Inclusion Criteria:

1. Male or non-pregnant females age 18-55 who have clinically and laboratory definite relapsing-remitting MS using the MacDonald criteria.

2. Subjects must be taking some form of interferon therapy (Rebif, Avonex or Betaseron) for a duration of 12 months with documented breakthrough disease as defined:

   • or = 1 documented clinical relapse in past 12 months while on interferon therapy. For eligibility, a pre-study relapse is defined as neurologic symptoms and signs documented by review of the history with the subject or in the medical record, of sufficient severity and duration to be determined by the investigator as consistent with an acute MS relapse.

   The relapse does not need to have been treated to qualify. the timing of the relapse is defined based on the onset of symptoms.

   OR

   > or = 1 documented Gd-enhancing lesion on cranial or spinal MRI. The presence of a Gd-enhancing lesion must be documented either by a report in the medical record or review of the films by the investigator.

3. The Kurtzke EDSS score must be between 0- 5.0.
4. All subjects must give written consent prior to evaluation and testing.

Exclusion Criteria:

1. Subjects with primary or secondary progressive MS.
2. Female patients may not be pregnant, attempting pregnancy or breastfeeding.
3. Female subjects must use an acceptable form of contraception during the study as defined by the investigators. The rhythm method is not to be used as the sole method of contraception.
4. Subjects unwilling or unable to give informed consent.
5. Subjects that are NAB+ (titers > or = 20).

6. Abnormal baseline blood test exceeding any of the limits defined below:

   1. ALT or AST > 2x upper limit of normal (ULN)
   2. CPK > 2x upper limit of normal (ULN)
   3. Total WBC < 3,000/mm3
7. No chronic infections (including HIV and Hepatitis B/C) may be present.