Immunogenicity is the ability of tumors to induce a specific immune response. It depends on different biological properties, including tumor mutational burden, the expression of immune checkpoint inhibitors such as programmed death-ligand 1 (PD-L1), and the expression of major histocompatibility complex 1 (MHC-1). The immune classification of tumors is still problematic. Studies have shown that radiotherapy can enhance tumor immunogenicity. In this study, we cytometrically determined the MHC-1 and PD-L1 expression on live cells after irradiation with doses ranging from 6 to 24 Gy in vitro. Furthermore, we tested and compared the proliferation and radiosensitivity of B16F10, CT26 and 4T1 cells using proliferation and clonogenic assays, respectively. We showed that proliferation rate of cells B16F10, CT26 and 4T1 was comparable. B16F10 cells are significantly more radiosensitive than CT26 and 4T1 cells. MHC-1 expression was significantly higher in non-irradiated CT26 and 4T1 (>99 %) cells compared to non-irradiated B16F10 cells (~2.4 %). Ionizing radiation significantly increased MHC-1 expression on B16F10 cells with all doses tested, while MHC-1 expression on CT26 and 4T1 cells remained unchanged. Moreover, PD-L1 expression was increased on B16F10, CT26 and 4T1 cells after irradiation (6-24 Gy). To conclude, our study showed that irradiation affects PD-L1 and MHC-1 expression on B16F10, 4T1 and CT26 tumor cells.
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