Immune checkpoint regulation is influenced by standard treatment in  in vitro and ex vivo HNSCC cultures

Introduction The inhibition of immunoregulatory checkpoints such as the PD-1/PD-L1 axis is currently a promising immunotherapeutic approach for head and neck squamous cell carcinoma (HNSCC), but the therapy often fails due to lacking tumor control. The combination of immune checkpoint inhibitors (ICI) with established therapies is currently being investigated in clinical studies, but the influence of these conventional treatments on immune checkpoint regulation remains unclear.

Methods An HNSCC 2D cell culture model was treated with fractionated irradiation (FR) alone and in combination with cisplatin/cetuximab. The effects of these therapy pillars on PD-L1 and signaling pathways that mediate therapy resistance were assessed using Western Blot, CFA and IHC and validated in an  ex vivo 3D HNSCC tissue culture model. The cultures were additionally treated with ICI to evaluate the therapeutic response of the tumor microenvironment, particularly of immune cells.

Results A strong induction of PD-L1 by cisplatin was observed in vitro. The combination of FR with cisplatin had even stronger effects. In comparison to single dose irradiation, the radioresistance-mediating MAP kinase phospho-ERK1/2 was upregulated after fractionated IR. The ex vivo model confirmed heterogeneity in PD-L1 expression and ERK phosphorylation.

Discussion Our results suggest a complex and probably context-dependent PD-L1 regulation during radiochemotherapy. Adapting MAPK to a fractionated irradiation scheme could indicate a mechanism of resistance. We consider the ex vivo technology as a promising tool for individualized efficacy testing of drugs.

Projektförderung durch das Land Baden-Württemberg (Förder-Nr.: 33-7533-6-1522/10/4)/ Project funding by the state of Baden-Württemberg (grant number 33-7533-6-1522/10/4)

Publication History

Article published online:
24 May 2022