Single-Dose Study of a New Formulation of BIIB061

Key Inclusion Criteria: * Males and postmenopausal (defined as no menses for 12 months and confirmed by follicle-stimulating hormone \[FSH\] levels determined at screening to be in the postmenopausal range) or surgically sterile females. * All male subjects must practice effective contraception during the study and be willing and able to continue male contraception for 3 months after the dose of study treatment. All male subjects must also be willing to refrain from sperm donation for at least 3 months after their dose of study treatment. * Must be in good health and have normal vital signs as determined by the Investigator, based on medical history and screening evaluations. * Body mass index of 18.0 to 30.0 kg/m2, inclusive. Key Exclusion Criteria: * History of or positive test result at screening for human immunodeficiency virus, hepatitis C virus antibody, or hepatitis B virus (defined as positive for hepatitis B surface antigen \[HBsAg\] or hepatitis B core antibody \[HBcAb\]). * Prior exposure to BIIB061. * History of any clinically significant cardiac, endrocrinologic, hematologic, hepatic, gastric, immunologic, metabolic, urologic, pulmonary, neurologic, dermatologic, psychiatric, renal, oncologic, or other major disease, as determined by the Investigator. * Treatment with any prescription medication within 28 days prior to and throughout the duration of the study. * Use of any over-the-counter products, including herbal or alternative health preparations within the 14 days prior to the study * Enrollment in any interventional clinical study in which an investigational drug, biologic, device, or approved therapy for investigational use is administered or used within 30 days prior to the study * Any live or attenuated immunization/vaccination given within 30 days prior to the study or planned to be given during the study. * Blood donation within 30 days prior to the study * Surgery within 3 months prior to the study NOTE: Other protocol defined Inclusion/Exclusion criteria may apply