We have identified human monocytic (THP-1) and myelogenous CD34(+) (KG-1) leukemia cell lines that can be differentiated rapidly into mature dendritic cells (DCs) when cultured in serum-free medium containing GM-CSF, TNF-alpha, and ionomycin. These hematopoietic cell line-derived DCs are highly pure and monotypic, and display the morphologic, phenotypic, molecular, and functional properties of DCs generated from human donor-derived monocytes or CD34+ hematopoietic progenitor cells. During differentiation into mature DCs, the cells exhibit de novo cell-surface expression of CD83, C1380, CD86, CD40, C13206, CD209, CD120a, CD120b, and intracellular synthesis of IL-10, increase their endocytotic capacity, and acquire characteristic stellate morphology. To further define the cells as DCs, cytosolic induction and upregulation of RelB and RelA (p65), transcription factors of the NF-kappa B/Rel family essential for differentiation and maturation of DCs, as well as upregulation of the immunoproteasome subunits LMP2, LMP7, and MECL-1, and the proteasome activator PA28 alpha, components essential for efficient MHC class I peptide antigen processing, were demonstrated during differentiation of the cells. In contrast to the cell lines, the cell line-derived mature DCs are capable of stimulating allogeneic CD4(+) and CD8(+) T cells, ultimately defining them as potent antigen-presenting cells. The approach to differentiate THP-1 and KG-1 cells into immature and mature DCs may serve as an experimental model to study molecular events and pathways that govern the differentiation of human malignant myeloid precursors, monocytes, and CD34+ hematopoietic progenitor cells into DCs. (c) 2005 Elsevier Inc. All rights reserved.