Inclusion Criteria:

          -  Histologically-proven, unresectable locally advanced or metastatic solid tumors of any
             histology that test positive for B7-H3 expression on tumor cells or vasculature for
             whom no approved therapy with demonstrated clinical benefit is available. For all
             tumor types, the requirement for previous systemic therapy may be waived if a patient
             was intolerant of or refused standard first-line therapy

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

          -  Life expectancy ≥ 12 weeks

          -  Measurable disease, with the exception of prostate cancer

          -  Tissue specimen available for B7-H3 and PD-L1 expression testing

          -  Acceptable laboratory parameters

          -  Patients who have previously received an immune checkpoint inhibitor (e.g., anti-
             PD-L1, anti-PD-1, anti-CTLA-4) prior to enrollment must have toxicities related to the
             checkpoint inhibitor resolved to ≤ Grade 1 or baseline (prior to the checkpoint
             inhibitor) to be eligible for enrollment. Patients who experienced previous
             hypothyroidism toxicity on a checkpoint inhibitor are eligible to enter study
             regardless of Grade resolution as long as the patient is well controlled on thyroid
             replacement hormones.

        Exclusion Criteria:

          -  Patients with history of prior central nervous system (CNS) metastasis must have been
             treated, must be asymptomatic, and must not have any of the following at the time of
             enrollment:

               1. No concurrent treatment for the CNS disease (e.g. surgery, radiation,
                  corticosteroids >10 mg prednisone/day or equivalent)

               2. No progression of CNS metastases on MRI or CT for at least 14 days after last day
                  of prior therapy for the CNS metastases

               3. No concurrent leptomeningeal disease or cord compression

          -  Patients with any history of known or suspected autoimmune disease with the specific
             exceptions of vitiligo, resolved childhood atopic dermatitis, psoriasis not requiring
             systemic treatment (within the past 2 years), and patients with a history of Grave's
             disease that are now euthyroid clinically and by laboratory testing

          -  Treatment with any, investigational therapy within the 4 weeks prior to the initiation
             of study drug administration

          -  Treatment with any systemic chemotherapy within 3 weeks

          -  Treatment with radiation therapy within 2 weeks

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

          -  Treatment with systemic corticosteroids (> 10 mg per day prednisone or equivalent) or
             other immune suppressive drugs within 2 weeks

          -  Clinically significant cardiovascular or pulmonary disease

          -  Evidence of active viral, bacterial, or systemic fungal infection requiring parenteral
             treatment within 7 days prior to the initiation of study drug. Patients requiring any
             systemic antiviral, antifungal, or antibacterial therapy for active infection must
             have completed treatment no less than one week prior to the initiation of study drug.

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

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