The study investigates the presence and proliferation of dendritic cell (DC) progenitors in human blood and their potential for clinical applications. CD34+ cells in cord blood and adult bone marrow are known to give rise to DCs, but their rarity in adult blood limits their use. The authors systematically searched for DC progenitors in various contexts, including cord blood and adult blood from patients receiving chemotherapy. They found that specific cytokines, such as granulocyte/macrophage colony-stimulating factor (GM-CSF) and tumor necrosis factor (TNF), could induce the formation of DC aggregates in cord blood and adult blood from cancer patients. However, in healthy adult blood, these cytokines only generated small aggregates that transformed into monocytes. The addition of interleukin 4 (IL-4) to GM-CSF and TNF led to the formation of large DC aggregates, which produced about 3-8 million DCs per 40 ml of blood. These DCs had a characteristic morphology, surface markers, and potent T cell-stimulating function. The study demonstrates that large numbers of DCs can be generated from blood progenitors using specific cytokines, facilitating future studies on theirFcεRI and CD4 receptors and their use in stimulating T cell-mediated responses to viruses and tumors.The study investigates the presence and proliferation of dendritic cell (DC) progenitors in human blood and their potential for clinical applications. CD34+ cells in cord blood and adult bone marrow are known to give rise to DCs, but their rarity in adult blood limits their use. The authors systematically searched for DC progenitors in various contexts, including cord blood and adult blood from patients receiving chemotherapy. They found that specific cytokines, such as granulocyte/macrophage colony-stimulating factor (GM-CSF) and tumor necrosis factor (TNF), could induce the formation of DC aggregates in cord blood and adult blood from cancer patients. However, in healthy adult blood, these cytokines only generated small aggregates that transformed into monocytes. The addition of interleukin 4 (IL-4) to GM-CSF and TNF led to the formation of large DC aggregates, which produced about 3-8 million DCs per 40 ml of blood. These DCs had a characteristic morphology, surface markers, and potent T cell-stimulating function. The study demonstrates that large numbers of DCs can be generated from blood progenitors using specific cytokines, facilitating future studies on theirFcεRI and CD4 receptors and their use in stimulating T cell-mediated responses to viruses and tumors.