Abstract LB-315: A critical role for T regulatory cells in driving Th17 cytokine profile and modulating their ability to affect glioma microenvironment
Authors: Cantini Gabriele , Pisati Federica , Finocchiaro Gaetano , Pellegatta Serena 
Published: February 2011

IL-17, produced by Th17 cells, may play a dual role in antitumor immunity. Using the GL261 murine glioma model, we have investigated how Th17 cells can affect tumor growth and microenvironment. We first obtained TIL from fresh GL261-glioma 10 and 20 days after tumor implantation, and evaluated by flow cytometry infiltrating-Th17 as a percentage of total CD4+ cells. Th17 increased from 7.9±1.9 on day 10 to 13.1±5.2 on day 20 (p=0.03). To characterize the direct effects of Th17 cells on GL261-glioma and on tumor microenvironment, we isolated IL-17 producing cells enriched using Miltenyi technology from splenocytes derived from naïve or glioma-bearing mice (Gb) and pre-stimulated in vitro with or without TGF-ß. Th17 derived from naïve (nTh17) or Gb splenocytes (GbTh17) were co-injected subcutaneously with GL261 cells in immune-competent mice. Gliomas in mice co-injected with nTh17 were smaller than gliomas obtained from GL261 cells only (34±39.5mm3 vs 235.3±22.0mm3 respectively, p=0.003). In these gliomas, using RT-PCR we also found enhanced expression in IFN- and decreased expression of IL-10, TGF- and VEGF. Opposite results were obtained in gliomas of mice co-injected with Gb-Th17 (866±627 mm3, p=0.01 vs GL261, p&lt;0.001 vs nTh17). To gain hints on Th17 involvement in glioma progression or suppression, we studied their cytokine profile before injection in mice.

By MTT assay and kinetic proliferation we found that IL-17 per se did not exert effects on GL261 proliferation. Because Th17 may differentiate under the influence of TGF-ß as well as regulatory T cells (Treg), we characterized both Treg and Th17. Treg were significantly higher in splenocytes from Gb than naïve mice (19.8±2.8% vs 3.5±0.05% respectively, p=0.01). nTh17 produced higher levels of IFN- than IL-10 (9.7±0.7% vs 2.2± 1.5, respectively, p=0.01) suggesting a suppressive function on tumor microenvironment. In contrast, GbTh17 produced more IL-10 than IFN- (9.3±1.4% vs 1.6±0.7%, respectively, p=0.02), suggesting a promoting function on tumor growth. To determine the potential influence of Treg in driving Th17 cytokine profile, using PC61 we depleted the Treg fraction in Gb splenocytes from 19.5±2.0% to 1.3±0.6% (p&lt;0.0001). After depletion we found a significant increase of IL-17/IFN- cells (from 1.7±0.5% to 6.1±0.9% p=0.007) and a significant decrease of IL-17/IL-10 cells (from 9.2±2.2% to 3.2±0.2%, p=0.03). These results suggest that Th17 polarization may be induced by Treg and the possibility that Th17 in glioma might mediate an anti-tumor effect depending on locally produced cytokines.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-315.