Summary

This is a global, open-label, multi-arm, multi-cohort, multi-center, phase 1/2 study to
determine the safety, tolerability, efficacy, PK of bb2121 in combination with other
therapies in adult subjects with R/RMM.

The following combinations will be

- Arm A will test bb2121 in combination with CC-220 (± low-dose dexamethasone)

- Arm B will test bb2121 in combination with BMS-986405 (JSMD194)

Combination agents being tested may be administered before, concurrently with and/or
following (ie, maintenance) bb2121 infusion.

The study will consist of 2 parts: dose finding (Phase 1) and dose expansion (Phase 2).
Dose expansion may occur in one or more arms.

Eligibility

1. Inclusion Criteria: Participants must satisfy the following criteria to be enrolled in the study: - Participant has documented diagnosis of MM and measurable disease, defined as: 1. M-protein (serum protein electrophoresis [sPEP = 0.5 g/dL] or urine protein electrophoresis [uPEP]): uPEP = 200 mg/24 hours and/or 2. Light chain MM without measurable disease in the serum or urine: Serum immunoglobulin free light chain = 10 mg/dL (100 mg/L) and abnormal serum immunoglobulin kappa lambda free light chain ratio - Participant has received: 1. at least 3 prior MM regimens for Arm A Cohort 1 and Arm B 2. at least 1 but no greater than 3 prior MM regimens for Arm A Cohort 2 - Arm A Cohort 1 and Arm B: Participant has received prior treatment with an immunomodulatory agent, a proteasome inhibitor and an anti-CD38 antibody-containing regimen for at least 2 consecutive cycles. - Arm A Cohort 2: Participant has received prior treatment with an immunomodulatory agent for at least 2 consecutive cycles. - Evidence of PD during or within 6 months (measured from the last dose of any drug within the regimen) of completing treatment with the last antimyeloma regimen before study entry. - Participant achieved a response (minimal response [MR] or better) to at least 1 prior treatment regimen. - Participant has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. Exclusion Criteria: The presence of any of the following will exclude a participant from enrollment: - Participant has non-secretory MM or has history of or active plasma cell leukemia, Waldenstrom's macroglobulinemia, POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, monoclonal protein, and skin changes) or amyloidosis. - Participant has any of the following laboratory abnormalities: 1. ANC and Platelets count as reported below 2. Hemoglobin < 8 g/dL (< 4.9 mmol/L) (transfusion is not permitted within 21 days of screening) 3. Creatinine clearance (CrCl) as reported below 4. Corrected serum calcium > 13.5 mg/dL (> 3.4 mmol/L) 5. Serum aspartate aminotransferase (AST) or alanine aminotransferase (ALT) > 2.5 ×upper limit of normal (ULN) 6. Serum total bilirubin > 1.5 × ULN or > 3.0 mg/dL for participants with documented Gilbert's syndrome 7. International normalized ratio (INR) or activated partial thromboplastin time (aPTT) 1.5 × ULN, or history of Grade = 2 hemorrhage within 30 days, or participant requires ongoing treatment with chronic, therapeutic dosing of anticoagulants (eg, warfarin, low molecular weight heparin, Factor Xa inhibitors) - Participant has inadequate pulmonary function defined as oxygen saturation (SaO2) < 92% on room air. - Participant has known chronic obstructive pulmonary disease (COPD) with a forced expiratory volume in 1 second (FEV1) 50% of predicted normal. - Prior exposure to CC-220 (± low-dose dexamethasone) as part of their most recent antimyeloma treatment regimen (Arm A). - Prior exposure to BMS-986405 (JSMD194) (Arm B). - Previous history of an allogeneic hematopoietic stem cell transplantation, treatment with any gene therapy-based therapeutic for cancer, investigational cellular therapy for cancer or BCMA targeted therapy. - Treatment Arm A Cohort 1 and Arm B: participant has received autologous stem cell transplantation (ASCT) within 12 weeks prior to leukapheresis. - Treatment Arm A Cohort 2: participant has received autologous stem cell transplantation (ASCT) within 12 months prior to leukapheresis.