Our previous work has revealed that human ex vivo expanded/activated γδ T cells kill primary high-grade glioma in vitro and will also slow tumor progression and improve survival in immunodeficient mice bearing solid tumors derived from glioblastoma multiforme cell lines. However, the response of γδ T cells to high-grade glioma has not been investigated in a fully immunocompetent mouse model. In this report, we describe the interactions between the early- and late-stage syngeneic GL261 intracranial gliomas and circulating γδ T cells in WT C57BL/6 mice. Tumors were established in mice by injection of GL261 cells (5 x 105) into the right caudate nucleus, forming classical high-grade gliomas resulting in a mean survival of 30 days. Circulating absolute γδ T cell count, phenotype, Vγ/Vδ repertoire, tumor histopathology, NKG2D ligands expression, and T cell invasion were assessed at day 11+ 1 post-injection and at end stage. The GL261 cell line expresses NKG2D ligands MULT-1 and RAE-1. NKG2DL expression is, however, significantly down regulated when cells are cultured under hypoxic (5%O2) conditions. MULT-1 expression was found to be variable in GL261-derived tumors. At 11 days, small established tumors were noted without evidence of neurologic symptoms. The circulating γδ T cell count was significantly higher for 11-day glioma-bearing mice (p = 0.003) vs. healthy controls with a significant percentage of γδ T cells expressing Annexin V (p = 0.0019). Conversely, γδ T cell counts at end-stage disease were significantly lower than controls (p = 0.0001) and 11-day glioma-bearing mice (p < 0.001). Examination of the γδ T cell receptor (TCR) repertoire did not reveal significant changes in the Vγ1, Vγ2, Vγ7 or Vδ1 subsets from controls either post-tumor injection day 11+1 or at the termination of the experiment. Although the Vδ4 and Vδ6.3 ratios also did not change at day 11+1, the Vδ6.3 population fell significantly at end stage tumor growth (p = 0.0003) offset by a corresponding increase in the proportion of Vδ4 cells (p = 0.0410). Vγ2Vδ4 IL-17 producing γδ T cells and did show a modest increase at post-tumor injection day 11+1 that did not reach statistical significance (p = 0.0954). TCR subsets Vγ3 and Vδ3 were negligible. GL261 cells were also moderately sensitive to ex vivo lysis by activated syngeneic γδ T cells. Mice that received a single stereotactic-guided injection 1.5 x 106 ex vivo activated γδ T cells 15 minutes following GL261 injection did not show a survival advantage over untreated controls, however, gross and histologic examination revealed local inhibition of tumor growth near the injection site. In summary, early-stage gliomas elicit a generalized expansion of circulating γδ T cells that are subsequently depleted in end-stage tumor growth. Consistent with the known immunosuppressive properties pf high-grade gliomas, activated γδ T cells did not invade the tumor in substantial numbers or prolong survival but show evidence of tumor growth inhibition when injected into the tumor bed.
Citation Format: Hyung Kim, Rebecca O'Brien, George Yancey Gillespie, Gretchen A. Cloud, Cathy Langford, Lualhati Harkins, Lawrence S. Lamb. Characterization of the γδ T-cell response in high-grade glioma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 643A. doi:10.1158/1538-7445.AM2014-643A