Irradiation Mediates IFN alpha and CXCL9 Expression in Non-Small Cell Lung Cancer to Stimulate CD8(+) T Cells Activity and Migration toward Tumors

Irradiation-broken DNA fragments increase type I interferon and chemokines secretion in tumor cells. Since radiotherapy may augment tumor immunotherapy, we hypothesize that the chemokines increased by irradiation could recruit CD8(+) T cells to suppress tumor proliferation. This study intended to unveil the secreted factors activating and recruiting CD8(+) T cells in non-small-cell lung cancer (NSCLC). EGFR-positive A549 was selected and treated by X-irradiation (IR) to identify the overexpression of chemokines associated to CD8(+) T cell cytotoxicity and recruitment. A transwell assay with Alexa 488-labeled CD8(+) T cells was used to evaluate CD8(+) T cell motility in vitro. A nuclear imaging platform by In-111-labeled nivolumab was used to track CD8(+) T cells homing to tumors in vivo. The activation markers GZMB, PRF-1, and IFN gamma, migration marker CD183 (CXCR3), and inhibitory marker CD274 (PD-1), were measured and compared in CD8(+) T cells with A549 co-cultured, chemokines treated, and patients with late-stage lung cancer. We found that IR not only suppressed A549 proliferation but also induced IFN alpha and CXCL9 expression (p < 0.05). IFN alpha majorly increased IFN gamma levels in CD8(+) T cells (p < 0.05) and synergistically with CXCL9 enhanced CD8(+) T cell migration in vitro (p < 0.05). We found that CXCR3 and PD-1 were down-regulated and up-regulated, respectively, in the peripheral blood CD8(+) T cells in patients with lung cancer (n = 4 vs. healthy n = 3, both p < 0.05), which exhibited reduction of cell motility (p < 0.05). The in vivo nuclear imaging data indicated highly CD8(+) T cells migrated to A549-induced tumors. In addition, we demonstrated that healthy PBMCs significantly suppressed the parallel tumor growth (p < 0.05) and the radioresistant tumor growth in the tumor xenograft mice (p < 0.05), but PBMCs from patients with lung cancer had lost the anti-tumor capacity. We demonstrated that IR induced IFN alpha and CXCL9 expression in A549 cells, leading to CD8(+) T cell migration. This study unveiled a potential mechanism for radiotherapy to activate and recruit CD8(+) T cells to suppress lung tumors.