"Thymokidney" transplanted in pigs induces graft tolerance.

Transplantation of a composite "thymokidney"-a kidney with vascularized autologous thymic tissue under its capsule-in pigs whose thymus glands had been removed induced graft tolerance despite mismatching between donor and recipient, according to a report in the March 15 issue of the Journal of Immunology.

David Sachs, MD and colleagues at Massachusetts General Hospital in Boston said this strategy "eventually may be clinically applicable for the induction of transplantation tolerance to xenografts, which is the ultimate goal of these experiments."

The team compared outcomes in pigs that underwent 3 different protocols for kidney transplantation from a class I-mismatched donor. Some of the animals received a kidney allograft alone, some received a composite allogeneic thymokidney, and some received separate kidney and nonvascularized thymic grafts from the same donor. All recipient pigs had their thymus glands removed 3 weeks prior to transplantation to rule-out the possibility of tolerance induction by usual host mechanisms.

The study is the first to demonstrate induction of transplantation tolerance by a vascularized thymic graft in large animals, Dr. Sachs and co-authors wrote. The team will next test induction of tolerance with thymokidney transplants across a 2-haplotype mismatch barrier.