The purpose of this trial is to evaluate the effects of Rebif® 44 mcg subcutaneous (sc) three times a week (tiw) on a) remyelination/demyelination, b) lesion and brain volume, c) central nervous system (CNS) iron deposition, and d) immune status in subjects with relapsing-remitting multiple sclerosis (RRMS) RRMS via several MRI techniques.

Inclusion Criteria:

1. Male and female subjects, 18-65 years of age, inclusive, at the time of informed consent signature
2. RRMS diagnosed according to the McDonald criteria, treatment naïve or currently using any of the FDA-approved DMDs (excluding natalizumab (Tysabri®), mitoxantrone or Rebif®)
3. Have a disease duration of up to twenty years
4. Be willing and able to comply with the study procedures for the duration of the trial
5. Have given written informed consent and signed Health Insurance Portability and Accountability Act (HIPAA) Authorization before any study- related activities are carried out
6. Female subjects must not be either pregnant or breast-feeding and must lack childbearing potential, as defined by either:

The following inclusion criteria must be fulfilled by the Healthy Control subjects:

1. Male and female subjects, 18-65 years of age, inclusive, at the time of informed consent signature
2. Be willing and able to comply with the study procedures for the duration of the trial
3. Have given written informed consent and signed Health Insurance Portability and Accountability Act (HIPAA) Authorization before any study- related activities are carried out
4. Female subjects must not be either pregnant or breast-feeding and must lack childbearing potential, as defined by either:

Exclusion Criteria:

1. Have received treatment within three months prior to Screening with interferon-beta-1a (Rebif®), IVIG or plasmapheresis
2. Have received treatment within thirty days prior to screening with immunosuppressant agents (e.g. including but not limited to mitoxantrone, cyclophosphamide, cladribine, fludarabine, cyclosporine or total body irradiation) or any other concomitant immunomodulatory therapies (e.g., azathioprine, methotrexate, CellCept®, natalizumab, alemtuzumab/Campath and other immunomodulators/monoclonal agents)
3. Have had a relapse within thirty days prior to the Screening Visit
4. Have received steroid treatment within thirty days prior to the initial MRI scan date at Study Day 1
5. Have inadequate liver function, defined by a alanine aminotransferase (ALT) > 2.5x upper limit of normal (ULN), or alkaline phosphatase > 2.5x ULN, or total bilirubin > 1.5x ULN
6. Have inadequate bone marrow reserve, defined as a total white blood cell count < 3.0x 109/L, platelet count < 75x109/L, hemoglobin < 100g/L
7. Have complete transverse myelitis or simultaneous-onset bilateral optic neuritis
8. Have a history of alcohol or drug abuse
9. Have thyroid dysfunction
10. Have moderate to severe renal impairment
11. Have a major medical or psychiatric illness that in the opinion of the investigator creates undue risk to the subject or could affect compliance with the study protocol
12. Have a history of seizures not adequately controlled by treatment
13. Have serious or acute cardiac disease, such as uncontrolled dysrhythmias, uncontrolled angina pectoris, cardiomyopathy, or uncontrolled congestive heart failure
14. Have, in the opinion of the investigator, any visual, physical or cognitive impairment that would preclude the subject from complying with the study protocol
15. Have a known hypersensitivity or allergy to interferon-beta or any of the excipients
16. Have received an investigational drug or experimental procedure within the past thirty days
17. Are pregnant or attempting to conceive

The following exclusion criteria must be fulfilled by the Healthy Control subjects:

1. Have met any of the above noted criteria