Clinical responses to immune checkpoint blockade by anti-PD-1/PD-L1 monoclonal antibodies in non-small-cell lung cancer (NSCLC) may be associated with PD-L1 expression. This study was undertaken to determine the expression profile of PD-L1 in patients with Kras-mutant lung adenocarcinoma (LUAD) and to investigate the activation of Kras codon subtypes as a mechanism of PD-L1 regulation.
PD-L1 expression was evaluated by IHC (SP142 clone, Ventana) on 117 LUAD (KrasWT, n = 51; Krasmut, n = 66). Stable cell lines were generated by transfection of Kras-G12D, G12V, G12C and WT plasmids into Beas2B bronchial cells.
IHC analysis showed higher expression of PD-L1 in both tumor and immune cells in Kras-mutant LUAD compared with KrasWT tumors (37% vs. 18%; P = 0.005). Kras-mutant PD-L1+ tumors had increased CD66b+ neutrophil infiltrates and lower CD8+ T-cell content than PD-L1− tumors. In vitro, mutant Kras led to significantly higher cell-surface PD-L1 expression and PD-L1 transcripts, notably in KrasG12C and KrasG12V cells, suggesting PD-L1 transcriptional regulation. There was differential activation of NF-kB, ERK and Pi3k/Akt pathways between Kras-mutant subtypes. In addition, PD-L1 was upregulated 3-fold by stimulation with IFNɣ, independently of the Kras codon subtypes. Instead, hypoxia significantly increased PD-L1 expression in KrasG12C and KrasG12D cells. Co-culture experiments with human PBMCs from healthy patients were performed to determine the functional effect of altered PD-L1 expression. Increased PD-L1 expression by tumor cells induced by Kras mutations led to decreased PBMCs proliferation and increased apoptosis. An anti-PD-L1 checkpoint inhibitor is currently being tested as single agent or in combination with ERK or PI3K inhibitors in our Kras cell models.
PD-L1 is expressed in 37% of Kras mutant LUAD, suggesting PD-L1 as a therapeutic target in this subset. According to the Kras mutation subtype, potential drugs targeting the NF-kB, ERK or Pi3k/Akt pathways may additionally increase the antitumor adaptive immune responses.
Clinical trial identification
Legal entity responsible for the study
Pasteur Hospital, Nice
All authors have declared no conflicts of interest.