Hopes that the debilitating symptoms of Parkinson鈥檚 disease can be eased by implants of pig cells have been dashed by disappointing results from the first major trial of the technique.
After an 18-month study, it turned out that the 10 patients who received the fetal pig cells did no better than eight 鈥渃ontrol鈥� patients who underwent a sham version of the treatment.
鈥淯nfortunately, we didn鈥檛 get the results we鈥檇 hoped for,鈥� says Tom Fraser, president of Diacrin, the company in Charlestown, Massachusetts co-developing the technique with Genzyme General of Cambridge, Massachusetts.
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The news follows poor results in a trial in which human fetal cells were implanted into Parkinson鈥檚 sufferers, although this experiment was criticised by other experts (Think again).
Limitless supply
Patients with Parkinson鈥檚 develop jerky, uncontrolled movements because they lose cells which make dopamine, a neurotransmitter which relays signals between brain cells.
To compensate for the loss, researchers have for 15 years tried treating the disease by injecting patients with dopamine-producing brain tissue extracted from miscarried human fetuses.
However, it requires tissue from six fetuses to treat a single Parkinson鈥檚 patient and so researchers were investigating the possibility of using pig tissue. Supplies of this are theoretically limitless and its use would also circumvent the ethical constraints on using human cells.
Despite the lack of success in the trial, Diacrin is not giving up. It says that although treated patients were no better off overall, some had specific symptoms which eased. They had fewer and milder attacks of uncontrolled jerky movements called dyskinesia, while these actually intensified in 鈥渃ontrol鈥� patients. 鈥淭here seems to be a sub-group of people who respond quite positively,鈥� says Fraser.
No PERVs
Also very encouraging for the company was that the implanted pig cells didn鈥檛 appear to harm the patients. 鈥淲e鈥檙e definitely not seeing adverse effects,鈥� says Fraser.
Nor was there any sign that viruses spread from the pig tissue to the patients. One major fear relating to 鈥渪enotransplants鈥� of pig tissue is that so-called porcine endogenous retroviruses (PERVs) which live harmlessly in pig DNA would somehow cause hitherto unknown diseases in humans.
Fraser and other experts are now trawling the clinical data for possible refinements which might improve the success rate.
Some patients did suffer side effects whether they were treated or given the sham version, but this was traced to the effects of the immunosuppressive drugs given to prevent patients rejecting their grafts.
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