RT-PCR analysis confirmed that ECP broadly activates genes distinctive of monocyte maturation to DCs. Study of negatively enriched ECP-processed monocytes from 4 normal donors, to 95% population purity, confirmed the microarray finding that ECP rapidly initiates monocyte entry into the DC pathway. Expression of each of 11 examined DC-distinctive genes was significantly enhanced by ECP processing, 3 and > 1000-fold over that manifested by pretreatment monocytes. Nearly indistinguishable findings from identical analysis of nonpurified mononuclear populations indicates that ECP-lethally damaged lymphocytes do not discernibly contribute to the observed expression of these genes, even when present in the study population.