A Randomized, Open-Label Study to Assess the Effects of Tysabri Treatment on Vaccination Response and Lymphocyte Subsets in Subjects With Relapsing Forms of Multiple Sclerosis

The primary objectives of this study were: to evaluate the effect of Tysabri® (natalizumab) on antibody responses after immunization with a neoantigen (keyhole limpet hemocyanin [KLH]) and a recall antigen (tetanus toxoid [Td]), and to evaluate the effect of Tysabri on circulating lymphocyte subsets (CD3+, CD4+, CD8+, CD19+, and CD56+) over time in participants with relapsing forms of multiple sclerosis (MS). The secondary objective was to assess alpha4-integrin saturation and alpha4-integrin expression levels over time.