If the donor and recipient are of different species, how is the graft classified?

When the donor and recipient of a graft are from different species, the graft is classified as xenogeneic. This term specifically refers to transplantation between different species, such as a graft taken from a pig being placed into a human. This type of graft can pose unique challenges and considerations, including a higher risk of rejection due to the significant genetic differences between the species involved, leading to different immune responses.

The other classifications refer to different scenarios: allogeneic grafts involve donors and recipients from the same species but with different genetic backgrounds, syngeneic grafts involve identical twins (same genetic makeup), and isogeneic refers to grafts between genetically identical individuals or populations, like in inbred strains. These terms highlight the importance of genetic compatibility in transplant success, but in the case of xenogeneic grafts, the critical distinction is the interspecies nature of the donor-recipient relationship.