CD28 and acute myeloid leukemia: Responder CD4+CD25-CD45RA+ T cells (naïve Tconv) were sorted (purity > 95%) from healthy donor PBMCs using a FACSAria II cytometer (BD), stained with carboxyfluorescein succinimidyl ester (CFSE), and then co-cultured with different numbers of AML cells in the presence of IL-2 and CD3/CD28 beads.