A comparative quantitative study of human myeloid dendritic cell progenitors in cord blood, bone marrow, peripheral blood and their mobilization kinetics in the peripheral blood of cancer patients undergoing leucaphaeresis

Dendritic cell (DC)-based immunotherapy has potential for use in the treatment of cancer, infections and transplantation. Generating large numbers of DC from haemopoietic progenitor cells (HPC) is a key step in this process, often achieved by the aphaeresis of HPC, following their mobilization from the bone marrow into peripheral blood (PB) with chemotherapy and growth factor support (usually, granulocyte-colony stimulating factor, G-CSF). The objective of this work was to identify the optimum time for leucaphaeresis of DC progenitors. An established clonogenic assay specific for colony-forming cell (CFC) DC was used and validated with linearity, dose-response experiments and morphological confirmation. The optimal numbers of mononuclear and CD34+ (or AC133+) cells for plating were 5x104 and l-2xl03 respectively. The optimal concentrations of recombinant cytokines were also determined. Kinetic studies were done in patients with solid tumours, and HPC mobilization was achieved with conventional chemotherapy and G-CSF. The best time for harvesting large numbers of DC progenitors was when the leucocyte count rose rapidly from its nadir at a median 10 days (range 7-13) post chemotherapy. Comparative studies identified mobilized PB as the richest source of CFC-DC (mean, 1,481/ ml PB), with at least, 1.5-fold more progenitors per unit volume than cord blood (CB). These data suggest that venesection alone could provide sufficient CFC-DC to generate mature DC, after ex vivo culture and expansion. This might obviate the need for leucaphaeresis thus making DC-based immunotherapy potentially more widely available. In all the haemopoietic tissues examined the majority of DC and granulo (G)-monocytic (M) progenitors, was found within the CD34+AC133+ cell population. It is concluded that the kinetics of mobilization of CFC-DC are very similar to those of other HPC like CFC- GM and erythroid progenitors. This has important implications for designing immunotherapy protocols to isolate DC precursors from CD34+ HPC for ultimate use in DC-based immunotherapy.