A Safety Study of SEA-BCMA in Patients With Multiple Myeloma

Inclusion Criteria:

1. Histologically confirmed diagnosis of MM
2. Must have MM that is relapsed or refractory
3. Has received a proteasome inhibitor, an immunomodulatory drug, and an anti-CD38 antibody
4. 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.
5. Eastern Cooperative Oncology Group (ECOG) status score of 0 or 1
6. Life expectancy of greater than 3 months in the opinion of the investigator
7. Adequate hematologic, renal, and hepatic function

Exclusion Criteria:

1. Parts A and D: Prior treatment with a BCMA-directed therapy
2. History of another malignancy within 3 years
3. Active cerebral or meningeal disease related to the underlying malignancy
4. Uncontrolled Grade 3 or higher infection
5. 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