The human microbiota corresponds to an extremely rich and varied set of microorganisms that colonize our various epitheliums from birth, including the intestine, lungs and skin, where they interact continuously with our immune system. Changes in microbial composition and function, termed dysbiosis, have been linked to alterations in immune responses and to disease development, such as psoriasis. Recent research has shown that the gut microbiota can condition the therapeutic response to checkpoint inhibitors and that fecal microbiota transplant overcomes resistance to these therapy, suggesting a direct role for the microbiota in the ability to shape a therapeutic immune response. Antibiotic exposure during the course of cancer therapy negatively correlates with patients' response to anti-PD-1 treatment response, thus highlighting the link between the enrichment of specific microbial taxa in intestines and the response to immunotherapy. This observation suggests that treatments capable of modulating microbial networks and promoting specific bacterial clades may modulate the host's immune response. Hence, beyond their expected effect in the targeted tissue, part of the therapeutic effect of drugs could rely on this mechanism. In psoriasis patients, observational studies suggest that gut microbiome is altered differently after the use of anti-IL17 or anti-IL23 biologic agents.

Main objective: To determine the evolution of microbial composition of fecal samples issued to patients who responded to a biologic agent (IL-17 inhibitors, IL-23 inhibitors) and have stopped their treatment for 2 to 4 weeks before the index date, at baseline and 6 months or clinical relapse after treatment discontinuation

Design of the study: Prospective french multicentre observational cohort study

Population of study participants: Patients with psoriasis in remission after IL23i or IL17inhibitor treatments and who have stopped their medication for 2 to 4 weeks.

Number of participants included: 50 adult patients considered in remission and have stopped for at least 2 weeks and a maximum of 4 weeks, one of the following biologic agent: secukinumab, ixekizumab, brodalumab, bimekizumab, guselkumab, tildrakizumab, or risankizumab

Inclusion Criteria:

• Subject over 18 years of age
• Subject diagnosed with psoriasis considered in remission (as defined by absolute PASI<2 within 6 months of follow-up)
• Subject who has stopped his biologic agent including IL-17 inhibitors or IL-23 inhibitors for 2 to 4 weeks.
• Written informed consent for participation in the study

Exclusion Criteria:

• Subject currently experiencing or having a history of other concomitant skin conditions that would interfere with evaluation of psoriasis
• Subject treated by NSAIDs, antibiotics, antifungals, antivirals or proton-pump inhibitors within 4 weeks before inclusion (or foreseeable use during the study)
• Subject with a concomitant diagnosis of cirrhosis, coeliac disease or signs of bacterial infection
• Subject has concurrent acute or chronic viral hepatitis B or C or human immunodeficiency virus (HIV) infection
• Subject having a personal or familial history of psoriatic arthritis or inflammatory bowel disease
• Subject with BMI<18.5 or BMI>35
• Subject consuming probiotics or using specific diet with many dietary exclusions according to the discretion of the investigator
• Pregnant and /or breastfeeding woman,
• Subject deprived of liberty by judicial or administrative decision or patient under guardianship
• Subject unable to understand the purpose and conditions of the study and unable to give consent

Patients with psoriasis in remission after IL23i or IL17inhibitor treatments and who have stopped their medication for 2 to 4 weeks.