In cancer immunotherapy, it is the most important that the cancer antigen-specific T cells are derived by the peptide presented by HLA antigen, and dendritic cells (DC) are useful to drive them. For preparation of sufficient quantity of DC, a large number of monocytes are required, and apheresis, a somehow invasive procedure, is generally conducted. As a means to facilitate the generation of DC, we herein report a method to amplify human monocytes. We found that lentivirus-mediated transduction of cMYC along with BMI1 induced proliferation of CD14⁺ monocytes derived from 9 out of 12 blood donors, and we named this proliferating cell CD14 cell-derived myeloid cell line (CD14-ML). The proliferation of CD14-ML began after a culture start in 3–5 weeks in the presence of M-CSF and GM-CSF, resulting in 20–1000-fold amplification. When we added IL-4 and TNF α or OK432 in the expanded CD14-ML, the cell differentiated into DC (CD14-ML-DC) having strong T cell stimulation activity. We successfully stimulated autologous CD8⁺ T cells with CD14-ML-DC pulsed with cytomegalovirus peptide or MART-1 peptide to generate antigen-specific CTL lines. This is the first report describing the method for in vitro expansion of human peripheral blood monocytes.

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