Study of IMGN632 in Patients With Relapse/Refractory AML, BPDCN, ALL, Other CD123+ Hem Malignancies

The study comprises a dose escalation phase followed by a dose expansion phase to further
characterize the safety profile and confirm the MTD. IMGN632 will be administered IV on Day 1
of each cycle, with cycles repeating every 21 days. Treatment will continue for up to 2
cycles (6 weeks) in the absence of disease progression (PD), treatment intolerance, or
withdrawal of consent.

Inclusion Criteria:

- Disease Characteristics and allowable prior therapy:

- Patients in dose escalation and all expansion cohorts except first relapse AML may
have received up to three prior lines of therapy.

- Dose Escalation - Relapsed or refractory AML (excluding acute promyelocytic leukemia)
or BPDCN, based on World Health Organization Classification. All patients enrolled on
this study will have CD123+ disease.

- Dose Expansion Cohort #1 - Patients will have relapse of CD123+ BPDCN. Patients with
prior CD123-targeting agents will be allowed as long as the blasts still have
detectable CD123 expression.

- Dose Expansion Cohort #2 - Patients will have first relapse of CD123+ AML.

- Dose Expansion Cohort #3 - Patients will have relapse of CD123+ ALL.

- Dose Expansion Cohort #4 - Patients will have relapse of CD123+ "other" hematologic
malignancies not included in the cohorts above (e.g., high-risk/very high-risk MDS,
MPN, CMML, CML blast crisis). Other CD123+ malignancies may be considered upon
discussion with the Medical Monitor.

Exclusion Criteria:

- Patients who, in the judgment of their treating physician, have available standard of
care therapies will be excluded

- AML patients with active central nervous system (CNS) disease will be excluded.

- Patients with a history of venous occlusive disease of the liver

- Patients with a history of Grade 3-4 capillary leak syndrome, or non-cardiac Grade
edema are ineligible, e.g., related to SL-401 or other etiology

- Myocardial infarction within six months prior to enrollment or has New York Heart
Association Class III or IV heart failure, uncontrolled angina, severe uncontrolled
ventricular arrhythmias, or electrocardiographic evidence of acute ischemia or active
conduction system abnormalities prior to study entry

- Patients who have received any anti-cancer therapy including chemotherapy,
immunotherapy, radiotherapy, hormonal, biologic, or any investigational agents within
14 days or five half-lives, whichever is greater (with exception of hydroxyurea),
prior to drug administration on this study.