CD28 and cancer: Senescent T cells exhibit abnormal phenotypes, including the downregulation of the co‐stimulatory molecule CD28 and the upregulation of CD57, Tim‐3, TIGIT, and CTLA‐4, which are closely associated with malignant tumors.[33] Functional experiments demonstrated that these GzmK+GzmB+ CD8 T cells are major cytokine producers with low cytotoxic potential,[34] suggesting that this subset may be a regulator of the immune response instead of effector cells.