Generation of a large number of functional dendritic cells from human monocytes expanded by forced expression of cMYC plus BMI1

Anticancer vaccination therapies with monocyte-derived dendritic cells (DC) are widely conducted. A large number of primary monocytes (approximately 108 cells) are needed to generate the number of DC required to achieve an effect upon vaccination, and monocytes are usually purified from peripheral blood mononuclear cells obtained by apheresis procedure, which is somehow invasive for cancer patients. As a means to facilitate the generation of DC for therapeutic use, 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 the monocyte-derived proliferating cells CD14-ML. Their proliferation continued for 3-5 weeks in the presence of M-CSF and GM-CSF, resulting in 20-1000-fold amplification. Importantly, the expanded CD14-ML differentiated into fully functional DC (CD14-ML-DC) upon the addition of IL-4 to the culture. 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.