1997: Clinical studies suggest that transplants of isolated foreign cells may fare better than whole organs. In 1997, researchers report on the first clinical trial using nerve cells from fetal pigs to treat a dozen patients with Parkinson’s disease. The patients show marked clinical improvement—one even takes up golf after being totally bedridden. In another recipient (who died of unrelated causes eight months after the transplant), the injected pig cells appear to survive and grow.

Meanwhile, other researchers try wrapping animal cells in a capsule that prevents immune cells from getting at them. The capsule—made of material containing very tiny pores—still admits nutrients and allows the cells to deliver their molecular products to the patient. For example, researchers at a biotech company in California encapsulate pancreatic islet cells from pigs for use in treating people with diabetes. The cells secrete insulin (which diabetics can’t make themselves) and could help control patients’ blood sugar levels. And about 100 cancer patients receive encapsulated adrenal cells—from fetal calves—that secrete natural painkillers called enkephalins and other neurotransmitter molecules that help to ease their pain.