Generation of functional PDCs from CML CD34⁺ progenitors in the presence of imatinib. CD34⁺ hematopoietic progenitors from CML patients in chronic phase at diagnosis were cultured in the presence of Flt3L as described in “Study design” (A) in the absence or (B) in the presence of imatinib. CD4, CD123, and BDCA-2 expression was analyzed by flow cytometry. Empty histograms show the background staining with isotype control monoclonal antibodies, and solid histograms represent specific staining of the indicated cell-surface markers. Representative of 4 independent experiments. (C) IFN-α secretion by PDCs generated from CD34⁺ CML progenitors in the presence of imatinib. Cells (10⁶) from cultures described in panels A and B were stimulated with HSV without prior PDC sorting or any additional cytokine. Supernatants were harvested after 48 hours of stimulation with HSV. IFN-α secretion was analyzed by ELISA. Results are represented as the mean and SEM of IFN-α concentration obtained from 3 independent experiments. (D) Expression of Flt3 by flow cytometry is shown on CD34⁺ CML progenitors before (top panel), and after 24 hours of incubation of PBMCs from CML with imatinib. Empty histogram shows the background staining with isotype control monoclonal antibody, and solid histogram represents specific staining of Flt3. Representative of 6 different patients with CML in chronic phase at diagnosis.