Baboon bone marrow recipient Jeff Getty.

1995: Jeff Getty receives a baboon-bone marrow transplant, in hopes that the immune cells in the baboon’s marrow will replace the immune cells that Getty has lost to the AIDS virus. The baboon cells—which are naturally resistant to HIV—only function for a brief time, but Getty remains healthy (and is still alive today).

Getty’s transplant may not have been a technical success, but many scientists continue to investigate how pretreating transplant recipients with marrow taken from donors might create a "chimeric" immune system that contains cells both animal and human. Such "preconditioning" might trick the body into accepting subsequent xenografts as not really foreign after all.