Inclusion Criteria:

* Age ≥18 and ≤75
* A clinical diagnosis of IIM, based on the 2017 The European League Against Rheumatism/American College of Rheumatology classification criteria
* Diagnosis of DM, ASyS, IMNM based on the presence of serum myositis-specific antibodies
* Evidence of active disease, despite prior or current treatment with standard of care treatments, as defined by the presence of elevated creatine kinase (CK), DM rash, or active disease on muscle biopsy, magnetic resonance imaging (MRI), or electromyography
* Presence of muscle weakness

Exclusion Criteria:

* Contraindication to leukapheresis
* History of anaphylactic or severe systemic reaction to fludarabine, cyclophosphamide or any of their metabolites
* Active infection requiring medical intervention at screening
* Current symptoms of severe, progressive, or uncontrolled renal, hepatic, hematological, gastrointestinal, pulmonary, psychiatric, cardiac, neurological, or cerebral disease, including severe and uncontrolled infections, such as sepsis and opportunistic infections.
* Concomitant medical conditions that, in the opinion of the investigator, might place the subject at unacceptable risk for participation in this study, interfere with the assessment of the effects or safety of the investigational product or with the study procedures
* Significant lung or cardiac impairment
* Previous CAR T cell therapy
* Prior solid organ (heart, liver, kidney, lung) transplant or hematopoietic cell transplant

Note: Other protocol defined Inclusion/Exclusion Criteria may apply.

Eligibility last updated 10/07/2024. Questions regarding updates should be directed to the study team contact.