Foetal tissue transplants

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. 

Unfortunately transplants require 6-7 foetal brains to obtain enough transplantable material for one patient, which itself raises ethical considerations, and as the tissue cannot diffuse its influence is restricted, even with multiple injection sites, and only a fraction (approx. 20%) of the neurons survive. Also without knowledge of the cause of PD the transplant could meet the same fate as the original neurons. The concept, however, demands perseverance and a number of variants are being tried. 

Among the experimentally tested transplantation sites are the spleen, kidneys, lungs, pancreas, peritoneum, greater omentum and fatty tissue. Up to now, the spleen has proved to be the most suitable. The transplantation of foetal liver cells into the spleen may even culminate in a liver lobule-like formation with bile ducts and veins — however, the functional results have (so far) been no better than with normal hepatocytes. 

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. 

---