The fate of human glial cells following transplantation in normal rodents and rodent models of neurodegenerative disease

Concise Review: Human-Animal Neurological Chimeras: Humanized Animals or Human Cells in an Animal?

Blastocyst complementation is an emerging methodology in which human stem cells are transferred into genetically engineered preimplantation animal embryos eventually giving rise to fully developed human tissues and organs within the animal host for use in regenerative medicine. The ethical issues surrounding this method have caused the National Institutes of Health to issue a moratorium on funding for blastocyst complementation citing the potential for human cells to substantially contribute to the brain of the chimeric animal. To address this concern, we performed an in-depth review of the neural transplantation literature to determine how the integration of human cells into the nonhuman neural circuitry has altered the behavior of the host. Despite reports of widespread integration of human cell transplants, our review of 150 transplantation studies found no evidence suggestive of humanization of the animal host, and we thus conclude that, at present, concerns over humanization should not prevent research on blastocyst complementation to continue. We suggest proceeding in a controlled and transparent manner, however, and include recommendations for future research with careful consideration for how human cells may contribute to the animal host nervous system. Stem Cells 2019;37:444-452.

Transplanted Human Neural Precursor Cells Migrate Widely but Show no Lesion-Specific Tropism in the 6-Hydroxydopamine Rat Model of Parkinson's Disease

Parkinson's disease (PD), while primarily associated with degeneration of nigrostriatal dopamine neurons, is now increasingly recognized to have more widespread cell loss and so the most effective cell replacement therapy should target all these neuronal losses. Neural precursor cells might be ideal in this regard as in certain circumstances they have been shown to migrate widely following transplantation into the CNS. The aim of this study was to investigate whether transplanted human expanded neural precursor cells (hENPs) could migrate to sites of established or evolving pathology in the adult brain using the 6-hydroxydopamine (6-OHDA) rat model of PD. hENPs were grafted into the striatum prior to, at the same time as, or after the animals received a 6-OHDA lesion to the medial forebrain bundle. The presence of donor cells was then assessed in a distant site of cell loss (substantia nigra) or sites where cell death would not be expected (frontal cortex and globus pallidus). Donor cells were found distant from the site of implantation but the migration of these hENPs was not significantly greater in the 6-OHDA-lesioned brain and the cells did not specifically target the site of cell loss in the substantia nigra. The temporal relationship of grafting relative to the lesion, and therefore dopaminergic cell death, did not affect the migration of hENPs nor their differentiation. We conclude that while transplanted hENPs are capable of migration away from the site of implantation, they show no specific tropism for sites of ongoing or established nigral dopaminergic cell loss in this lesion model. Therefore, the use of such cells to replace the range of neurons lost in PD is likely to require a deeper understanding of the migratory cues in the damaged adult brain and some manipulation of these cells prior to transplantation.

Organization and Histochemical Phenotype of Human Fetal Cerebellar Cells following Transplantation into the Cerebellum of Nude Mice

Previous rodent studies have demonstrated the capacity of cerebellar transplants to organize into trilaminar cell layers typically observed in the normal cerebellum. In Purkinje Cell (PC)-deficient animals, PCs will migrate into the host and form synaptic connections. Recently, fetal cerebellar grafts transplanted into the Purkinje cell degeneration (pcd) mutant mouse were shown to result in an improvement of motor behaviors. These studies indicate the potential therapeutic use of neural transplantation in patients with cerebellar degeneration. In the present study, human fetal cerebellar tissue (8.5 wk postconception) was dissociated and transplanted into the normal cerebellum of nude mice. Six months following transplantation, histological analysis revealed donor cells in recipient mice. Immunostaining for the 28 kDa calcium-binding protein (calbindin) revealed the presence of donor PCs that were organized in discrete cellular layers within the transplant neuropil. In most cases the dendritic processes were oriented in a planar fashion perpendicular to the transplant cell layer. Human neurofilament immunostaining revealed bundles of donor fibers within the core of the transplant and/or at the periphery. These bundles were found to be calbindin positive (PC fibers). Three animals provided evidence of donor PC axon growth ventrally into host white matter, and in one case, this ventral migration reached the deep cerebellar nuclei. Most notable was the development of a pronounced folia-like organization by the implanted cell suspensions. Glial processes within the grafts were aligned perpendicular to the long axis of the transplant folia. These results demonstrate the capacity of human fetal cerebellar cell suspension to reorganize into cell layers typical of the normal cerebellum following transplantation into the rodent cerebellum, and develop an organotypic folia-like organization.

Human ESC-derived dopamine neurons show similar preclinical efficacy and potency to fetal neurons when grafted in a rat model of Parkinson's disease

Considerable progress has been made in generating fully functional and transplantable dopamine neurons from human embryonic stem cells (hESCs). Before these cells can be used for cell replacement therapy in Parkinson’s disease (PD), it is important to verify their functional properties and efficacy in animal models. Here we provide a comprehensive preclinical assessment of hESC-derived midbrain dopamine neurons in a rat model of PD. We show long-term survival and functionality using clinically relevant MRI and PET imaging techniques and demonstrate efficacy in restoration of motor function with a potency comparable to that seen with human fetal dopamine neurons. Furthermore, we show that hESC-derived dopamine neurons can project sufficiently long distances for use in humans, fully regenerate midbrain-to-forebrain projections, and innervate correct target structures. This provides strong preclinical support for clinical translation of hESC-derived dopamine neurons using approaches similar to those established with fetal cells for the treatment of Parkinson’s disease.

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Transplants of hESC-DA survive long term and restore DA neurotransmission in vivo

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The functional potency of hESC-DA is similar to human fetal midbrain DA neurons

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hESC-DA are capable of long-distance, target-specific innervation of the host brain

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The axonal outgrowth capacity of hESC-DA meets the requirements for use in humans

Integration of genetically modified adult astrocytes into the lesioned rat spinal cord

Combination of ex vivo gene transfer and cell transplantation is now considered as a potentially useful strategy for the treatment of spinal cord injury. In a perspective of clinical application, autologous transplantation could be an option of choice. We analyzed the fate of adult rat cortical astrocytes genetically engineered with a lentiviral vector transplanted into a lesioned rat spinal cord. Cultures of adult rat cortical astrocytes were infected with an HIV-1-derived vector (TRIP-CMV-GFP) and labeled with the fluorescent dye Hoechst. Transfected and labeled astrocyte suspension was injected at T11 in rats in which spinal cord transection at T7-T8 levels had been carried out 1 week earlier. Six weeks after grafting, the animals were sacrificed and transplants were retrieved either by Hoechst fluorescence or by immunohistochemistry for detection of glial fibrillary acidic protein (GFAP) and vimentin. Grafted astrocytes expressing green fluorescent protein (GFP) were found both at the injection and transection sites. Genetically modified astrocytes thus survived, integrated, and migrated within the host parenchyma when grafted into the completely transected rat spinal cord. In addition, they retained some ability to express the GFP transgene for at least 6 weeks after transplantation. Adult astrocytes infected with lentiviral vectors can therefore be a valuable tool for the delivery of therapeutic factors into the lesioned spinal cord.

Migration of cells from primary transplants of allo- and xenografted foetal striatal tissue in the adult rat brain

Primary neural cells derived from human xenografts migrate extensively following transplantation into the adult rat CNS. However, it is unknown whether cells from allografts have the same capability to migrate within the adult rat brain. Moreover, it is unclear whether human-derived cells migrate to this extent as an inherent property of being in a xenograft environment, or whether it is due to the large size of the developed human brain compared with the adult rat brain. In order to address these issues we have designed an experimental paradigm to investigate the potential for cells derived from grafts of primary rat, mouse and human foetal striatal tissue to migrate following intrastriatal transplantation in an adult rat model of Huntington's disease (HD). Green fluorescent protein (GFP)-expressing rat and mouse donors and an antibody specific to human nuclear antigen enabled identification of graft-derived cells within the host brain, and double-labelling with GFP and neuronal nuclear antigen or immunostaining with human-specific tau identified graft-derived neurons. Twelve weeks post-transplantation, cells had migrated throughout the host in all groups; however, human cells and neurons had migrated significantly more than rat or mouse cells. These results demonstrate that neural cells derived from allografts are capable of migrating in the adult rat CNS and that the extent of migration is most likely determined by the size of the mature donor adult brain. This has important implications for the use of allo- and xenogeneic tissue as a source for transplantation in treating diffuse neurodegenerative disorders such as HD.

The cellular repair of the brain in Parkinson's disease—past, present and future

Damage to the central nervous system was once considered irreparable. However, there is now growing optimism that neural transplant therapies may one day enable complete circuit reconstruction and thus functional benefit for patients with neurodegenerative conditions such as Parkinson's disease (PD), and perhaps even those with more widespread damage such as stroke patients. Indeed, since the late 1980s hundreds of patients with Parkinson's disease have received allografts of dopamine-rich embryonic human neural tissue. The grafted tissue has been shown to survive and ameliorate many of the symptoms of the disease, both in the clinical setting and in animal models of the disease. However, practical problems associated with tissue procurement and storage, and ethical concerns over using aborted human fetal tissue have fuelled a search for alternative sources of suitable material for grafting. In particular, stem cells and xenogeneic embryonic dopamine-rich neural tissue are being explored, both of which bring their own practical and ethical dilemmas. Here we review the progress made in neural transplantation, both in the laboratory and in the clinic with particular attention to the development of stem cell and xenogeneic tissue based therapy.

Intracerebral transplantation and successful integration of astrocytes following genetic modification with a high-capacity adenoviral vector

To investigate the ability of genetically modified astrocytes to integrate into adult rat brain, two spontaneously immortalized cell lines and the allogenic nontumorigenic glioma cell line F98 were transduced with a high-capacity adenoviral vector (HC-Adv) expressing the EGFP gene from the hCMV promoter. In organotypic slice cultures the transduced astrocytes were shown to integrate into the brain tissue. Following transplantation of the transduced astrocytes into the striatum of adult rats, the transplanted cells survived at least for 6 weeks, continuously expressed the EGFP transgene, in close neighborhood with cells of the recipient tissue executing their differentiation capacity along the glial lineage. Thus, HC-Adv transduced astrocytes are promising vehicles to locally deliver therapeutic proteins for the treatment of neurodegenerative diseases.

Neural cells from primary human striatal xenografts migrate extensively in the adult rat CNS

Primary neural cells do not appear to migrate significantly following transplantation into the adult rodent CNS, which is in contrast to expanded neural precursor cells where migration is well-documented. However, most transplant studies of primary neural tissue have been performed in an allograft situation in which it is difficult to identify graft-derived cells. We have, therefore, used a xenograft paradigm to investigate the potential for cells derived from grafts of primary human fetal striatal tissue (gestational age of 66-72 days) to migrate following intrastriatal transplantation in an athymic adult rat model of Huntington's disease. The use of an antibody specific to human nuclear antigen enabled clear identification of graft-derived cells within the host brain, and specific neural phenotypes were determined using human-specific tau for neurons, glial fibrillary acidic protein for mature astrocytes and Ki67 for proliferative cells. At 6 weeks, the graft mass was very dense with a high proliferative index, few cells had migrated away from the graft, and the cells that had differentiated both within and away from the graft were mainly neurons. In contrast, at 6 months, the graft core was dispersed significantly more and a large number of graft-derived cells had migrated throughout the brain as far rostral as the olfactory bulb and as caudal as the substantia nigra. Cells had differentiated into both neurons and astrocytes and the level of proliferation was significantly lower within the graft. These results demonstrate that primary neural xenografts contain proliferative cells that possess the ability to migrate and differentiate into both neurons and astrocytes, and suggest that these cells could contribute to normal graft function. This property may be a consequence of the xenograft situation and could potentially be exploited to provide the opportunity to target regions of distant pathology in neurodegenerative diseases using xenotransplantation of embryonic neural tissue.

Migration patterns and phenotypic differentiation of long-term expanded human neural progenitor cells after transplantation into the adult rat brain

We have examined long-term growth-factor expanded human neural progenitors following transplantation into the adult rat brain. Cells, obtained from the forebrain of a 9-week old fetus, propagated in the presence of epidermal growth factor, basic fibroblast growth factor, and leukemia inhibitory factor were transplanted into the striatum, subventricular zone (SVZ), and hippocampus. At 14 weeks, implanted cells were identified using antisera recognizing human nuclei and the reporter gene green fluorescent protein. Different migration patterns of the grafted cells were observed: (i) target-directed migration of doublecortin (DCX, a marker for migrating neuroblasts)-positive cells along the rostral migratory stream to the olfactory bulb and into the granular cell layer following transplantation into the SVZ and hippocampus, respectively; (ii) non-directed migration of DCX-positive cells in the grey matter in striatum and hippocampus, and (iii) extensive migration of above all nestin-positive/DCX-negative cells within white matter tracts. At the striatal implantation site, neuronal differentiation was most pronounced at the graft core with axonal projections extending along the internal capsule bundles. In the hippocampus, cells differentiated primarily into interneurons both in the dentate gyrus and in the CA1-3 regions as well as into granule-like neurons. In the striatum and hippocampus, a significant proportion of the grafted cells differentiated into glial cells, some with long processes extending along white matter tracts. Although the survival time was over 3 months in the present study a large fraction of the grafted cells remained undifferentiated in a stem or progenitor cell stage as revealed by the expression of nestin and/or GFAP.

Transplantation of human neural progenitor cells into the neonatal rat brain: extensive migration and differentiation with long-distance axonal projections

Here we examined the ability of human neural progenitors from the embryonic forebrain, expanded for up to a year in culture in the presence of growth factors, to respond to environmental signals provided by the developing rat brain. After survival times of up to more than a year after transplantation into the striatum, the hippocampus, and the subventricular zone, the cells were analyzed using human-specific antisera and the reporter gene green fluorescent protein (GFP). From grafts implanted in the striatum, the cells migrated extensively, especially within white matter structures. Neuronal differentiation was most pronounced at the striatal graft core, with axonal projections extending caudally along the internal capsule into mesencephalon. In the hippocampus, cells migrated throughout the entire hippocampal formation and into adjacent white matter tracts, with differentiation into neurons both in the dentate gyrus and in the CA1-3 regions. Directed migration along the rostral migratory stream to the olfactory bulb and differentiation into granule cells were observed after implantation into the subventricular zone. Glial differentiation occurred at all three graft sites, predominantly at the injection sites, but also among the migrating cells. A lentiviral vector was used to transduce the cells with the GFP gene prior to grafting. The reporter gene was expressed for at least 15 weeks and the distribution of the gene product throughout the entire cytoplasmic compartment of the expressing cells allowed for a detailed morphological analysis of a portion of the grafted cells. The extensive integration and differentiation of in vitro-expanded human neural progenitor cells indicate that multipotent progenitors are capable of responding in a regionally specific manner to cues present in the developing rat brain.

Human neural stem cells improve cognitive function of aged brain

The capability for in vitro expansion of human neural stem cells (HNSCs) provides a well characterized and unlimited source alternative to using primary fetal tissue for neuronal replacement therapies. The HNSCs, injected into the lateral ventricle of 24-month-old rats after in vitro expansion, displayed extensive and positional incorporation into the aged host brain with improvement of cognitive score assessed by the Morris water maze after 4 weeks of the transplantation. Our results demonstrate that the aged brain is capable of providing the necessary environment for HNSCs to retain their pluripotent status and suggest the potential for neuroreplacement therapies in age-associated neurodegenerative disease.

Therapeutic strategies in multiple sclerosis. II. Long-term repair

Spontaneous myelin repair in multiple sclerosis (MS) provides a striking example of the brain's inherent capacity for sustained and stable regenerative tissue repair--but also clearly emphasizes the limitations of this capacity; remyelination ultimately fails widely in many patients, and disability and handicap accumulate. The observation of endogenous partial myelin repair has raised the possibility that therapeutic interventions designed to supplement or promote remyelination might have a useful and significant impact both in the short term, in restoring conduction, and in the long term, in safeguarding axons. Therapeutic remyelination interventions must involve manipulations to either the molecular or the cellular environment within lesions; both depend crucially on a detailed understanding of the biology of the repair process and of those glia implicated in spontaneous repair, or capable of contributing to exogenous repair. Here we explore the biology of myelin repair in MS, examining the glia responsible for successful remyelination, oligodendrocytes and Schwann cells, their 'target' cells, neurons and the roles of astrocytes. Options for therapeutic remyelinating strategies are reviewed, including glial cell transplantation and treatment with growth factors or other soluble molecules. Clinical aspects of remyelination therapies are considered--which patients, which lesions, which stage of the disease, and how to monitor an intervention--and the remaining obstacles and hazards to these approaches are discussed.

Site-specific migration and neuronal differentiation of human neural progenitor cells after transplantation in the adult rat brain

Neural progenitor cells obtained from the embryonic human forebrain were expanded up to 10(7)-fold in culture in the presence of epidermal growth factor, basic fibroblast growth factor, and leukemia inhibitory growth factor. When transplanted into neurogenic regions in the adult rat brain, the subventricular zone, and hippocampus, the in vitro propagated cells migrated specifically along the routes normally taken by the endogenous neuronal precursors: along the rostral migratory stream to the olfactory bulb and within the subgranular zone in the dentate gyrus, and exhibited site-specific neuronal differentiation in the granular and periglomerular layers of the bulb and in the dentate granular cell layer. The cells exhibited substantial migration also within the non-neurogenic region, the striatum, in a seemingly nondirected manner up to approximately 1-1.5 mm from the graft core, and showed differentiation into both neuronal and glial phenotypes. Only cells with glial-like features migrated over longer distances within the mature striatum, whereas the cells expressing neuronal phenotypes remained close to the implantation site. The ability of the human neural progenitors to respond in vivo to guidance cues and signals that can direct their differentiation along multiple phenotypic pathways suggests that they can provide a powerful and virtually unlimited source of cells for experimental and clinical transplantation.

"...those left behind." Biology and oncology of invasive glioma cells

Although significant technical advances in surgical and radiation treatment for brain tumors have emerged in recent years, their impact on clinical outcome for patients has been disappointing. A fundamental source of the management challenge presented by glioma patients is the insidious propensity of the malignant cells to invade into adjacent normal brain. Invasive tumor cells escape surgical removal and geographically dodge lethal radiation exposure. Recent improved understanding of the biochemistry and molecular determinants of glioma cell invasion provide valuable insight to the underlying biological features of the disease, as well as illuminating possible new therapeutic targets. Heightened commitment to migrate and invade is accompanied by a glioma cell's reduced proliferative activity. The microenvironmental manipulations coincident to invasion and migration may also impact the glioma cell's response to cytotoxic treatments. These collateral aspects of the glioma cell invasive phenotype should be further explored and exploited as novel antiglioma therapies.

Toward autologous ex vivo gene therapy for the central nervous system with human adult astrocytes

The combination of gene transfer techniques and cell transplantation is a promising approach to deliver therapeutic molecules into the CNS. To optimize gene transfer systems, several neural and nonneural cell types are currently under investigation. Among these cells, astrocytes are particularly well suited because of their CNS origin, their efficient secretory mechanisms, and their role as neuronal support. Most importantly, the use of human adult astrocytes as cellular vehicles for ex vivo gene transfer may open the way to autologous transplantation, thus obviating immunological rejection and the side effects of immunosuppressors. In the present study, we report the ability of these cells to be expanded and genetically modified in vitro. Astrocytes derived from human adult cerebral cortex were grown and maintained in vitro as pure primary cultures for at least 10 months. In addition, cells were efficiently transduced by an adenoviral vector encoding human tyrosine hydroxylase (hTH) under the negative control of the tetracycline-based regulatory system (tet-off). The infected cells synthesized large amounts of active hTH and released L-dopa. In addition, doxycycline, a potent analog of tetracycline, efficiently regulated transgene expression. This work is a first step toward the development of therapeutic strategies based on the use of genetically engineered human adult astrocytes for autologous transplantation in human neurodegenerative diseases and CNS trauma.

Long-term survival of human central nervous system progenitor cells transplanted into a rat model of Parkinson's disease

Progenitor cells were isolated from the developing human central nervous system (CNS), induced to divide using a combination of epidermal growth factor and fibroblast growth factor-2, and then transplanted into the striatum of adult rats with unilateral dopaminergic lesions. Large grafts were found at 2 weeks survival which contained many undifferentiated cells, some of which were migrating into the host striatum. However, by 20 weeks survival, only a thin strip of cells remained at the graft core while a large number of migrating astrocytes labeled with a human-specific antibody could be seen throughout the striatum. Fully differentiated graft-derived neurons, also labeled with a human-specific antibody, were seen close to the transplant site in some animals. A number of these neurons expressed tyrosine hydroxylase and were sufficient to partially ameliorate lesion-induced behavioral deficits in two animals. These results show that expanded populations of human CNS progenitor cells maintained in a proliferative state in culture can migrate and differentiate into both neurons and astrocytes following intracerebral grafting. As such these cells may have potential for development as an alternative source of tissue for neural transplantation in degenerative diseases.

Localization of dopamine receptors and associated mRNA in transplants of human fetal striatal tissue in rodents with experimental Huntington's disease

Huntington's Disease (HD) is characterized by deficits in motor and cognitive functions. This neurodegenerative disease shows an extensive loss of medium-sized spiny projection neurons (GABAergic) within the neostriatum. With the loss of these neurons, there is a concomitant loss of associated receptors, such as those for GABA, glutamate, and dopamine. In the present study, we have addressed the question of whether dopamine receptors are re-established in the lesioned rodent striatum following the transplantation of human striatal cells. Human striatal cell suspension or saline (transplant controls) was injected into the striatum of rats previously lesioned with quinolinic acid (QA). Three nine months following transplantation, the animals were sacrificed and the brains were processed for receptor autoradiography and in situ hybridization of dopamine D1 and D2 receptor subtypes. Our results demonstrate that animals transplanted with human striatal cells show a significant increase in D1 receptors following transplantation when compared to the lesion area in control animals, while D1 receptor mRNA remains unchanged. In contrast to D1 receptor binding, D2 receptor levels are not increased in the lesioned and transplanted area of the striatum when compared to controls; however, D2 receptor mRNA levels are significantly increased. These results demonstrate that at the times the animals were examined, D1 and D2 receptors were differentially regulated. Our results further indicate that human striatal primordium will survive following transplantation and will express D1 receptors and D2 receptor mRNA that are depleted in the QA lesioned rodent striatum. This study compliments and extends previous findings on human striatal cell transplantation in rodent models of HD.

Human fetal astrocytes as an ex vivo gene therapy vehicle for delivering biologically active nerve growth factor

The therapeutic use of neurotrophic factors for neurodegenerative diseases is promising, however, optimal methods for continuous delivery of these substances to the human central nervous system (CNS) remains problematic. One approach would be to graft genetically engineered human cells that continuously secrete high levels of a biologically produced and processed neurotrophic factor. This ex vivo gene therapy approach has worked well in animal models of neurodegenerative diseases using a variety of nonneuronal cell types to deliver the transgene. In our studies, we have been investigating the potential of astrocytes, a cell type normally present in the CNS, as a vehicle for ex vivo gene therapy. Here, we demonstrate that astrocytes in the human fetal cortex can be isolated and efficiently infected with an amphotropic retrovirus harboring mouse beta-nerve growth factor (NGF). These transduced astrocytes express high levels of NGF mRNA and secrete bioactive NGF protein as demonstrated by stimulation of neurite outgrowth from adrenal chromaffin cells. NGF ELISA showed that these astrocytes secrete NGF protein at a rate of 41 ng/day per 10(5) cells after 2 weeks in vitro, whereas NGF is undetectable in medium conditioned by normal astrocytes. These data suggest that human fetal astrocytes can be used for delivering biologically produced neurotrophic factors to the human CNS.

Developmental features of human striatal tissue transplanted in a rat model of Huntington's disease

Areas of striatal grafts which contain neurons that are characteristic of the striatum are called P-zones. We have investigated whether the paucity of P-zones in human xenografts of lateral ganglionic eminence (LGE) tissue in a rat model of Huntington's disease is due (i) to an absence of the appropriate target cells of LGE neurons or (ii) to the persistence of an immature morphology. Striatal tissue from human embryos of varying sizes (21, 24, and 30 mm in crown-to-rump length) was grafted into the ibotenate-lesioned striatum of immunosuppressed rats, which were killed after 15-17 weeks. In most cases, tissue from the LGE and medial ganglionic eminence (MGE) was transplanted together, whereas some rats received grafts of only LGE tissue. Both types of grafts exhibited positive immunostaining for PCNA (proliferating cells), Vimentin (immature astrocytes), and GAP-43 (outgrowing fibers), which indicates that graft maturation is still ongoing up to 4 months after grafting. Graft survival seemed better when MGE was cografted with LGE, suggesting that the MGE may provide trophic support for LGE neurons and can affect the overall survival of human striatal xenografts. However, the extent of P-zone formation was not increased in MIXED, i.e., LGE plus MGE, grafts.

Transplantation of human striatal tissue into a rodent model of Huntington's disease: phenotypic expression of transplanted neurons and host-to-graft innervation

The present study was undertaken to investigate the phenotypic expression and integration of human striatal neurons transplanted into an animal model of Huntington's disease. Sprague-Dawley rats were anesthetized and subjected to quinolinic acid lesions of the left striatum. Three human fetal cadavers were utilized for transplantation in this study (7, 8, and 10 weeks in gestation). The striatal primordia was dissected from each fetus and subsequently dissociated into cell suspensions. Following the initial lesion surgeries (3-4 months), the rats were reanesthetized and transplanted with human striatal cells (400,000 cells per rat). The animals were processed for histochemical analysis 9-17 weeks posttransplantation. Histochemistry was performed utilizing thionin (Nissl staining), acetylcholinesterase, NADPH-diaphorase, and antibodies against tyrosine hydroxylase and glial fibrillary acidic protein. Examination of stained brain sections demonstrate that human striatal transplants grow to fill a substantial portion of the remaining striatum, and contain clusters of immature and mature cells. Acetylcholinesterase activity is present in the transplant neuropil, varying in intensity, and distributed in a heterogeneous fashion. In addition, host afferent dopaminergic fibers penetrate into the transplant, and are occasionally found in patches. NADPH-diaphorase histochemistry revealed medium sized aspiny striatal neurons of donor origin in the transplants. The results of this study are similar to those obtained with rodent fetal striatal transplants, and suggest that human striatal tissue is capable of surviving, expressing normal striatal cell phenotypes, and receiving host dopaminergic innervation.