Background: NK cells play a crucial role in the antitumor immune response and are involved in controlling tumor formation, progression and metastases. Glioblastoma (GBM) is the most devastating brain tumor, associated with very poor prognosis. While immunotherapy emerged as a promising approach for anti cancer therapy, GBM appears immune resistant. Here, we studied the role of NK cells in targeting glioblastoma and possible mechanisms of NK immune evasion.

Methods: NK cells were isolated from freshly resected GBM tissue, matching peripheral blood and the blood of healthy controls. Flow cytometry was used to characterize the cells and their ability to produce cytokines, and chromium release assay was perfumed to assess their cytotoxicity. In vitro assays were performed by co-culturing GBM stem cells (GSCs) with healthy donor NK cells.

Results: We found that whereas NK cells were abundant in primary GBM tissue and could efficiently target GBM stem cells (GSCs), GBM infiltrating NK cells (TiNKs) displayed an abnormal phenotype with downregulation of many activating receptors including CD16, NKG2D, DNAM, NKp30, NKp46, 2B4 and NKG2C and upregulation of inhibitory proteins such as PD-1. This inhibitory phenotype was associated with impaired NK cell function when compared with NK cells isolated from the peripheral blood of patients and healthy donors. GSC-NK cell-cell contact resulted in release of TGF-β by GCSs, which in turn led to NK dysfunction through constitutive activating of the p-Smad pathway. TGF-β activation, in turn, is partially mediated by the matrix metalloproteases MMP-2 and MMP-9, secreted by GSCs upon contact with NK cells and enhanced upon TGF-β exposure. We demonstrated that inhibition of the TGF-β axis, in particular by the small molecule inhibitor, galunisertib, can prevent GSC-induced NK cell dysfunction but is unable to inactivate the p-Smad pathway, thus, cannot reverse existing dysfunction.

Conclusions: Our results indicate that NK-GBM cross-talk plays an important role in tumor escape and highlight the importance of developing future adoptive transfer therapies with the intent of limiting tumor escape from antitumor immunity.

Note: This abstract was not presented at the meeting.

Citation Format: Hila Shaim, Abdullah Alsuliman, Konrad Gabrusiewicz, Jun Wei, John Yu, Rafet Basar, May Daher, Lucila Kerbauy, Mayela Mendt, Muharrem Muftuoglu, Li Li, Enli Liu, Nobuhiko Imahashi, Sonny Ang, Young Gi, Pinaki Banerjee, David Marin, Richard Champlin, Elizabeth Shpall, Amy Heimberger, Katayoun Rezvani. TGF-β is a key mediator of NK cell dysfunction in gliolastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2949. doi:10.1158/1538-7445.AM2017-2949

©2017 American Association for Cancer Research.
2017
American Association for Cancer Research.