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

This study is designed to evaluate the safety, tolerability, and antitumor activity of
SEA-BCMA in adults with relapsed or refractory multiple myeloma (RRMM). The study will be
conducted in 2 parts:

Part 1 - Dose-escalation: Approximately 25 patients will be treated to evaluate the safety
and tolerability of SEA-BCMA, and to identify the maximum tolerated dose (MTD) or optimal
dose.

Part 2 - Dose expansion: approximately 40 patients will be treated at the MTD or optimal dose
to further characterize the safety and antitumor activity of SEA-BCMA.

In both parts, SEA-BCMA will be administered at the assigned dose every 2 weeks (or every 4
weeks if recommended by the Safety Monitoring Committee) by intravenous (IV) infusion.
Patients may continue on treatment until disease progression or unacceptable toxicity.

Inclusion Criteria:

- Histologically confirmed diagnosis of multiple myeloma (MM)

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

- Must have MM that is relapsed or refractory and must not have other therapeutic
options available known to provide clinical benefit in MM

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

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

- Patients of childbearing potential or who can father children must agree to
consistently use 2 effective forms of birth control for at least 6 months after the
final dose of study drug administration

- Adequate hematologic, renal, and hepatic function

- 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 10 mg/dL or higher and abnormal serum immunoglobulin
kappa lambda free light chain ratio.

Exclusion Criteria:

- Prior treatment with a BCMA targeted therapeutic

- Patients who are pregnant or breastfeeding

- 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.