The primary objective of this study is to evaluate the immunogenicity of natalizumab (BG00002) 300 mg subcutaneous (SC) administered to participants with relapsing multiple sclerosis (RMS). The secondary objectives of the study are to evaluate the safety of natalizumab SC injections and to evaluate the efficacy of natalizumab SC injections on relapses and on new magnetic resonance imaging (MRI) lesions.