Tissue transplants Parkinson disease

Foetal mesencephalic tissue has been implanted in the striatum of patients with the juvenile form of Parkinson s disease and has been shown to develop functional axons this has enabled the dose of L-dopa to be reduced. Both imaging and pharmacological studies have now shown that functional dopaminergic neurons can develop in the brain of the patient following tissue transplantation. However, a major ethical objection has been raised to such transplants as six to seven foetal brains are required to obtain sufficient tissue. In addition, only about 20% of neurons survive transplantation. The ethical problem may be overcome by using brain transplants from domestic animals such as pigs. Such xenotransplants have been shown to survive in the human brain but the main problem with the extensive use of such transplants is the possible spread of viruses and prion infections. 

Today, with the exception of bone marrow for hematopoietic reconstitution, therapeutic cellular transplantation is an emerging technology. In recent years novel approaches in the potential restoration of function through cellular transplantation have included the use of fetal human or xenogeneic neural tissue for Parkinson s disease, ectopically implanted pancreatic islets for diabetes, Schwann cells and olfactory ensheathing glia for spinal cord injury, encapsulated chromaffin cells for pain, and various types of stem cells for the treatment of diabetes, cardiac disease, and central nervous system injuries or disease [2], There have also been trials of encapsulated cells to provide enzymes that either remove toxic products or provide activation of prodrugs to therapeutics, usually anticancer derivatives. 

The potential benefits of alleviating dopamine deficiency in the brains of Parkinson s patients by tissue implantation have been widely discussed from both clinical and ethical perspectives. Conventional dopamine replacement therapy suffers from well known and serious limitations. The most recent data indicate that fetal-tissue transplants into patients with idiopathic or MPTP-induced Parkinson s disease are clinically encouraging and may be highly beneficial for at least some patients (6,7). 

Aging (skin and other tissues), myocardial infarct or stroke, inflammation, rheumatoid arthritis, atherosclerosis, pulmonary disorders (asthma and chronic obstructive pulmonary diseases), radiation injury, organ transplant rejection, psoriasis, hypertension, AIDS, multiple types of cancer, neuro-degenerative diseases (Parkinson s), diabetes, muscular dystrophy... 

A potentially promising, although very controversial, approach to the treatment of Parkinson s disease is replacement of dopaminergic neurons. The grafting of fetal substantia nigra tissue, which contains the dopamine neurons, into the striatum of parkinsonian patients has been modestly successful. The procedure will remain experimental, however, until the many practical problems and ethical issues associated with the use of fetal tissue are resolved. The discovery of pluripotent stem cells is also being viewed as a possible way of developing dopamine neurons for transplant purposes. 

A population of desired cell types that have the potential to produce new tissues should be generated. The potential of embryonic totipotent stem cells could be exploited in the transplantation of retinal pigment epithelium, myocardial progenitor cells capable of restoring cardiac function and contractility, dopaminergic neurons for the treatment of Parkinson s disease, pancreatic cells for the treatment of diabetes, and others.55... 

Recently, transplantation of foetal brain tissue has been carried out in a number of patients in the hope of reversing the symptoms of Parkinson s disease by providing neurons that produce dopamine. 

Kordower, J.H., Freeman, T.B., Snow, B.J., et al. Neuropathological evidence of graft survival and striatal reinnervation after the transplantation of fetal mesencephalic tissue in a patient with Parkinson s disease. N. Engl. J. Med. 332, 1118-1124 (1995). doi 10.1056/NEJM199504273321702... 

Xenotransplantation is a medical procedure in which live cells, tissues, or whole organs are surgically transplanted from one animal species to another, such as transplanting pig hearts or baboon livers into humans. It is a potential solution to the shortage of human organs and tissues available for transplant. Xenotransplantation also offers many other potential therapeutic applications, including the treatment of diabetes, spinal cord injury, and Parkinson s disease. However, the use of xenotransplantation has raised many ethical and safety concerns. 

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