Irradiation Suppresses IFNγ-Mediated PD-L1 and MCL1 Expression in EGFR-Positive Lung Cancer to Augment CD8+ T Cells Cytotoxicity

The current understanding of the immune landscape relative to radiotherapy across tumor types

Radiotherapy is part of the standard of care treatment for a great majority of cancer patients. As a result of radiation, both tumor cells and the environment around them are affected directly by radiation, which mainly primes but also might limit the immune response. Multiple immune factors play a role in cancer progression and response to radiotherapy, including the immune tumor microenvironment and systemic immunity referred to as the immune landscape. A heterogeneous tumor microenvironment and the varying patient characteristics complicate the dynamic relationship between radiotherapy and this immune landscape. In this review, we will present the current overview of the immunological landscape in relation to radiotherapy in order to provide insight and encourage research to further improve cancer treatment. An investigation into the impact of radiation therapy on the immune landscape showed in several cancers a common pattern of immunological responses after radiation. Radiation leads to an upsurge in infiltrating T lymphocytes and the expression of programmed death ligand 1 (PD-L1) which can hint at a benefit for the patient when combined with immunotherapy. In spite of this, lymphopenia in the tumor microenvironment of 'cold' tumors or caused by radiation is considered to be an important obstacle to the patient's survival. In several cancers, a rise in the immunosuppressive populations is seen after radiation, mainly pro-tumoral M2 macrophages and myeloid-derived suppressor cells (MDSCs). As a final point, we will highlight how the radiation parameters themselves can influence the immune system and, therefore, be exploited to the advantage of the patient.

Radiotherapy enhances CXCR3highCD8+ T cell activation through inducing IFNγ-mediated CXCL10 and ICAM-1 expression in lung cancer cells

Radiotherapy (RT) not only damages tumors but also induces interferon (IFN) expression in tumors. IFNs mediate PD-L1 to exhaust CD8⁺ T cells, but which also directly impact tumor cells and potentially activate anti-tumor immune surveillance. Little is known about the contradictory mechanism of IFNs in regulating CD8⁺ T-mediated anti-tumor activity in lung cancer. This study found that RT induced IFNs and CXCL9/10 expression in the RT-treated lung cancer cells. Specifically, RT- and IFNγ-pretreated A549 significantly activated CD8⁺ T cells, resulting in significant inhibition of A549 colony formation. RNAseq and consequent qPCR results revealed that IFNγ induced PD-L1, CXCL10, and ICAM-1, whereas PD-L1 knockdown activated CD8⁺ T cells, but ICAM-1 knockdown diminished CD8⁺ T cell activation. We further demonstrated that CXCR3 and CXCL10 decreased in the CD8⁺ T cells and nonCD8⁺ PBMCs, respectively, in the patients with lung cancer that expressed lower reactivation as co-cultured with A549 cells. In addition, inhibitors targeting CXCR3 and LFA-1 in CD8⁺ T cells significantly diminished CD8⁺ T cell activation and splenocytes-mediated anti-LL/2shPdl1. In conclusion, we validated that RT suppressed lung cancer and overexpress PD-L1, CXCL10, and ICAM-1, which exhibited different roles in regulating CD8⁺ T cell activity. We propose that CXCR3^highCD8⁺ T cells stimulated by CXCL10 exhibit anti-tumor immunity, possibly by enhancing T cells-tumor cells adhesion through CXCL10/CXCR3-activated LFA-1-ICAM-1 interaction, but CXCR3^lowCD8⁺ T cells with low CXCL10 in patients with lung cancer were exhausted by PD-L1 dominantly. Therefore, RT potentially activates CD8⁺ T cells by inducing IFNs-mediated CXCL10 and ICAM-1 expression in tumors to enhance CD8⁺ T-tumor adhesion and recognition. This study clarified the possible mechanisms of RT and IFNs in regulating CD8⁺ T cell activation in lung cancer.

Sorafenib suppresses radioresistance and synergizes radiotherapy-mediated CD8+ T cell activation to eradicate hepatocellular carcinoma

Radiotherapy (RT) is applied to eradicate tumors in the clinic. However, hepatocellular carcinoma (HCC) exhibits resistance against RT. It is demonstrated that RT directly inhibits tumor growth but which induces type I interferons (IFNs) expression to phosphorylate STATs and increase STATs-downstream PD-L1 levels in the survival tumor cells. Since sorafenib is capable of suppressing STATs, we, therefore, hypothesize that sorafenib suppresses IFNs-mediated radioresistance and PD-L1 in the residual tumor cells and may synergistically enhance RT-mediated reactivation of CD8⁺ T immunological activity to eradicate HCC cells. We found that combined RT, sorafenib, and PBMCs significantly suppress the colony formation in the HCC cells, whereas CD8⁺ T cells expressed high granzyme B (GZMB) and perforin (PRF1) in co-cultured with RT-treated HCC cells. We demonstrated RT significantly inhibited HCC cell viability but induced IFNα and IL-6 expression in the RT-treated HCC cells, resulting in immune checkpoint PD-L1 and anti-apoptosis MCL1 and BCL2 overexpression in the non-RT HCC cells. We found that sorafenib decreased RT-PLC5 medium (RT-PLC5-m)-mediated cell growth by suppressing IFNα- and IL-6-mediated STAT1 and STAT3 phosphorylation. Sorafenib also reduced IFNα-mediated PD-L1 levels in HCC cells. Meanwhile, RT-PLC5-m reactivated CD8⁺ T cells and non-CD8⁺ PBMCs, resulting in high IFNγ and IL-2 levels in CD8⁺ T cells, and cytokines IFNα, IFNγ, IL-2, and IL-6 in non-CD8⁺ PBMCs. Particularly, CD8⁺ T cells expressed higher GZMB and PRF1 and non-CD8⁺ PBMCs expressed higher IFNα, IFNγ, IL-2, IL-6, CXCL9, and CXCL10 in co-cultured with RT-treated HCC cells compared to parental cells. Although we demonstrated that sorafenib slightly inhibited RT-mediated GZMB and PRF1 expression in CD8⁺ T cells, and cytokines levels in non-CD8⁺ PBMCs. Based on sorafenib significantly suppressed IFNα- and IL-6-mediated radioresistance and PD-L1 expression, we demonstrated that sorafenib synergized RT and immune surveillance for suppressing PLC5 cell viability in vitro. In conclusion, this study revealed that RT induced IFNα and IL-6 expression to phosphorylate STAT1 and STAT3 by autocrine and paracrine effect, leading to radioresistance and PD-L1 overexpression in HCC cells. Sorafenib not only suppressed IFNα- and IL-6-mediated PLC5 cell growth but also inhibited IFNα-mediated PD-L1 expression, synergistically enhancing RT-mediated CD8⁺ T cell reactivation against HCC cells.