A Study to Learn More About the Safety of a Single Dose of BIIB144 and How it is Processed in the Body of Healthy Adult Participants Ages 18 to 55 Years Old as Compared to a Placebo

Key Inclusion Criteria: * Have a body mass index (BMI) between 18 and 32 kilograms per square metre (kg/m\^2), inclusive, at Screening. * Must be in good health as determined 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 1 year prior to Day -1). * History of, or positive test result at Screening for, human immunodeficiency virus (HIV). * Any live or attenuated immunization or vaccination given within 14 days prior to Screening, between Screening and Day -1, or planned to be given during the study period. Note: Other protocol-defined Inclusion/Exclusion criteria may apply.