A Safety, Tolerability, Pharmacokinetic, and Pharmacodynamic Study of BIIB091, a Bruton's Tyrosine Kinase (BTK) Inhibitor, in Healthy Adult Participants

Key Inclusion Criteria: * Ability to understand the purpose and risks of the study and provide signed and dated informed consent and authorization to use confidential health information in accordance with applicable participant privacy regulations. * Have a body mass index between 18 and 30 kg/m2, inclusive. * All male participants must practice highly effective methods of contraception and not donate sperm during the study and for at least 1 spermatogenic cycle (90 days) after administration of last dose of study treatment. * All female participants of childbearing potential must practice highly effective methods of contraception and not donate eggs during the study and for at least 90 days after their last dose of study treatment. * Must be in good health as by the Investigator, based on medical history and screening evaluations. Key Exclusion Criteria: * History of any clinically significant cardiac, endocrine, gastrointestinal, hematologic,hepatic, immunologic, metabolic, urologic, pulmonary, neurologic, dermatologic, psychiatric, or renal disease, or other major disease, as determined by the Investigator. * History of severe allergic or anaphylactic reactions, or of any allergic reactions that in the opinion of the Investigator are likely to be exacerbated by any component of the study treatment. * History of, or ongoing, malignant disease, including solid tumors and hematologic malignancies (with the exception of basal cell carcinomas and squamous cell carcinomas that have been completely excised and considered cured at least 12 months prior to Check-in). * Current enrollment or plan to enroll in any other drug, biological, device, or clinical study, or treatment with an investigational drug or approved therapy for investigational use within 30 days prior to Check-in, or 5 half-lives of the drug or therapy, whichever is longer. * Breastfeeding, pregnant, or planning to become pregnant during study participation. NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.