Transplant rejection occurs when a patient's body does not recognize the new organ and attacks it. Patients who have kidney transplants must take drugs to prevent transplant rejection. Alemtuzumab is a man-made antibody used to treat certain blood disorders. The purpose of this study is to test the safety and effectiveness of using alemtuzumab in combination with two other drugs, sirolimus and tacrolimus, to prevent organ rejection after kidney transplantation. This study will also test whether this combination of medications will allow patients to eventually stop taking antirejection medications entirely.