Immune correlates of CD73 expression in patients with urothelial carcinoma (UC).

Abstract

4548 Background: Checkpoint inhibitors have improved outcomes in UC. However, response rates are low and additional mechanisms of immune evasion need to be ascertained. CD73 (encoded by NT5E) converts extracellular AMP to adenosine, which exerts an immunosuppressive effect in the tumor microenvironment by inhibiting infiltrating T and NK cells. Utilizing The Cancer Genome Atlas (TCGA) bladder cancer dataset, we evaluated correlations between NT5E expression and the immune milieu in UC. Methods: RNA-seq data from 411 primary UC tumor samples were obtained from the TCGA. Patients were split into low, intermediate, and high NT5E expression groups (≤ -1, -1 to 1 and ≥1 standard deviation from the overall mean). A tumor inflammation signature (TIS) reflecting an inflamed tumor phenotype was calculated based on the averaged expression of 18 previously validated genes (Ayers et al, 2017). NT5E expression was compared between tumors with high and low TIS scores and among the TCGA molecular subtypes. Abundance of infiltrating immune cell subsets was estimated based on expression of previously identified 782 immune metagenes and compared between NT5E expression groups (Charoentong et al, 2017). The Mann-Whitney U test assessed statistical significance, and the Bonferroni correction was used to control for false discovery rate. Results: NT5E expression was significantly higher in tumors with a high TIS score compared to those with low TIS score (P<0.0001) and correlated with expression of other immune checkpoints such as PD-L1, IDO and LAG-3 (each P<0.01). Patients with basal/squamous subtype had the highest NT5E expression compared to luminal or neuronal subtypes. High NT5E expression was associated with increased infiltrating NK cells, neutrophils, Tregs and decreased Type 2 T helper cells. Conclusions: High expression of NT5E in UC patients with an inflamed tumor phenotype was associated with an increase in infiltrating Tregs, and the basal/squamous subtype. Our findings highlight a potential role of CD73-adenosine pathway as a mechanism of immune evasion and a novel therapeutic target in UC. Further studies to assess the clinical impact of NT5E expression on outcomes in UC patients treated with immunotherapy are needed. AT and NA: equal contribution.