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