Treatment that lowers the activity of the body’s immune system. This reduces its ability to fight infections and other diseases, such as cancer. Immunosuppressive therapy may be used to keep a person from rejecting a bone marrow or organ transplant. It may also be used to treat conditions in which the immune system is overactive, such as autoimmune diseases and allergies. Some types of immunosuppressive therapy may increase a person’s risk of cancer by lowering the body’s ability to kill cancer cells.