Study of KYV-101 Anti-CD19 CAR T Therapy in Adult Dermatomyositis

Inclusion Criteria: 1. Diagnosis of probable or definite (\>55%) IIM and subgroup classification as dermatomyositis according to the 2017 EULAR/ACR classification criteria for idiopathic inflammatory myopathies. 2. Age \> 25 years and \< 72 years at time of signing informed consent Refractory disease: subject with previous failure (or intolerance) to glucocorticoids and at least two non-glucocorticoid immunosuppressive therapies (including mycophenolate mofetil or mycophenolic acid, cyclophosphamide, azathioprine, methotrexate, calcineurin inhibitors, tofacitinib or other JAK inhibitors, rituximab, or IVIG) administered for at least 12 weeks within 24 months prior to screening. .Moderate-to-severe dermatomyositis as per EITHER: muscle weakness, defined as Manual Muscle Testing (MMT-8) score \<142/150; or cutaneous disease as per Cutaneous Dermatomyositis Assessment and Severity Index-activity subscore (CDASI-a)\>=19. PLUS at least 2 other abnormal IMACS Core Set Measures (CSMs) from the following: * Patient global VAS≥2 cm. * Physician's global VAS ≥2 cm. * Global extramuscular activity score ≥2 cm. * Elevation of at least one of the muscle enzymes (CK, AST, ALT, aldolase, LDH) \>1.5 times upper limit of normal. * HAQ-DI≥0.25. 2.For patients enrolling on the MMT-8 criterion, muscle disease must be active, as deemed by one of the following: * Creatine kinase, aldolase, LDH, AST, or ALT (if deemed due to muscle inflammation by investigator) ≥2×ULN. * MRI evidence of active myositis within last 3 months. * EMG evidence of active myositis within last 3 months. Other inclusion criteria: Subject must sign a written ICF prior to any screening procedures. 1. Subject must be ≥25 and ≦72 years of age. 2. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 3. Adequate organ function as per table below. Haematology Haemoglobin: ≥10.0 g/dl (without prior red blood cell transfusion within 7 days before the laboratory test)a Platelets: ≥100,000/ μL (without transfusion support within 7 days before the laboratory test). Absolute Lymphocyte Count (ALC):≥700/μL Absolute Neutrophil Count (ANC) 1,500/μL (prior growth factor support is permitted but must be without support in the 7 days prior to the laboratory test) Hepatic AST and ALT: ≤2.5×upper limit of normal (ULN) unless deemed by the investigator to be secondary to DM. Total bilirubin ≤1.5×ULN; except in subjects with congenital bilirubinaemia, such as Gilbert syndrome (in which case direct bilirubin ≤1.5×ULN is required) Renal Creatinine clearance Calculated creatinine clearance ≥45 mL/min/1.73 m2 (measured by Cockcroft-Gault equation) Pulmonary Grade≤1 dyspnoea Oxygen saturation measured by pulse oximetry ≥92% on room air a .For subjects who meet the inclusion criteria at screening, transfusion of red blood cells is permitted after screening as needed to maintain a haemoglobin level ≥8.0 g/dL. 4. Must be up to date on all recommended vaccinations, including against COVID-19/ SARS CoV-2, per Centers for Disease Control and Prevention or institutional guidelines for immune-compromised individuals. 5. Women of childbearing potential must have a negative pregnancy test at screening using a highly sensitive serum pregnancy test (β-human chorionic gonadotropin \[β-hCG\]). Women of childbearing potential are defined as a sexually mature woman who has not undergone a hysterectomy or tubal ligation or who has not been naturally postmenopausal for at least 24 consecutive months. 6. Female subjects of childbearing potential who have a fertile male sexual partner must agree to use a highly effective method of contraception (failure rate of \<1% per year when used consistently and correctly) from the time of signing the ICF until 1 year after the KYV-101 infusion. Examples of highly effective method of contraception include: * Established use of hormonal methods of contraception associated with inhibition of ovulation (eg, oral, inserted, injected, implanted, transdermal), provided the subject or male subject's female partner plans to remain on the same treatment throughout the entire study and has been using that hormonal contraceptive for an adequate period of time to ensure effectiveness. * Correctly placed copper containing- intrauterine device or intrauterine hormone-replacing system. * Male sterilization with absence of sperm in the post-vasectomy ejaculate. * Female sterilization (bilateral tubal ligation/bilateral salpingectomy or bilateral tubal occlusive procedure (provided that occlusion has been confirmed). * Sexual abstinence, defined as completely and persistently refraining from all heterosexual intercourse (including during the entire period of risk associated with the study treatments) may obviate the need for contraception ONLY if this is the preferred and usual lifestyle of the subject. 7. Male subjects, if not surgically sterilized, must agree to use highly effective method of contraception and not donate sperm from the time of signing the ICF until 1 year after the KYV-101 infusion. 8. For females: a negative pregnancy test at screening and prior to lymphodepletion chemotherapy. 9. Women and men must agree not to donate eggs (ova, oocytes) or sperm, respectively, until at least 1 year after receiving a KYV-101 infusion. EXCLUSION CRITERIA: DM-related exclusion criteria 1. Evidence of any of the following: * Severe muscle damage as per one of the following criteria: 1. Myositis Global Damage Index (MDI) ≥5. 2. Severe proximal muscle atrophy of upper or lower extremity on MRI. 3. Severe proximal muscle atrophy of upper or lower extremity on clinical examination. 4. Wheelchair-bound at home. 5. MMT-8 of ≤80. * MDA5-positive rapidly progressing interstitial lung disease (subjects with stable ILD not requiring supplemental oxygen are eligible). * Findings of muscular inflammation or myopathy other than the indication, such as polymyositis (PM), immune mediat