Xenotransplantation is the transfer of living cells, tissues or organs between species. In this context we are dealing specifically with transfers from a non-human animal to a human body.
This form of treatment has been occurring for centuries. Evidence of xenotransfusion has been discovered from as early as the 16th century, and reports of attempted cell and tissue xenotransplantation as early as the 1800s (Deschamps et al. 2005). Now thanks to modern medicine, we are developing the immunosuppression science we need to make this process feasible.
In addition to the development of immunosuppressive drugs, this technology involves genetically engineering animals with transgenic modifications to make their organs compatible with human bodies (Dahl et al. 2003). Without these changes, our bodies would immediately reject the transplanted organ as a foreign invader and put our immune systems into overdrive.