BCD-085-3 is a next step in clinical investigation of BCD-085. BCD-085 is a monoclonal antibody to interleukin 17. During the trial patients with active ankylosing spondylitis will receive 40, 80 or 120 mg of BCD-085 subcutaneously at weeks 0, 1, 2, 4, 6, 8, 10, 12. Efficacy and safety parameters will be evaluated.

Inclusion Criteria:

• Written informed consent
• Age between 18 and 65 years
• Active ankylosing spondylitis according to modified criteria of New York classification (1984), that was diagnosed at least 3 months prior to screening.
• Active disease according to BASDAI (score 4 or more) if nonsteroidal antiinflammatory drugs were used in the last 3 month prior to screening.
• Mean backache intensity equals 4 points or more.
• If patient have had biologic therapy to treat ankylosing spondylitis for at least 3 months, there was no positive results of such treatment or patient revealed intolerance to the drug. This therapy must be discontinued at least 12 weeks before enrollment in the study.
• Female patients have negative urine pregnancy test.
• Patient has no history of tuberculosis.
• Patients have negative results of Diaskintest.
• Patient has no history of alcohol or drug abuse.

Exclusion Criteria:

• Total spinal ankylosis.
• Allergy or intolerance of monoclonal antibodies or any excipients of study drugs.
• Previous receipt of anti-interleukin 17 drugs or anti-interleukin 17 receptor drugs.
• Prior use of two or more biologics to tumor necrosis factor alfa.
• Prior use of two or more biologics to other targets. Previous receipt of monoclonal antibodies if they were cancelled less that in 12 weeks before signing informed consent.
• Patient is taking corticosteroids for up to 4 weeks in a dose more than 10 mg (recalculated to prednisolone) before signing informed consent and during screening, or in a dose less than 10 mg (recalculated to prednisolone) if it was not stable.
• Prior use of disease-modifying antirheumatic drugs including methotrexate, sulfasalazin, chloroquine or hydroxychloroquine for up to 4 weeks before randomization, if their dose was not stable for up to 4 weeks before signing informed consent and during screening.
• Prior use of live or attenuated vaccines for up to 8 weeks before signing informed consent.
• Prior use of alkylating agents for up to 12 months prior to signing informed consent.
• Intraarticular use of corticosteroids for up to 4 weeks before randomization.