A Study to Test the Efficacy and Safety of Bimekizumab in the Treatment of Subjects With Active Psoriatic Arthritis

Inclusion Criteria:

• An Institutional Review Board (IRB)/Independent Ethics Committee (IEC) approvedwritten Informed Consent form is signed and dated by the subject

• Subject is male or female at least 18 years of age

• Female subject must be postmenopausal, permanently sterilized or willing to use ahighly effective method of contraception

• Documented diagnosis of adult-onset Psoriatic Arthritis (PsA) meeting theClassification Criteria for Psoriatic Arthritis (CASPAR) for at least 6 months priorto Screening with active PsA and must have at Baseline tender joint count (TJC) >=3out of 68 and swollen joint count (SJC) >=3 out of 66

• Subject must be negative for rheumatoid factor and anti-cyclic citrullinated peptide (CCP) antibodies

• Subject must have at least 1 active psoriatic lesion(s) and/or a documented historyof psoriasis (PSO)

• Subject must be a suitable candidate for treatment with adalimumab and has nocontraindications to receive adalimumab as per the local label as assessed by theInvestigator

• Subjects currently taking NSAIDs, cyclooxygenase 2 (COX-2) inhibitors, analgesics (including mild opioids), corticosteroids, methotrexate (MTX), leflunomide (LEF),sulfasalazine (SSZ), hydroxychloroquine (HCQ) AND/OR apremilast can be allowed ifthey fulfill specific requirements prior to study entry

Exclusion Criteria:

• Female subjects who are breastfeeding, pregnant, or plan to become pregnant duringthe study

• Subjects with current or prior exposure to any biologics for the treatment ofPsoriatic Arthritis (PsA) or Psoriasis (PSO)

• Subject has an active infection or a history of recent serious infections

• Subject has known tuberculosis (TB) infection, is at high risk of acquiring TBinfection, or has current or history of nontuberculous mycobacterium (NTMB)infection

• Subject has a diagnosis of inflammatory conditions other than PSO or PsA. Subjectswith a diagnosis of Crohn's disease, ulcerative colitis, or other inflammatory boweldisease (IBD) are allowed as long as they have no active symptomatic disease atScreening or Baseline

• Subject had acute anterior uveitis within 6 weeks of Baseline

• Subject has any active malignancy or history of malignancy within 5 years prior tothe Screening Visit EXCEPT treated and considered cured cutaneous squamous or basalcell carcinoma, or in situ cervical cancer

• Subject has a form of PSO other than chronic plaque-type (eg, pustular,erythrodermic and guttate PSO, or drug-induced PSO)

• Presence of active suicidal ideation, or moderately severe major depression orsevere major depression

• Subject has a history of chronic alcohol or drug abuse within 6 months prior toScreening