Glioblastoma multiforme (GB) is the most common type of primary brain tumors, that virtually always relapses, despite initial treatment with surgical resection, radio- and chemotherapy. Nowadays new promising approaches are developed in treating GB based on dendritic cell (DC) vaccines for the enhancement of the anti-tumor immune response. IFNα-induced monocyte-derived DCs possess properties of myeloid DCs, plasmacytoid DCs and NK cells. The present study focuses on the role of death-inducing mechanisms in DC cytotoxicity against GB cells.
The study was conducted in 26 donors and 21 GB patients. DCs were generated by culturing of plastic-adherent peripheral blood mononuclear cells in the presence of GM-CSF and IFN-α followed by the addition of LPS. The tumor cell lines were obtained from tissues of 14 GB patients. DC cytotoxicity against tumor cells was studied using MTT-assay.
Donor DCs induced death of GB cell lines (min-max cytotoxicity 11-80%). The lysis of GB cells was accompanied with the increase of Annexin V+ apoptotic tumor cells. GB cells expressed death receptors TNF-R1, TRAIL-R2 and Fas. To examine death receptor-mediated killer activity, donor DC were pretreated with soluble forms of TNF family receptors. The blocking of TNF-R1-signaling pathway decreased DC cytotoxicity against GB cells by 25% on average. rhTRAIL-R2 or rhFas pretreatment slightly abolished DC cytotoxicity (with an average of 10%). The most blocking effect on DC cytotoxicity against GB cells was observed if DCs were pretreated with concanamicin A, an inhibitor of granule-dependent killing (Δ up to 60%). GB patient DCs were characterized by reduced cytotoxicity against autologous GB cell lines compared to donor values. Low cytotoxicity of patient DCs was associated with decreased level of membrane TNFα (mTNFα), but intact FasL, TRAIL, perforin and granzyme B molecule expression. The addition of IL-2 into patient DCs enhanced cytotoxicity of DCs towards autologous GB cells and increased mTNFα expression on DCs.
Thus, DCs with tumoricidal activity and ex vivo regulation of DC cytotoxic function may become a new approach to obtain effective anti-tumor DC-vaccines.
Elena Chernykh.
Grant of the Foundation of the President of the Russian Federation.
All authors have declared no conflicts of interest.