Inclusion Criteria:
1. Age 18 to 80 years, inclusive, regardless of sex.
2. Good compliance and willingness to receive study treatment and complete follow-up visits and assessments as required by the protocol.
3. For participants with IgG4-related disease:
* Diagnosis of IgG4-related disease for at least 6 months, according to the 2019 ACR/EULAR Classification Criteria or the 2020 Revised Comprehensive Diagnostic Criteria for IgG4-related Disease.
* Evidence of IgG4-related lung involvement, including but not limited to bronchial wall thickening, bronchovascular bundle thickening, pulmonary nodules, or interstitial lung disease on chest high-resolution computed tomography (HRCT).
4. For participants with systemic sclerosis:
* Diagnosis of systemic sclerosis for at least 6 months, according to the 2013 ACR/EULAR Classification Criteria.
* Evidence of lung involvement on chest HRCT, including bronchial involvement, pulmonary nodules considered related to the underlying disease, and/or interstitial lung disease, with or without impaired pulmonary function.
5. Able to understand the study purpose, procedures, and possible discomforts, and willing to provide written informed consent.
6. Female participants of childbearing potential and male participants, including their female partners, must use highly effective contraception from screening until at least 6 months after the last dose. Participants must have no plan for pregnancy, sperm donation, or egg donation from screening until at least 6 months after the last dose.
Exclusion Criteria:
1. Diagnosis before screening of any connective tissue disease other than IgG4-related disease or systemic sclerosis, or diagnosis of another interstitial lung disease, such as idiopathic pulmonary fibrosis or interstitial pneumonia with autoimmune features.
2. Inadequate organ function reserve, including any of the following:
* Respiratory system: pulmonary arterial hypertension with pulmonary artery systolic pressure greater than 55 mmHg by echocardiography or mean pulmonary arterial pressure greater than 40 mmHg by right heart catheterization; severe impairment of diffusing capacity of the lung for carbon monoxide, defined as DLCO less than 30% of predicted; respiratory failure, defined as arterial oxygen tension less than 8 kPa or less than 60 mmHg and/or arterial carbon dioxide tension greater than 6.7 kPa or greater than 50 mmHg at rest without oxygen supplementation.
* Renal function: creatinine clearance less than 30 mL/min/1.73 m².
* Cardiac function: clinical symptoms of refractory congestive heart failure; left ventricular ejection fraction less than 35% by myocardial scintigraphy or echocardiography; chronic atrial fibrillation requiring oral anticoagulation; uncontrolled ventricular arrhythmia; or pericardial effusion causing hemodynamic instability by echocardiography.
* Liver function: persistent alanine aminotransferase, aspartate aminotransferase, or bilirubin greater than 3 times the upper limit of normal, or severe hepatic impairment, Child-Pugh class C.
3. Allergic constitution or history of potentially life-threatening drug allergy.
4. Clinically significant chronic or recurrent infection, defined as 3 or more infections of the same type within 1 year, or recent severe infection, such as pneumonia or sepsis. Participants will also be excluded if, within 1 month before baseline, they required inhaled, intramuscular, or systemic antibiotic treatment, systemic antiviral treatment, hospitalization, or prolonged hospitalization for infection.
5. History of organ transplantation or currently awaiting organ transplantation.
6. Positive screening test results for hepatitis B, hepatitis C, human immunodeficiency virus, or syphilis, as defined below:
* Hepatitis B surface antigen positive.
* Hepatitis B surface antigen negative but hepatitis B core antibody positive, with hepatitis B virus DNA above the upper limit of normal.
* Hepatitis C virus antibody positive, with hepatitis C virus RNA above the upper limit of normal.
* Human immunodeficiency virus antibody positive.
* Treponema pallidum antibody positive with positive rapid plasma reagin or toluidine red unheated serum test.
7. Possible active tuberculosis infection based on interferon-gamma release assay, such as QuantiFERON-TB Gold or T-SPOT.TB, clinical symptoms, and/or chest imaging. Participants with evidence of previously active tuberculosis that has been adequately treated may be enrolled after investigator assessment. Participants with latent tuberculosis may continue screening or be enrolled after at least 4 weeks of anti-tuberculosis treatment, if there is no liver injury before baseline and the investigator determines that the risk is controlled.
8. Prior treatment with stem cells or extracellular vesicles.
9. Any documented active or suspected malignancy, or history of malignancy, within 5 years before screening, except adequately treated basal cell carcinoma of the skin, squamous cell carcinoma in situ of the skin, or carcinoma in situ of the cervix.
10. Self-harm or suicidal ideation within 1 year before screening.
11. History of alcohol or drug abuse within 6 months before screening.
12. Major surgery or clinically significant surgery within 6 months before screening, or planned major surgery during the study.
13. Any of the following cardiovascular or cerebrovascular events within 6 months before screening: unstable angina requiring hospitalization, myocardial infarction, coronary artery bypass grafting, percutaneous coronary intervention, moderate to severe congestive heart failure defined as New York Heart Association class III or IV, atrial or ventricular arrhythmia requiring hospitalization, pacemaker or defibrillator implantation, cerebrovascular accident such as stroke, or planned coronary artery bypass grafting or revascularization during the study.
14. History of psychiatric illness, epilepsy, or other central nervous system disease.
15. Severe systemic disease, including but not limited to myocardial infarction, unstable angina, heart failure, liver cirrhosis, or acute glomerulonephritis.
16. Participation in any other clinical trial within 3 months before screening or within 5 half-lives of the investigational product, whichever is longer.
17. Pregnancy or breastfeeding.
18. Poor compliance or inability to complete study procedures.
19. Any condition that, in the investigator's opinion, may increase participant risk or interfere with interpretation of study results.
