<qa>  What is the name of the drug that suppresses the immune system of patients who have hadThe Food and Drug Administration has approved sirolimus for suppressing the immune system of patients who have had a kidney transplant to reduce the risk of organ rejection. The drug does not have certain side effects that have caused problems for patients treated with other immunosuppressants, such as: prednisone weight gain, round face, diabetes, weak and fractured bones, and cataracts; cyclophosphamide fertility problems, bladder injury and bladder cancer, and other cancers; chlorambucil fertility problems, seizures, acute leukemia, and other cancers; and cyclosporine kidney toxicity, increased facial hair, and seizures. 