Telitacicept 160 mg subcutaneously once a week.

Subjects will be given subcutaneous placebo once a week.

The EULAR Sjogren's syndrome (SS) disease activity index (ESSDAI) is a systemic disease activity index that was designed to measure disease activity in patients with primary SS. It includes 12 domains (ie, organ systems: cutaneous, respiratory, renal, articular, muscular, peripheral nervous system (PNS), central nervous system (CNS), haematological, glandular, constitutional, lymphadenopathic, biological). Each domain is divided into 3-4 levels of activity (no, low, moderate, high). Overall score is calculated as sum of all individual weighted domain scores (ranges from 0 (best) to 123 (worst activity). A higher score indicates worsening of the disease

The EULAR Sjogren's syndrome (SS) disease activity index (ESSDAI) is a systemic disease activity index that was designed to measure disease activity in patients with primary SS. It includes 12 domains (ie, organ systems: cutaneous, respiratory, renal, articular, muscular, peripheral nervous system (PNS), central nervous system (CNS), haematological, glandular, constitutional, lymphadenopathic, biological). Each domain is divided into 3-4 levels of activity (no, low, moderate, high). Overall score is calculated as sum of all individual weighted domain scores (ranges from 0 (best) to 123 (worst activity). A higher score indicates worsening of the disease.

The EULAR Sjogren's Syndrome Patient Reported Index (ESSPRI) is a patient-reported, subjective symptom index for primary Sjögren's syndrome. It consists of three questions covering the cardinal symptoms of Sjögren's syndrome: dryness, fatigue and pain (articular and/or muscular). Each domain scored on scale of 0-10 (0 =no symptom at all and 10 = worst symptom imaginable), and an overall score is calculated as the mean of the three individual domains.

The multidimensional fatigue inventory (MFI-20) is a 20-item self-report instrument designed to measure fatigue. It covers the following dimensions: general fatigue, physical fatigue, reduced activity, reduced motivation and mental fatigue. Each question is scored from one to five and each dimension consists of five questions. The dimensional score consequently ranges from 4 to 20 (a higher score indicates more fatigue).

An adverse event (AE) is any untoward medical occurrence in a patient or clinical investigation subject administered a pharmaceutical product and which does not necessarily have a causal relationship with this treatment. A serious adverse event (SAE) is any untoward medical occurrence that at any dose results in death; is life-threatening experience; requires inpatient hospitalization or prolongation of existing hospitalization; results in persistent or significant disability/incapacity; or is a congenital anomaly/ birth defect; or any other important medical event that may not be immediately life-threatening or result in death or hospitalization but may require intervention to prevent one of the other serious outcomes listed in the definition above.