Inclusion Criteria - Diagnosis of Systemic Lupus Erythematosus (SLE) defined as follows:. i) Fulfilling the 2019 ACR/EULAR classification criteria of SLE. ii) Presence of anti-dsDNA, anti-histone, anti-chromatin, or anti-Sm antibodies. - SLE disease activity. i) Active disease at screening, defined as ≥ 1 major organ system with a BILAG A score (excluding musculoskeletal, mucocutaneous, and/or constitutional organ system). ii) Inadequate response to glucocorticoids and to at least 2 of the following treatments, used for at least 3 months each: cyclophosphamide, mycophenolic acid or its derivatives, belimumab, azathioprine, anifrolumab, methotrexate, rituximab, obinutuzumab, cyclosporin, tacrolimus or voclosporin. A. Insufficient response is defined as lack of response, insufficient response or lack of sustained response to appropriate doses. Intolerance is not considered insufficient response. B. Methotrexate and azathioprine use will count as 1 for the purposes of the number of failed treatments. - Diagnosis of Idiopathic Inflammatory Myopathy (IIM) defined as follows:. i) Fulfilling the 2017 ACR/EULAR classification criteria for probable or definite IIM. ii) Participant diagnosed with the following IIM subgroups: DM, immune-mediated necrotizing myopathy (IMNM), and anti-synthetase syndrome (ASyS). iii) Presence of at least 1 myositis specific (MSA), associated antibody (MAA), or ANA at screening or prior to screening. - IIM disease activity. i) Severe muscle AND/OR skin involvement. ii) Proof of activity as documented by:. A. An active myositis-associated rash OR. B. A recent muscle biopsy OR. C. An elevated CK > 3 times the upper limit of normal. iii) Inadequate response to glucocorticoids and at least 2 of the following treatments used for at least 3 months: azathioprine, methotrexate, cyclosporin A, tacrolimus, MMF, cyclophosphamide, leflunomide, IVIG, and rituximab. - Diagnosis of Systemic Sclerosis (SSc) defined as follows:. i) Fulfilling 2013 ACR and European League Against Rheumatism classification criteria for SSc. ii) Antinuclear Antibody (ANA) positive at screening or prior to screening. - SSc disease activity. i) Participants diagnosed with diffuse or limited cutaneous SSc AND progressive ILD. ii) Inadequate response to at least 1 of the following treatments used for at least 3 months: mycophenolate, cyclophosphamide, rituximab, or tocilizumab. Exclusion Criteria - Diagnosis of drug-induced SLE rather than idiopathic SLE. - Other systemic autoimmune diseases (eg, multiple sclerosis, psoriasis, inflammatory bowel disease, etc) are excluded. Participants with type I autoimmune diabetes mellitus, thyroid autoimmune disease, Celiac disease, or secondary Sjögren's syndrome are not excluded. - SLE overlap syndromes including, but not limited to, rheumatoid arthritis, scleroderma, and mixed connective tissue disease, are excluded. - Recent or present clinically significant CNS pathology. - IIM disease activity. i) Other forms of IIM: Inclusion Body Myositis, Amyopathic DM, any form of juvenile myositis. ii) Myositis other than IIM, eg, drug-induced myositis and PM associated with HIV. iii) Participants with severe muscle damage (Physician VAS for muscle damage in Myositis Damage Index > 7 cm on a 10 cm scale), permanent weakness due to a non-IIM cause (eg, stroke), or myositis with cardiac involvement. - SSc disease activity. i) SSc related PAH requiring active treatment. ii) Rapidly progressive SSc related lower GI (small and large intestines) involvement (requiring parenteral nutrition); active gastric antral vascular ectasia. iii) Prior scleroderma renal crisis. - Other protocol-defined Inclusion/Exclusion criteria apply.