Dendritic cells (DC) are potent antigen-presenting cells that are integral to the initiation of T cell immunity. The ability to culture these cells in vitro has allowed DC immunotherapy to be investigated as a mechanism of enhancing immune responses against various malignancies. We examined the optimal time for generating DC and compared DC generated from normal donors for allogeneic blood stem cell transplantation, or patient's with non-Hodgkin's lymphoma or breast cancer undergoing high-dose chemotherapy and autologous stem cell transplantation. Experiments were conducted to compare DC cultured prior to and post mobilization chemotherapy. Blood was obtained from consenting patients prior to granulocyte colony-stimulating factor (G-CSF) administration with (non-Hodgkin lymphoma and breast cancer) or without (normal donors) chemotherapy. A sample of apheresis product (AP) was obtained at the time of apheresis. DC were generated from peripheral blood mononuclear cells by culturing the adherent cells in the presence of interleukin-4 and granulocyte-macrophage colony-stimulating factor. Resultant DC were harvested and examined for yield, morphology, phenotype, and function. All cell populations yielded highly pure DC, as assessed by light microscopy and flow cytometry. The average cellular yield was significantly greater from AP than steady-state blood in paired and unpaired samples. Yield did not correlate with the percentage of CD14(+) cells, and it negatively correlated with CD34 counts. DC from breast cancer patients functioned significantly better than DC from lymphoma patients in a mixed lymphocyte reaction. These data suggest that the optimal timing of culturing DC is after mobilization, and that differences may exist in the functional capabilities of DC derived from different patient populations.