Inclusion Criteria:

          -  Age ≥18 years.

          -  Participants with histologically confirmed, locally advanced, unresectable, or
             metastatic solid tumours that have failed up to 2 prior regimens for metastatic
             disease and standard therapy has proven to be ineffective, intolerable, or is
             considered inappropriate.

          -  For participants who have failed 1 prior immune-checkpoint blockade (ICB)-containing
             regimen, prior biomarker status must be documented; the minimum treatment duration was
             12 weeks; and disease progression is documented for participants in the accelerated
             titration and confirmed for participants in later cohorts.

          -  Measurable disease.

          -  Eastern Cooperative Oncology Group Performance Status ≤1.

          -  The participant agrees to undergo a pretreatment and on-treatment biopsy of the tumor.

          -  Highly effective contraception.

          -  Willing and able to provide written informed consent.

        Exclusion Criteria:

          -  Participants with clinically relevant COVID-19 disease risk will be excluded from
             enrolment during the COVID-19 pandemic.

          -  Prior therapy with any OX40 agonist, CD137 (4-1BB) agonist, CD40 agonist, GITR, or
             CD27 targeting therapy (single agent or combination); prior therapy with more than 1
             line of treatment with immune-checkpoint inhibitors (including ICB combination
             therapy).

          -  Participants with active autoimmune disease.

          -  History of uncontrolled intercurrent illness.

          -  Significant laboratory abnormalities.

          -  Participants with haematological malignancies; participants with treatment-refractory
             chronic bone marrow insufficiency; participants unresponsive and/or refractory to
             transfusions and supportive care for disease-related or treatment-related
             haematological toxicity(ies).

          -  Participants with prior allogeneic or autologous bone marrow transplantation or other
             solid organ transplantation.

          -  Known infections.

          -  Uncontrolled central nervous system (CNS) metastases, primary CNS tumours, or solid
             tumours with CNS metastases as the only measurable disease.

          -  Prior history of any grade ≥3 immune-related AE (irAE) that has not improved to grade
             ≤1; significant (grade ≥3 NCI CTCAE Version 5.0) treatment-related cytokine release
             syndrome (CRS); systemic inflammatory response syndrome (SIRS).

          -  Use of immunosuppressive agents, hypersensitivity or intolerance to monoclonal
             antibodies or their excipients, persistent grade >1 NCI CTCAE Version 5.0 toxicity
             related to prior therapy or any condition that would significantly impair and/or
             prohibit the participant's participation in the study, as per the investigator's
             judgment.

          -  Vaccination with a live vaccine within 30 days before first dose of study drug.