Inhibition of diacylglycerol kinase alpha to augment antitumor effector T cells in tumor-bearing host.

Abstract

293 Background: Diacylglycerol kinases (DGKs), lipid kinases transforming diacylglycerol to phosphatidic acid, play important roles in intracellular signal transduction. Diacylglycerol kinase alpha (DGKa), an isozyme of DGKs, is well-known to promote proliferation of cancer cells by suppression of the apoptosis. Additionally, a previous report demonstrated that activation of DGKa induced anergy state of T lymphocytes in vivo. In this study, we investigated whether inhibition of DGKa not only suppress the tumorigenesis of cancer cells but also activate anti-tumor immunity. Methods: We first investigated the effect of DGKa inhibitor on in vitro proliferation of murine hepatoma cell lines (Hepa1-6) by cell proliferation assay. Cytokine and Granzyme B productions by CD8+ T cells from OT-1 mice after the OVA antigen stimulation were evaluated by ELISA and flowcytometry, respectively. Next, we established a tumor-bearing mice model by injection of mCherry-transfected Hepa1-6 cells into spleen. Tumorigenesis and tumor-infiltrating T cells in the liver were evaluated by in vivo imaging system, HE staining, and immunohistochemistry. CD8+ T cells were collected from the liver and stimulated with PMA and Ca2+ ionophore and the IFN-g production levels were evaluated by flowcytometry. Results: Proliferation of Hepa1-6 cells were suppressed in the presence of DGKa inhibitor in vitro. IL-2 production levels of OT-1 CD8 T cells in control group was augmented by the addition of DGKa inhibitor (246 vs 579 pg/ml, p < 0.05). Granzyme B-positive cells in OT-1 CD8+ T cells were increased by the treatment with DGKa inhibitor compared to the control group (4.4 vs 8.9 %, P < 0.05) after the antigen stimulation. In vivo administration of DGKa inhibitor significantly suppressed the tumor size (fluorescence (AU) 2.0x1010 vs 6.3x109, area (μm2) 1.5x107 vs 0.9x107, p < 0.05) in the liver of tumor bearing mice. Then, the number of tumor-infiltrating T cells (582 vs 1506, 5 HPF, p < 0.05) and the IFN-g-producing cells (9.2 vs 16.0 %) in CD8+ T cells were elevated by the DGKa treatment. Conclusions: Inhibition of DGKa not only suppressed the proliferation of hepatoma but also activated anti-tumor effector T cells in vivo.