• Age ≥18 years;

• Meet several CTD diagnostic criteria (RA, IIM, SSc) and UCTD/IPAF classification criteria;

• HRCT diagnosis confirmed interstitial lung disease (ILD) with corresponding clinical manifestations;

• Patients who were able to complete vital capacity (FVC) or carbon monoxide dispersion (DLco) tests (with Hb correction).

• Patients with clinical deterioration more than 1 month after diagnosis of ILD history, or poor response or intolerance to Glucocorticoids or immunosuppressants treatment, or poor response or intolerance to other antifibrotic drugs (acetyl hemitrine, nidanib, etc.), or effective use of PFD, and exacerbation of clinical symptoms or ILD indicators more than 3 months after withdrawal of the drug.

• Poor response was defined as no improvement in one of the following:

⁃ (1) Symptoms of dyspnea such as cough, chest tightness, breathlessness, shortness of breath after activity, or decreased activity endurance;

⁃ (2) the worst decrease in oxygen saturation as measured by pulse oxygen saturation (SpO2) observed during 6MWD;

⁃ (3) There was no improvement in pulmonary ventilation (FVC%) or lung dispersion (DLco%);

⁃ (4) HRCT findings: new onset, fibrosis tendency or density of ILD lesions were not decreased;

⁃ Clinical deterioration was defined as meeting one of three criteria:

• Clinical deterioration or dyspnea within 4 weeks;

• New or worsening radiological abnormalities on chest X-ray or high-resolution CT;

• Objective deterioration of pulmonary function tests or gas exchange, defined as meeting at least one of the following criteria:

⁃ 1\) Start long-term oxygen therapy or increase oxygen supplementation by at least 1 L/min to maintain resting oxygen saturation of at least 90%;

⁃ 2\) FVC decreased by more than 5% compared with the previously measured value; Or a decrease in DLCO of more than 10% from previous measurements; Or a 20% decrease in 6MWD from previous measurements.

⁃ 7\. If concomitant therapy with immunosuppressants was used, the dose was stable for at least 4 weeks before the baseline period. The types of immunomodulator hydroxychloroquine (HCQ) or immunosuppressive agents are MMF, TAC, JAKi, CTX, LEF, AzA, iguratimod etc.

⁃ 8\. Concomitant glucocorticoids: IIM patients with glucocorticoids dose (calculated as the equivalent dose of prednisone) ≤60mg/d and relatively stable disease; For other CTD patients, the glucocorticoids dose (calculated as prednisone equivalent dose) was ≤40mg/ day for at least 1 month.