Background: Active human dendritic cells (DCs), generated from human monocytes using GM-CSF and interleukin-4 (IL-4), efficiently induce immune responses through their function as professional antigen-presenting cells. On the other hand, interferon-α inducible DCs (IFN-DCs) from monocytes incubated with GM-CSF and IFN-α, exhibits direct anti-tumor activity. Here, we studied the phenotypes and functions of IFN-DCs compared to conventional IL-4-DCs.
Methods: Human monocytes were collected and prepared using apheresis. IFN-DCs were produced from 3-days culture of monocytes using GM-CSF and IFN-α. The IFN-DCs were then used to generate mature IFN-DCs (mIFN-DCs) after incubating with OK-432 (streptococcal preparation). Alternatively, immature IL-4-DCs (imIL-4-DCs) were generated from 5 days culture of monocytes using GM-CSF and IL-4. ImIL-4-DCs were subsequently stimulated with OK-432 to prepare mature IL-4-DCs (mIL-4-DCs). The following analyses were performed: 1) surface antigen on DCs, 2) pinocytotic and phagocytotic assay 3) cytotoxic T lymphocytes (CTL) induction in vitro, and 4) cytotoxicity assay.
Results: The expression of CD14 and human leukocyte antigen (HLA)-DR were higher on mIFN-DCs compared to mIL-4-DCs. In contrast, mIL-4-DCs exhibited strongly elevated expression of CD40, CD83, and CD197. Expression of CD86 and HLA-DR, the minimum criteria of DC vaccine for clinical trials, on mIFN-DCs were comparable to that of mIL-4-DCs. FITC-dextran uptake and degradation of DQ-ovalbumin indicated that the pinocytotic and phagocytotic activities of mIFN-DCs were similar to that of mIL-4-DCs. The percentages of CTLs induced by each mature DCs did not differ significantly. Interestingly, direct anti-tumor activity of mIFN-DCs significantly increased compared to mIL-4-DCs correlating with the expression of surface CD56, a marker for natural killer (NK) cells.
Conclusions: This study demonstrated that mIFN-DCs have efficiency comparable to mIL-4-DCs with regard to pinocytosis, phagocytosis, and antigen-presentation and exhibited increased anti-tumor activity. The mIFN-DCs would be suitable for clinical trials to induce acquired immunity and adoptive anti-tumor activity.