 The primary objective of the study is to characterize the pharmacokinetics PK of BIIB033-B and to compare the PK profile with that of BIIB033-A in healthy volunteers. Secondary objectives are: To assess the safety and tolerability of BIIB033-A and BIIB033-B; To assess the secondary PK parameters of BIIB033-A and BIIB033-B; To assess the immunogenicity of BIIB033-A and BIIB033-B. 