Regenerative medicine in Huntington's disease: current status on fetal grafts and prospects for the use of pluripotent stem cell.

Huntington's disease is currently incurable, but cell therapy is seen as a promising alternative treatment. We analyze the safety and efficacy of the intrastriatal transplantation of human fetal neuroblasts from ganglionic eminences in patients with Huntington's disease. A few rare surgical incidents were reported, but the main difficulty associated with this therapeutic approach is the occurrence of recipient alloimmunization against the graft and the lack of availability, standardization and quality control for the fetus-derived products required for cell therapy. Some patients showed sustained cognitive improvement over periods of more than six years, and motor improvements for more than four years. Grafting outcomes are variable even within individual transplantation centers. The reasons for this variability are poorly understood, highlighting the need for further research in this specific area. With the perspective of additional trials in the future, we review here the development of human pluripotent stem cell-derived cell therapy products for HD, and their advantages and disadvantages with respect to fetal cells.

Transplantation of embryonic neurones to replace missing spinal motoneurones.

Loss of spinal motoneurones results in severe functional impairment. The most successful way to replace missing motoneurones is the use of embryonic postmitotic motoneurone grafts. It has been shown that grafted motoneurones survive, differentiate and integrate into the host cord. If grafted motoneurones are provided with a suitable conduit for axonal regeneration (e.g. a reimplanted ventral root) the grafted cells are able to grow their axons along the whole length of the peripheral nerves to reach muscles in the limb and restore function. Grafted motoneurones show excellent survival in motoneurone-depleted adult host cords, but the developing spinal cord appears to be an unfavourable environment for these cells. The long term survival and maturation of the grafted neurones are dependent on the availability of a nerve conduit and one or more target muscles, no matter whether these are ectopic nerve-muscle implants or limb muscles in their original place. Thus, grafted and host motoneurones induce functional recovery of the denervated limb muscles when their axons regenerate into an avulsed and reimplanted ventral root. On the other hand, motoneurone-enriched embryonic grafts placed into a hemisection cavity in the cervical spinal cord induce axonal regeneration from great numbers of host motoneurones, possibly by the bridging effect of the grafts. In this case the regenerating host motoneurones reinnervate their original target muscles while the graft provides few axons for the reinnervation of muscles. These results suggest that reconstruction of the injured spinal cord with embryonic motoneurone-enriched spinal cord graft is a feasible method to improve severe functional motor deficits.

Huntington's disease: new frontiers for molecular and cell therapy.

Huntington's disease (HD) is an incurable, adult-onset, dominantly inherited neurodegenerative disease, caused by a CAG expansion in the 5' coding region of the gene HD [encoding huntingtin (htt), which is ubiquitously expressed in all tissues]. The disease progresses inexorably with devastating clinical effects on motor, cognitive and psychological functions; death occurring approximately 18 years from the time of onset. These clinical symptoms primarily relate to the progressive death of medium-spiny GABA-ergic neurons of the striatum and in the deep layers of the cortex; during the later stages of the disease, the degeneration extends to a variety of brain regions, including the hypothalamus and hippocampus. The mechanism by which mutant htt leads to neuronal cell death and the question of why striatal neurons are targeted both remain to be further investigated. Certainly htt is required for cell survival and impairment of wild-type htt function can be involved in neurodegeneration, but considerable evidence also shows that trinucleotide repeat expansion into glutamine (polyQ domain) endows the protein with a newly acquired toxic activity. The increasing availability of HD animal models have allowed not only to investigate the function of htt, but also to screen and test potential therapeutic drugs in the promising area of neurotherapeutics. So, thorough analysis of these molecular and biochemical events, assessing the validity of candidate mechanisms, provides a means to identify effective therapeutic strategies for cellular repair. Here, the rationale and efficacy of different therapies are compared and alternative therapies are reviewed including intrastriatal transplantation of human fetal striatal tissue to support the cell replacement strategy in HD. Since functional restoration through neuronal replacement probably could be combined with neuroprotective strategies for optimum clinical benefit, in vivo and ex vivo gene therapy for delivery of neuroprotective growth factor molecules are also considered.

Tissue engineered fetal skin constructs for pediatric burns.

The management of patients with partial thickness (second degree) burns is problematic due to the different treatments needed for varying depths of injury. A report recently published in The Lancet describes a novel treatment for deep second degree burns using a fetal skin construct (FSC). The authors included eight pediatric patients with small second degree burns. They showed that FSCs reduced the need for autografting of deep second degree burns, with little hypertrophy of new skin and no skin contraction. This technology is new and exciting, but in our opinion several issues must be addressed before FSCs can enter the clinical arena. All of the patients were included in the treatment group, and therefore no comparison with conventional skin substitutes was possible. There is no mention of the use of laser Doppler in any initial assessment of patients. The debridement carried out before application of the FSC is not elaborated upon, and the surface areas involved in the study were very small in most cases, which limits the relevance to patients with larger burns. The use of FSCs gives us an additional option in a range of possible treatments for this notoriously difficult-to-treat patient group.

Nonhematopoietic stem cells of fetal origin--how much of today's enthusiasm will pass the time test?

Stem cells originating at fetal age are for many reasons superior as a material for the regenerative medicine purposes, when compared to their adult counterparts. While hematopoietic cells, isolated from fetal liver or cord blood, have been well known for a long time and have passed practical tests as clinical transplantation material, the non-hematopoietic cells are newly recognized, and the knowledge of their phenotype and differentiation potential is rather insufficient. We, and the others, have identified a subpopulation of cord blood cells phenotypically different from hematopoietic cells (CD34-, CD45-, CD29+, CD44+, CD51+, CD105+, SH-2, SH-3), in vitro plastic adherent, and capable of multilineage differentiation. The other candidates for multipotential stem cells are cells extracted from umbilical cord or placental tissue. The preliminary observations suggest, that these cells, phenotypically similar to the nonhematopoietic cord blood cells, are capable of extensive replication in vitro and of multilineage differentiation into a variety of tissues including cardiac muscle, bone and cartilage, adipocytes, and nerve cells. The other possible medical applications include "rejuvenation" of selected tissues and systems in senile patients, and therapeutical cloning - for both purposes, cells at the fetal stage of genetic regulation may be more useful than cells collected from adult donors. There is still, however, a high level of uncertainty concerning future medical applications of fetal stem cells. Their numbers and characteristics may differ from the preliminary observations, and their behavior in vivo may not fulfill the expectations originating from the in vitro studies. Finally, the autologous applications of stem cells collected at the stage of birth may need the involvement of technical and financial resources for the storage of frozen cell samples throughout the period of life of their potential user. Such procedure seems possible from technical point of view, but may be inadequately substantiated by the eventual advantages.

Cellular replacement therapy for Parkinson's disease--where we are today?

The concept of replacing lost dopamine neurons in Parkinson's disease using mesencephalic brain cells from fetal cadavers has been supported by over 20 years of research in animals and over a decade of clinical studies. The ambitious goal of these studies was no less than a molecular and cellular "cure" for Parkinson's disease, other neurodegenerative diseases, and spinal cord injury. Much research has been done in rodents, and a few studies have been done in nonhuman primate models. Early uncontrolled clinical reports were enthusiastic, but the outcome of the first randomized, double blind, controlled study challenged the idea that dopamine replacement cells can cure Parkinson's disease, although there were some significant positive findings. Were the earlier animal studies and clinical reports wrong? Should we give up on the goal? Some aspects of the trial design and implantation methods may have led to lack of effects and to some side effects such as dyskinesias. But a detailed review of clinical neural transplants published to date still suggests that neural transplantation variably reverses some aspects of Parkinson's disease, although differing methods make exact comparisons difficult. While the randomized clinical studies have been in progress, new methods have shown promise for increasing transplant survival and distribution, reconstructing the circuits to provide dopamine to the appropriate targets and with normal regulation. Selected promising new strategies are reviewed that block apoptosis induced by tissue dissection, promote vascularization of grafts, reduce oxidant stress, provide key growth factors, and counteract adverse effects of increased age. New sources of replacement cells and stem cells may provide additional advantages for the future. Full recovery from parkinsonism appears not only to be possible, but a reliable cell replacement treatment may finally be near.

Cell replacement strategies for neurodegenerative disorders.

Cell transplantation has over the last two decades emerged as a promising approach for restoration of function in neurodegenerative diseases, in particular Parkinson's and Huntington's disease. Clinical trials have so far focused on the use of implants of embryonic mesencephalic tissue containing already fate-committed dopaminergic neuroblasts with the capacity to develop into fully mature dopamine neurons in their new location in the host brain. However, the recent demonstration that immature neural progenitor cells with multipotent properties can be isolated from both the developing and adult CNS and that these cells can be maintained and propagated in culture, has provided a new interesting tool for restorative cell replacement and gene transfer therapies. Embryonic stem cells, obtained from the early stages of embryonic development, and neural stem cells, obtained from the developing brain, may provide renewable sources of cells for therapeutic purposes, and could eventually offer a powerful alternative to primary fetal CNS tissue in clinical transplantation protocols. The purpose of this review is to discuss the prospects of the emerging progenitor cell technology for cell replacement and restorative therapies in neurodegenerative diseases, and consider some of the critical issues that must be solved in order to make progenitor cells useful in studies of brain repair.

Neurobiology of human neurons (NT2N) grafted into mouse spinal cord: implications for improving therapy of spinal cord injury.

Emerging data suggest that current strategies for the treatment of spinal cord injury might be improved or augmented by spinal cord grafts of neural cells, and it is possible that grafted neurons might have therapeutic potential. Thus, here we have summarized recent studies of the neurobiology of clonal human (NT2N) neurons grafted into spinal cord of immunodeficient athymic nude mice. Postmitotic human NT2N neurons derived in vitro from an embryonal carcinoma cell line (NT2) were transplanted into spinal cord of neonatal, adolescent and adult nude mice where they became integrated into the host gray and white matter, did not migrate from the graft site, and survived for > 15 months after implantation. The neuronal phenotype of the grafted NT2N cells was similar in gray and white matter regardless of host age at implantation, and some of the processes extended by the transplanted NT2N neurons became ensheathed by oligodendrocytes. However, there were consistent differences between NT2N processes traversing white versus gray matter. Most notably, NT2N processes with a trajectory in white matter extended over much longer distances (some for > 2 cm) than those confined to gray matter. Thus, NT2N neurons grafted into spinal cord of nude mice integrated into gray as well as white matter, where they exhibited and maintained the morphological and molecular phenotype of mature neurons for > 15 months after implantation. Also, the processes extended by grafted NT2N neurons differentially responded to cues restricted to gray versus white matter. Further insight into the neurobiology of grafted human NT2N neurons in the normal and injured spinal cord of experimental animals may lead to novel and more effective strategies for the treatment of spinal cord injury.

Towards a definition of recovery of function.

In this review we consider recovery of function after spinal cord injury, and, in particular, recovery improved following intraspinal cellular transplants. Some recovery occurs spontaneously and this can be especially dramatic in neonates, supporting the notion that developing and adult spinal cord respond differently to injury. Recovery can be improved in both neonates and adults by appropriate cellular transplants into the injury site. We describe several functional tests used in animals with spinal lesions and transplants. We compare the effects of transplants of fetal tissue and genetically modified fibroblasts into neonatal and adult injury sites on recovery of motor and sensorimotor function. Fetal tissue transplants support greater recovery and elicit more regeneration in neonates than in adults. Transplants of fibroblasts modified to produce neurotrophic factors however support both recovery and axonal growth even in adults. The contribution of the transplant to recovery is shown by the loss of function that follows a second lesion just rostral to the original lesion/transplant site. The effect of the re-lesion indicates that the recovery is mediated by the presence of the transplant but the way in which transplants act to promote recovery may include a number of mechanisms, including regeneration and sprouting, neuroprotection, and modifications of organization of spared CNS structures.

Human fetal tissue research: practice, prospects, and policy.

Tissue from human fetal cadavers has long been used for medical research, experimental therapies, and various other purposes. Research within the last two decades has led to substantial progress in many of these areas, particularly in the application of fetal tissue transplantation to the treatment of human disease. As a result, clinical trials have now been initiated at centers around the world to evaluate the use of human fetal tissue transplantation for the therapy of Parkinson's disease, insulin-dependent diabetes mellitus, and a number of blood, immunological and, metabolic disorders. Laboratory studies suggest a much wider range of disorders may in the future be treatable by transplantation of various types of human fetal tissue. A combination of characteristics renders fetal tissue uniquely valuable for such transplantation, as well as for basic research, the development of vaccines, and a range of other applications. Although substitutes for human fetal tissue are being actively sought, for many of these applications there are at present no satisfactory alternatives. Important issues remain unresolved concerning the procurement, distribution, and use of human fetal cadaver tissue as well as the effects of such use on abortion procedures and incidence. These issues can be addressed by the introduction of appropriate guidelines or legislation, and need not be an impediment to legitimate research and therapeutic use of fetal tissue.

Current state of stem cell research for the treatment of Parkinson's disease.

Current findings suggest that multipotent stem cells may be suitable for cell replacement therapies in the treatment of neurodegenerative disorders. Embryonic stem (ES) cells are pluripotent cells isolated from the inner cell mass of the preimplantation blastocyst, which give rise to all cells in the organism. Similarly, multipotent stem cells are also able to regenerate, but are believed to have a more restricted potential than ES cells, and are often defined by the organ from which they are derived. Neural stem cells have been categorized as multipotent stem cells derived from the nervous system with the capacity to regenerate and to give rise to cells belonging to all three cell lineages in the nervous system: neurons, oligodendrocytes, and astrocytes. It is hoped that research on stem cells may reveal methods for producing an infinite supply of dopamine neurons for transplant into Parkinson's disease (PD) patients. The problem is controlling cell growth and differentiation. We will briefly review the current state of stem cell research and will critically discuss the potential of stem cells for the treatment of PD.

The human pluripotent stem cell: impact on medicine and society.

OBJECTIVE: To discuss the current state of the science surrounding human pluripotent stem cells and to show that the derivation of such cells from donated preimplantation human embryos should be eligible for federal funding provided that certain protections are met. DESIGN: A literature search focusing on the scientific aspects of pluripotent stem-cell research and analyses of current and past legislation and federal panel recommendations. CONCLUSION(S): The current federal laws regulating the permission necessary to obtain fetal tissue from elective pregnancy terminations are intended to insulate the decision to terminate a pregnancy from the potential positive influence of fetal tissue transplantation. A similar situation can be created for the derivation of cells from excess preimplantation human embryos produced by IVF programs. If, as in fetal tissue research, assurances can be made that the research will have no influence on the decision to dispose of the embryo, the derivation of pluripotent stem cells from embryo should proceed with federal funding.

Current trends in neural transplantation.

Basic laboratory studies in neural transplantation have promulgated some principles for clinical transplantation some of which are challenged by clinical experience. Chief amongst them are the restricted transplantation 'window' and the use of immunosuppression. Neural transplantation in man has largely been directed to Parkinson's Disease although other neurodegenerative diseases may prove suitable candidates.

[Intracerebral grafts in Parkinson disease. Current experiences and perspectives]. / Greffes intracérébrales dans la maladie de Parkinson. Expérience actuelle et perspectives.

Six patients with advanced Parkinson's disease have been grafted with human fetal neuronal cells. This clinical work is based on the technique originally described by the groups of Lund, Sweden and Créteil, France, with which we closely collaborate. A first group of 3 patients was grafted between 1995 and 1996, with neuronal tissue obtained from same-day abortions. We have observed bilateral improvement of motor functions after unilateral transplantation into the putamen. One patient had a second graft, into the heterolateral putamen, one year after the first one. Another group of 3 patients was operated between 1997 and 1998, and received grafts of hibernated tissue, in order to facilitate the technical organization of the transplantation procedure. Altogether, these clinical results are encouraging, but the technical and ethical limitations related with the use of human fetal tissue prompted us to develop alternative solutions, such as the use of xenografts and the transplantation of genetically modified cells.

[Future cure of hearing disorders? Gene therapy and stem cell implantation are possible new therapeutic alternatives]. / Framtida bot för hörselskador? Genterapi och implantation av stamceller möjliga nya behandlingsvägar.

Hearing loss is a very common disorder; nearly 10 per cent of the population is affected. Recently, a few findings such as the roles of neurotrophins, nitric oxide, reactive oxygen species and glutamate receptors in the peripheral hearing system have been highlighted. In this review, focus is set on possible mechanisms of peripheral hearing disorders, and on recent advances to prevent and treat hearing loss. Clinically useful treatment strategies, especially gene therapy and the use of embryonic stem cells, are particularly stressed.

[Results and outlooks of using cell technologies in the treatment of neurological diseases]. / Itogi i perspektivy ispol'zovaniia kletochnykh tekhnologii v lechenii nevrologicheskikh zabolevanii.

An attempt was undertaken in the last decade of the 20th century to use a principally new approach to the treatment of neurological diseases--cell therapy. Main efforts were focused on developing a method related with replacement of neurons dying in neurodegenerative pathology, primarily, in Parkinson disease (PD). Outlined below are the key elements of the technology:--ensuring, in experiment, of a prolonged therapeutic effect in transplantation, to the affected part, first of embryonic neurons of the animal of the same species (allografting) and then of homologous embryonic neurons of man (heterografting);--obtaining, standardization and preparation (for transplantation) of embryonic nervous tissue of man; transplantation of embryonic nervous tissue of man to the brain of patient and evaluation, in situ, of the functional activity of its neurons; and evaluation of the therapeutic effect of grafting. Cell suspension of meseencephalon of 6-9 week human fetus containing around 10% of differentiating dopaminergic neurons was used for grafting in PD. Embryonic dopaminergic neurons, administered stereotactically into the striatum of patient, established synaptic links with neurons of the recipient, which was accompanied by the onset of synthesis and reverse uptake of dopamine (DA) as well as by the onset of spontaneous and stimulated release of DA. Neurografting ensured a temporary improvement of the condition in a part of PD patients but did not cure them. Moreover, such positive therapeutic effect was registered only in patients with the akineticorigid but not trembling variation of the disease. Hence, although there was a certain progress in clinical neurografting, the approach cannot be now recommended for introduction in neurology and neurosurgery. The limited therapeutic effect of the treatment method is primarily explained by a low rate of survival of transplanted dopaminergic neurons and, consequently, by the persisting DA deficit in patient's body. Therefore, the outlooks for perfecting the cell technology are related with increasing the survival rate of implanted dopaminergic neurons and with stimulating the innervation of target neurons in patient's striatum as well as with using the neural (glia) and non-neural (fibroblasts, myoblasts) cells with modified gene and stem cells. Finally, despite a certain progress of advancing the cell technology in neurology the approach still needs more research, which would enable further clinical trials.

[Transplantation of the retina--the near or distant future?]. / Przeszczepienie siatkowki--bliska czy daleka przyszlosc?

In the review the results of the recently published experimental papers concerning transplantations of embryonic retina, retinal pigment epithelium and photoreceptors are discussed. The results of these studies indicate that in humans transplantation of the whole retina is the matter of the distant future but in the near future one can expect transplantation of the isolated retinal layers namely pigment epithelium and photoreceptors.

[Transplantation of fetal tissues in otorhinolaryngology: current status and prospects for the future]. / Ispol'zovanie transplantatsii fetal'nykh tkanei v otorinolaringololgii. Analiz sostoianiia problemy i perspektivy razvitiia.

Insufficient efficacy of treatment of neurosensory hypoacusis makes investigators search for new methods. Transplantation of fetal tissue taken from healthy embryos of gestation stage II tried in various fields of medicine, such as neurology, endocrinology, surgery, etc., was also tested in management of various forms of neurosensory hypoacusis. Endonasal, endaural, endolumbal and intracochlear methods of the transplantation are detailed. Results of combined dynamic audiological control of these patients including tonal threshold audiometry in extended frequency range are presented. A 1-year follow-up provided evidence in favour of endolumbal and intracochlear transplantation. Further investigations are needed.

Fetal dopaminergic transplantation trials and the future of neural grafting in Parkinson's disease.

Clinical use of allografts of fetal ventral mesencephalic tissue as a treatment to replace dopaminergic neurons in patients with Parkinson's disease was first done more than 20 years ago. Since then, many patients have received transplants, with variable results. During this time, our knowledge of Parkinson's disease has changed and the nature and extent of problems associated with the disorder have been better defined. Our understanding on how best to implement this cell-replacement strategy for patients has grown, but gaining this insight has entailed critical reappraisal of data from transplant trials that have already been undertaken.