Inclusion Criteria: - Systemic lupus erythematosus (SLE) population:. i) Diagnosis of SLE based on the 2019 American College of Rheumatology (ACR)/European League Against Rheumatism (EULAR). ii) Participant must be positive for at least one of the following antibodies at screening: anti-nuclear antibody, anti-dsDNA, anti-histone, anti-chromatin or anti-Sm antibody. iii) Inadequate response or intolerance to steroids and immunosuppressive therapies. iv) Participants must have active disease at screening. - Inflammatory myopathy (IIM) population:. i) Participants meeting the 2017 American College of Rheumatology (ACR) / European League Against Rheumatism (EULAR) classification criteria. ii) Participants must meet criteria for with severe, refractory IIM. iii) Participants who had inadequate response to steroids and prior immunosuppressive therapies. iv) Evidence of active disease. - Systemic sclerosis (SSc) population:. i) Participant must fulfill the 2013 American College of Rheumatology (ACR)/ European League Against Rheumatism (EULAR) classification criteria for systemic sclerosis. ii) Inadequate disease response or intolerance to prior therapies. iii) Participants diagnosed with progressive systemic sclerosis including skin disease and/or interstitial lung disease. - Rheumatoid arthritis (RA) population:. i) Participants with difficult to treat RA. ii) Participants with a diagnosis of RA meeting 2010 ACR/EULAR criteria. iii) Rheumatoid arthritis disease activity at screening and baseline visit. iv) Inadequate disease response or intolerance to standard of care therapy. Exclusion Criteria: - All participants:. i) Any other systemic autoimmune disease. ii) Pregnant or nursing women. iii) Active hepatitis B, C or HIV. iv) Prior history of malignancies. v) Uncontrolled or active infection. vi) History of certain cardiovascular conditions within 6 months prior to screening. vii) Previous CAR-T cell therapy. viii) Significant lung impairment. ix) Inadequate organ function. x) Active, clinically significant, central nervous system (CNS) disorders. - SLE population:. i) Participants who have SLE because of drugs or have other autoimmune diseases along with SLE. - IIM population:. i) Participants who have other forms of myopathies other than IIM. ii) Severe muscle damage. - SSc population:. i) People who have high blood pressure in the arteries of the lungs caused by SSc, which needs regular treatment to keep it under control. ii) Rapidly deteriorating SSc, or history of severe kidney disease. - RA population:. i) People who have additional autoimmune diseases along with RA. - Other protocol-defined inclusion/exclusion criteria apply.