A Phase 1, First-in-Human, Open-Label, Dose Escalation and Cohort Expansion Study of MGD019, a Bispecific DART® Protein Binding PD-1 and CTLA-4 in Patients With Unresectable or Metastatic Neoplasms

• Dose escalation: Patients with histologically proven, unresectable, locally advanced or metastatic solid tumors for whom no approved therapy with demonstrated clinical benefit is available or patients who are intolerant to standard therapy.

• Cohort Expansion Phase:

• Checkpoint inhibitor-naïve squamous cell NSCLC, including:

‣ Patients that have progressed during or following treatment with platinum-based chemotherapy for advanced disease. Patients harboring an activating epidermal growth factor receptor (EGFR) mutation or anaplastic lymphoma kinase (ALK) rearrangement must have progressed following at least one available EGFR or ALK targeted therapy. ROS1 rearrangement or BRAF mutation must have progressed following at least 1 available EGFR (including osimertinib for EGFR T790M-mutated NSCLC), ALK, ROS1 or BRAF targeted therapy, respectively

⁃ Patients that have progressed during or following treatment with platinum-based chemotherapy for advanced disease and patients with previously untreated squamous cell NSCLC without activating mutations for whom checkpoint inhibitor therapy is not approved or available.

• Advanced non-microsatellite instability-high colorectal cancer (CRC) with recurrence, progression, or intolerance to standard therapy consisting of at least 2 prior standard regimens. CRC harboring an activating EGFR mutation must have progressed during or following at least one available EGFR targeted therapy. Patients who are inappropriate candidates for or have refused treatment with these regimens are also eligible. Patients should have received no more than 4 prior lines of systemic therapy.

• Checkpoint inhibitor-naïve mCRPC that has progressed during or following no more than 2 prior lines of an androgen receptor antagonist or androgen synthesis inhibitor (e.g., enzalutamide or abiraterone, respectively), if approved and available, with a PSA value of at least 2 ng/mL and meeting at least one of the following:

• Progression in measurable disease (RECIST v1.1).

• Appearance of 2 or more new bone lesions according to Prostate Cancer Working Group 2 (PCWG-2).

• Rising PSA defined as at least two sequential rises in PSA.

• Eligible patients may have received prior chemotherapy (i.e. docetaxel), and patients with known homologous recombination (HRR) pathway gene alterations must have received the applicable approved therapy (e.g. olaparib).

• Cutaneous melanoma that has progressed during or following systemic treatment for unresectable, locally advanced, or metastatic disease. Patients will have received PD-(L)1 and/or CTLA-4 pathway inhibitors where available and indicated.

• Eastern Cooperative Oncology Group (ECOG) performance status of 0-1

• Life expectancy ≥ 12 weeks.

• Measurable disease as per RECIST 1.1 for the purpose of response assessment must either (a) not reside in a field that has been subjected to prior radiotherapy or (b) have demonstrated clear evidence of radiographic progression since the completion of prior radiotherapy and prior to study enrollment.

• All patients must have an identified formalin-fixed, paraffin embedded (FFPE) tumor specimen (up to 20 slides or a block) for immunohistochemical evaluation of pharmacodynamic markers of interest. Patients may undergo a fresh tumor biopsy during the screening period if a tumor sample is not available. Patients in the mCRPC expansion cohort with bone only disease not amenable to fresh biopsy may be eligible in consultation with the Sponsor.

• Acceptable laboratory parameters and adequate organ reserve.