Sirolimus Patients will be given sirolimus starting at the oral daily dose of 3 mg, with periodical whole blood level measurements. The daily dose will be adjusted to keep sirolimus concentration within 10-15 ng/ml. Drug levels will be assessed at day 5 after starting treatment and every two weeks for the first month; subsequently sirolimus concentrations will be monitored at monthly intervals (or 5 days after drug dose adjustments) until the end of the study.