A Study to Evaluate the Pharmacokinetics, Safety and Immunogenicity of BIIB800 Subcutaneously (SC) Compared to Actemra® in Healthy Male Participants

Key Inclusion Criteria:

• Have a body mass index between 18.5 and 29.9 kilograms per meter square (kg/m^2), inclusive.
• Total body weight between 60.0 and 90.0 kg, inclusive.
• Systolic blood pressure <135 millimeters of mercury (mmHg) or >85 mmHg at Screening, after being supine for at least 5 minutes.
• No clinically significant (as determined by the Investigator) 12-lead electrocardiogram (ECG) abnormalities, no cardiac pacemaker.

Key Exclusion Criteria:

• History or positive test result at Screening for human immunodeficiency virus (HIV).
• History of hepatitis C infection or positive test result at Screening for hepatitis C virus antibody.
• Current hepatitis B infection (defined as positive for hepatitis B surface antigen [HBsAg] and total hepatitis B core antibody [anti-HBc]).
• Serious infection (as determined by the Investigator) within the 6 months prior to Screening.
• History of systemic hypersensitivity reaction to the active drug substance, the excipients contained in the formulation, and if appropriate, any diagnostic agents to be administered during the study.
• History of immunodeficiency or other clinically significant immunological disorders, or autoimmune disorders.
• History of clinically significant (in the opinion of the Investigator) atopic allergy (e.g., asthma, urticaria, eczematous dermatitis, allergic rhinitis), hypersensitivity, or allergic reactions.
• History of angioedema.
• A positive diagnostic tuberculosis test result within 35 days prior to Day -1, defined as a positive QuantiFERON® test result or 2 successive indeterminate QuantiFERON test results.
• Any prior exposure to tocilizumab or to any other agent directly acting on IL-6 or on its receptors including investigational products (e.g., siltuximab, sarilumab etc.).
• Administration of immunoglobulins for anti-tetanus and anti-rabies post-exposure prophylaxis within 3 weeks prior to administration of study drug.
• Any live or attenuated immunization or vaccination given within 30 days prior to Day -1 or planned to be given during the study period.

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.