This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The purpose of this study is to evaluate the immunogenicity of natalizumab high titer material administered intravenously to subjects with relapsing forms of MS. The secondary objective of this study is to evaluate the safety of natalizumab high titer material