Abstract
BACKGROUND: Targeting the mutations and amplifications in the epidermal growth factor receptor (EGFR) gene has curative effects on cancers of the lung, oral cavity, and gastrointestinal system. However, a systemic immune inflammation is an adverse effect of this therapeutic strategy. In this study, we aimed to identify the possible changes in the tumor microenvironment that contribute to the anti-cancer activity of EGFR inhibition. METHODS: Squamous-cell cancers were induced by the syngeneic transplantation of either EGFR-null or wild-type mouse primary keratinocytes that had been transduced with an oncogenic H-ras retrovirus. The mice were treated with gefinitib. Then, flow cytometric was used to detect the ratio of T cells and the expression of programmed cell death receptor 1 (PD-1). RT-PCR was used to detect the expression of cytokines and chemokines. RESULTS: Tumors that formed from EGFR-null keratinocytes were smaller, had fewer infiltrating FoxP3+ Treg cells, lower Foxp3 RNA, and lower percentage of PD-1 positive CD4 cells than those formed from wild-type keratinocytes. These results indicated that tumor cells can autonomously regulate the tumor microenvironment. Hosts with wild-type cancers and that were treated with gefitinib for 1 week tended to have smaller tumors. The treated mice in the short-term pharmacological model tended to have reduced FoxP3+ cells and FoxP3 RNA in the tumor microenvironment, as well as a substantially increased ratio of IL-1A/IL-1RA transcripts. These results suggested that the brief systemic inhibition of EGFR signaling alters the immune environment of the targeted cancer. CONCLUSIONS: The autonomous (genetic) or systemic (pharmacologic) inhibition of EGFR signaling in tumor cells reduces tumor growth and Treg infiltration in the tumor microenvironment. An EGFR-dependent Treg function supports the growth of squamous cancers. Therefore, Treg is a target in the therapeutic strategy of EGFR inhibition.