Dendritic cells pulsed with tumor extract–cationic liposome complex increase the induction of cytotoxic T lymphocytes in mouse brain tumor

Abstract.

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that locate in peripheral organs. It has been thought that a systemic immune response does not play a role in regression of central nervous system (CNS) tumors, because the CNS is an immunologically privileged site. However, recent advances in immunology have led to the possibility of immunotherapy using peripheral DCs against CNS tumors. Here, we investigated whether DCs pulsed with tumor extract could induce an antitumor effect against malignant glioma. Furthermore, we also investigated whether the antitumor effect become higher by pulsation with tumor extract–liposome complex, compared to pulsation with tumor extract alone. As a liposome, we used cationic small unilamellar vesicles composed of N-(α-trimethylammonioacetyl)-didodecyl-D-glutamate chloride (TMAG), dilauroylphosphatidylcholine (DLPC), and dioleoylphosphatidylethanolamine (DOPE) in a molar ratio of 1:2:2. After intracerebral inoculation of mouse malignant glioma GL261 cells into syngeneic C57BL/6 mice, DCs pulsed with extract from the glioma cells by sonication were administered intraperitoneally thrice weekly on days 7, 14 and 21. Tumor growth inhibition was evaluated by measuring the tumor size 1 month after the tumor inoculation. The group treated with DCs pulsed by tumor extract was inhibited in tumor progression compared with the control non-pulsed DCs group, and the group treated with DCs pulsed by tumor extract and liposomes showed substantial tumor volume reductions in all the mice. Among the mice, there were several with no visible masses in their brains. Immunohistochemical study showed that the CD8-positive cytotoxic T cells (CTLs) were strongly recognized among the almost disappearing tumor cells of pulsed DCs groups. The CTLs showed a specific antitumor activity for GL261 mouse glioma cells. These findings indicated that DCs pulsed with tumor extract and liposomes might play an important role in the activation of an immune response in malignant glioma.