CD28 and cancer: It involves (i) a number of factors (such as glucose competition and cAMP), (ii) the display of aberrant T cell phenotypes, such as the upregulation of CD57 and the downregulation of CD27 and CD28, which are closely linked to malignant tumors, and (iii) genetic and pharmacological intervention (such as interleukin-7 recombination and NAD+ activation).