Patient description: A 17 year old boy complains of vomiting, non-bloody diarrhea, abdominal pain, fever, chills and loss of appetite for the past 3 days. He ate a salad at a restaurant prior to his diarrhea onset. Physical exam was remarkable for pallor, jaundice, and diffuse abdominal tenderness. Lab results were as follows: Hemoglobin: 9.7 g/dL Platelet: 110,000 /cu.mm Creatinine: 3.6 mg/dL blood urea nitrogen (BUN): 73 mg/dL direct bilirubin: 2.4 mg/dL lactate dehydrogenase (LDH): 881 IU/L (normal: 110-265 IU/L) Peripheral blood smear showed a moderate number of schistocytes and helmet cells. Shiga-like toxin-producing E. coli (STEC) stx1/stx2 were found in stools. He has no other underlying disease and he is not on any medications.

Clinical trial eligibility criteria: eligible ages (years): 18.0-73.0,  Myeloma-Multiple Myeloma, Plasma-Cell Multiple Myeloma BCMA expression must be detected on malignant plasma cells from either bone marrow or a plasmacytoma by flow cytometry or immunohistochemistry. If patient has plasmacytomas, one plasmacytoma must be biopsied to demonstrate BCMA expression. A specific quantitative level of BCMA expression for is not specified, but patients with multiple myeloma cells that are negative for BCMA by flow cytometry and immunohistochemistry on either bone marrow biopsy or plasmacytoma biopsy will not be enrolled. These assays must be performed at the National Institutes of Health (NIH). It is not required that the specimen used for BCMA determination comes from a sample that was obtained after the patient s most recent treatment. If paraffin embedded unstained samples of bone marrow involved with MM or a plasmacytoma are available, these can be shipped to the NIH for BCMA staining, otherwise new biopsies will need to be performed for determination of BCMA expression BCMA expression will need to be documented on the majority of malignant plasma cells by flow cytometry at the NIH at some time after the original anti-BCMA CAR T-cell infusion in all patients undergoing a second anti-BCMA CAR T-cell infusion Bone marrow plasma cells must make up less than 50% of total bone marrow cells based on a bone marrow biopsy performed within 24 days of the start of protocol treatment Patients must have received at least 3 different prior treatment regimens for multiple myeloma Must have prior exposure to an "IMiD" such as lenolidamide and a proteasome inhibitor Patients must have measurable MM as defined by at least one of the below One or more of these abnormalities defines measurable multiple myeloma Serum M-protein greater or equal to 1.0 g/dL Urine M-protein greater or equal to 200 mg/24 h  Patients on any anticoagulants except aspirin Patients that require urgent therapy due to tumor mass effects or spinal cord compression Patients that have active hemolytic anemia Patients with second malignancies in addition to multiple myeloma are not eligible if the second malignancy has required treatment within the past 3 years or is not in complete remission. There are two exceptions to this criterion: successfully treated non-metastatic basal cell or squamous cell skin carcinoma Women of child-bearing potential who are pregnant or breastfeeding because of the potentially dangerous effects of the preparative chemotherapy on the fetus or infant. Women of child bearing potential cannot have a positive pregnancy test. Women of child-bearing potential are defined as all women except women who are post menopausal or who have had a hysterectomy. Postmenopausal will be defined as women over the age of 55 who have not had a menstrual period in at least 1 year Active systemic infections (defined as infections causing fevers or requiring anti- microbial treatment), active coagulation disorders or other major uncontrolled medical illnesses of the cardiovascular, respiratory, endocrine, renal, gastrointestinal, genitourinary, neurologic, or immune system, history of myocardial infarction, active cardiac arrhythmias including active atrial fibrillation history of any arrhythmias other than sinus tachycardia, or atrial fibrillation, currently taking any anti-arrythmic or congestive heart failure medications, active obstructive or restrictive pulmonary disease Any form of primary immunodeficiency (such as Severe Combined Immunodeficiency Disease) Systemic corticosteroid steroid therapy of greater than 5 mg/day of prednisone or equivalent dose of another corticosteroid (prednisone, dexamethasone, etc) is not allowed within 2 weeks prior to either the required leukapheresis or within 2 weeks prior to CAR T-cell infusion (and at any time after the CAR T cell infusion) History of severe immediate hypersensitivity reaction to any of the agents used in this study