GZMB and neoplasm: As a activation marker upregulated earliest following T cell activation, and the most commonly used biomarker for identifying antigen-responsive T cells in in vitro assays 44, CD69 expression was elevated in GBP5-overexpressed T cell, while IFNγ and GZMB (effector molecules mediating T cell cytotoxicity against tumor cells 45) expressions were downregulated significantly.