Search

Clinical trials testing the hypothesis that fetal dopamine grafts would provide antiparkinsonian benefit in patients who had already developed side effects from their long-term use of L-dopa revealed, in some cases, the presence of dyskinesias even in the absence of L-dopa. The form, intensity, and frequency of these dyskinesias were quite variable, but their manifestation slowed the clinical development of cell replacement therapies. Rodent models of graft-induced dyskinesias (GIDs) have been proposed, but their accuracy in modeling GIDs has been questioned because they usually require amphetamine for their presentation. The present study attempted to model GIDs in parkinsonian monkeys and, for the first time, to test the effect of grafts on previously dyskinetic monkeys. Toward this end, monkeys were rendered parkinsonian with n-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and dyskinetic with levodopa. They then received intraputamenal grafts of fetal dopaminergic cells, control cerebellar cells, or vehicle bilaterally and were studied for 18 months. Dopaminergic cells were grafted in a manner designed to produce either "hot spot" or "widespread" striatal innervation. Although levodopa-induced dyskinesias could be elicited postoperatively, GIDs were never observed in any animal at any time after grafting. Grafted monkeys were also challenged with levodopa but did not show any greater responses to these challenges than before grafting. These studies support the development of future dopamine neuron cell transplantation therapy-based approaches, indicating that in relevant primate models with appropriate cell preparation methodology, with successful graft survival and putamenal dopamine innervation, there is no evidence of graft-induced dyskinesias. J. Comp. Neurol. 525:498-512, 2017. © 2016 Wiley Periodicals, Inc., (© 2016 Wiley Periodicals, Inc.)

While pharmaceutical options remain the overwhelmingly accepted treatment of choice for neurological and psychiatric diseases, significant accomplishments in regenerative neuroscience research have demonstrated the potential of cellular and synaptic functional repair in future therapies. Parkinson's disease stands out as an example in which repair by dopaminergic neurons appears a viable potential therapy. This article describes the basic neurobiological underpinnings of the rationale for cell therapy for Parkinson's disease and the challenges ahead for the use of regenerative medicine in the treatment for this disease.

Postmortem analysis of five subjects with Parkinson's disease 9-14 years after transplantation of fetal midbrain cell suspensions revealed surviving grafts that included dopamine and serotonin neurons without pathology. These findings are important for the understanding of the etiopathogenesis of midbrain dopamine neuron degeneration and future use of cell replacement therapies.

Surgeries involving transplantation of fetal dopamine (DA) neurons into the caudate-putamen of patients with Parkinson's disease (PD) have been performed in various clinical trials to examine a potential restoration of motor function. The absence of studies in non-human primates to define the best transplantation protocols have lead to the use of a broad variety of techniques that potentially could have a major impact on the clinical outcome. The effects of using different cell and tissue preparation, and surgical targets, remain unknown. For this purpose, 20 St. Kitts African Green Monkeys (AFG) rendered parkinsonian by i.m. injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were balanced into 4 groups and unilaterally grafted in the (a) caudate or (b) putamen with fetal ventral mesencephalic (VM) tissue as (c) solid pieces or as a (d) cell suspension. By 9 months post-transplantation all animals showed significant and similar behavioral improvement as determined by a UPDRS based PD scale. Postmortem analyses showed that VM transplants survived in all animals. They were located in both surgical target sites, producing a broad DA reinnervation of the targeted nuclei that could also extend to the non-grafted nucleus on the ipsilateral side. Although no differences between groups were found in survival of DA neurons or degree of DA reinnervation, there was a significant correlation between striatal reinnervation and behavioral recovery only in animals transplanted in the putamen surgical target. Additionally, there was in general a stronger glial reaction to solid grafts than to cell suspensions. These studies provide data for the optimal time course, cell preparation and surgical targets for systematic examinations of both potential benefits and side effects of dopamine neuron cell transplantation in primate models of PD.

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.

Although progressive neurodegenerative diseases have very different and highly specific causes, the dysfunction or loss of a vulnerable group of neurons is common to all these disorders and may allow the development of similar therapeutic approaches to the treatment of diseases such as amyotrophic lateral sclerosis, Parkinson's disease, and Huntington's disease. When a disease is diagnosed, the first step is to instigate protective measures to prevent further degeneration. However, most patients are symptom-free until almost all of the vulnerable cells have become dysfunctional or have died. There are known molecular mechanisms and processes in stem cells and progenitor cells that may be of use in the future design and selection of cell-based replacement therapies for neurological diseases. This review provides examples of conceptual and clinical problems that have been encountered in the development of cell-based treatments, and specific criteria for the effective use of cells in the future treatment of neurodegenerative diseases.

The lack of supply and access to human tissue has prompted the development of xenotransplantation as a potential clinical modality for neural cell transplantation. The goal of the present study was to achieve a better understanding of the immune factors involved in neural xenograft rejection in primates. Initially, we quantified complement mediated cell lysis of porcine fetal neurons by primate serum and demonstrated that anti-C5 antibody treatment inhibited cell death. We then developed an immunosuppression protocol that included in vivo anti-C5 monoclonal antibody treatment, triple drug therapy (cyclosporine, methylprednisolone, azathioprine) and donor tissue derived from CD59 or H-transferase transgenic pigs and applied it to pig-to-primate neural cell transplant models. Pre-formed alphaGal, induced alphaGal and primate anti-mouse antibody (PAMA) titers were monitored to assess the immune response. Four primates were transplanted. The three CD59 neural cell recipients showed an induced anti-alphaGal response, whereas the H-transferase neural cell recipient exhibited consistently low anti-alphaGal titers. Two of these recipients contained surviving grafts as detected by immunohistochemistry using selected neural markers. Graft survival correlated with high dose cyclosporine treatment, complete complement blockade and the absence of an induced PAMA response to the murine anti-C5 monoclonal antibodies.

Neural and stem cell transplantation is emerging as a potential treatment for neurodegenerative diseases. Transplantation of specific committed neuroblasts (fetal neurons) to the adult brain provides such scientific exploration of these new potential therapies. Huntington's disease (HD) is a fatal, incurable autosomal dominant (CAG repeat expansion of huntingtin protein) neurodegenerative disorder with primary neuronal pathology within the caudate-putamen (striatum). In a clinical trial of human fetal striatal tissue transplantation, one patient died 18 months after transplantation from cardiovascular disease, and postmortem histological analysis demonstrated surviving transplanted cells with typical morphology of the developing striatum. Selective markers of both striatal projection and interneurons such as dopamine and c-AMP-related phosphoprotein, calretinin, acetylcholinesterase, choline acetyltransferase, tyrosine hydroxylase, calbindin, enkephalin, and substance P showed positive transplant regions clearly innervated by host tyrosine hydroxylase fibers. There was no histological evidence of immune rejection including microglia and macrophages. Notably, neuronal protein aggregates of mutated huntingtin, which is typical HD neuropathology, were not found within the transplanted fetal tissue. Thus, although there is a genetically predetermined process causing neuronal death within the HD striatum, implanted fetal neural cells lacking the mutant HD gene may be able to replace damaged host neurons and reconstitute damaged neuronal connections. This study demonstrates that grafts derived from human fetal striatal tissue can survive, develop, and are unaffected by the disease process, at least for 18 months, after transplantation into a patient with HD.

Objective: To assess the safety and the effect on standardized clinical rating measures of transplanted embryonic porcine ventral mesencephalic (VM) tissue in advanced PD., Methods: Twelve patients with idiopathic PD underwent unilateral implantation of embryonic porcine VM tissue; six received cyclosporine immunosuppression and six received tissue treated with a monoclonal antibody directed against major histocompatibility complex class I. Patients were followed for 12 months and assessed by clinical examination, MRI, and 18F-levodopa PET. Porcine endogenous retrovirus testing was conducted by PCR-based method on peripheral blood mononuclear cells., Results: Cell implantation occurred without serious adverse events in all patients. Cultures were negative for bacterial and unknown viral contamination. No porcine endogenous retrovirus DNA sequences were found. MRI demonstrated cannula tracts within the putamen and caudate, with minimal or no edema and no mass effect at the transplant sites. In the medication-off state, total Unified Parkinson's Disease Rating Scale scores improved 19% (p = 0.01). Three patients improved over 30%. There were two patients with improved gait. 18F-levodopa PET failed to show changes on the transplanted side., Conclusions: Unilateral transplantation of porcine embryonic VM cells into PD patients was well tolerated with no evidence of transmission of porcine endogenous retrovirus. Changes in standardized clinical PD rating measures were variable, similar to the results of the first trials of unilateral human embryonic allografts that transplanted small amounts of tissue.

The observation that fetal neurons are able to survive and function when transplanted into the adult brain fostered the development of cellular therapy as a promising approach to achieve neuronal replacement for treatment of diseases of the adult central nervous system. This approach has been demonstrated to be efficacious in patients with Parkinson's disease after transplantation of human fetal neurons. The use of human fetal tissue is limited by ethical, infectious, regulatory, and practical concerns. Other mammalian fetal neural tissue could serve as an alternative cell source. Pigs are a reasonable source of fetal neuronal tissue because of their brain size, large litters, and the extensive experience in rearing them in captivity under controlled conditions. In Phase I studies porcine fetal neural cells grafted unilaterally into Parkinson's disease (PD) and Huntington's disease (HD) patients are being evaluated for safety and efficacy. Clinical improvement of 19% has been observed in the Unified Parkinson's Disease Rating Scale "off" state scores in 10 PD patients assessed 12 months after unilateral striatal transplantation of 12 million fetal porcine ventral mesencephalic (VM) cells. Several patients have improved more than 30%. In a single autopsied PD patient some porcine fetal VM cells were observed to survive 7 months after transplantation. Twelve HD patients have shown a favorable safety profile and no change in total functional capacity score 1 year after unilateral striatal placement of up to 24 million fetal porcine striatal cells. Xenotransplantation of fetal porcine neurons is a promising approach to delivery of healthy neurons to the CNS. The major challenges to the successful use of xenogeneic fetal neuronal cells in neurodegenerative diseases appear to be minimizing immune-mediated rejection, management of the risk of xenotic (cross-species) infections, and the accurate assessment of clinical outcome of diseases that are slowly progressive.

Neuroimmunophilin ligands have been shown to enhance neurite outgrowth in several neuronal systems in culture, including primary dopaminergic neurons from fetal ventral mesencephalon. We investigated the ability of neuroimmunophilin ligands to enhance outgrowth of transplanted fetal dopamine neurons in vivo. Rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal dopamine system were transplanted with rat embryonic day 14 ventral mesencephalon into the striatum, then treated orally with a neuroimmunophilin ligand (15mg/kg) or vehicle once per day for 14 days. All transplanted animals regained dopamine function over a 10 week behavioral test period, as indicated by decrease and reversal of amphetamine-induced rotation. In addition, neuroimmunophilin ligand-treated animals showed a more pronounced motor response during the first 10min after amphetamine injection, possibly reflecting increased striatal reinnervation or increased functional capacity. At post-mortem analyses, neuroimmunophilin ligand-treated rats showed a significantly higher density of tyrosine hydroxylase-positive fibers reinnervating the lesioned striatum, both immediately surrounding the transplant (92% of unlesioned density in neuroimmunophilin-treated rats vs 67% of unlesioned levels in vehicle-treated rats) and at some distance from the transplant/host interface. The number of tyrosine hydroxylase-positive cells within the transplants was not different between groups. This study demonstrates that short-term oral administration of a neuroimmunophilin ligand can enhance neurite outgrowth from fetal dopamine neuronal transplants.

The anatomical specificity of axon growth from fetal pig septal xenografts was studied by transplanting septal cells from E30-35 pig fetuses into cholinergic deafferented (192-IgG-saporin-infused) rats or into aged rats (> 18 months). Cell suspensions (100,000 cells/microl) were injected bilaterally into the dorsal and ventral hippocampus of immunosuppressed rats (10 mg/kg/day cyclosporine A). To assess axonal growth and synapse formation, acetylcholinesterase histochemistry, an antibody to choline acetyltransferase (ChAT), and three pig-positive/rat-negative antibodies: bovine 70kD neurofilament (NF70), human low-affinity NGF receptor (hNGFr), and human synaptobrevin (hSB) were used. In rats with surviving grafts at 6 months, NF70 axonal labeling was more extensive than either ChAT or hNGFr labeling. All three markers demonstrated graft axons extending selectively through the hippocampal CA fields and the molecular layer of the dentate gyrus. Graft axons did not extend into adjacent entorhinal cortex or neocortex. The distribution of pig hSB-positive synapses correlated with AChE-positive fiber outgrowth in to the host. Electron microscopic analysis of hSB-immunostained hippocampal sections revealed pig presynaptic terminals in contact with normal rat postsynaptic structures in the CA fields and the dentate gyrus. These data demonstrate target-appropriate growth of pig cholinergic axons and the formation of cross-species synapses in the deafferented or aged rat hippocampus.

Adults rats were lesioned with 192-IgG-saporin, an immunotoxin that targets cholinergic neurons in the basal forebrain expressing the low-affinity nerve growth factor receptor (p75). One month later, rats received E30-35 porcine cholinergic neurons bilaterally into the hippocampus, and were tested in the Morris water maze and the passive avoidance task 4.5-6 months after transplantation (in two experiments, rats were retested in the water maze) followed by histological and cellular analyses. The 192-IgG-saporin-lesioned animals displayed clear cognitive deficits in the Morris water maze. In all experiments the lesioned animals had spatial probe deficits on day 5 testing. A large variance was found among the transplanted animals, with individual animals exhibiting improved performance, but little overall improvement when compared to lesion-alone animals as a group. The relationships between behavioral performance and graft cholinergic factors were established by histological analyses. Grafted animals exhibited an increase in cholinergic innervation of the dentate gyrus (DG) region of the dorsal hippocampus when compared to lesion-alone animals. There was a significant correlation between the level of cholinergic innervation in the dentate gyrus and spatial navigation performance (latency and spatial probe) in the Morris water maze task. These data provide evidence of memory and spatial deficits following cholinergic denervation, and of target-specific growth of xenogeneic cholinergic neurons into the hippocampus. The lack of a clear treatment (transplant) effect in the behavioral measures leads us to believe that functional restoration of cognitive function would require cholinergic reinnervation of both the hippocampus and the neocortex in this 192-IgG-saporin animal model.

Positron emission tomography (PET) and carbon-11-labeled 2B-carbomethoxy-3B-(4-fluorophenyl)tropane (11C-CFT or 11-WIN 35,428) were used as molecular markers for striatal presynaptic dopamine (DA) transporters in a unilateral Parkinson's disease rat neurotransplantation model. In the lesioned striatum, the binding ratio measured by the DA presynaptic marker was reduced to 15% to 35% of the intact side (or unoperated control). After grafting with non-DA cells (from dorsal mesencephalon), the DA binding ratio remained reduced to levels observed before transplantation and rats showed no behavioral recovery. In contrast, after DA neuronal transplantation, behavioral recovery occurred only after the 11C-CFT binding ratio had increased to 75% to 85% of the intact side. This study provides direct in vivo evidence for the dopaminergic molecular basis of functional recovery in the lesioned nigrostriatal system after neural transplantation.

Currently, fetal tissue transplantation into patients with Parkinson's disease utilizes the entire ventral mesencephalon (VM) as donor tissue. However, the resulting mixture of cell types contains a relatively low proportion of therapeutically relevant dopamine (DA) neurons. We show that differential dissection of a medial region of embryonic day 14 rat VM yields a significantly higher proportion of DA neurons (8-10%) than is found in lateral VM (2%) or whole VM (4-5%). Medial VM also contained a larger number of the specific subpopulation of DA neurons (aldehyde dehydrogenase-positive; AHD) that project to dorsolateral motor region of the striatum. Selective dissection of fetal medial VM selectively enriches DA neurons in cell preparations useful for transplantation in Parkinson's disease.

The retinoic acid-generating enzyme, aldehyde dehydrogenase (AHD), is expressed in a subpopulation of dopaminergic neurons found in the substantia nigra. Using AHD and tyrosine hydroxylase (TH) as immunohistochemical markers, we determined whether differential dissection of the embryonic (E16) ventral mesencephalon (VM) into its lateral and medial portions contributed equally to the number of TH cells surviving transplantation, if grafted AHD/TH neurons reinnervate the host striatum according to their normal projection patterns, and examined the functional recovery caused by the implanted cells as assessed by amphetamine-induced rotation in a 6-OHDA-lesioned model of Parkinson's disease. The embryonic tissue was transplanted as solid pieces injected via a 20-gauge lumbar puncture needle into the center of the deafferented striatum. Groups received either one complete ventral mesencephalic piece (VM), two medial pieces of ventral mesencephalic tissue (MVM), or two lateral pieces of ventral mesencephalic tissue (LVM). Both VM and MVM groups showed a significant decrease in amphetamine-induced rotation over time and, there was no difference in the degree of reduction observed between the two groups. Histological evaluation of the transplants revealed a much larger total number of surviving TH cells in grafts from the VM and MVM groups compared to the LVM group. Surviving AHD/TH neurons were found in all groups. Whereas TH staining of the transplanted striatum displayed a halo of graft-derived fibers all around the transplant and integration of these fibers into the host neuropil, AHD staining showed a preferential reinnervation of the dorsolateral striatum corresponding to the normal projection pattern of AHD/TH neurons. In summary, selective dissection of the embryonic ventral mesencephalon is possible, functional recovery as assessed by amphetamine-induced rotation in animals transplanted with MVM is similar to that seen in animals grafted with VM, and AHD/TH neurons have a selective reinnervation pattern in the PD transplantation paradigm. These findings may have implications for the grafting of fetal mesencephalic tissue in PD patients.

The movement disorder in Parkinson's disease results from the selective degeneration of a small group of dopaminergic neurons in the substantia nigra pars compacta region of the brain. A number of exploratory studies using human fetal tissue allografts have suggested that transplantation of dopaminergic neurons may become an effective treatment for patients with Parkinson's disease and the difficulty in obtaining human fetal tissue has generated interest in finding corresponding non-human donor cells. Here we report a post-mortem histological analysis of fetal pig neural cells that were placed unilaterally into the caudate-putamen brain region of a patient suffering from Parkinson's disease. Long-term (over seven months) graft survival was found and the presence of pig dopaminergic neurons and other pig neural and glial cells is documented. Pig neurons extended axons from the graft sites into the host brain. Furthermore, other graft derived cells were observed several millimeters from the implantation sites. Markers for human microglia and T-cells showed only low reactivity in direct proximity to the grafts. This is the first documentation of neural xenograft survival in the human brain and of appropriate growth of non-human dopaminergic neurons for a potential therapeutic response in Parkinson's disease.

Fetal neural transplantation has recently been demonstrated to ameliorate motor and other behavioral deficits in animals models of Huntington's disease, and reconstruct many of the damaged striatal circuits. However, there has been significant variability in the histological appearance of these grafts, most likely related to differences of the regions of dissection of the donor tissue. Selective dissection and transplantation of the lateral ventricular eminence in rodents has resulted in grafts consisting of primarily striatal-like tissue. This data, combined with data from our own and other laboratories has led to a description of the development of human striatum, with a particular emphasis on the relevance of human striatal development to the field of fetal tissue transplantation for the treatment of Huntington's disease. If the goal of transplantation is to graft GABAergic striatal projection neurons, it is our impression that optimal grafting results will occur when transplants are derived from the lateral ventricular eminence and the lateral aspect of the body of the ventricular eminence anterior to the foramen of Monro. Optimal results are likely to occur when donor ages range from Stage 19 to 23, with possible graft success when donor age extends to as late as postovulatory week 22.

Axonal growth from cortically placed fetal neural transplants to subcortical targets in adult hosts has been difficult to demonstrate and is assumed to be minimal; however, experiments using xenogeneic neural grafts of either human or porcine fetal tissues into the adult rat striatum, mesencephalon, and spinal cord have demonstrated the capability for long-distance axonal growth. This study reports similar results for porcine cortical xenografts placed in the adult rat cerebral cortex and compares these findings with results from cortical allografts. Adult rats that previously received unilateral cortical lesions by an oblique intracortical stereotaxic injection of quinolinic acid, were implanted with suspensions of either E14 rat or E38 xenogeneic porcine fetal cortical cells. Xenografted rats were immunosuppressed by cyclosporin A. The corpus callosum was intact in all cases and grafts were confined to the overlying cortex. After a 31-34 wk posttransplant survival period, acetylcholinesterase (AChE) staining and tyrosine hydroxylase (TH) immunocytochemistry revealed that both allo- and xenografts received host afferents. Retrograde tracer injections into the ipsilateral striatum and cerebral peduncle in allografted animals failed to show any axonal growth to either subcortical target. Using a porcine-specific axonal marker in xenografted animals, we found graft axons in white matter tracts (corpus callosum, internal capsule, cingulum bundle, and medial forebrain bundle) and within the caudate-putamen and both the ipsilateral and contralateral cerebral cortex. Graft axons were not found in the thalamus, midbrain, or spinal cord. In addition, using an antibody to porcine glial fibers, we observed more extensive graft glial fiber growth into the same host fiber tracts, as far caudally as the cerebral peduncle, but not into gray matter targets outside the cortex. These results demonstrate that porcine cortical xenograft axons and glia can extend from lesioned cerebral cortex to cortical and subcortical targets in the adult rat brain. These findings are relevant for prospects of repairing cortical damage and obtaining functional recovery.

To determine the role of major histocompatibility complex (MHC) class I in immunological rejection of neural xenotransplants, F(ab')2 fragments of a monoclonal antibody to porcine MHC class I were used to mask this complex on porcine fetal striatal cells transplanted into rat striata previously lesioned with quinolinic acid. Presence of MHC class I on the surface of porcine striatal cells was confirmed by fluorescence-activated cell sorting prior to F(ab')2 treatment. At three to four months post-transplantation, survival of F(ab')2-treated xenografts was assessed by means of donor-specific immunostaining and compared to that of untreated xenografts in non-immunosuppressed rats and in rats immunosuppressed with cyclosporine A. In this study, masking of donor MHC class I by F(ab')2 treatment resulted in enhanced xenografts survival compared to the non-immunosuppressed controls (graft survival rates, 52% and 7%, respectively; P < 0.005) at survival times up to four months. While xenograft survival in F(ab')2-treated animals was not significantly different from that in cyclosporine-treated rats (74% graft survival), mean graft volume in F(ab')2-treated animals was smaller than that in cyclosporine-treated animals (1.07 +/- 0.30 mm3 versus 3.14 +/- 0.51 mm3; P < 0.005). The cytoarchitectonic organization of the xenografts was similar in F(ab')2- and cyclosporine-treated animals, and grafts in both groups exhibited long distance target-directed axonal outgrowth. The pattern of immunoreactivity to porcine MHC class I in the xenografts corresponded to the regional distribution of donor glia. In xenografts undergoing rejection, infiltration with host inflammatory cells was restricted to necrotic graft remnants and spared the nearby host structures. We conclude that MHC class-I-restricted immune mechanisms play an important role in neural xenograft rejection and that masking of this complex on donor cells may provide a useful strategy for immunoprotection of neural xenografts.

In order to determine whether the lateral ganglionic eminence (LGE) of the fetal telencephalon is the primary source of striatal precursors in striatal transplants and tissue cultures, cells derived exclusively from the LGE of fetal rat brains were transplanted into the quinolinic-acid-lesioned striatum of adult rats. After 2-3 months they produced grafts that were almost entirely AChE-positive as well as DARPP-32-, TH-, and calbindin-immunoreactive. The grafts were integrated into the host striatum so that host corticofugal fiber tracts interdigitated with graft tissues similar to the way they penetrate the gray matter of the normal striatum. Fast Blue dye injected into the ipsilateral globus pallidus of LGE grafted produced retrogradely labeled neurons within the grafts, but Fluorogold dye injected into the ipsilateral substantia nigra did not. In a separate experiment using DARPP-32-immunohistochemstry as a striatal marker, fetal (E16) and neonatal (P2) rat brains showed DARPP-32 immunoreactivity in the LGE but not in the adjacent medial ganglionic eminence (MGE). In summary, both fetal LGE cells and LGE grafts express specific striatal markers, and LGE grafts integrate into the host striatum and innervate the major striatal efferent target within the host brain. These data suggest that the LGE is the origin of cells committed to striatal phenotypes in the developing brain.

Selective replacement of degenerated neurons in the adult brain with allogeneic fetal neuroblasts is a promising therapeutic modality for human neurodegenerative diseases, but is confounded with practical and potential ethical problems. To evaluate the potential of xenogeneic donors as a cell source for neural transplantation, we have critically examined the available experimental evidence in animal models pertaining to the survival, integration and function of xenogeneic fetal neuroblasts in the host brain. A statistical meta-analysis across multiple studies revealed that immunologically-related transplantation parameters (immunosuppression and donor-host phylogenetic distance) were the main determinants of neural xenograft survival. The immunological basis for xenograft rejection is reviewed in the context of novel immunoprotection strategies designed to enhance xenograft survival. Furthermore, the evidence for behavioral recovery based on anatomical and functional integration of neural xenografts in the host brain is examined with an awareness of developmental considerations. It is concluded that neural xenotransplantation offers a unique opportunity for effective neuronal replacement with significant potential for clinical use.

Fetal striatal grafts are found to have a modular organization revealed by acetylcholinesterase (AChE) histochemistry. The AChE-rich zones represent the only portions of these grafts that are anatomically and functionally integrated into the host brain. In this study, the medial and lateral ganglionic eminences (MGEs and LGEs) were selectively dissected from the basal telencephalon of embryonic-day-14 (E14) rat fetuses to compare their relative contributions to the AChE-rich fraction of intrastriatal grafts. Separate cell suspensions prepared from either eminence were stereotaxically implanted into excitotoxically lesioned neostriatum of adult rats. Eight weeks after transplantation, grafts of the MGE were compared with those of the LGE with respect to the proportion of AChE-rich zones, graft size, graft morphology, and afferent dopaminergic innervation as revealed by tyrosine hydroxylase (TH) immunostaining. The mean AChE-rich fraction in LGE grafts (87% +/- 4%) was markedly greater than the AChE-rich fraction in MGE grafts (25% +/- 10%). The LGE grafts were also morphologically better incorporated into the lesioned host striatum, partially reconstituting the striatal morphology. There was no statistically significant difference in graft size between the two groups. The AChE-rich LGE grafts were TH immunoreactive, whereas the AChE-poor MGE grafts were not. We conclude that grafts derived exclusively from the fetal LGE reconstitute the striatal morphology and consist almost entirely of AChE-rich zones.

In this article, we show that 1) computed tomographic (CT)-guided stereotactic infusion of an excitotoxin into the striatum of a nonhuman primate provides a useful neuropathologic and behavioral model for Huntington's disease. 2) High-resolution positron emission tomography (PET) can be used to image the decreased glucose utilization and the preservation of dopaminergic terminals in the lesioned striatum by using 2-fluoro-deoxy-D-glucose (2FDG) and N-(C-11)-methyl-2-beta-carbomethoxy-3-beta-phenyl tropane (CPT) as tracers. 3) Transplantation of cross-species striatal fetal tissue into the lesioned caudate-putamen reduces many of the abnormal motor movements and behavioral changes seen in the Huntington's disease primate model. 4) Graft rejection results in the return of the abnormal signs of the pregrafted state. These results indicate that treatment of the neuronal deficit in Huntington's disease can involve intervention at the local neuronal circuit level. CT-guided stereotactic implantation of cells that might protect or replace this defective circuitry may eventually provide an effective treatment for Huntington's disease.