A Clinical Study of Tulisokibart (MK-7240) to Treat Radiographic Axial Spondyloarthritis (MK-7240-013)

Researchers are looking for new ways to treat radiographic axial spondyloarthritis (r-axSpA). R-axSpA is a type of arthritis that causes pain, stiffness, and inflammation (swelling) in the spine and joints in the pelvis (hip bone). Radiographic means the damage it causes can be seen on X-rays. This study will help find out if a study medicine called tulisokibart can treat symptoms of r-axSpA. Researchers will look at different doses of tulisokibart. Researchers want to know if at least one of the study doses of tulisokibart works better than a placebo to improve r-axSpA symptoms. A placebo looks like the study medicine but has no study medicine in it. Using a placebo helps researchers better understand the effects of the study medicine.

This study consists of a 16-week Placebo-controlled Period and a 124-week Long-term Extension (LTE), which is composed of a 40-week Main Extension and an 84-week Optional Extension.

Inclusion Criteria: The main inclusion criteria include but are not limited to the following: * Has a clinical diagnosis of axial spondyloarthritis (axSpA) and meets the Assessment of SpondyloArthritis international Society (ASAS) classification criteria for axSpA including ≥3 months of back pain with age at symptom onset \<45 years * Meets the radiographic criterion of the modified New York criteria for ankylosing spondylitis (AS) as determined by central reading at Screening * Has active disease at Screening and Randomization * Has a history of inadequate response (IR)/intolerance to nonsteroidal anti-inflammatory drugs (NSAIDs) and is biologic disease-modifying antirheumatic drug (bDMARD)-naive, or has a history of IR/intolerance to up to a maximum of 2 bDMARD classes Exclusion Criteria: The main exclusion criteria include but are not limited to the following: * Has any arthritis with onset before age 17 years or current diagnosis of inflammatory joint disease other than radiographic axial spondyloarthritis (r-axSpA) (such as, but not limited to, rheumatoid arthritis, systemic lupus erythematosus, psoriatic arthritis (PsA), systemic sclerosis, myositis, etc.), or any other conditions that may, in the judgment of the investigator, interfere with the assessment of r-axSpA * Has a history of cancer (except fully treated non-melanoma skin cancers or cervical carcinoma in situ after complete surgical removal) within the last 5 years * Has any active infection * Has known allergies, hypersensitivity, or intolerance to tulisokibart or its excipients