Inclusion Criteria:

          -  Histologically confirmed diagnosis of MM

          -  Must have MM that is relapsed or refractory

          -  Has received a proteasome inhibitor, an immunomodulatory drug, and an anti-CD38
             antibody

          -  Measurable disease, as defined by at least one of the following: (1) serum M protein
             0.5 g/dL or higher, (2) urine M protein 200 mg/24 hour or higher, and (3) serum
             immunoglobulin free light chain (FLC) 10 mg/dL or higher and abnormal serum
             immunoglobulin kappa lambda FLC ratio.

          -  Eastern Cooperative Oncology Group (ECOG) status score of 0 or 1

          -  Life expectancy of greater than 3 months in the opinion of the investigator

          -  Adequate hematologic, renal, and hepatic function

        Exclusion Criteria:

          -  Prior treatment with a BCMA-directed therapy

          -  History of another malignancy within 3 years

          -  Active cerebral or meningeal disease related to the underlying malignancy

          -  Uncontrolled Grade 3 or higher infection

          -  Prior antitumor therapy that is not completed at least 4 weeks prior to first dose of
             study drug, or at least 2 weeks if progressing. Prior CAR-T-cell therapy must be
             completed 8 weeks before first dose of study drug.

          -  Combination therapy only:

               1. Known intolerance to corticosteroids

               2. Uncontrolled psychoses