Cell therapy of neurodegenerative diseases
Therapy of neurodegenerative diseases: opportunities and prospects
G.NIKKA, MD, Professor, T. PIROT, MD, Professor
Department of Stereotactic Neurosurgery of the University Neurological Center of Freiburg, Germany
Journal "Medical Council" No.7-8 (2010)
Published on the website "Remedium"
Despite the fact that neurotransplantation has been tested on several hundred patients, it is an experimental method for the treatment of neurodegenerative diseases. Transplantation of human fetal tissues in Parkinson's disease allows not only to reduce symptoms, primarily akinesia and rigidity, but also to eliminate dyskinesia and tremor in many patients. In some cases, severe secondary motor disorders may develop. Currently, the trigger factors of these adverse events and prognostic criteria are being studied.
Studies of the possibilities of neurotransplantation in Huntington's disease have shown that donor tissues are preserved surrounded by affected areas of the brain without any signs of involvement in the pathological process. The data on the change in functional status turned out to be ambiguous. Nevertheless, a group of French transplantologists using an improved protocol managed to demonstrate the effectiveness of cell therapy.
Neurotransplantation is a promising innovative way to treat neurodegenerative diseases. With the use of an optimized technique, stable clinical remission can be achieved. In the course of further studies, it is necessary to determine the conditions necessary for successful therapy with minimal risk of side effects. At the same time, fundamental work is underway to find alternative sources of cells, and new strategies for their cultivation allow this method to be widely implemented.
Introduction
Neurodegenerative diseases, especially idiopathic Parkinsonism and Huntington's chorea, reduce the quality of life of patients, lead to loss of independence and cause the need for constant care.
Typical manifestations of Parkinson's disease are impoverishment of the motor sphere, muscle rigidity and tremor caused by degeneration of dopaminergic neurons of the striatum and, as a consequence, dopamine deficiency in the basal ganglia. Unfortunately, currently modern medicine does not have the means that could stop this process.
The cause of Huntington's disease is a mutation of the gene encoding the huntingtin protein. However, the mechanisms triggering cell death and the pathogenesis of functional limitations have not yet been fully elucidated. This pathology is characterized by motor symptoms (hyper- or bradykinesia), and as the disease progresses, the development of cognitive and mental disorders. Therapeutic measures are limited to symptomatic therapy.
Parkinsonism and Huntington's chorea have been the cornerstone of clinical research on neuropreservation therapy for many years [1].
Neurodegenerative diseases, especially idiopathic Parkinsonism and Huntington's chorea, reduce the quality of life of patients, lead to loss of independence and cause the need for constant care.
Intracerebral transplantation in animal models
Parkinson's and Hangtington's diseases develop only in humans. However, their manifestations and pathogenetic features can be reproduced in animals by chemical means. To simulate Parkinsonism, a neurotoxin – 6-hydroxydophamine is injected into rats between the anterior cerebral tract and the striatum or directly into the striatum. Transplantation of ventral mesencephalon tissues into the striatum of affected animals reduces akinetic-rigid symptoms. Combined homotopic transplantation into the black matter of the brain provides additional functional advantages and stabilizes the result [1].
Figure 1. Animal model of Parkinson's disease (A) obtained by unilateral injection of 6-hydroxydofamine,
causing the loss of dopaminergic innervation of the hemisphere while completely preserving it from the opposite side
and the corresponding contralateral deficit of sensorimotor reactions.
Microsurgically isolated ventral mesencephalon tissues
processed mechanically and enzymatically.
The cell suspension is stereotaxically implanted into the affected area of the brain.Similarly, with the introduction of ibotenic or quinolic acids, Huntington's disease is modeled.
The positive effect of transplantation on the motor and cognitive functions of such animals has been proven. Transgenic mice with Huntington's pathology were rarely used to evaluate the effectiveness of such therapy. However, the experiments carried out on them made it possible to confirm the viability of the graft [2].
Clinical studies on neurotransplantation
Neurotransplantation is a promising innovative way of treating neurodegenerative diseases, with the use of an optimized technique, stable clinical remission can be achieved.
Parkinson's disease
Parkinson's disease was the first neurodegenerative disease on which cell transplantation was tested. As part of the tests, operations were carried out already in the late 80s and in the 90s of the last century. Clinical trials in Europe started with the unilateral transplantation of fetal human cells to two patients from the Swedish city of Lund, but the results were not impressive. Later, in an uncontrolled open study, the operational technique was optimized. Stereotactic intervention was performed with the intended purpose in the area of the lenticular or caudate nuclei. The improvement on the UPDRS scale reached up to 40%. Reduction of akinesia, rigidity, tremor and dyskinesia was objectively noted. It was possible to reduce the doses of medications [3,4].
The effect was delayed and occurred after about 6 months. The periods of "inclusion" were gradually lengthened, and drug dosages were significantly reduced. Patients who had a history of requiring drug therapy to correct dyskinesia did without it after transplantation [3,4]. According to positron emission tomography (PET) data, a long-term recovery of cerebral carbohydrate metabolism was observed, including outside the basal ganglia [4,5].
In the course of two controlled studies conducted in the USA in the 90s, the effectiveness of neurotransplantation was studied. Some patients were injected with ventral mesencephalon cells, and patients in the control group underwent placebo surgery. The primary endpoints were not reached in both works. Researchers have recorded a severe side effect – a new independent form of dyskinesia that occurs within a year after transplantation and, due to causality, is designated as graft-associated (GID, Graft induced dyskinesia). There was no significant improvement in the condition of patients in the intervention group. At the same time, when analyzing by subgroups in one of the studies, there was a positive trend, but only against the background of taking immunosuppressants (6 months) and with regression after their cancellation. With a different approach to the division of the sample, patients under 60 years of age received significant benefits from transplantation. The studies were discontinued due to the development of secondary dyskinesia of unknown etiology in some of its participants. Anamnestic indications of dyskinesia before surgery, immunological reactions, methods of tissue processing or serotonergic neuron transplantation were considered as hypotheses. Some patients had previously observed dyskinesia after the intervention [6,7].
Numerous methodological discrepancies in the collection and storage of material or the choice of target brain structures distinguished these works from previously open studies. An international consortium of leading neurotransplantation centers in North America and Europe analyzes the data of transplanted individuals in order to develop protocols for future studies that will achieve a stable positive result of treatment and minimize the likelihood of complications.
Although only a few patients achieved clinical improvement in controlled studies, in the majority it was obvious and persistent [3,4,8,9]. Post-mortem histological examination showed that the transplanted fetal tissues remain viable for at least 16 years and are transformed into mature dopaminergic neurons [10-12]. Donor cells establish connections with the recipient's nervous system. At the same time, in some patients, already 3 years after the intervention, a full-fledged innervation of the shell of the lentil-shaped nucleus occurs due to the graft.
Figure 2. A: Graft stained with cresyl violet, with a small magnification.
Cells from dark purple clusters settle on the periphery (fuzzy edge).
B+C: Large increase after immunofluorescence staining.
Red cells are a specific strial type (graft).
The green fibers belong to the recipient and form contacts with the bodies of the injected neuronsHuntington's Disease
Unlike Parkinsonism, in Hangtington's disease, GABAergic nerve cells of ganglion tubercles are transplanted.
In a systematic study conducted in the USA, which included 3 patients [Kopyov, 1998], 2 of them showed a slight improvement in motor and neuropsychic functions. Cells of the lateral ganglion tubercle were used. As in the case of Parkinson's disease, the source of tissue was abortive material. The target area was the caudate and lenticular nuclei.
In another American study involving 7 patients from Tampa (Florida), cells of the lateral tubercle were also implanted [13]. One patient was excluded due to a volumetric subdural hematoma that occurred during a fall and significantly aggravated his condition. For the rest of the operated patients, improvements in the motor sphere were reported 12 months after the intervention. Meanwhile, PET performed after 2 years revealed a significant decrease in the density of strial D1 and D2 receptors compared to the control group. The authors avoided an unambiguous interpretation of these data, citing the lack of histological confirmation. Variants of graft death or the effect of dissection technique were discussed [15].
Encouraging results were obtained by a group of French scientists who performed transplantation in 5 patients as part of a pilot study after a two-year preoperative follow-up. After 24 months, 4 patients had sustained improvement in cognitive and motor functions [16]. PET confirmed an increase in glucose metabolism in the frontal lobe and striatum of the three most stable patients. The fourth, who won clinically to a lesser extent, had a cyst formed in the graft area. Attention should be paid to the methodological features of this work: tissues from a single or a maximum of two donors were injected from each side, the ganglion area was excised entirely and 3-fold immunosuppression was performed. After 6 years, the effect remained in all three patients. Over the years, the clinic of the disease has increased slightly. Cognitive disorders responded positively to therapy [17].
The Association of UK neurotransplantologists under the leadership of the Kadriff Brain Center set a goal to study the safety of cell transplantation in the NEST-UK study. Absolutely no intra- or perioperative complications were registered in 4 recruited patients. However, due to the adoption of new legal norms, the work was suspended and its resumption is planned at the end of 2010.
Currently, a controlled multicenter European study of the effectiveness of cell therapy is being conducted. The design of the study suggests performing transplantation 6 or 18 months after randomization, which will test the hypothesis about the benefits of early intervention.
Figure 3. Planning of human fetal stem cell transplantation
a patient with Huntington's diseaseIn the Freiburg transplant series, 18 patients were transplanted.
All operations were carried out without complications. The risk of disease transmission from donor to recipient is minimized thanks to a thorough screening program of biological samples. According to the literature data, during postmortem histological studies, innervation of the graft by the recipient's neurons was noted. The transplanted cells showed no signs characteristic of Hangtington's disease [18]. The graft was not affected by the pathological process and mature neurons expressing region-specific markers were identified in it [19]. A postmortem histological preparation of one patient was obtained in Freiburg. His graft was isolated from the tissues of the entire ganglion region. At the time of the study, the transplanted cells already had signs of regional differentiation, although not all markers of mature neurons were present yet. It should be noted that this case was distinguished by the shortest period after the operation described in the literature [20].
The subject of the next study is massive pathological reactions on the part of the graft. The results of autopsy of 3 patients who were injected with cells of lateral tubercles are reported [21]. A distinctive feature was the severity of damage to the recipient's cerebral tissues. Along with this, corticostrial glutamatergic projections were detected for the first time in a human preparation, which are regarded on the basis of experience with animal models as a sign of functional integration of the graft. Nevertheless, the researchers came to the conclusion about the pathological role of these changes, arguing that the pathogenic environment damages the transplanted cells through such connections. A similar mechanism has been discussed in Parkinson's disease. On the other hand, ubiquitin aggregates typical of Hangtington's disease were not found in the graft.
In addition, massive local immune activity was noted in the studied samples, possibly indicating a rejection reaction. This interpretation is in harmony with other references to transplant rejection and emphasizes the need to study the neuroimmunological foundations of allotransplantation.
Prospects of neurotransplantation and tasks of future research
The conducted studies have shown that with proper methodology and compliance with the selection criteria, cell transplantation is an effective and safe method of treatment. In the future, the study of stem cells will help replace ethically questionable fetal tissues with other cellular resources, for example, induced pluripotent stem cells. In turn, at the present stage, scientific research with fetal tissues has already made a great contribution to the development of neurotransplantation: it allowed us to determine indications and contraindications for its implementation, as well as optimize the methodology.
Experiments on animals with atypical Parkinson's syndrome have indicated the possibilities of neuro-surgical therapy in the treatment of this pathology in humans. The positive results of clinical trials should inspire scientists to intensify work in this area in the coming years. Nevertheless, given the large number of unresolved problems and open questions, cell therapy cannot yet be released beyond the scope of scientific research.
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