The Bioartificial Pancreas

Instead of using genetic therapy, as Dr. Block suggests, foreign cells that secreted a particular protein could be used to replace the patients own-- if a way was found to protect the cells from the host's immune system. This is exactly the idea behind the "bioartificial pancreas" which researchers hope will replace insulin injections as a therapy for diabetics. The insulin-secreting cells form pancreatic islets, usually taken from a pig, are placed in semi-porous capsules and implanted in the body. The capsules must be biologically and chemically inert; that is, their chemical composition cannot induce inflammation or other reaction from the body, and they must resist decomposition. The capsules must contain pores small enough to exclude the mobile cells of the immune system, macrophages and lymphocytes, but large enough to allow a physiological release of insulin in response to blood glucose levels. Obviously, long term survival of the cells is also a requirement. According to Anthony Sun, of the University of Toronto, diabetic monkeys have become insulin independent using the bioartificial pancreas for periods longer than two years. Other researchers have shown similar results in dogs and rats. Islet cells have been recovered after a year of implantation and shown to be still viable. A limited trial using human beings that was carried out in China was so successful, according to Dr. Sun, that patients tried to bribe the doctors to continue the experimental procedure. Clinical trials have now been only recently approved by the FDA in the United States using microencapsulated porcine cells in human patients.