Abbreviated inclusion criteria:  Diagnosis of r/r MM with measurable disease by at least one of the following:  Serum M-protein ≥1.0 g/dL Urine M-protein ≥200 mg/24 hours Involved serum free light chain level ≥10 mg/dL, with an abnormal kappa-lambda ratio if the serum M-protein <1.0 g/dL and/or urine M-protein <200 mg/24 hours Regimens A and A1: MM relapsed or progressed after ≥3 prior approved therapies, including an IMiD, proteosome inhibitor, and anti-CD38 mAb Regimens B and B1: MM relapsed or progressed after ≥2 prior approved therapies, including an IMiD and PI  Note: for all Regimens, prior BCMA CAR T-cell therapy and BCMA-targeted therapy (e.g., bi-specific engagers or antibody-drug conjugates) is allowed  * Abbreviated exclusion criteria:  Eastern Cooperative Oncology Group Performance Status (ECOG PS) ≥2  Evidence of insufficient hematologic function:  ANC <1000/µL without growth factor support ≤7 days prior to measurement Platelet count <75,000/µL without platelet transfusion ≤72 hours prior to measurement  Evidence of insufficient organ function  CrCL <50 ml/min by Cockcroft-Gault or other institutional method T bilirubin >1.5x ULN, except for Gilbert's syndrome AST >3x ULN or ALT >3x ULN, unless directly due to underlying malignancy O2 sat <92% on room air  Clinically significant cardiovascular disease:  Myocardial infarction within 6 months of first treatment Unstable angina or CHF of NYHA Grade 2 or higher Cardiac EF <40%  Subjects with prior central nervous system (CNS) involvement of MM must have completed effective treatment of their CNS disease at least 3 months prior to Day 1 with no evidence of disease clinically and at least stable findings on relevant CNS imaging  Non-malignant CNS disease such as stroke, epilepsy, CNS vasculitis, or neurodegenerative disease or receipt of medications for these conditions in the 2-year period leading up to study enrollment  Currently receiving or likely to require systemic immunosuppressive therapy (e.g., prednisone >5 mg daily) for any reason during the treatment period, with the exception of corticosteroids.  Clinically significant infections, including:  HIV positive by serology HBV positive by serology or PCR HCV positive by serology or PCR  Live vaccine <6 weeks prior to start of conditioning  Receipt of an allograft organ transplant  Prior allogeneic HSCT or allogeneic CAR T/CAR NK within 6 months of Day 1, or ongoing requirement for systemic graft-versus-host therapy  Plasma cell leukemia defined as a plasma cell count >2000/mm^3  Washout periods from prior therapies:  For all subjects (Regimens A, A1, B and B1), receipt of the following: Chemotherapy, or radiation therapy, except for palliative purposes, within 14 days prior to Day 1 or five half-lives, whichever is shorter; Investigational therapy within 30 days prior to the first dose of study treatment or five half-lives, whichever is shorter; Biologic therapy (except for anti-CD38 mAbs), including antibody-drug conjugates or bi-specific immune-cell engaging antibody within 30 days prior to Day 1 For subjects in Regimens B and B1 only, receipt of the following: Anti-CD38 therapy alone or in combination within 3 months prior to the start of daratumumab