Inclusion Criteria:

          -  Refractory/relapsed CD20+ B-NHL (including malignant transformation like Richter's
             transformation) with no curative treatment option.

          -  At least 18 years of age

          -  Estimated life expectancy of more than 3 months

          -  ECOG performance status (Eastern cooperative oncology group) of 0-2

          -  Negative serological HBV (Hepatitis B virus) test, negative testing of HCVAb
             (Hepatitis C virus Antibody), negative HIV1/2 (Human immunodeficiency virus 1/2 ) test
             within 6 weeks prior to enrollment

          -  No childbearing potential or negative pregnancy test at screening and before
             chemotherapy in women with childbearing potential.

          -  Signed and dated informed consent before conduct of any trial-specific procedure

        Exclusion Criteria:

          -  Participation in another interventional trial that could interact with this trial

          -  Any evidence 0f CNS (Central nervous system) involvement

          -  Known history or presence of clinically relevant CNS pathology

          -  Patients with history of primary immunodeficiency,

          -  Patients with any history of auto-immune induced condition such as those caused by
             checkpoint inhibitors, MEK inhibitors or BRAF inhibitors, for example pituitary
             hypophysitis must be excluded

          -  Patients with Chronic Lymphocytic Leukemia unless suffering from malignant
             transformation

          -  Active systemic fungal, viral or bacterial infection

          -  Serious cardiac functional incapacity (class III or IV as defined by the New York
             Heart Association Classification)

          -  Severe pulmonary disease (DLCO (Transfer factor of the lung for carbon monoxide)
             and/or FEV1 (Forced expiratory volume in 1 second) < 65%, dyspnea at rest)

          -  Liver dysfunction as indicated by a total bilirubin, AST (Aspartate Aminotransferase),
             and ALT (Alanine aminotransferase) ≥ 2 the institutional ULN (Upper limit of normal)
             value, unless directly attributable to the patient's tumor

          -  Creatinine clearance <50 ml/min calculated according to the modified formula of
             Cockcroft and Gault

          -  Pregnant or lactating women

          -  Active secondary malignancy requiring treatment (except basal cell carcinoma or
             malignant tumor curatively treated by surgery) within the last 5 years before
             enrollment.

          -  Medical condition requiring prolonged use of systemic corticosteroids (> 1 month)

          -  Prior therapy with genetically modified substances

          -  Use of anti-CD20 antibodies within 4 weeks before leukapheresis

          -  Chemotherapy within 4 weeks prior to leukapheresis

          -  Other treatment within 4 weeks or two half-lives, whichever is longer before
             MB-CART20.1 infusion. This pertains to immunomodulatory therapies such as checkpoint
             inhibitors because of the influence on the immune system

          -  Concurrent systemic radiotherapy

          -  Hypersensitivity against any drug or its ingredients/impurities that is scheduled or
             likely to be given during trial participation e.g. as part of the mandatory
             lymphodepletion protocol, pre-medication for infusion, rescue medication/salvage
             therapies for treatment of related toxicities

          -  Patients in which such medication is contraindicated for other reasons than
             hypersensitivity (e.g. live vaccines and fludarabine)

          -  Patients in which trial related procedures are contraindicated as judged by the
             investigator, e.g. lumbar punctures for CSF (Cerebrospinal fluid) sampling

          -  Patient's lack of accountability, inability to appreciate the nature, meaning and
             consequence of the trial and to formulate his/her own wishes correspondingly

          -  Patients who have a relationship of dependence or employer employee relationship to
             the sponsor or the investigator

          -  Committal to an institution on judicial or official order

          -  Cerebral dysfunction, legal incapacity

          -  Other investigational treatment within 4 weeks before IMP (Investigational Medicinal
             Product) infusion

          -  Clinically relevant autoimmune diseases or history of autoimmune disease