A Study to Evaluate the Efficacy and Safety of ABC008 for Inclusion Body Myositis

Inclusion Criteria:

   - Adult males and females age >40 years at the time of the first dose of study
   medication;

   - Weight >40 and <150 kg;

   - Diagnosis of either clinico-pathologically defined IBM, clinically defined IBM, or
   probable IBM according to the European Neuromuscular Centre (ENMC) IBM 2011 research
   diagnostic criteria (Rose et al., 2013). Documented histopathology results must be
   available prior to Baseline (Day 1) to confirm eligibility;

   - Able to arise from a chair (with armrests), with use of their arms but without support
   from another person or device (e.g., cane, walking stick), at Screening and Baseline
   (Day 1);

   - Able to walk 3 meters, turn around, walk back to the chair, and sit down, with or
   without assistive device. Once arisen from the chair, subject may use any walking
   device but cannot be supported by another person, furniture, or a wall;

Exclusion Criteria:

   - Any other form of myositis or myopathy other than IBM, e.g., metabolic or drug-induced
   myopathy, drug-induced myositis, anti-synthetase syndrome, polymyositis or
   dermatomyositis, cancer-associated myositis (myositis diagnosed within 3 years, either
   before or after), myositis in overlap with another autoimmune disease (e.g., systemic
   lupus, systemic sclerosis, rheumatoid arthritis), or muscular dystrophy;

   - Any condition, e.g., severe degenerative arthritis with limited range of motion, which
   precludes the ability to quantitate muscle strength or perform functional assessments
   (e.g., mTUG), in the Investigator's opinion;.

   - Presence of another autoimmune or autoinflammatory disease other than indication under
   study, e.g., rheumatoid arthritis, psoriatic arthritis, axial spondyloarthropathy,
   inflammatory bowel disease, systemic lupus erythematosus. Subjects with Sjogren's
   syndrome, T-cell large granular lymphocyte leukemia (T-LGLL), or well-controlled
   thyroid disease are permitted;