Pig-cell grafts ease symptoms of Parkinson’s

Pig brain cells transplanted into the brains of patients with advanced Parkinson’s disease help some of the patients regain mobility and the ability to do basic tasks.

A daring form of surgery that transplants tiny amounts of pig brain tissue into people seems to benefit some patients with severe Parkinson’s disease, a new study shows. The findings raise the prospect that such operations might help patients in whom traditional drug therapy no longer has much effect.

Parkinson’s disease strikes when brain cells die and the brain fails to make adequate quantities of dopamine, a neurotransmitter required for nerves to deliver brain signals to muscles.

For their study, the first of its kind, researchers enrolled 10 patients who had tremors, muscle rigidity, or other symptoms of advanced Parkinson’s. To replace the lost cells, researchers injected the brain of each patient with 12 million cells taken from the area of fetal pigs’ brains where dopamine is made.

One year after the transplants, which occurred in 1995 and 1996, mobility and performance of simple tasks had dramatically improved in three patients and was moderately better in three others, says study coauthor Jonathan H. Dinsmore of the biotechnology firm Diacrin in Charlestown, Mass. The condition of the other four patients held steady or declined slightly, he says. The report appears in the March 14 Neurology.

The pig-cell recipients achieved an average improvement after one year comparable to that reached by patients who had received brain tissue taken from human fetuses. Three-year data on the pig-cell recipients show that some patients have maintained benefits from the treatment, Dinsmore told Science News.

While transplantation of animal tissue avoids the ethical and legal questions clouding use of human fetal cells, animal tissue poses health risks. To minimize them, the team used only embryonic tissue from pigs raised in controlled conditions and screened it for bacteria and viruses. Up to 5 years after surgery, no porcine pathogens are detectable in any of the patients, Dinsmore says.

“All these [experiments] are somewhat scary,” says Douglas Kondziolka, a neurosurgeon at the University of Pittsburgh. “These are courageous patients who want something done now.” Meanwhile, the supply of reliable pig tissue for use in transplants may soon grow (see box on this page).

Any transplanted tissue, whether from a person or animal, can incite immune rejection. To prevent that, Dinsmore and his colleagues gave 4 of the 10 patients a standard antiimmune drug. The others received pig cells treated to make them innocuous to the host. No patient has suffered any obvious immune rejection, Dinsmore says.

“I think this is exciting,” says Paul R. Sanberg, a neuroscientist at the University of South Florida in Tampa. The operation proved to be safe, which was the primary goal, he says. Moreover, he says, the study proves the principle that cross-species transplants can work.

Curiously, brain scans of the patients don’t show additional dopamine being made, even in those who improved the most. It could be that the number of transplanted cells that survive—and the dopamine they produce—is enough to benefit the patient yet not enough to show up on the scans, Kondziolka says.

Dinsmore suggests that the relatively low number of transplanted cells has only “borderline effectiveness” in these patients. The same team has begun a study of 18 patients who will receive four times as many pig embryonic brain cells, says study coauthor Samuel A. Ellias, a neurologist at Boston University.

Past work has found improvements in Parkinson’s patients who got a sham surgery and no cell grafts. Dinsmore doubts that that could explain the recent patients’ gains. The current research includes a sham surgery group, he says.