A Study to Evaluate the Efficacy and Safety of Bimekizumab in Adult Study Participants With Active Psoriatic Arthritis

Prior treatment

• Participant has a history of chronic alcohol or drug abuse within 6 months prior to Screening.
• Study participants taking psoriatic arthritis (PsA) medications other than MTX, SSZ, apremilast, hydroxychloroquine (HCQ), LEF, nonsteroidal anti-inflammatory drug (NSAIDs)/ cyclooxygenase-2 (COX-2) inhibitors, oral corticosteroids, and analgesics as outlined in the Inclusion criteria.
• Study participant is taking or has taken prohibited PsA or PSO medications without meeting the mandatory wash-out period relative to the Baseline Visit or is taking or has taken weight management medications without meeting the mandatory dose stability period/washout period relative to the Baseline Visit.
• Study participant is taking or has taken janus kinase (JAK) inhibitor.
• Study participant is taking or has taken bDMARDs, including bimekizumab or risankizumab, with the exception of having received 1 prior TNFα inhibitor.
• Study participant previously participated in another study of a medical device under investigation within the 4 weeks prior to the Screening Visit or is currently participating in another study of a medical device under investigation.

Other illness

• Study participant has any medical or psychiatric condition that, in the opinion of the Investigator, could jeopardize or would compromise the study participant's ability to participate in this study.
• Participant has an active infection or a history of recent serious infections.
• Participant has known tuberculosis (TB) infection, is at high risk of acquiring TB infection, or has current or history of nontuberculous mycobacterium (NTMB) infection.
• Study participant has a diagnosis of inflammatory conditions other than PSO or PsA including, but not limited to, rheumatoid arthritis, sarcoidosis, systemic lupus erythematosus, reactive arthritis, and axial spondyloarthritis.
• Study participants with a history of anterior uveitis are allowed if they have no active symptoms at Screening or Baseline. Study participants with a diagnosis of Crohn's disease or ulcerative colitis are allowed if they have no active symptomatic disease at Screening or Baseline.
• Participant has any active malignancy or history of malignancy within 5 years prior to the Screening Visit EXCEPT treated and considered cured cutaneous squamous or basal cell carcinoma, or in situ cervical cancer.

Other

• Female participants who are breastfeeding, pregnant, or plan to become pregnant during the study.
• Study participants with fibromyalgia or osteoarthritis symptoms that in the Investigator's opinion would have potential to interfere with efficacy assessments.

• Study participants must have a documented diagnosis of adult-onset PsA classified by and that meets the CASPAR classification criteria for at least 6 months prior to Screening with active PsA (despite previous csDMARD or apremilast therapy) and must have at Baseline tender joint count (TJC) ≥3 out of 68 joints and swollen joint count (SJC) ≥3 out of 66 joints (dactylitis of a digit counts as 1 joint each).
• Study participant must have at least 1 active psoriatic lesion(s) and/or a documented history of chronic plaque-type psoriasis (PSO).
• Study participants may currently be on conventional synthetic disease-modifying antirheumatic drug (csDMARD) therapy and must have previously been treated with at least 1 csDMARD (methotrexate (MTX), leflunomide (LEF), sulfasalazine (SSZ)). Study participants must have had an inadequate response to therapy or discontinued due to intolerance. (Inadequate response is determined by the Investigator and is defined as not achieving the minimal response after 12 weeks of therapy.)
• Study participants can either be biological disease-modifying antirheumatic drug (bDMARD)-naïve or have received not more than 1 prior tumor necrosis factor alpha (TNFα) inhibitor. Study participants who have been on a TNFα inhibitor previously must not have discontinued the TNFα inhibitor due to financial or health insurance reasons and must have either:
• experienced an inadequate response to previous treatment given at an approved dose for at least 3 months, or
• been intolerant to administration (eg, had a side-effect/adverse event (AE) that led to discontinuation).