LYell SYndrome MEsenchymal Stromal Cells Treatment

Inclusion Criteria: * Patients ≥ 18 and ≤ 75 years-old * Admission ≤ 10 days after the index date (date of the first symptoms of the disease) * Patient with confirmed SJS-TEN diagnosis hospitalized in the department of Dermatology or intensive care medicine * At least 10 % of detachable-detached body surface area at any time during the first 10 days after the index date (date of the first symptoms of the disease) * Who, after the nature of the study has been explained to them or a support person (if applicable), and prior to any protocol specific procedures being performed, have given written consent according to local regulatory requirements * Affiliated to a social security scheme Exclusion Criteria: * Pregnant or breastfeeding women * History of malignant disease within the past ten years and or presence of metastasis * Positive serology for HIV * Active infection for hepatitis B or C * Detection of Coronavirus SARS CoV-2 RNA on admission (positive RT-PCR), if performed in the usual care * Decompensated cardiac failure * Uncontrolled epilepsia * Previous history of allogenic bone marrow transplantation * Participation in other interventional drug research Patient deprived of liberty by a judicial or administrative decision or under the protection of justice * Any psychological, familial, sociological or geographical condition potentially hampering compliance with the research protocol and follow-up schedule * Patient under tutorship or curatorship * Patient under psychiatric care according to art. L1121-6 CSP