Abstract
Immunotherapy approaches currently make their way into the clinics to improve the outcome of standard radiochemotherapy (RCT). The programed cell death receptor ligand 1 (PD-L1) is one possible target that, upon blockade, allows T cell-dependent antitumor immune responses to be executed. To date, it is unclear which RCT protocol and which fractionation scheme leads to increased PD-L1 expression and thereby renders blockade of this immune suppressive pathway reasonable. We therefore investigated the impact of radiotherapy (RT), chemotherapy (CT), and RCT on PD-L1 surface expression on tumor cells of tumor entities with differing somatic mutation prevalence. Murine melanoma (B16-F10), glioblastoma (GL261-luc2), and colorectal (CT26) tumor cells were treated with dacarbazine, temozolomide, and a combination of irinotecan, oxaliplatin, and fluorouracil, respectively. Additionally, they were irradiated with a single dose [10 Gray (Gy)] or hypo-fractionated (2 × 5 Gy), respectively, norm-fractionated (5 × 2 Gy) radiation protocols were used. PD-L1 surface and intracellular interferon (IFN)-gamma expression was measured by flow cytometry, and IL-6 release was determined by ELISA. Furthermore, tumor cell death was monitored by AnnexinV-FITC/7-AAD staining. For first in vivo analyses, the B16-F10 mouse melanoma model was chosen. In B16-F10 and GL261-luc2 cells, particularly norm-fractionated and hypo-fractionated radiation led to a significant increase of surface PD-L1, which could not be observed in CT26 cells. Furthermore, PD-L1 expression is more pronounced on vital tumor cells and goes along with increased levels of IFN-gamma in the tumor cells. In melanoma cells CT was the main trigger for IL-6 release, while in glioblastoma cells it was norm-fractionated RT. In vivo, fractionated RT only in combination with dacarbazine induced PD-L1 expression on melanoma cells. Our results suggest a tumor cell-mediated upregulation of PD-L1 expression following in particular chemoradiation that is not only dependent on the somatic mutation prevalence of the tumor entity.
Highlights
A promising new cancer treatment strategy is combining classical radiochemotherapy (RCT, chemoradiation) with immunotherapy (IT)
The B16-F10 melanoma cells proved to be highly resistant against radiation, since 24 h after the respective treatments only few tumor cells died via apoptosis or necrosis
To a lesser extent but still significant when compared to mock-treated cells, single dose irradiation with 10 Gy or DTIC treatment led to an increase in programed cell death receptor ligand 1 (PD-L1) surface expression (Figures 2B,C)
Summary
A promising new cancer treatment strategy is combining classical radiochemotherapy (RCT, chemoradiation) with immunotherapy (IT). As certain chemotherapeutic agents such as anthracyclines [3], ionizing radiation is capable of rendering the tumor cell and its microenvironment immunogenic by inducing the upregulation of activation markers for immune cells and death receptors on tumor cells and by further inducing the release of danger signals and cytokines [4,5,6]. Besides these immune-stimulating properties of radiation, it can induce the upregulation of immune suppressive molecules. The pro-inflammatory cytokine interferon (IFN)-gamma has been shown to induce upregulation of PD-L1 on the surface of tumor cells [11]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
