Inclusion Criteria:
* Male or female, aged 18 to 75 years (inclusive) at the time of signing the informed consent form (ICF), and willing to comply with the study protocol requirements.
* Body weight ≥ 45 kg at screening.
* Voluntary compliance with the protocol requirements for permitted/prohibited concomitant therapies.
* Definitive diagnosis of primary Sjögren's disease (SjD) according to the 2016 American College of Rheumatology (ACR)/European League Against Rheumatism (EULAR) classification criteria, and meeting all of the following requirements:
1. Seropositive for at least one SjD-related autoantibody.
2. Prior treatment with at least two systemic therapies for SjD symptoms.
3. Active disease at screening, defined as Clinical EULAR Sjögren's Syndrome Disease Activity Index(ClinESSDAI) ≥ 5.
* No better therapeutic alternative available for the study participant.
Exclusion Criteria:
* Presence of other systemic autoimmune diseases besides primary Sjögren's disease.
* Presence of other autoimmune or inflammatory diseases.
* Presence of any other medical condition with clinical manifestations overlapping with primary Sjögren's disease or that may interfere with result interpretation.
* Presence of active, life-threatening, or organ-threatening SjD complications at screening.
* History of severe allergic reactions (as judged by the investigator), or history of hypersensitivity to monoclonal antibodies or any component of CM336.
* Presence of congenital immunodeficiency, or acquired immunodeficiency not related to the participant's autoimmune disease or its medical treatment.
* Positive HIV antibody, positive Treponema pallidum antibody, or history of hepatitis B virus (HBV) or hepatitis C virus (HCV) infection.
* History of tuberculosis infection.
* Active infection requiring intravenous anti-infective treatment within 3 months before first dose of study drug, or oral anti-infective treatment within 2 weeks before first dose of study drug.
* History of disseminated herpes zoster, or ocular/Central Nervous System herpes zoster, or systemic herpes simplex or symptomatic herpes zoster infection within 3 months before first dose of study drug.
* Deep vein thrombosis or pulmonary embolism within 6 months before first dose of study drug.
* History of severe cardiovascular or cerebrovascular disease, including but not limited to:
1. Unstable arrhythmia, unstable angina pectoris.
2. New York Heart Association (NYHA) functional class III or IV.
3. Uncontrolled hypertension (average systolic blood pressure ≥160 mmHg or diastolic blood pressure ≥100 mmHg on two measurements despite optimal treatment).
4. Fridericia-corrected QT interval(QTcF) \>450 ms for males or \>470 ms for females
* History of pulmonary arterial hypertension with WHO functional class II or above.
* Presence of uncontrolled asthma or chronic obstructive pulmonary disease (COPD); uncontrolled diabetes mellitus; uncontrolled thyroid or other endocrine disorders; uncontrolled psychiatric disorders.
* Presence of any of the following during screening:
1. Neutrophil count \<1×10⁹/L, platelet count \<100×10⁹/L, or hemoglobin \<80 g/L (applicable only to patients without hematologic involvement).
2. Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) \>2× upper limit of normal (ULN).
3. estimated Glomerular Filtration Rate(eGFR) \<40 mL/min/1.73m² (2021 Chronic Kidney Disease Epidemiology Collaboration formula).
4. Prothrombin time (PT) or activated partial thromboplastin time (APTT) \>1.5×Upper Limit of Normal.
* Major surgery within 3 months before screening or planned during the study period (requiring hospitalization and general anesthesia, excluding diagnostic procedures).
* History of malignancy within 5 years before first dose of study drug (except cured basal cell carcinoma, squamous cell carcinoma of the skin, and cervical carcinoma in situ without evidence of recurrence).
* Prior treatment with any anti-B-cell maturation antigen targeted therapy (including cell therapy or antibody therapy, etc.).
* Receipt of prohibited medications within the corresponding timeframes.
