Human Dendritic Cells Engineered to Express Alpha Tumor Necrosis Factor Maintain Cellular Maturation and T-Cell Stimulation Capacity

Dendritic cell (DC) vaccine has been demonstrated to induce antitumor immunity in animal models. It has been shown that the efficiency of antitumor immunity by DC vaccine is closely correlated with DC maturation status. The mature human DCs generated from peripheral blood mononuclear cells (PBMCs) in the presence of granulocyte macrophage–colony-stimulating factor (GM-CSF), interleukin (IL)-4, and tumor necrosis factor (TNF)-α have widely contributed to their growing use in cancer vaccination trials. Although the objective clinical immune responses have been observed, the treatment results have proved to be somewhat disappointing. One question of whether these ex vivo–generated mature DCs can maintain their maturation status in vivo after DC vaccination is unclear. In this study, we investigated the influence of different culture media (RPMI 1640/10% fetal calf serum [FCS] versus serum-free AIM-V medium) on DC maturation and the change of maturation status of these ex vivo generated mature DCs during further culturing in medium without inflammatory cytokine TNF-α. We previously constructed a recombinant adenovirus AdV-TNF-α expressing the transgene human TNF-α. We transfected human DCs with AdV-TNF-α at multiplicity of infection of 100, resulting in engineered DCs secreting TNF-α (4.6 ng/mL/10⁶ cells/24 hours). We also conducted kinetic studies to compare the maturation status and the T-cell stimulation capacity by ex vivo–generated mature DCs and TNF-α- transgene-engineered DCs during further culturing in medium without TNF-α. Our data show that mature DCs can be generated from PBMCs in both Dulbecco's modified Eagle's medium plus 10% FCS and serum-free AIM-V medium containing GM-CSF (100 ng/mL), IL-4 (100 ng/mL), and TNF-α (10 ng/mL). However, these mature DCs gradually lost their maturity and became immature ones when culturing in medium in the absence of TNF-α. On the contrary, the human DCs engineered to express TNF-α can (i) stably maintain their cellular maturation and (ii) efficiently stimulate T-cell proliferation even during culturing ex vivo in medium without TNF-α stimulation. Therefore, DCs engineered to express TNF-α may also maintain their maturation status and induce more efficient antitumor immune responses when applied in vivo for vaccination. Thus, our results may be important in designing DC-based cancer vaccines in the future.