tokens: Although CD28 is constitutively expressed , its expression is transiently down-regulated following T cell activation and declines progressively with in vitro senescence .
folded_tokens: although cd28 is constitutively expressed , its expression is transiently down-regulated following t cell activation and declines progressively with in vitro senescence .
labels: O B-protein_molecule O O O O O O O O O O B-other_name I-other_name I-other_name O O O O O O O O