PD-L1 copy number loss in NSCLC associates with reduced PD-L1 tumour staining and a cold immunophenotype.

Abstract

PD-L1 copy number gains may be predictive of clinical response to immunotherapy in NSCLC. This study investigated PD-L1 copy number variations in tumour resection and bronchoscopy biopsies and its relationship with PD-L1 tumour cell staining and inflammatory gene expression. PD-L1 gene copy number and mRNA expression were evaluated by real time PCR in surgically resected NSCLC tumour biopsies (n= 87) and control biopsies (n=20). A second cohort (n= 15) of bronchoscopy derived tumour biopsies were analysed, including multiple biopsies from the same patient across different anatomical sites. PD-L1 mRNA levels strongly correlated with PD-L1 tumour staining (r= 0.55, p< 0.0001). Interferonγ (IFNγ) mRNA expression associated with PD-L1 immune cell staining, but not PD-L1 tumour cell staining. In contrast, PD-L1 copy number positively associated PD-L1 tumour staining, but not PD-L1 immune cell staining. PD-L1 copy number analysis detected loss (15/87= 17%) and gain (5/87= 7%) of copy number. Tumours with low PD-L1 copy number expressed significantly reduced levels of inflammatory (INFγ, IL-6, IL-1, MMP-9) and immunosuppressive (IL-10, TGFβ) mediators. Analysis of bronchoscopy derived biopsies demonstrated low heterogeneity in copy number values across different anatomical sites, in contrast to more variable PD-L1 mRNA expression. Low PD-L1 copy number tumours display reduced PD-L1 expression, reduced PD-L1 tumour cell staining and an immunological cold tumour microenvironment. Since PD-L1 copy number values are highly stable across different tumour regions, its evaluation may represent a robust and complimentary biomarker for predicting response to immunotherapy, where low copy number may predict lack of response.