Islet-cell transplants sans rejection.

Islet-cell transplants sans rejection

Since 1973, researchers have attempted to cure insulin-dependent (Type I) diabetes by substituting healthy, insulin-secreting islet cells for nonfunctioning ones in the pancreas. But the body rejects these grafts within six months, even with the use of immunosuppressive drugs. A new study now suggests the key to successful islet-cell grafts may involve their implantation in the thymus.

Researchers at the University of Pennsylvania in Philadelphia found that the thymus -- a gland that lies just above the heart and gives white blood cells the ability to attack foreign antigens -- can be manipulated to remove or inactivate certain white blood cells, known as T-lymphocytes, that might otherwise destroy islet-cell grafts placed in the gland. They triggered this unusual thymus response in diabetic rats with the injection of antibodies programmed to eliminate the graft-destroying lymphocytes. When healthy islet cells were subsequently implanted into the thymus of those animals, blood sugar levels returned to normal within three days. The cells survived for more than 200 days. Further, test implants of islet cells in the kidneys of the same rats survived without rejection, even after removal of grafted islet cells from the thymus, reports Andrew M. Posselt, one of the study's authors.

Thymus implantation could establish islet-cell grafts as a key therapy for Type I diabetes, the researchers say, if human studies -- which may not begin for several years -- show similar success. However, Posselt cautions that he and his co-workers limited their work to rats whose diabetes had been induced by an islet-cell toxin. he hopes the new technique also proves useful in helping the thymus establish similar transplant tolerance in animals with naturally occurring Type I diabetes -- in which the immune system is believed to kill the body's own islet cells, as well as foreign grafts.