A paper published in the 'Proceedings of the National Academy of Sciences' has outlined disappointing conclusions surrounding the use of brain tissue transplants to treat Huntington's disease. Thomas Freedman and colleagues at the University of South Florida in Tampa, US, report that transplanting portions of fetal brain tissue is not as successful as was previously believed.
Huntington's disease is an inherited genetic disorder which causes the production of mutant huntingtin protein in the patient's brain. The build up of this mutant protein in turn leads to the loss of neurons in different parts of the brain, most significantly in the striatum. The subsequent degeneration of the brain causes defects in movement and cognitive behaviour in the patient, and is ultimately fatal.
The use of neural transplants has been used as an experimental treatment for Huntington's disease since the 1990s. The method involves transplanting healthy neural tissue from fetal brains, obtained with consent from women undergoing elective abortions. This tissue is grafted into the patients striatum, typically the worst affected part of the brain. It had been thought that this method offered a good chance of success, since laboratory experiments had shown good levels of behavioural recovery in rodents and non-human primates.
The paper published last week reported the results of the examination of three patients who received transplants ten years before their death. The autopsies investigated why the transplants were not effective for longer, but had some more serious implications for the whole process. While previous studies had noted successful and healthy transplants at 18 months and even up to six years after the procedure, the transplanted tissue at ten years had undergone degeneration and damage similar, and even worse to the host tissue, even though it did not possess the mutant huntingin gene. It is suspected that the severe damage done to the transplant tissue is due to the same toxic environment shared by the host tissue.
Commenting on the study, Dr Freedman said: 'Based on our earlier results we were expecting that the grafts would endure. This tells us we'll have to do a lot of work in the laboratory before going back to the clinic'.
The conclusions drawn from the study are that the risks and mild benefits associated with the tissue graft do not warrant further transplants being carried out at present. The paper also suggests that before this sort of treatment can be successful, lots more work will need to be done on how to control the inflammatory and immune responses in the host tissue.