A Safety Study of SGN-CD123A in Patients With Acute Myeloid Leukemia

This study is designed to evaluate the safety, tolerability, and preliminary estimate of
antitumor activity of SGN-CD123A. The study will be conducted in 2 parts:

1. Part A is the dose-escalation portion of the trial, designed to identify the maximum
tolerated dose (MTD) of SGN-CD123A

2. Part B is the dose-expansion portion of the trial, designed to evaluate SGN-CD123A in
patients with differing CD123 expression levels

Dose-escalation in Part A will be conducted using a 3+3 study design. Patients with
CD123-detectable AML will be enrolled in cohorts at escalating doses of study drug and will
receive up to 2 induction cycles of SGN-CD123A treatment at an assigned dose level in 3-week
cycles.

After completion of dose-escalation, patients will be enrolled in Part B of the study.
Patients enrolled in Part B will receive up to 2 induction cycles of SGN-CD123A treatment at
a dose level and frequency determined by results in Part A.

For both Part A and Part B, a third induction cycle may be permitted with the approval of the
study medical monitor. If a patient achieves a complete remission or complete remission with
incomplete hematologic recovery, optional post-remission cycles of SGN-CD123A may be
administered.

Inclusion Criteria:

- Relapsed/refractory acute myeloid leukemia following at least 2 but no more than 3
prior regimens

- Patients may be eligible after only 1 previous regimen if in a high risk category

- Adequate baseline renal and hepatic function

- Eastern Cooperative Oncology Group Status of 0 or 1

- CD123-detectable leukemia

Exclusion Criteria:

- Cerebral/meningeal disease related to underlying malignancy

- Promyelocytic leukemia

- History of clinically significant pulmonary fibrosis or documented diffusing capacity
of the lung for carbon monoxide <50% predicted

- Prior hematopoietic stem cell transplant

- Antileukemia or experimental treatment within 4 weeks of study drug (other than
hydroxyurea or 6-mercaptopurine)

- Cardio or cerebral vascular event within 6 months