Study of ADCT-402 in Patients With Relapsed or Refractory B-cell Lineage Acute Lymphoblastic Leukemia (B-ALL)

Study ADCT-402-102 is the first clinical study with ADCT-402 in patients with B-cell lineage
acute lymphoblastic leukemia (ALL).

ADCT-402 is an antibody drug conjugate (ADC) composed of a humanized antibody directed
against human cluster of differentiation 19 (CD19), stochastically conjugated via a
valine-alanine cleavable, maleimide linker to a pyrrolobenzodiazepine (PBD) dimer cytotoxin.

The study will be conducted in 2 parts. In Part 1 (dose escalation) patients will receive an
infusion of ADCT-402 either be on weekly administration or every 3-week administration.
Patients on weekly administration will receive an infusion of ADCT-402 on Days 1, 8, and 15
of each 3 week treatment cycle. Patients on 3-week administration will receive an infusion of
ADCT-402 on Day 1, every 3 weeks. Dose escalation will continue until the maximum tolerated
dose (MTD) is determined.

In Part 2 (expansion), all patients will be assigned to the recommended dose and/or schedule
of ADCT-402 identified in Part 1 by the Dose Escalation Steering Committee.

For each patient, the study will include a screening period (up to 28 days), a treatment
period (until withdrawal), and a follow-up period to assess disease progression and survival
for up to 12 months after the last dose of study drug. The total study duration will be
dependent on overall patient tolerability to the study drug and response to treatment. It is
anticipated that the duration of the entire study (Parts 1 and 2) could be approximately 3
years from first patient treated to last patient completed.

Inclusion Criteria:

- Male or female patients, ages 12 years and older, with relapsed or refractory B-ALL
who have failed, or are intolerant to, any established therapy; or for whom no other
treatment options are available.

- Eastern Cooperative Oncology Group (ECOG) performance status 0-2.

- Serum/plasma creatinine ≤1.5mg/dL.

- Serum/plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤2
times the upper limit of normal (ULN); ≤5 times ULN if there is liver or bone
involvement.

- Total serum/plasma bilirubin ≤1.5 times ULN.

- White Blood Cell Count value of <15,000 cells/μL prior to Cycle 1 Day 1.

- Negative urine or serum beta-human chorionic gonadotropin (β-HCG) pregnancy test
within 7 days prior to the Cycle 1, Day 1 visit, for women of childbearing potential.

- Males, and female patients who are biologically capable of having children, must agree
to use a medically acceptable method of birth control.

Exclusion Criteria:

- Patients who have an option for other treatment for B-ALL at the current state of
disease.

- Known active central nervous system (CNS) leukemia.

- Patients with Burkitt's leukemia/lymphoma.

- Active graft-versus-host disease.

- Autologous or allogenic transplant within the 60 days prior to Screening.

- Known history of immunogenicity or hypersensitivity to a CD19 antibody.

- Known history of positive serum human ADA.

- Active autoimmune disease, motor neuropathy considered of autoimmune origin, or other
central nervous system autoimmune disease.

- Known seropositive for human immunodeficiency (HIV) virus, hepatitis B surface antigen
(HbsAg), or antibody to hepatitis C virus (anti-HCV).

- History of Stevens-Johnson syndrome or toxic epidermal necrolysis syndrome.

- Pregnant or breastfeeding women.

- Significant medical comorbidities, including uncontrolled hypertension (diastolic
blood pressure >115 mm Hg), unstable angina, congestive heart failure (greater than
New York Heart Association class II), severe uncontrolled ventricular arrhythmias,
electrocardiographic evidence of acute ischemia, poorly controlled diabetes, severe
chronic pulmonary disease, coronary angioplasty, myocardial infarction within 6 months
prior to Screening, or uncontrolled atrial or ventricular cardiac arrhythmias.

- Use of any other experimental medication(s) within 14 days or 5 half-lives, but in no
case <14 days prior to the start of treatment on Cycle 1, Day 1, except if approved by
the Sponsor.

- Major surgery, chemotherapy, systemic therapy (excluding hydroxyurea,steroids and any
targeted small molecules or biologics), or radiotherapy, within 14 days or 5
half-lives (whichever is shorter) prior to the Cycle 1, Day 1 treatment, except if
approved by the Sponsor.

- Failure to recover from acute non hematologic toxicity (except alopecia or Grade 2 or
lower neuropathy), due to previous therapy, prior to Screening.

- Isolated extramedullary relapse.

- Congenital long QT syndrome or a corrected QTc interval of ≥450 ms at the Screening
visit.

- Active second primary malignancy other than non-melanoma skin cancers, nonmetastatic
prostate cancer, in situ cervical cancer, ductal or lobular carcinoma in situ of the
breast, or other malignancy determined not be exclusionary.

- Any other significant medical illness, abnormality, or condition that would make the
patient inappropriate for study participation or put the patient at risk.