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

Percentage of Participants Achieving Assessment of Spondyloarthritis International Society (ASAS) 40 Response at Week 16

Timeframe: Week 16

ASAS 40 is defined as a relative improvement of ≥40% and an absolute improvement of ≥2 units from baseline in ≥3 of 4 domains, with no deterioration in the fourth domain. The 4 domains include Patient Global Assessment (PtGA), total spinal pain, physical function, and morning stiffness. Each domain is measured on a 10-point numeric scale from 0 = no disease symptoms/impact to 10 = extreme disease symptoms/impact, with a higher score indicating more severe impairment.

Percentage of Participants Achieving Ankylosing Spondylitis Disease Activity Score (ASDAS) <2.1 at Week 16

Timeframe: Week 16

ASDAS is a disease activity measure calculated from the assessments of total spinal pain, duration of morning stiffness, peripheral pain/swelling, PtGA, and high sensitivity C-reactive protein (hsCRP) as follows: 0.121 × total spinal pain (Bath Ankylosing Spondylitis Disease Activity Index \[BASDAI\] question 2) + 0.110 × PtGA + 0.073 × peripheral pain/swelling (BASDAI question 3) + 0.058 × duration of morning stiffness (BASDAI question 6) + 0.579 × natural logarithm (ln) of (hsCRP + 1). ASDAS \<2.1 indicates low disease activity and a higher score indicates greater disease activity.

Change From Baseline in Bath Ankylosing Spondylitis Functional Index (BASFI) at Week 16

Timeframe: Baseline and Week 16

The BASFI is a validated 10-item measure assessing individual-reported function (8 items) and ability to cope with everyday life (2 items) over the past week. Responses are recorded for each item on an 11-point numeric rating scale (NRS) from 0 "easy" to 10 "impossible". A mean score of the 10 items will be calculated to reflect the overall functional impairment, with higher scores indicating greater disability.

Change From Baseline in the Spondyloarthritis Research Consortium of Canada (SPARCC) Magnetic Resonance Imaging (MRI) Score for Spine at Week 16

Timeframe: Baseline and Week 16

The SPARCC MRI score for spine is a validated scoring system developed to assess inflammation in the spine related to axSpA. The 6 most abnormal discovertebral units are selected, and 3 consecutive sagittal slices are assessed. Each discovertebral unit is divided into 4 quadrants, scored as 1 if increased signal is present or 0 if normal, with a maximum of 12 points per discovertebral unit. Additional points are added for lesions that exhibit intense signal or deep (≥1 cm), increasing the maximum score per unit to 18. Summed over 6 slices, the maximum total score is 108. Higher scores indicate more extensive and/or intense spinal inflammation.

Change From Baseline in the SPARCC MRI Score for Sacroiliac Joint (SIJ) at Week 16

Timeframe: Baseline and Week 16

The SPARCC MRI score for SIJ is a validated scoring system to assess SIJ inflammation in axSpA. Six consecutive SIJ coronal slice images are assessed by dividing into 4 quadrants and scored as 1 if increased signal is present or 0 if normal, with a maximum of 8 points per slice for both joints. Additional points are added for lesions that exhibit intense signal or deep (≥1 cm), increasing the maximum score per unit to 12. Summed over 6 slices, the maximum total score is 72. Higher scores indicate more extensive and/or intense SIJ inflammation.

Change From Baseline in Total Spinal Pain Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) Question 2 at Week 16

Timeframe: Baseline and Week 16

The BASDAI is a validated 6-item questionnaire used to assess disease activity in radiographic axial spondyloarthritis. It assesses individual-reported fatigue, total spinal pain, peripheral pain/swelling, tenderness, intensity of morning stiffness, and duration of morning stiffness over the past week. To access individual-reported total spinal pain experienced over the past week, participants are asked BADSAI question 2, "How would you describe the overall level of ankylosing spondylitis neck, back, or hip pain you have had?" Responses are recorded on an 11-point NRS ranging from 0 "none" to 10 "very severe." Higher score indicates more severe total spinal pain.

Change From Baseline in Nocturnal Spinal Pain at Week 16

Timeframe: Baseline and Week 16

The NRS is an 11-point scale (numeric version of the visual analog scale) to assess the pain intensity in individuals who can self-report. Participants will be asked to report their average nighttime spinal pain over the past week on an 11-point NRS. The score range is from 0 "no pain" to 10 "most severe pain." Higher score indicates more severe nocturnal spinal pain.

Change From Baseline in Assessment of Spondyloarthritis International Society Health Index (ASAS HI) at Week 16

Timeframe: Baseline and Week 16

The ASAS HI assesses overall functioning and health and is a validated 17-item individual-reported measure of pain, emotional functions, sleep, sexual function, mobility, self-care, and community life, with response options of "I agree" (1) or "I do not agree" (0). The ASAS HI is a total summary score ranging from 0 to 17 with a lower score indicating a better and a higher score indicating an inferior health status.

Change From Baseline in Short Form-36 Health Survey (SF-36) Physical Component Summary (PCS) at Week 16

Timeframe: Baseline and Week 16

The SF-36 is a widely used general health status questionnaire that assesses 8 domains of functional health and well-being: physical functioning, role limitations due to physical health problems, bodily pain, social functioning, mental health, role limitations due to emotional problems, vitality, and general health perceptions. The PCS score is a composite score derived from the SF-36 that summarizes the physical health aspects of the survey. It combines information primarily from the physical domains (physical functioning, role limitations due to physical health problems, bodily pain, and general health perceptions). All SF-36 scores range from 0 = worst health state to 100 = best health state, with higher scores indicating a better health-related quality of life (QoL).

Change From Baseline in BASDAI at Week 16

Timeframe: Baseline and Week 16

The BASDAI is a validated 6-item measure, assessing individual-reported fatigue, total spinal pain, peripheral pain/swelling, tenderness, intensity of morning stiffness, and duration of morning stiffness over the past week. Responses are recorded for each item on an 11-point NRS from 0 "none" to 10 "very severe." BASDAI is calculated by averaging the response for question 5 and question 6, adding this result to the sum of question 1 through question 4, and then dividing the result by 5. A higher score indicates greater disease activity.

Change From Baseline in Maastricht Ankylosing Spondylitis Enthesitis Score (MASES) at Week 16 in the Subgroup of Participants With Enthesitis (MASES>0) at Baseline

Timeframe: Baseline and Week 16

The MASES is a validated method to assess peripheral enthesitis in axSpA. It assesses pain on palpation at the following anatomic sites: first costochondral joint (right \& left); seventh costochondral joint (right \& left); anterior superior iliac spine (right \& left); iliac crest (right \& left); posterior superior iliac spine (right \& left); fifth lumbar spinous process; Achilles tendon, proximal insertion (right \& left). Each site is scored based on participant response as either 0 (nontender) or 1 (tender), the final score ranges from 0 (absence of enthesitis) up to a score of 13 (enthesitis present at all sites). Injected enthesitis sites will be considered not assessable for 90 days from the time of the injection. Higher score indicates more tender or inflamed enthesitis sites. Resolution of enthesitis is defined as MASES score equal to zero.

Change From Baseline in Bath Ankylosing Spondylitis Metrology Index Linear (BASMI lin) at Week 16

Timeframe: Baseline and Week 16

The BASMI lin is a validated tool to assess mobility in axSpA. The BASMI lin evaluates the range in centimeters of 5 components of hip and spinal mobility (components: tragus-to-wall, lateral lumbar flexion, cervical rotation angle, lumbar flexion, and maximal intermalleolar distance). For tragus to wall, lateral lumber flexion, and cervical rotation angle, the average measurements from left and right would be used as the component score. Component score range is from 0 (no mobility limitation) to 10 (very severe mobility limitation). Higher score indicates more severe mobility limitation.

Change From Baseline in Functional Assessment of Chronic Illness Therapy - Fatigue Scale (FACIT-Fatigue) at Week 16

Timeframe: Baseline and Week 16

The FACIT-Fatigue is a validated 13-item measure that assesses individual-reported fatigue and its impact on daily activities and function during usual activities over the past week. Responses are recorded on a 5-point Likert scale (0 = not at all to 4 = very much), individual item scores are then summed to provide the final score with range from 0 (worst score/extreme fatigue) to 52 (best score/no or minimal fatigue). Higher total scores represent lower levels of fatigue.

Number of Participants With One or More Adverse Events (AEs)

Timeframe: Up to approximately 154 weeks

An AE is any untoward medical occurrence in a clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention.

Number of Participants Who Discontinue Study Intervention Due to an AE

Timeframe: Up to approximately 140 weeks

An AE is any untoward medical occurrence in a clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention.