A Safety Study of SGN-CD48A in Patients With Multiple Myeloma

This study is designed to evaluate the safety, tolerability, and antitumor activity of
SGN-CD48A in patients with relapsed or refractory multiple myeloma. This study will be
conducted in 2 parts:

1. Dose escalation: This part will evaluate increasing doses of SGN-CD48A to identify the
maximum tolerated dose.

The first group of patients enrolled on the study will receive the lowest dose of
SGN-CD48A. Once this dose is shown to be safe, a second group of patients will be
enrolled at the next higher dose. Patients will continue to be enrolled in groups
receiving increasing doses until the maximum tolerated dose level is reached. Patients
can only be enrolled into a higher dose level once the lower doses have been
demonstrated safe. Dose escalation will be conducted using a modified toxicity
probability interval (mTPI) study design.

2. Dose expansion: This part will further evaluate the safety, tolerability, and antitumor
activity of up to 2 dose levels of SGN-CD48A shown to be safe in the first part of the
trial.

Inclusion Criteria:

- Diagnosis of MM requiring systemic therapy (per the International Myeloma Working
Group [IMWG])

- Patients must not have other therapeutic options known to provide clinical benefit in
MM available to them. Prior lines of therapy must include at least a proteasome
inhibitor, an immunomodulatory drug, and an anti-CD38 antibody.

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

- Adequate hematologic, renal, and hepatic function

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

- Life expectancy greater than 3 months

- A negative pregnancy test (for females of childbearing potential)

- Patients must provide written consent

Exclusion Criteria:

- Pre-existing peripheral neuropathy Grade 2 or higher

- History of malignancy other than MM within the past 3 years

- Active cerebral/meningeal disease related to the underlying malignancy

- Uncontrolled Grade 3 or higher infection

- Known to be positive for HIV or hepatitis B, or known to have active hepatitis C
infection

- Previous allogeneic stem cell transplant

- History of cerebral vascular event, unstable angina, myocardial infarction, or cardiac
symptoms consistent with congestive heart failure within the last 6 months

- Treatment with any known P-gp inducers/inhibitors or strong CYP3A inhibitors within 14
days prior to the first dose of study drug

- 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.

- Females who are pregnant or breastfeeding