Inclusion Criteria:
1. Voluntary signing of informed consent;
2. Age 18-65 years old (including the threshold), male and female;
3. Diagnosis of SSc according to the 2013 American College of Rheumatology (ACR)/European League Against Rheumatism (EULAR) diagnostic criteria for systemic sclerosis (SSc);
4. Patients diagnosed with diffuse scleroderma after previous treatment with two or more modalities such as hormones, immunosuppressants, and biologics.
Exclusion Criteria:
1. Percentage of patient's predicted lung function FVC (forceful lung volume) \<50% at screening;
2. A previous diagnosis of moderate-to-severe pulmonary hypertension or systolic pulmonary artery pressure \>45 mmHg measured by echocardiography at screening;
3. The following conditions existed before the screening: (1) myocardial infarction, stroke, renal crisis, severe intestinal disease, severe hypertension (≥160/100mmHg) uncontrolled patients with the onset or exacerbation of clinical symptoms within 6 months; (2) unstable ischemic heart disease, uncontrolled arrhythmia, cardiac arrhythmia, cardiac tachyarrhythmia, and cardiac tachycardia (≥160/100mmHg) uncontrolled patients with the onset or aggravation of clinical symptoms within 3 months. controlled arrhythmia, heart failure, New York Heart Association stage III/IV or echocardiography suggesting left ventricular ejection fraction \<50%, renal insufficiency, renal hypertension, etc;
4. Patients with pre-screening comorbid autoimmune connective tissue diseases other than systemic sclerosis, but with secondary dry syndrome were allowed to participate in this trial;
5. Presence of any of the following laboratory findings at the time of screening:
① the presence of abnormal blood routine: hemoglobin \<100g / L; white blood cell count \<3.0 × 10\^9 / L; absolute neutrophil count \<1.5 × 10\^9 / L; platelet count \<100 × 10\^9 / L;
② abnormal liver function: ALT or AST \>3 times the upper limit of normal (ULN); total bilirubin \>3 times the ULN; (iii) Abnormal renal function: estimated glomerular filtration rate (eGFR) \<60mL/min/1.73m\^2 or any uncontrolled clinically significant laboratory test abnormality judged by the investigator to be likely to affect the interpretation of the study data or the subject's participation in the study;
6. Patients with a positive human immunodeficiency virus antibody (anti-HIV-Ab) test, active syphilis, active hepatitis C (hepatitis C antibody positive and HCV-RNA positive), HBsAg positive and HBV-DNA positive during the Screening Period may not be enrolled in the study; and patients with a history of severely active or recurrent bacterial, viral, fungal, parasitic or other infections during the Screening Period ;
7. Live/attenuated vaccination within 2 months prior to enrollment;
8. Any of the following within 3 months prior to enrollment: (i) major trauma or major surgery (including joint surgery), or major surgery required during the study period, which, in the opinion of the investigator, poses an unacceptable risk to the subject; (ii) treatments such as plasma exchange or extracorporeal light replacement; (iii) subjects participating in any other clinical trial;
9. History of any malignancy within 5 years prior to enrollment, except adequately treated or excised basal cell carcinoma of the skin or squamous cell carcinoma of the skin or cervical cancer in situ;
10. Intolerance or contraindication to study treatment, including any of the following:
(i) Hypersensitivity or allergy to any of the components in the excipients of the product; (ii) No peripheral venous access;
11. Have plans to have children for at least 2 years after injection administration, or are unwilling to use effective contraception with their partner, or have plans for sperm or egg donation;
12. Those who are not suitable for PET/CT, such as those who suffer from claustrophobia;
13. Persons who, in the judgment of the investigator, are not suitable for participation in the study.
