Mechanisms controlling the age-associated gradual acquisition by CD8T cells of natural killer cell receptors negatively regulating lymphocyte stimulation have remained obscure. Now, data from Li and colleagues(1) imply that a state of transcriptional activation and histone stoichiometry in CD8 but not CD4T cells from elderly people results in epigenetic control of KIR genes by a mechanism involving displacement ofDNAmethyltransferase 1.