Pig cell implants in Huntington's trial

PIG brain cells could be implanted into human brains by the start of next year if trials of a pioneering treatment for Huntington's disease are approved in the US.

Similar tests on primates have proved "astonishingly successful" in treating the degenerative brain disease, according to researchers who carried out the work at Living Cell Technologies (LCT) in Auckland, New Zealand.

The injection of live animal cells into human brains is likely to raise ethical concerns and fears of pig viruses being transmitted to humans. But researchers say the benefits of a cure outweigh such concerns. "Yes, we have created a chimera, but one that is tolerated and beneficial," says Bob Elliott, LCT's medical director.

Huntington's disease, which affects one in 10,000 people, has a prognosis so terrifying that many people with the gene in their family decline to be tested, preferring to live in ignorance of their fate. Symptoms usually develop between the age of 30 and 50, and include uncontrollable twisting movements, progressing rapidly to disability, dementia and early death.

The pig brain cells used in the treatment are not neurons but come from the lining of a brain structure known as a choroid plexus. They have a nurturing role, mopping up toxins, producing cerebrospinal fluid and secreting a range of hormones and proteins called neurotrophins that are essential for brain cell function and protection. In Huntington's disease, there is a significant reduction in these chemicals.

Researchers introduced quinolinic acid, a nerve poison, into the brains of seven primates to simulate the disease, which is characterised by lesions in an area of the brain known as the striatum. Three of the animals were then injected with live pig brain cells. Those that did not receive the transplanted cells showed lesions in 50 per cent of their striata, while those with the transplants suffered damage in less than 10 per cent of their entire brain tissue.

The work is not yet published but follows similar studies in rats that also showed a neuroprotective effect (NeuroReport, vol 15, p 2521).

"The findings are so remarkable that I am confident that the FDA [US Food and Drug Administration] will fast-track approval of clinical trials for early next year, and we will see product approval in two years," says Al Vasconcellos, head of LCT's BioPharma subsidiary in Providence, Rhode Island, which plans to carry out the human trials. "It's the first time the disease itself can be treated rather than simply the symptoms."

The FDA has approved similar xenotransplantation trials, for example for Parkinson's disease. But results have been disappointing, because the transplanted cells are often rejected by the recipient, says Mary Groesch, executive director of the Secretary's Advisory Committee on Xenotransplantation at the US National Institutes of Health.

To try to overcome this, the New Zealand team have encapsulated the pig cells in alginate, a derivative of seaweed. This protects the cells from the immune system, allows oxygen and nutrients to circulate and lets the cells release their neurotrophins. The pig cells were also taken from a "clean" line of pigs, minimising the chances of disease transmission from pig to human.