Experience soon taught surgeons greater respect for the complexity of overcoming the immune system's power to reject donated tissue.

Over the last half-century, the improved understanding of how to prevent the body's immune system from rejecting foreign tissue has turned what began as an experiment into a routine procedure.

The jelly-like collagen, processed to remove molecules that would lead humans to reject tissue from cattle, is injected under the skin, where it incorporates into the patient's own collagen, Ms. Mathieson said.

Anti-Rejection Medicine (immunosuppressive drugs)-Medicines that reduce or prevent the body's ability to reject a transplanted organ or tissue.

One of his projects involves an enzyme critical to the health of T cells, the cells of the immune system involved in rejecting foreign tissue, like cancers and transplanted organs.

Now 64 years old, Starzl is spearheading the use of an extraordinary new drug, FK-506, a highly specific immunosuppressant that prevents patients from rejecting transplanted tissue.

Performed the first successful liver transplants and developed techniques for suppressing the body's natural attempt to reject transplanted tissue.

The studies involved mice that lacked normal immune systems and so did not reject human tissue as foreign cells.

THERE are two big drawbacks to transplant surgery - the propensity of the body's defences to reject foreign tissue, and the shortage of donors with organs to give.

Barton knew about transplants-how the body's own immune reactions rejected foreign tissue.