Sponsor decision.

This is an open-label study to evaluate the effects of bimekizumab in patients with psoriasis vulgaris and who also have active psoriatic arthritis (PsA).

This study is being conducted to evaluate the effects of bimekizumab administered subcutaneously (SC) to patients with psoriasis vulgaris and who also have active PsA who have an inadequate skin response to anti-interleukin (IL)23 therapy. Approximately 20 adult subjects with psoriasis vulgaris and active PsA who have an inadequate skin response to anti-IL23 will receive bimekizumab 320 mg solution administered SC every 4 weeks for 16 weeks.

Inclusion Criteria:

1. Male or female patient 18 years of age or older at the time of consent.
2. Patient with a history of psoriasis vulgaris and PsA (as determined by the investigator) for ≥ 6 months prior to the screening visit.
3. Patient with moderate-to-severe psoriasis vulgaris before initiating treatment with an anti-IL23 agent.
4. Patient with an inadequate skin response to at least 12 weeks treatment with an anti-IL23 agent for the treatment of psoriasis vulgaris as defined by a PGA ≥ 2 and plaque psoriasis covering ≥ 1% of total BSA (excluding palms and soles) at the screening and Day 1 visits.
5. Patient with active PsA as defined by ≥ 1 joint that is tender (TJC68) and/or swollen (SJC66) at Day 1.

Exclusion Criteria:

1. Female who is breastfeeding, pregnant, or who is planning to become pregnant during the study or within 4 months after the last study product administration.
2. Patient with evidence of erythrodermic, pustular, predominantly guttate psoriasis, or drug-induced psoriasis.
3. Patient with any known clinically significant medical condition or presence of a skin or rheumatologic disease that would, in the opinion of the investigator, put the patient at undue risk or interfere with the interpretation of study results.
4. Patient who plans to receive a live or live-attenuated vaccine during the study and up to 4 weeks or 5 half-lives (of the study product), whichever is longer, after the last study product administration.
5. Patient with an active infection (except common cold) that would place them at increased risk, a recent serious infection, or a history of opportunistic, recurrent, or chronic infections.
6. Patient with a diagnosis of inflammatory bowel disease (Crohn's disease or ulcerative colitis).
7. Patient with known or suspected hypersensitivity to bimekizumab or any component of the investigational product, including any nonmedicinal ingredient, or component of the container.
8. Patient who has received any marketed or investigational biological agent, except anti-IL23 agents, within 12 weeks or 5 half-lives (whichever is longer) prior to Day 1.
9. Patient who has received treatment with bimekizumab prior to Day 1.