A Phase 1, First-in-Human, Open Label, Dose Escalation Study of MGD009, A Humanized B7-H3 x CD3 Dual-Affinity Re-Targeting (DART®) Protein in Patients with Unresectable or Metastatic B7-H3-Expressing Neoplasms and Neoplasms whose Vasculature Expresses B7-H3

The purpose of this study is to evaluate the safety of MGD009 when given to patients with
B7-H3-expressing tumors. The study will also evaluate what is the highest dose of MGD009 that
can be given safely. Assessments will be done to see how the drug acts in the body
(pharmacokinetics (PK), pharmacodynamics (PD) and to evaluate potential anti-tumor activity
of MGD009.

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