Abstract LB-315: A critical role for T regulatory cells in driving Th17 cytokine profile and modulating their ability to affect glioma microenvironment

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 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 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.