This is a multicenter, open label, phase I trial to evaluate the safety and tolerability, pharmacokinetic/ pharmacodynamic characteristics and to assess the preliminary efficacy of SIM0348 as monotherapy or with sintilimab in adult subjects with advanced and metastatic solid tumors. The trial starts with a dose escalation and dose expansion part (Part 1) followed by a cohort expansion part (Part 2).

Inclusion Criteria:

• Adults 18 years of age or older
• Must have failed at least one established standard anti-cancer therapies
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
• Life expectancy at least 12 weeks
• Adequate hematologic and end organ function
• Histologic documentation of locally advanced, recurrent, or metastatic incurable malignancy that has progressed after at least one available standard therapy; or for which standard therapy has proven ineffective, intolerable, or considered inappropriate; or for which a clinical trial of an investigational agent is a recognized standard of care
• Confirmed availability of representative tumor specimens
• Measurable disease according to RECIST Version 1.1

Exclusion Criteria:

• Malignancies other than disease under study within 2 years prior to Day 1 of Cycle 1
• Primary central nervous system (CNS) malignancy, or untreated/active CNS metastases
• History of interstitial lung disease, evidence of active pneumonitis (history of radiation pneumonitis in the radiation field [fibrosis] is permitted), and active pneumonia that are considered inappropriate by the investigator
• History of severe hypersensitivity reactions to chimeric or humanized antibodies or fusion proteins
• History of autoimmune disease
• Positive human immunodeficiency virus (HIV) test
• Severe infection within 2 weeks prior to the first dose of study treatment
• Significant cardiovascular disease
• History of allogeneic tissue/solid organ transplant or graft-versus-host disease
• Known clinically significant liver disease