Exploratory Study on the Efficacy and Safety of Low-Dose Blinatumomab in the Treatment of Moderate to Severe Primary Sjögren's Syndrome

The goal of this clinical trial is to learn if blinatumomab works to treat moderate-to-severe primary Sjögren\'s Syndrome. It will also learn about the safety of low-dose blinatumomab. The main questions it aims to answer are: Is low-dose blinatumomab more effective in patients with moderate-to-severe primary Sjögren\'s Syndrome who have an inadequate response or intolerance to conventional treatment? How does blinatumomab affect B cells, antibody levels, and the immune system in these participants? Researchers will compare background treatment plus low-dose Blinatumomab with background treatment only to see if low-dose Blinatumomab works to treat moderate-to-severe primary Sjögren\'s Syndrome. Participants will: Receive background treatment for 24 weeks, including hydroxychloroquine 400 mg each day, methylprednisolone 8 mg each day, and sodium hyaluronate eye drops 4 times each day. If assigned to the blinatumomab group, receive blinatumomab by continuous intravenous infusion for 5 days during week 1 and again for 5 days during week 3. The dose will be 9 micrograms per day. Attend regular follow-up visits for clinical assessments, laboratory tests, and monitoring of treatment effectiveness and safety.