The purpose of this study is to evaluate the safety, tolerability, pharmacokinetics, pharmacodynamics, as well as preliminary efficacy of mRNA encoding CD19/CD3 T cell engager (ABO2203) in patients with refractory autoimmune diseases who received inadequate response or relapsed from standard of care (SoC). The trial included dose escalation and dose expansion parts.

Inclusion Criteria:

1. ≥18 years of age at time of informed consent.
2. Diagnosis of autoimmune diseases according to the corresponding disease classification criteria.
3. Inadequate response to SoCs or relapsed after the treatment.
4. Patients were on a stable dose of SoCs for at least 4 weeks prior to enrollment.
5. Sufficient organ function.

Exclusion Criteria:

1. Active infection, including tuberculosis, active or relapsed peptic ulcer, etc.
2. Severe hypogammaglobulinemia or IgA deficiency.
3. Active hepatitis or with a history of severe liver disease.
4. History of rapid allergic reactions, eczema or asthma that cannot be controlled by topical corticosteroids.
5. Severe cardiovascular diseases.
6. History of cancer within past 5 years.
7. Have other serious medical conditions.
8. Received any of B cell targeted therapies and biologic therapies within the defined time window.
9. History of severe allergies or known allergies to any active or inactive component of the study drug(s).
10. A history of organ transplantation, bone marrow transplantation or hematopoietic stem cell transplantation.