• General:

‣ Subjects must understand and voluntarily sign an informed consent form including written consent for data protection,

⁃ Adults aged ≥ 18 years at time of consent,

⁃ Adequate renal (eGFR \> 30 ml/min/m2), liver (no Child Pugh C), heart (at worst NYHA III, EF \> 30%) and pulmonary (FV and DLCO \> 30%) function,

⁃ Male subjects unless surgically sterile, must agree to use two acceptable methods for contraception (e.g. spermicide and condom) during the trial and refrain from fathering a child starting from the time of signing the Informed Consent Form (ICF) until 12 months after dosing of the IMP,

⁃ Females of childbearing potential (FCBP) must have a negative urine pregnancy test at screening and must agree to use a highly effective contraceptive method (Pearl in-dex \<1) starting from the time of signing the ICF and for 12 months after dosing of the IMP,

⁃ Must be able to adhere to the study visit schedule and other protocol requirements,

⁃ Double vaccination against SARS-CoV-2 or SARS-CoV-2 within the last 6 months.

• SLE specific:

‣ Fulfilling the 2019 ACR/EULAR classification criteria of SLE,

⁃ Positivity of anti-dsDNA (\> 4 U/l), anti-histone (+ or more), anti-nucleosome (+ or more) or anti-Sm antibodies (+ or more),

⁃ Active disease at screening, defined as ≥ 1 organ system with a British Isles Lupus Assessment (BILAG) A score (severe disease activity) or ≥ 2 organ systems with a BILAG B score (moderate disease activity),

⁃ Insufficient response or intolerance/ contraindication to glucocorticoids and to at least 2 of the following treatments: hydroxychloroquine, mycophenolate mofetil, belimumab, methotrexate, rituximab, cyclophosphamide. Insufficient response is defined as having increased disease activity based on the definition explained in the previous bullet point.

• SSc specific:

‣ Fulfilling the 2013 ACR/EULAR classification criteria of SSc),

⁃ Positivity (+ or more) for at least one SSc-specific parameter (Scl70, RNA polymerase, Th/To, RP11/12, U3RNP autoantibodies),

⁃ Signs for fast progression including (i) disease duration ≤ 5 years (from onset of first non-Raynaud manifestation), (ii) mRSS score 10-35 at screening, (iii) elevated acute phase reactant levels (CRP ≥ 6 mg/L, ESR ≥ 28mm/h or platelet count ≥ 330 G/L), (iii) mRSS increase ≥ 3 units or involvement of one new body area or mRSS increase ≥ 2 units in one body area or ≥ 1 tendon friction rub over 6 months,

⁃ Insufficient response or intolerance/ contraindication to at least 2 of the following treatments: mycophenolate mofetil, azathioprine, nintedanib, methotrexate, rituximab. Insufficient response is defined as having increased disease activity based on the definition explained in the previous bullet point.

• DM/PM specific:

‣ Fulfilling the 2017 ACR/EULAR classification criteria for probable or definite DM or PM,

⁃ Presence of active myositis in muscle biopsy or muscle MRI and/or signs of interstitial lung disease related to DM/PM,

⁃ Positivity (+ or more) for at least one myositis-specific antibody (aminoacyl tRNA synthetases, Mi2, MDA5, SAE, SRP, ARS, HMGCR, MJ, TIF1gamma),

⁃ Muscle weakness as define by MMT \< 142 and 2 of the following criteria: VAS patients Global ≥2cm, VAS physician Global ≥ 2cm, HAQ \> 0.25, at least one muscle enzyme \> 1.3 times upper limit of normal, VAS global extra muscular activity ≥ 2cm,

⁃ Insufficient response or intolerance/ contraindication to glucocorticoids and to at least 2 of the following treatments: mycophenolate mofetil, ciclosporin A, tacrolimus, methotrexate, rituximab, intravenous immunoglobulins. Insufficient response is defined as having increased disease activity based on the definition explained in the previous bullet point.