Safety and Efficacy of REGN2477+REGN1033 in Patients With Sporadic Inclusion Body Myositis

Key Inclusion Criteria: * Men and postmenopausal\* women * Diagnosed with sIBM based on the European Neuromuscular Centre (ENMC) IBM Research Diagnostic Criteria * Ability to walk ≥150 meters, with or without a walking aid such as cane or walker, in 6 minutes. * Ability to climb 4 steps of stairs unassisted (may use handrails) * Willing and able to comply with clinic visits and study-related procedures Key Exclusion Criteria: * Other neurological conditions (eg, hemiplegia post stroke, Parkinson's) or musculo-skeletal conditions (eg, severe osteoarthritis) causing mobility impairment * Mini-Mental State Examination (MMSE) score \<24 * Ongoing, chronic, high-dose (\>20 mg prednisone equivalent per day), systemic corticosteroid therapy within 6 weeks prior to screening. * Any condition that precludes adequate intake of energy and protein; malnutrition; presence of an eating disorder. * Unintentional weight loss of ≥10% in the past 6 months (patient-reported) * Hospitalization for heart failure in last year or New York Heart Association Class 4 * History of hypertrophic cardiomyopathy * Any drugs known to influence muscle mass and performance such as anabolic steroids or growth hormone within 6 weeks prior to screening * Unable to fit on the site's DXA scanner table, within borders for scanning of total lean mass Note: Other protocol Inclusion/Exclusion criteria apply