Abstract 1019: EGFR signal induces T cell non-inflamed tumor microenvironment (TME) through suppression of chemokine production from human EGFRmt lung adenocarcinoma

Abstract

Abstract EGFR mutation-positive (EGFRmt) lung adenocarcinoma (LA) is refractory to immune checkpoint inhibitors, such as anti-PD-1/anti-PD-L1 mAbs. However, the refractory mechanism remains to be elucidated. We found CD8A mRNA level was significantly lower in EGFRmt LA than in EGFRwt LA in TCGA data, which was validated at protein expression levels by immunohistochemistry of surgically obtained LA tissues (p<0.0001). We identified several chemokines showing positive correlations to the CD8A mRNA level on the TCGA data set, some of which were significantly lower in EGFRmt LA than in EGFRwt LA, suggesting that oncogenic EGFR signal might be related to the suppression of chemokine expression in the TME, leading to the less recruitment of CD8 T cells to the tumor. We conducted multiplex chemokine assays of several EGFRmt LA cell lines, and found EGFR-TKI of osimertinib treatment significantly increased several chemokine expressions in the culture supernatant compared to control DMSO (p<0.005), indicating EGFR signal may inhibit tumor intrinsic chemokine production, which may explain the T cell non-inflamed TME. Among the upregulated chemokines, IFN-responsive chemokines, CXCL9, 10, and 11, showed prominent increase (by 30 to 167-fold) under osimertinib treatment and IFN-γ stimulation. A T cell migration assay revealed CXCL10 was a major chemokine contributing to the chemotaxis. We further examined the suppressive mechanisms of CXCL10 expression via EGFR signal. siRNA experiments against EGFR confirmed the specific inhibition of CXCL10 expression by EGFR signal. Inhibitor experiments for the downstream of EGFR signal revealed that MAPK, but neither PI3K nor STAT3 signal, partially contributed to CXCL10 suppression. The increase of CXCL10 expression by osimertinb treatment occurred at an mRNA level. But an mRNA stability test revealed that EGFR signal did not decrease, but increased the mRNA stability of CXCL10, suggesting that EGFR signal might suppress the promoter activity of CXCL10. We conducted the promoter analysis of proximal 2kb of CXCL10 gene, however, the regulatory elements within the region, such as NFκB or IRF-1, were not accounted for the CXCL10 up-regulation upon EGFR-TKI treatment, suggesting the transcriptional control with EGFR signal at more remote cis-element(s). The data indicate that EGFR signal might work as a T cell excluding signal in human EGFRmt LA by suppressing several chemokine productions from the cells. Citation Format: Hidetoshi Sumimoto, Atsushi Takano, Koji Teramoto, Yataro Daigo. EGFR signal induces T cell non-inflamed tumor microenvironment (TME) through suppression of chemokine production from human EGFRmt lung adenocarcinoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1019.