Safety Study of MGD009 in B7-H3-expressing Tumors

This study is a Phase 1 open-label, dose escalation, cohort expansion, and efficacy follow-up
study of MGD009 administered intravenously (IV) on an every-other-week schedule for up to one
year (14 cycles).

The dose escalation phase is designed to characterize the safety and tolerability of MGD009
and to define the maximum tolerated or maximum administered dose (MTD/MAD). This phase will
enroll patients with mesothelioma, bladder cancer, melanoma, squamous cell carcinoma of the
head and neck (SCCHN), non-small cell lung cancer (NSCLC), clear cell renal cell carcinoma
(ccRCC), ovarian cancer, thyroid cancer, triple-negative breast cancer (TNBC), pancreatic
cancer, colon cancer, soft tissue sarcoma, or prostate cancer.

In the cohort expansion phase, 6 cohorts of 16 patients each will be enrolled to further
evaluate the safety and potential efficacy of MGD009 administered at the MTD/MAD dose in
patients with mesothelioma, bladder cancer, melanoma, SCCHN, NSCLC, or other specific tumors
that express high levels of B7-H3. Pre- and on-study biopsies are required for melanoma
patients in the cohort expansion phase. Two additional cohorts (up to15 patients each) will
evaluate the use of prophylaxis therapies to mitigate toxicity.

The survival follow-up phase consists of the 2-year period after the final dose of study
drug.

All tumor evaluations will be carried out by both Response Evaluation Criteria in Solid
Tumors (RECIST) and immune-related response criteria (irRC).

Inclusion Criteria:

- Histologically and/or cytologically proven unresectable locally advanced or metastatic
tumors that express B7-H3 on the membrane or vasculature. The requirement for previous
systemic therapy may be waived if a person was intolerant of standard front-line
therapy

- Dose escalation phase prior systemic treatment requirements:

- pleural mesothelioma, pancreatic cancer: 1-3 prior treatments

- urothelial, SCHNN, prostate, soft tissue sarcoma, prostate cancer, TNBC, ccRCC, NSCLC:
1-5 prior treatments

- ovarian cancer: 2-4 prior treatments

- colon cancer: 2-4 prior treatments

- cutaneous melanoma: at least 1 prior treatment (including immunotherapy).

- Patients with prior immune checkpoint inhibitors must have related toxicities reduced
to Grade 0, 1, or baseline

- Measurable disease per RECIST 1.1 criteria

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

- Acceptable laboratory parameters and adequate organ reserve.

Exclusion Criteria:

- Patients with central nervous system (CNS) involvement must have been treated, be
asymptomatic, do not exhibit progression of CNS metastases on MRI or CT within 28
days, and do not have concurrent leptomeningeal disease or cord compression.

- Clinically significant pulmonary compromise within 28 days of first dose, including
pneumonia, pneumonitis, requirement for supplemental oxygen). use to maintain adequate
oxygenation, or pleural effusion sufficient to warrant pleurocentesis or any history
of ≥ Grade 3 drug induced or radiation pneumonitis.

- History of autoimmune disease with certain exceptions such as vitiligo, resolved
childhood atopic dermatitis, psoriasis not requiring systemic therapy within the past
2 years, patients with history of Hashimoto's or Grave's disease that are now
euthyroid clinically and by lab testing

- History of clinically-significant cardiovascular disease, or cardiac arrhythmias,
including atrial fibrillation at screening or day of treatment

- History of clinically-significant gastrointestinal (GI) disease; GI perforation within
1 year; GI bleeding or acute pancreatitis within 3 months; or diverticulitis within 4
weeks of first study drug administration

- Active viral, bacterial, or systemic fungal infection requiring parenteral treatment
within 7 days of first study drug administration

- Known history of hepatitis B or C infection or known positive test for hepatitis B
surface antigen or core antigen, or hepatitis C polymerase chain reaction (PCR)

- Known positive testing for human immunodeficiency virus or history of acquired immune
deficiency syndrome

- History of allogeneic bone marrow, stem cell, or solid organ transplant

- Treatment with systemic cancer therapy or investigational therapy within 3 weeks of
first study drug administration; radiation within 2 weeks; corticosteroids (greater
than or equal to 10 mg prednisone or equivalent per day) or other immune suppressive
drugs within 2 weeks of first study drug administration

- Trauma or major surgery within 4 weeks of first study drug administration

- Known hypersensitivity to recombinant proteins, polysorbate 80, or any excipient
contained in the drug or vehicle formulation for MGD009