In contrast to T cells stimulated with soluble anti-CD3 antibody (OKT3) and IL-2, which produce more effector memory-type T cells with a significantly reduced number of CD62L+, CD28+ and CD27+ T cells that manifest inferior in vivo anti-leukemia ability compared with cells generated with CD3/CD28 beads,40 the majority of the REP-expanded T cells included both central memory and effector memory T cells and maintained a young phenotype (CD28+, CD27+ and CD62L+). This evidence concerns the gene CD28 and leukemia.