In a melanoma mouse model, compared with tumor-ignorant bystander CD8+ T cells, tumor-specific CD8+ T cells infiltrating the same tumor had significantly higher levels of PD-1, LAG-3, CD69 (activation marker), and 4-1BB (costimulatory molecule) expression and gained 1,414 activation-related (but not exhaustion-related) accessible chromatin regions (14). This evidence concerns the gene PDCD1 and melanoma.