MB-CART19.1 in Refractory SLE

Patients will be treated in cohorts of 3. After each cohort, the Safety Monitoring Board (SMB) will meet to assess whether the next higher dose level can be opened. The follow-up of the patients will be performed in 3 steps: * Until day 28 after treatment, the patients will be followed up closely by monitoring vital functions and lab parameters for signs of AEs and DLTs. Blood samples for the determination of persistence and phenotype of infused CAR+ cells will be taken. B cell aplasia in peripheral blood will be determined together with other secondary and exploratory biomarkers, response will be assessed and AEs will be documented. * In the second follow-up phase until 1 year, blood samples for the determination of persistence and phenotype of infused CAR+ cells will be taken, B cell aplasia will be determined, response will be assessed and AEs will be documented until end of week 12, afterwards serious AEs (SAE) and AEs of special interest (AESI) will be documented, serious adverse reactions (SAR)/AESI will be reported. * All patients irrespective of the clinical response will be followed up then for 1 more year or until the patient is lost to follow-up or has died. After completion of this last follow-up phase, patients will be rolled over to a subsequent follow-up observation for up to further 13 years.