A transplanted organ is attacked because the immune system reads its surface proteins as foreign, and the drugs that prevent this work by suppressing that response generally rather than selectively. The consequence is a trade that every transplant patient makes for life: the organ survives, and the same suppression that protects it raises the risk of infection and of certain cancers, while the drugs themselves damage the kidneys over time. Survival statistics for transplantation have improved substantially, and much of the improvement has come from managing this trade more precisely rather than from any advance in preventing rejection itself. The problem was not solved so much as rendered chronic. Patients are counselled on this at the outset, though the weight of it tends to arrive later.