Inclusion Criteria:
* Adults aged 18 to 69 years, regardless of gender.
* Adequate bone marrow, coagulation, cardiopulmonary, hepatic, and renal function.
* Participants who are not pregnant or breastfeeding and who agree to use effective contraception for 12 months after drug infusion, if applicable.
* Diagnosis of systemic lupus erythematosus (SLE) according to the 2019 EULAR/ACR classification criteria, with a history of SLE for at least 6 months; during screening, participants must have positive antinuclear antibody (ANA), and/or positive anti-double-stranded DNA antibody, and/or hypocomplementemia.
* Diagnosis of systemic sclerosis (SSc) according to the 2013 ACR/EULAR classification criteria, including limited cutaneous or diffuse cutaneous systemic sclerosis, with new or progressive skin manifestations within 6 months before screening.
Exclusion Criteria:
* Positive hepatitis B surface antigen (HBsAg), or positive hepatitis B core antibody (HBcAb) with detectable or quantifiable HBV DNA; positive hepatitis C antibody with detectable or quantifiable HCV RNA; positive HIV antibody; positive CMV DNA; or positive syphilis antigen or antibody.
* Presence of any other uncontrolled active infection.
* History of major solid organ transplantation (for example, heart, lung, liver, or kidney transplantation) or bone marrow/hematopoietic stem cell transplantation.
* Pregnant or breastfeeding women.
* Receipt of any mRNA-LNP product or other LNP-based drug within the past 2 years.
* History, within 6 months before screening, of any of the following cardiovascular conditions: NYHA Class III or IV heart failure, myocardial infarction, unstable angina, uncontrolled or symptomatic atrial arrhythmia, ventricular arrhythmia, or other clinically significant cardiac disease.
* Receipt of a live vaccine within 30 days before screening.
* History of asthma or severe allergy, if considered clinically significant by the investigator.
* Any condition that, in the investigator's opinion, would increase risk to the participant or interfere with study assessments.