A Randomized, Double-Blind, Placebo-Controlled, Parallel-Group, Dose-Ranging Study to Assess the Efficacy, Safety, Tolerability, and Pharmacokinetics of BIIB033 in Subjects With Relapsing Forms of Multiple Sclerosis When Used Concurrently With Avonex

The primary objective of the study is to evaluate the efficacy of BIIB033 in participants
with active relapsing multiple sclerosis (MS) when used concurrently with Avonex.

Secondary objectives of this study in this study population are to assess the safety,
tolerability, and population pharmacokinetics of BIIB033 when used concurrently with Avonex.