Summary:Dendritic cells (DCs) are antigen-presenting cells that are critical to the generation of immunologic tumor responses. Myeloid DCs (DC1) express myeloid antigen CD11c; lymphoid DCs (DC2) express CD123+ and are CD11c−. Analysis of DC subsets from peripheral blood progenitor cells (PBPC) collected from normal donors mobilized with G-CSF shows a predominance of DC2 cells. Whether PBPCs mobilization by chemotherapy yields different subsets of DCs has not been studied. We analyzed DC subsets in apheresis products from 44 patients undergoing autologous stem cell transplantation from 6/00 to 5/01. Patients received either G-CSF alone (10 μg/kg per day, n=11) or etoposide (2 g/m2) plus G-CSF (n=33) for progenitor cell mobilization. The patients were apheresed for 2–10 days (median 3) to reach a minimum of 2.0×106 CD34+ cells/kg. Patients receiving G-CSF alone mobilized significantly more total DC2s than did those receiving etoposide plus G-CSF (median 6.2×106/kg vs 2.9×106/kg, P=0.001). The DC2/DC1 ratio was also significantly different in the two groups, with the G-CSF group having a higher ratio (median 1.2 vs 0.4, P<0.001). We conclude that the combination of chemotherapy plus G-CSF yields different mobilized dendritic cell subsets than does G-CSF alone.