Inclusion Criteria:

          -  Subjects with advanced or metastatic solid tumor in subjects whose disease has
             progressed despite standard therapy, or who has no further standard therapy, or who is
             unsuitable for available standard treatment options.

          -  Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1 with adequate
             organ function

        For dose expansion study only:

          -  Advanced or metastatic gastric cancer, gastroesophageal junction carcinoma, esophageal
             adenocarcinoma, and pancreatic ductal adenocarcinoma without further standard therapy
             or unsuitable for available standard treatment options.

          -  Must have CLDN18.2-positive tumor expression as determined by the CLDN18.2 IHC assay

        Exclusion Criteria

          -  Prior exposure to CLDN18.2 -targeted therapy

          -  Prior exposure to 4-1BB agonists

          -  Known active or chronic Hepatitis B or Hepatitis C, other hepatitides

          -  Unstable/active ulcer or digestive tract bleeding within 6 weeks

          -  Active autoimmune disease requiring systemic treatment within the past 2 years

          -  Active interstitial lung disease (ILD) or pneumonitis or a history of ILD or
             pneumonitis requiring treatment

          -  Known active CNS metastases and/or carcinomatous meningitis. Subjects with previously
             treated brain metastases may participate provided they are clinically stable and
             without requirement of steroid treatment for at least 14 days prior to first dose of
             study treatment;

          -  New York Heart Association (NYHA) Class 3 or 4 congestive heart failure,
             severe/unstable angina, myocardial infarction (MI), symptomatic congestive heart
             failure, cerebrovascular accident, transient ischemic attack (TIA), arterial embolism,
             pulmonary embolism, percutaneous transluminal coronary angioplasty (PTCA), deep vein
             thrombosis, or coronary artery bypass grafting (CABG) in the previous 6 months

          -  Diagnosis of immunodeficiency such as known active HIV