A Study to Assess the Potential for Gastric-pH Dependent Drug-Drug Interactions of BIIB122 With a Proton Pump Inhibitor in Healthy Participants

Key Inclusion Criteria:

• Body mass index between 18 and 30 kilograms per square meter (kg/^m2), inclusive.

• Negative polymerase chain reaction test result for severe acute respiratory syndrome coronavirus (SARS-CoV-2) at Check-in.

• For participants ≥ 55 years of age, ongoing conditions must be considered by the Investigator to be stable and adequately controlled by allowed concomitant medications.

Key Exclusion Criteria:

• Plans to undergo elective procedures or surgeries at any time after signing the Informed Consent Form (ICF) through the follow-up visit.
• Any condition affecting study treatment absorption.
• History of gastrointestinal surgery, gastroesophageal reflux disease, or other clinically significant and active gastrointestinal condition per the Investigator's discretion.
• Clinically significant acute gastrointestinal symptoms within 30 days prior to study Check-in (Day -1).
• Chronic, recurrent, or serious infection, as determined by the Investigator, within 90 days prior to Screening or between Screening and Day -1.
• For participants < 55 years of age: Use of any prescription medication (excluding oral contraceptives and hormone replacement therapy), OTC oral medications including proton pump inhibitors (PPI), histamine H2-receptor antagonists (H2 blockers), and antacids (excluding acetaminophen and aspirin ≤ 100 mg daily), or nutraceuticals including vitamins/mineral supplements/herbal medicines within 28 days prior to Day -1 and throughout the study.
• For participants ≥ 55 years of age: Up to 5 medications are allowed if they are taken at a stable dose level and regimen.

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply