Radiation-induced acquired expression of PD-L1 and reprogramming of the tumor microenvironment in cervical cancer.

[OBJECTIVE] Although widely used for immune checkpoint inhibitors (ICIs) therapy patient selection, programmed death-ligand 1 (PD-L1) remains an imperfect biomarker for such selection. We explored the impact of radiotherapy (RT) on PD-L1 and the tumor microenvironment (TME) and delved into the mechanisms underlying this effect in cervical cancer.

[METHODS] Patients with treatment-naïve cervical cancer who underwent RT between March 2021 and October 2022 were included. Cancer tissue samples were collected during RT. PD-L1 expression was evaluated by immunohistochemical staining. Lymphocytes in the TME were detected by multiplex immunofluorescence (mIF). SiHa, CaSki, U14, and TC-1 cells verified the in vitro findings using western blot analysis.

[RESULTS] Among the 40 cases, although the expression changed constantly, PD-L1 was significantly upregulated in most patients exposed to doses of 10-14 and 18-22 Gy; this radiation-induced acquired PD-L1 expression was consistently observed regardless of patients' baseline PD-L1 status or concurrent chemotherapy. In vitro experiments confirmed increased PD-L1 post-RT. RNA sequencing revealed NF-κB signaling pathway enrichment in the CD274-elevated group. Western blotting indicated significant p-P65 and p-IKKα/β increases post-irradiation; PD-L1 decreased with NF-κB activation inhibitors. mIF demonstrated increased CD8 T cell and macrophage infiltration into tumor nests (P = 0.0496; P = 0.0017) and tumor stroma (P = 0.0049), with overall increased TME infiltration (P = 0.0139; P = 0.0321).

[CONCLUSION] RT induces PD-L1 expression and enhances CD8 T cell and macrophage infiltration into the TME of patients with cervical cancer. Therefore, it may establish an immunologically favorable context for synergistic action with subsequent immunotherapy.