The main objective of this trial is to search for biomarkers associated with the success of adalimumab treatment in order to generate an algorithm to predict the response to this treatment at 6 months in spondyloarthritis and to define its metrological properties on this cohort.

The algorithm will allow to better target patients who will have an important benefit/risk ratio for adalimumab treatment.

The general prevalence of spondyloarthritis (SpA) is 0.5% of the Caucasian population and that of ankylosing spondylitis (AS) is 0.3% in France.

First-line treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) is insufficiently effective in more than half of AS patients in hospitals. These patients are then treated with "anti-tumor necrosis factor alpha" (anti-TNFα). The use of these bio-drugs increasing each year, they become a significant public health and economic challenge. Their development is just beginning, because they are among the largest providers of pharmacy innovations.

The two main cost-drivers appear to be, on the most advanced forms of inflammatory rheumatism, the use of appropriate care structures or services and surgery, especially knee and hip surgery. Among patients treated with biotherapy, clinical practice shows that about one-third (33%) will not respond to selected biopharmaceuticals as these biologics are often prescribed empirically, mainly because of the lack of criteria based on scientific evidence and availability of tools able to predict the response or non-response to these molecules.

Until now, there is no algorithm which can predict the response to biotherapies like adalimumab. The aim of this trial is to search for biomarkers associated with the success of adalimumab treatment in order to generate an algorithm predicting the response to this treatment at 6 months for patients with SpA. This algorithm will be set up from patients' biological and clinical data available after 6 months of adalimumab treatment. A number of 50 patients seems to be statistically sufficient to assess the probability of response or non response to adalimumab in SA with the defined algorithm. A logistic regression model will be used by incorporating the set of available variables.

Then it will be necessary to set up a validation study to determine the metrological properties of the algorithm on an independent cohort.

Inclusion Criteria:

• Patients with spondyloarthritis validating ASAS or modified New York criteria for which adalimumab treatment is indicated, and performing the pre-biotherapy assessment;
• Between 18 and 70 years old;
• Biotherapy naive;
• Who can be regularly monitored for 6 months;
• Able to take all the treatment;
• Effective contraception for patients of childbearing age (oral contraceptive, intrauterine device, implant, spermicide, surgical sterilization or abstinence) during the study and at least for 5 months after the last injection;
• Able to read and understand the terms of the protocol;
• Having dated and signed the informed consent form of the trial;
• Affiliated to a social security scheme.

Exclusion Criteria:

• Patients having a contraindication to an anti-TNF;
• Surgical operation scheduled during the trial;
• Having difficulty understanding the French language;
• Having impaired upper functions (dementia of Alzheimer type, etc...);
• Psycho-social instability incompatible with regular follow-up (homeless, addictive behavior, history of psychiatric pathology or any other comorbidity which would make a free and informed consent impossible or limit adherence to the protocol);
• Having previously received a biotherapy. There is no other exclusion criteria taking into account prior therapies and the duration of these therapies;
• Described in articles L.1121-5 to L.1121-8 of the Personal Status Code: pregnant, parturient and nursing women; persons in detention by judicial or administrative decision; adults subject to a legal protection order;
• Already participating in interventional research.