or a C2C12-control capsule (n=8) concomitantly with human embryonic ventral mesencephalic cell suspension transplants. Our results show that fiber outgrowth in the area between the capsule and the graft is more extensive in rats with GDNF-releasing capsules than in rats with control capsules. We suggest that continuous and safe delivery of GDNF to the brain could be a potential way to optimize neural transplantation as a therapy for Parkinson's disease.

Cell type analysis of functional fetal dopamine cell suspension transplants in the striatum and substantia nigra of patients with Parkinson's disease

We report the first post-mortem analysis of two patients with Parkinson's disease who received fetal midbrain transplants as a cell suspension in the striatum, and in one case also in the substantia nigra. These patients had a favourable clinical evolution and positive 18F-fluorodopa PET scans and did not develop motor complications. The surviving transplanted dopamine neurons were positively identified with phenotypic markers of normal control human substantia nigra (n = 3), such as tyrosine hydroxylase, G-protein-coupled inward rectifying current potassium channel type 2 (Girk2) and calbindin. The grafts restored the cell type that provides specific dopaminergic innervation to the most affected striatal regions in the parkinsonian brain. Such transplants were able to densely reinnervate the host putamen with new dopamine fibres. The patients received only 6 months of standard immune suppression, yet by post-mortem analysis 3-4 years after surgery the transplants appeared only mildly immunogenic to the host brain, by analysis of microglial CD45 and CD68 markers. This study demonstrates that, using these methods, dopamine neuronal replacement cell therapy can be beneficial for patients with advanced disease, and that changing technical approaches could have a favourable impact on efficacy and adverse events following neural transplantation.

Functional properties and synaptic integration of genetically labelled dopaminergic neurons in intrastriatal grafts

Intrastriatal grafts of fetal ventral mesencephalic tissue, rich in dopaminergic neurons, can reverse symptoms in Parkinson's disease. For development of effective cell replacement therapy, other sources of dopaminergic neurons, e.g. derived from stem cells, are needed. However, the electrophysiological properties grafted cells need to have in order to induce substantial functional recovery are poorly defined. It has not been possible to prospectively identify and record from dopaminergic neurons in fetal transplants. Here we used transgenic mice expressing green fluorescent protein under control of the rat tyrosine hydroxylase promoter for whole-cell patch-clamp recordings of endogenous and grafted dopaminergic neurons. We transplanted ventral mesencephalic tissue from E12.5 transgenic mice into striatum of neonatal rats with or without lesions of the nigrostriatal dopamine system. The transplanted cells exhibited intrinsic electrophysiological properties typical of substantia nigra dopaminergic neurons, i.e. broad action potentials, inward rectifying currents with characteristic 'sag', and spontaneous action potentials. The grafted dopaminergic neurons also received functional excitatory and inhibitory synaptic inputs from the host brain, as shown by the presence of both spontaneous and stimulation-evoked excitatory and inhibitory postsynaptic currents. Occurrence of spontaneous excitatory and inhibitory currents was lower, and of spontaneous action potentials was higher, in neurons placed in the dopamine-depleted striatum than of those in the intact striatum. Our findings define specific electrophysiological characteristics of transplanted fetal dopaminergic neurons, and we provide the first direct evidence of functional synaptic integration of these neurons into host neural circuitries.

Cell transplantation in Parkinson's disease: how can we make it work?

Previous open-label clinical trials have provided proof of principle that intrastriatal transplants of fetal dopaminergic neurons can induce substantial and long-lasting functional benefits in patients with Parkinson's disease. However, in two recent NIH-sponsored double-blind trials, functional improvements were only marginal and the primary endpoints were not met. Severe off-phase dyskinesias were observed in a significant proportion of the transplanted patients, raising doubts about the viability of the cell-transplantation approach. Here, we discuss the problems raised by the NIH-sponsored trials and point to several shortcomings that might explain the overall poor outcome, and we identify several crucial issues that remain to be resolved to develop cell replacement into an effective and safe therapy.

Development of the dopaminergic neurons in the rodent brainstem

The loss of dopaminergic (DA) neurons in the ventral midbrain is the principal cause of Parkinson's disease. The search for candidate molecules that promote the genesis and survival capacities of DA neurons is a major area of investigation and hope. A better characterization of the developmental pathways that govern the specification, differentiation, and survival of these neurons will be essential in devising therapies aimed to rescue or replace midbrain DA neurons in Parkinson's patients. In this brief review, we will discuss the major steps in the normal development of midbrain DA neurons.

Improvement of bilateral motor functions in patients with Parkinson disease through the unilateral intraputaminal infusion of glial cell line—derived neurotrophic factor

Object. Glial cell line-derived neurotrophic factor (GDNF) has demonstrated significant antiparkinsonian actions in several animal models and in a recent pilot study in England in which four of five patients received bilateral putaminal delivery. In the present study the authors report on a 6-month unilateral intraputaminal GDNF infusion in 10 patients with advanced Parkinson disease (PD).

Methods. Patients with PD in a functionally defined on and off state were evaluated 1 week before and 1 and 4 weeks after intraputaminal catheter implantation in the side contralateral to the most affected side. Each patient was placed on a dose-escalation regimen of GDNF: 3, 10, and 30 µg/day at successive 8-week intervals, followed by a 1-month wash-out period.

The Unified Parkinson's Disease Rating Scale (UPDRS) total scores in the on and off states significantly improved 34 and 33%, respectively, at 24 weeks compared with baseline scores (95% confidence interval [CI] 18–47% for off scores and 16–51% for on scores). In addition, UPDRS motor scores in both the on and off states significantly improved by 30% at 24 weeks compared with baseline scores (95% CI 15–48% for off scores and 5–61% for on scores). Improvements occurred bilaterally, as measured by balance and gait and increased speed of hand movements. All significant improvements of motor function continued through the wash-out period. The only observed side effects were transient Lhermitte symptoms in two patients.

Conclusions. Analysis of the data in this open-label study demonstrates the safety and potential efficacy of unilateral intraputaminal GDNF infusion. Unilateral administration of the protein resulted in significant, sustained bilateral effects.

Expanded mesencephalic precursors develop into grafts of densely packed dopaminergic neurons that reinnervate the surrounding striatum and induce functional responses in the striatal neurons

The search for alternative sources of dopaminergic cells, other than primary fetal tissue for transplantation in Parkinson's disease has become a major focus of research. Different methodological approaches have led to generation in vitro of cells expressing DA-cell markers, although these cells are frequently unable to survive for a long time in vivo after transplantation and/or induce functional effects in the host brain. In the present study, we grafted cell aggregates treated with antibodies against fibroblast growth factor 4 into dopaminergic-denervated striata in rats. Furthermore, we grafted cell suspensions from primary mesencephalic fetal tissue. Grafts from expanded precursors were able to survive (at least 3 months postgrafting) and most decreased the lesion-induced ipsiversive rotation. In addition, immunolabeling for tyrosine hydroxylase and/or Fos showed that the grafts reinnervated the surrounding striatal tissue with dopaminergic terminals, and induced the expression of Fos in the striatal neurons of the reinnervated area after administration of amphetamine to the host rat. The number of dopaminergic cells in grafts from expanded precursors inducing rotational recovery was usually lower (1,226+/-314) than that in grafts from primary fetal tissue (1,671+/-122), but they were more densely packed in grafts that were of smaller volume and did not have the characteristic central nondopaminergic area observed in grafts from primary fetal tissue. The results suggest that long-term survival and functional integration into the DA-denervated striatum can be achieved with grafts of expanded mesencephalic precursors.

Stem cell-based therapy for Parkinson's disease

Motor dysfunctions in Parkinson's disease are considered to be primarily due to the degeneration of dopaminergic neurons in the substantia nigra pars compacta. Pharmacological therapies based on the principle of dopamine replacement are extremely valuable, but suffer from two main drawbacks: troubling side effects (e.g. dyskinesia) and loss of efficacy with disease progression. Transplantation of embryonic dopaminergic neurons has emerged as a therapeutic alternative. Enthusiasm following the success of the initial open-label trials has been dampened by the negative outcome of double-blind placebo controlled trials. Additionally, the emergence of graft-related dyskinesia indicates that the experimental grafting procedure requires further refinement before it can be developed into a therapy. Shortage of embryonic donor tissue limits large-scale clinical transplantation trials. We review three of the most attractive tissue sources of dopaminergic neurons for cell replacement therapy: human embryonic ventral mesencephalic tissue, embryonic and adult multipotent region-specific stem cells and embryonic stem cells. Recent developments in embryonic stem cell research and on their implications for a future transplantation therapy in Parkinson's disease are described. Finally, we discuss how human embryonic stem cells can be differentiated into dopaminergic neurons, and issues such as the numbers of dopaminergic neurons required for success and the risk for teratoma formation after implantation.

Dyskinesias and dopamine cell replacement in Parkinson's disease: a clinical perspective

Both increased and decreased dyskinesias have been reported from open label clinical trials of transplantation of human embryonic dopamine rich tissue in Parkinson's disease patients. In the first double-blind clinical transplantation trial, 15% of the grafted patients developed severe postoperative dyskinesias in the "off" phase. Since then, postoperative off-medication dyskinesias have been reported from two additional series of grafted patients. However, such dyskinesias are probably not a novel phenomenon. These dyskinesias have shown a different temporal development postoperatively compared to the antiparkinsonian graft effects, and no significant relationship with the magnitude of graft-derived dopaminergic reinnervation or symptomatic relief. However, positron emission tomography studies have indicated that an unbalanced putaminal dopaminergic function may contribute to this postoperative complication. While there is little doubt that intrastriatal grafts can induce dyskinesias, these appear to differ from common drug-induced dyskinesias. The term graft-induced dyskinesias (GID) is therefore suggested to more clearly identify this complication. While GID bear some phenomenological resemblance to biphasic drug induced dyskinesias, the mechanism(s) behind this complication remains obscure. Available data are scarce but allow for hypotheses to be generated that could (and should) be addressed in experimental animals.

Recovery and rehabilitation in stroke: stem cells

The recent demonstration that neurons for transplantation can be generated from stem cells and that the adult brain produces new neurons in response to stroke has raised hope for the development of a stem cell therapy for patients affected with this disorder. In this review we propose a road map to the clinic and describe the different scientific tasks that need to be accomplished to move stem cell-based approaches toward application in stroke patients.

Stem cell therapy for human neurodegenerative disorders-how to make it work

Recent progress shows that neurons suitable for transplantation can be generated from stem cells in culture, and that the adult brain produces new neurons from its own stem cells in response to injury. These findings raise hope for the development of stem cell therapies in human neurodegenerative disorders. Before clinical trials are initiated, we need to know much more about how to control stem cell proliferation and differentiation into specific phenotypes, induce their integration into existing neural and synaptic circuits, and optimize functional recovery in animal models closely resembling the human disease.

Neurodegenerative movement disorders: the contribution of functional imaging

PURPOSE OF REVIEW

Functional imaging such as positron emission tomography and single-photon emission computed tomography provide sensitive tools to assess functional brain abnormalities associated with neurodegenerative disease. This review discusses recent findings in this field, with a focus on the detection and characterization of receptor binding and presynaptic dopamine changes in movement disorders.

RECENT FINDINGS

The classical role of positron emission tomography and radioligands such as F-dopa and C-raclopride for investigating abnormalities of the presynaptic and postsynaptic dopaminergic system underlying Parkinson's disease, Parkinsonism and Huntington's disease has recently been made more powerful by the application of statistical mapping to localize changes in dopamine storage capacity and receptor binding across the whole brain at a voxel level. C-raclopride positron emission tomography provides an indirect marker of changes in levels of dopamine in the synaptic cleft. The application of this model in assessing dopamine changes in response to pharmacological, behavioural, motor task and magnetic stimulation in normal individuals and Parkinson's disease patients is reviewed. Recent studies using positron emission tomography and single-photon emission computed tomography to discriminate Parkinson's disease from essential tremor and Parkinsonism, the involvement of non-dopaminergic systems in Parkinson's disease and the role of cell transplantation in Parkinson's disease and Huntington's disease are also discussed.

SUMMARY

Functional imaging techniques provide insight into the pathophysiology of Parkinson's disease, Parkinsonism, and Huntington's disease and the mechanisms of the progression of these diseases. They also play a role in assessing the efficacy of putative neuroprotective and restorative therapy, such as striatal infusions of neurotrophic factors and implants of fetal cells.

Long-term hibernation of human fetal striatal tissue does not adversely affect its differentiation in vitro or graft survival: implications for clinical trials in Huntington's disease

Transplantation of human fetal CNS tissue is a promising therapy for neurodegenerative conditions such as Huntington's disease (HD), but its widespread adoption is limited by restricted tissue availability. One method of overcoming this problem would be to store the tissue in hibernation medium, an approach that we reported previously for human fetal striatal tissue stored for up to 24 h. We now demonstrate the feasibility of storing such tissue for up to 8 days in hibernation medium. When either fresh or 8-day hibernated striatal cells were cultured under standard conditions for 4 days, the proportion of DARPP-32-positive neurons did not differ significantly, although the total number of cells was significantly less from tissue that had been hibernated. Six weeks after transplantation into cyclosporin A-immunosuppressed unilateral quinolinic acid-lesioned rats, there was no significant difference between fresh and hibernated grafts, both in terms of graft volume and extent of striatal phenotypic markers. This study therefore clearly demonstrates that hibernation of human fetal striatal tissue for up to 8 days is not deleterious to its differentiation in culture or survival following transplantation, and is therefore an appropriate method of storage for this tissue.

Staging and preparation of human fetal striatal tissue for neural transplantation in Huntington's disease

Transplantation of human fetal central nervous system tissue has been shown to be of benefit in Parkinson's disease, and is currently being explored as a therapeutic option in Huntington's disease. The success of a neural transplant is dependent on a number of factors, including the requirement that donor cells are harvested within a given developmental window and that the cell preparation protocols take account of the biological parameters identified in animal models. Although many of the criteria necessary for a successful neural transplant have been defined in animal models, ultimately they must be validated in human studies, and some issues can only ever be addressed in human studies. Furthermore, because neural transplantation of human fetal tissue is limited to small numbers of patients in any one surgical center, largely due to practical constraints, it is crucial that tissue preparation protocols are clearly defined and reproducible, so that (i) multicenter trials are possible and are based on consistent tissue preparation parameters, and (ii) results between centers can be meaningfully analyzed. Here we describe the preparation of human fetal striatum for neural transplantation in Huntington's disease, and report on the validation of a method for estimating the developmental stage of the fetus based on direct morphometric measurements of the embryonic tissue.

Enhanced in vitro midbrain dopamine neuron differentiation, dopaminergic function, neurite outgrowth, and 1-methyl-4-phenylpyridium resistance in mouse embryonic stem cells overexpressing Bcl-XL

Embryonic stem (ES) cells provide a potentially unlimited source of specialized cells for regenerative medicine. The ease of inducing stable genetic modifications in ES cells allows for in vitro manipulations to enhance differentiation into specific cell types and to optimize in vivo function of differentiated progeny in animal models of disease. We have generated mouse ES cells that constitutively express Bcl-XL, an antiapoptotic protein of Bcl-2 family. In vitro differentiation of Bcl-XL overexpressing ES (Bcl-ES) cells resulted in higher expression of genes related to midbrain dopamine (DA) neuron development and increased the number of ES-derived neurons expressing midbrain DA markers compared with differentiation of wild-type ES cells. Moreover, DA neurons derived from Bcl-ES cells were less susceptible to 1-methyl-4-phenylpyridium, a neurotoxin for DA neurons. On transplantation into parkinsonian rats, the Bcl-ES-derived DA neurons exhibited more extensive fiber outgrowth and led to a more pronounced reversal of behavioral symptoms than wild-type ES-derived DA neurons. These data suggest a role for Bcl-XL during in vitro midbrain DA neuron differentiation and provide an improved system for cell transplantation in a preclinical animal model of Parkinson's disease.

Differentiation and migration of long term expanded human neural progenitors in a partial lesion model of Parkinson’s disease

Human neural progenitor cells (HNPCs) can be expanded in large numbers for significant periods of time to provide a reliable source of neural cells for transplantation in neurodegenerative disorders such as Parkinson's disease (PD). In the present study, HNPCs isolated from embryonic cortex were expanded as neurospheres in cell culture for 10 months. Just prior to transplantation, a proportion of the HNPCs were treated in a "predifferentiation" protocol in combination with the neurotropic factor NT4, in order to yield significant numbers of neurons. For transplantation, either undifferentiated HNPCs, or predifferentiated HNPCs were transplanted into the substantia nigra of a rat model of Parkinson's disease. At 12 weeks, there was good survival with proliferation of transplanted HNPCs occurring after transplantation but ceasing before the animals were sacrificed. Transplants of predifferentiated cells contained a higher proportion of neurons. The presence of a lesion in the striatum had a significant influence on the migration of transplanted cells from the substantia nigra into the striatum. There was no significant behavioural recovery or effect of transplanted HNPCs on the loss of dopaminergic cells from the host brain. In conclusion, HNPCs may provide a source of cells for use in the treatment of Parkinson's disease.

Improvement of embryonic dopaminergic neurone survival in culture and after grafting into the striatum of hemiparkinsonian rats by CEP-1347

Transplantation of embryonic nigral tissue ameliorates functional deficiencies in Parkinson's disease (PD). A main constraint of neural grafting is the poor survival of dopaminergic neurones grafted into patients. Studies in rats indicated that many grafted neurones die by apoptosis. CEP-1347 is a mixed-lineage-kinase (MLK) inhibitor with neuroprotective action in several in vitro and in vivo models of neuronal apoptosis. We studied the effect of CEP-1347 on the survival of embryonic rat dopaminergic neurones in culture, and after transplantation in hemiparkinsonian rats. CEP-1347 and the alternative MLK inhibitor CEP-11004 significantly increased the survival of dopaminergic neurones in primary cultures from rat ventral mesencephalon and in Mn2+-exposed PC12 cells, a surrogate model of dopaminergic lethal stress. Moreover, combined treatment of the grafting cell suspension and the host animal with CEP-1347 significantly improved the long-term survival of rat dopaminergic neurones transplanted into the striatum of hemiparkinsonian rats. Also, the protective effect of CEP-1347 resulted in an increase in total graft size and in enhanced fibre outgrowth. Thus, treatment with CEP-1347 improved dopaminergic cell survival under severe stress and might be useful to improve the positive outcome of transplantation therapy in PD and reduce the amount of human tissue required.

Neural transplantation in patients with Huntington's disease

The gene for Huntington's disease was identified in 1993 as being a CAG repeat expansion in exon 1 of a gene now known as huntingtin on chromosome 4. Although many of the downstream effects of this mutant gene were identified in the subsequent years, a more detailed understanding of these events will be necessary in order to design specific interventions to interfere with the disease process and slow disease progression. In parallel, a number of groups have been investigating alternative approaches to treatment of Huntington's disease, including cell and tissue transplantation. As the brunt of cell dysfunction and loss is borne by the striatum, at least in the early to mid-stages of disease, the goal is to identify methods for replacing lost cells with fetal neuroblasts that can develop, integrate into the host circuitry and thereby restore lost function. Clinical studies in which primary fetal neuroblasts were transplanted into the brains of patients with advanced Parkinson's disease have demonstrated benefit when the transplant methodology closely follows the biological principles established in animal experiments. On the basis of demonstrated benefit following striatal cell transplantation in animal models of Huntington's disease, a small number of studies have now commenced in patients with Huntington's disease. To date, these clinical studies have demonstrated the feasibility and safety of transplantation in this condition, but it will require several more years yet before the efficacy of the procedure can be confidently established.