ACCLAIM

Treatment tested

• Abatacept

  T-lymphocyte activation antigen CD80 inhibitor|T-lymphocyte activation antigen CD86 inhibitor

Placebo or sham

• Placebo

Other measures (13)

Inclusion Criteria: * Clinically definite Relapsing-remitting Multiple Sclerosis (RRMS) meeting McDonald's criteria * Expanded Disability Status Scale (EDSS) scores between 0 and 5 * Active disease as defined by at least one of the following criteria: 1. One or more documented clinical exacerbations in the past year prior to visit -2 2. One or more gadolinium (Gd)-enhanced MRI lesions in the past year * Willingness to forego available MS therapies * Ability and willingness to provide informed consent and comply with study requirements and procedures Exclusion Criteria: * Normal brain MRI at week -5 scan * Females who are pregnant, intending pregnancy, or lactating, and unwilling to undergo pregnancy testing * Females who are unwilling to use approved methods of contraception for the duration of the study * Any chronic medical disease, other than MS, that compromises organ function * Active infection * Diagnosis of secondary or primary progressive MS * Previous treatment with cyclophosphamide, mitoxantrone, cladribine, or rituximab at any time * Previous treatment with abatacept within the last 52 weeks prior to visit -2 * Previous treatment with systemic steroids, interferon, Copaxone, mycophenolate, or other immunosuppressive medications within the last 4 weeks prior to visit -2 * Previous treatment with Natalizumab within the last 26 weeks prior to visit -2 * Previous vaccination with live vaccine, or previous treatment with fingolimod, within the last 8 weeks prior to visit-2 * Diagnosis of malignancy other than basal cell carcinoma or cervical carcinoma in situ * Claustrophobia or other contraindications to Gd-enhanced MRI * Positive for human immunodeficiency virus (HIV) serology * Positive for hepatitis B surface antigen (HBsAg) * Positive for hepatitis C virus (HCV) serology * Purified protein derivative (PPD)-tuberculin skin test result greater than 5 mm induration * Hemoglobin less than 10.5 gm/dL * Platelets less than 100K/µL * Absolute lymphocyte count less than 700 cells/μL * Serum creatinine greater than 1.20 mg/dL * eGFR (estimated glomerular filtration rate) less than 60 mL/min/1.73 m\^2 * IgG anti-cardiolipin antibody greater than 15 GPL U/mL * Previous participation in another interventional clinical trial within the past 4 weeks prior to visit -2 * Allergy or sensitivity to any component of abatacept * The presence of any medical condition that the investigator deems incompatible with participation in the trial

The ACCLAIM study is testing whether the medication "abatacept" can be of benefit to patients with relapsing-remitting multiple sclerosis (MS). Although abatacept is an investigational medication for MS, it is not a new drug. Abatacept has been approved by the FDA to treat rheumatoid arthritis.