• Safety of sirolimus, including number of lesions detected by brain MRI
  
• tolerability of sirolimus
  
• mean number of new and overall total number of gadolinium-enhancing lesions reported on sequential brain MRIs
  

• Efficacy, as measured by change in the mean number of new and overall total number of gadolinium-enhancing lesions on pre-treatment brain MRIs, compared to post-treatment
  
• effect of sirolimus therapy on the immune function of patients with relapsing-remitting multiple sclerosis (RRMS)
  

MS is a chronic autoimmune disease of the central nervous system in which myelin, the protein sheath that protects nerve cells, is degraded by T cells and macrophages, leading to an eventual loss of neurologic function. MS can be classified as either relapsing-remitting, in which patients experience worsening in symptoms followed by partial or complete recovery of function; or progressive, in which patients have a gradual increase in symptoms, with or without relapses. Standard treatments used to treat relapsing-remitting MS are only modestly effective and may be associated with significant toxicity. There is a need to develop therapies with lower toxicities that can be administered early during the course of disease and have the potential to stop disease progression altogether. Sirolimus has been demonstrated to provide potent immunosuppression in recent clinical trials involving kidney transplantation, and may help people with autoimmune diseases like MS. This study will determine the benefit of sirolimus in MS patients.

Blood and urine collection will occur at screening. Participants will take daily doses of sirolimus for 6 months. There will be nine study visits; they will occur at Days 14, 28, 42, 56, 90, 120, 150, 180, and 225. Medication adverse events, concomitant medications, and vital signs will be recorded at Visits 1 through 8. At all visits, patient compliance to the sirolimus regimen will be measured, and blood and urine collection will occur. Physical and neurological exams, magnetic resonance imaging (MRI) brain scans, MS status tests, and a chest x-ray will be conducted at selected times throughout the study.