A Study to Evaluate the Efficacy and Safety of Different Doses of Bimekizumab in Subjects With Active Ankylosing Spondylitis

Inclusion Criteria

• Subject has active ankylosing spondylitis (AS), determined by documented radiologic evidence fulfilling the Modified New York criteria for AS including symptoms for >=3 months and age of onset =4
• Spinal pain >=4 on a 0 to 10 NRS (Numeric Rating Scale; from BASDAI item 2)
• Subjects must have at least 1 of the following:
• inadequate response to nonsteroidal anti-inflammatory drug (NSAID) therapy
• intolerance to administration of at least 1 NSAID
• contraindication(s) to NSAID therapy
• Subjects who are regularly taking NSAIDs/COX-2 inhibitors as part of their AS therapy are required to be on a stable dose for at least 14 days before Baseline
• Subjects taking corticosteroids must be on an average daily dose of <=10mg/day prednisone or equivalent for at least 14 days before Baseline and should remain on a stable dose up to Week 16
• Subjects taking methotrexate (MTX) (<=25mg/week) are allowed to continue their medication if started at least 12 weeks prior to Baseline, with a stable dose for at least 8 weeks before randomization
• Subjects taking sulfasalazine (up to 3grams/day) or hydroxychloroquine (up to 400mg per day total) are allowed to continue their medication if started at least 12 weeks prior to Baseline, with a stable dose for at least 8 weeks before randomization
• Subjects may be tumor necrosis factor (TNF) inhibitor-naïve or may have received 1 prior TNF inhibitor. Subjects who have been on a TNF inhibitor previously must have:
• experienced an inadequate response to previous treatment given for at least 12 weeks
• been intolerant to administration (eg, had a side effect/adverse event that led to discontinuation)
• lost access to TNF inhibitor for other reasons

Exclusion Criteria

• Subjects with a total ankylosis of the spine, or a diagnosis of any other inflammatory arthritis eg, rheumatoid arthritis (RA), sarcoidosis, systemic lupus erythematosus, or reactive arthritis
• Subjects with any current sign or symptom that may indicate an active infection (except for the common cold)
• Subjects with a history of chronic or recurrent infections, or a serious or life-threatening infection within the 6 months prior to the Baseline Visit
• Subjects receiving any live vaccination within the 8 weeks prior to Baseline
• Subjects with known tuberculosis (TB) infection, at high risk of acquiring TB infection, with latent TB infection or current or history of nontuberculous mycobacteria (NTMB) infection
• Subjects with concurrent malignancy or a history of malignancy during the past 5 years will be excluded, with following exceptions that may be included:
• <= 3 excised or ablated basal cell carcinomas of the skin
• One squamous cell carcinoma of the skin (stage T1 maximum) successfully excised, or ablated only (other treatments, ie, chemotherapy, do not apply), with no signs of recurrence or metastases for more than 2 years prior to Screening
• Actinic keratosis (-es)
• Squamous cell carcinoma-in-situ of the skin successfully excised, or ablated, more than 6 months prior to Screening