A Phase I, Dose Escalation, Open-label, Multicenter Study of EA5 Injection in Adults With APS and Recurrent Thrombosis

This is a Phase I, open-label, dose escalation, multicenter study to evaluate the safety, tolerability, preliminary efficacy, pharmacodynamics (PD), and pharmacokinetics (PK) of EA5 injection in adult participants with Antiphospholipid Syndrome (APS) and recurrent thrombosis who are receiving standard-of-care antithrombotic therapy. Approximately 12 participants will be enrolled. The whole study treatment cycle was 24 weeks. Administration of low-dose EA5: First, administer the loading dose regimen intravenously, then maintain administration subcutaneously every 2 weeks(Q2W). Administration of high-dose EA5: First, administer the loading dose regimen intravenously, then maintain administration subcutaneously every 2 weeks(Q2W).The primary objective is to assess safety and tolerability. Secondary objectives include evaluation of preliminary efficacy, immunogenicity, PK, PD (complement inhibition), and APS-related biomarker changes.

Inclusion Criteria: 1. Participants must be ≥18 years of age at the time of signing the Informed Consent Form (ICF). 2. Participants diagnosed with Antiphospholipid Syndrome (APS) according to the 2023 EULAR/ACR classification criteria, with at least two of the three antiphospholipid antibodies positive: anticardiolipin antibody (aCL), anti-β2-glycoprotein I antibody (anti-β2GPI), and lupus anticoagulant (LA). 3. Experienced ≥2 thrombotic events within the past 5 years under antithrombotic prophylactic therapy, confirmed by objective imaging. 4. Stable antithrombotic treatment regimen for at least 6 months prior to screening (dose adjustment of warfarin to achieve a stable INR is permitted). 5. Vaccination against Neisseria meningitidis (MPV-ACYW) within \