Abatacept remains the best example of the role xenogeneic transplantations will have in the future as the CTLA-4-fusion protein was first tested in xenogeneic transplantation models before moving into the clinic, where it has now become a highly promising candidate for preventing GVHD though its role in treating established GVHD remains uncertain (132, 133). The gene discussed is CTLA4; the disease is graft versus host disease.