A Multicenter, Randomized, Double-blind, Placebo-controlled, Dose-finding Clinical Trial in Patients With Active Psoriatic Arthritis to Investigate Efficacy, Tolerability, Safety, Pharmacokinetics and Immunogenicity of ABY-035

The study evaluates two dose levels of ABY-035, in comparison to placebo, in subjects with psoriatic arthritis. The clinical trial duration is 72 weeks (Screening - last FU visit) comprised of up to 4 weeks of screening, 44 weeks of double-blind-treatment, and 24 weeks of follow-up. Treatment Periods are: * Treatment Period I: from V1 (Week 0) to V9 (Week 16) * Treatment Period II: from V9 (Week 16) to V16 (Week 44: last dosing) At visit V1 (Week 0), patients who meet the entry criteria will be randomly assigned in equal rates (1:1:1) to one of three parallel groups (A, B, C). The treatment will be administered once every 2 weeks (Q2W). Patients assigned to groups A and B will receive active treatment from V1 to V16 (group A = 40 mg ABY-035; group B = 80 mg ABY-035). Patients initially assigned to placebo will switch to active treatment at visit V9 in a blinded fashion (group C = Placebo from V1 to V8 and 80 mg ABY-035 from V9 to V16).