A subset of myeloid dendritic cells derived from peripheral blood monocytes represented a predominant subset characterized by their potential tumor-inhibiting activity.

Besides their role as potent antigen-presenting cells, myeloid dendritic cells (MDCs), but not plasmacytoid dendritic cells (PDCs), have been reported to have cytotoxic or cytostatic activity on some tumor cells. In this article, we analyzed the tumoristatic potential of a distinct peripheral blood monocyte-derived MDC subset which co-expressed PDC-specific marker CD123. CD123(+) MDCs represented a subset of small-sized DCs and accounted for 45-60% of peripheral blood monocytes cultured with granulocyte-macrophage colony-stimulating factor and interleukine-4 (IL-4) for 7 d. They exhibited more significant antiproliferative activity toward hematological tumor cell lines of Jurkat, HL60, and myelodysplastic syndromes over-leukemia than CD123(-) MDCs even at a low effecter/target ratio. Pretreatment of MDC and their supernatant with TRAIL-R2:Fc significantly reduced the tumoristatic effect of CD123(+) MDCs but not of CD123(-) MDCs and their supernatant. CD123(+) MDCs expressed higher level of cytoplasmic TNF-alpha-related apoptosis-inducing ligand (TRAIL) than CD123(-) MDCs, whereas both expressed very little surface and soluble TRAIL. These results reveal that CD123(+) cells represented a predominant subset of MDCs generated from peripheral blood monocytes in vitro, characterized by their potential tumoristic activity partially via cytoplasmic TRAIL.