Abstract 5166: Extracellular matrix protein tenascin C increases phagocytosis mediated by CD47 loss-of-function in glioblastoma

Abstract

Abstract Glioblastomas (GBMs) are highly infiltrated by myeloid-derived innate immune cells that contribute to an immunosuppressive nature of the brain tumor microenvironment (TME). CD47 has been shown to mediate immune evasion as the CD47-SIRPα axis prevents phagocytosis of tumor cells by macrophages and other myeloid cells. In this study, we established CD47 homozygous deletion (CD47-/-) in human and mouse GBM cells by genome editing to investigate the impact of eliminating the “don’t eat me” signal on tumor growth and tumor-TME interactions. CD47 knockout (KO) did not significantly alter tumor cell proliferation in vitro, but significantly increased phagocytosis of tumor cells by macrophages in co-cultures. Compared with CD47 wild type xenografts, orthotopic xenografts derived from CD47-/- tumor cells grew much slower with enhanced tumor cell phagocytosis and increased recruitment of M2-like tumor associated microglia/macrophages (TAMs). CD47 KO increased tumor-associated extracellular matrix protein tenascin C (TNC) in xenografts, which was further examined in vitro. CD47 loss-of-function upregulated TNC expression in tumor cells via a Notch pathway mediated mechanism. ShRNA-based TNC knockdown in tumor cells enhanced the growth of CD47-/-xenografts in vivo, and decrease the number of TAMs. TNC knockdown inhibited phagocytosis of CD47-/- tumor cells in co-cultures. Furthermore, TNC stimulated release of pro-inflammatory factors including TNF-α via a toll-like receptor 4 (TLR4) and STAT3-dependent mechanism in human macrophage cells. These results reveal a vital immunomodulation role of TNC in brain tumor biology and demonstrate the prominence of the TME extracellular matrix in affecting the anti-tumor function of brain innate immune cells. Citation Format: Ding Ma, Senquan Liu, Bachchu Lal, John Laterra, Mary Ann Wilson, Shuli Xia. Extracellular matrix protein tenascin C increases phagocytosis mediated by CD47 loss-of-function in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5166.