Why do kidney transplants between identical twins have especially high success rates?

Kidney transplants between identical twins have exceptionally high success rates because they are genetically identical, meaning they share the same major histocompatibility complex (MHC) antigens.12

In standard transplant surgery, the recipient's immune system often identifies the donor organ as foreign because of differences in these surface molecules, known as human leukocyte antigens (HLA). This recognition triggers a rejection response, where T lymphocytes infiltrate and destroy the graft.31

Because identical twins possess the same transplantation antigens, the recipient's immune system does not recognize the donor kidney as "nonself," effectively eliminating the risk of rejection. Consequently, these procedures—classified as isografts—avoid the complications associated with immune-mediated graft destruction that typically necessitate the use of immunosuppressive drugs in other transplant cases.145