ABY-035 in the Treatment of Subjects With Ankylosing Spondylitis

ABY-035-204 is a double-blind, randomized, parallel-group, placebo-controlled study. The primary objective is to estimate the relationship between different dose regimens of ABY-035 and clinical response as assessed by Assessment of Spondyloarthritis International Society 40 (ASAS40) response at Week 16 in subjects with active AS. The study will include the following 3 periods: 1. Screening Period: Up to 35 days prior to baseline randomization. 2. Treatment Period 1: Day 0-Week 16 Cohort 1: Eligible subjects will be randomized 1:1:1:1 to receive 1 of 4 treatments (ABY-035 High Dose every 2 weeks (Q2W), ABY-035 Low Dose every 2 weeks (Q2W), ABY-035 High Dose every 4 weeks (Q4W), or placebo Q2W), and will remain on their allowable background medication. Cohort 2: Eligible subjects will be randomized 1:1:1 to receive 1 of 3 treatments (ABY-035 High Dose every week (QW), ABY-035 Low Dose every week (QW), or placebo QW), and will remain on their allowable background medication. Randomization will be stratified by region (North Eastern Asia and North America) and previous tumor necrosis factor alpha (TNFα) inhibitor exposure (TNFα inhibitor treated or TNFα inhibitor naïve). Maximum 30% of subjects will be TNFα inhibitor-treated subjects to ensure a representative population for the assessment of efficacy and safety. Treatment Period 1 ends at Week 16 after all trial assessments have been done and Treatment Period 2 starts at Week 16 with the IMP injection. 3. Treatment Period 2 (Extension Period): Week 16-Week 52 Cohort 1: Subjects will receive ABY-035 High Dose Q2W treatment in an open-label manner. Cohort 2: Subjects will receive ABY-035 High Dose QW treatment in an open-label manner. At Week24, subjects who could not achieve an ASAS20 response from baseline are defined as non-responders and will discontinue the study treatment.