GPT and neutropenia: The most clinically relevant adverse events associated with the use of 4-1BB agonist antibodies involve defects in immune homeostasis (e.g., neutropenia, thrombocytopenia, and reduced B cell numbers) (171, 172), as well as moderate to severe liver inflammation characterized by immune infiltration and concomitant elevation in serum levels of liver transaminases (e.g., AST, ALT).