Indoleamine 2,3-dioxygenase (IDO1), PD-L1, and overall survival (OS) of patients diagnosed with esophageal cancer.

Abstract

50 Background: Immune checkpoint inhibition of PD-L1 is emerging as an important therapeutic target for patients with advanced esophageal cancer. However, response rates to therapy remain low. IDO1 is a rate-limiting immunosuppressive enzyme that has emerged as an important immunotherapeutic target in human cancer. The role, expression pattern, and relevance of IDO1 in esophageal cancer are currently unknown. Here, we utilize gene expression analysis of the cancer genome atlas and quantitative immunohistochemistry (IHC) to understand whether IDO1 contributes to a poor esophageal cancer patient prognosis. Methods: mRNA expression was assessed using Hi-RNA sequencing in an esophageal squamous cell carcinoma (SCC) cohort of 87 patients and an adenocarcinoma (AC) cohort of 97 patients. Survival data was obtained from the Cancer Genome Atlas. Patient survival was analyzed by the Kaplan-Meier Method. IHC for a second cohort of 93 cases of esophageal SCC were stained for IDO1, PD-L1, and CD3ε, followed by light microscopic immunoscoring analysis. Correlation between markers was analyzed using Fisher’s exact test. Results: The median OS for high versus low IDO1 mRNA levels was 15.9 months vs 41.5 months, respectively (p =0.02) in the SCC cohort. The median OS was 20.1 months and 58.6 months in the high vs low IDO1 mRNA levels, respectively (p = 0.036) in the esophageal AC cohort. High co-expression for IDO1 and PD-L1 vs low co-expression of these markers, demonstrated a median OS of 15.1 months and 41.5 months, respectively, in the SCC cohort, and 13.7 months and 41.5 months, respectively, in the AC cohort. IHC for IDO1 SCC showed a significant correlation with PD-L1 (p = < 0.0001) and CD3ε (p = < 0.0001). PD-L1 expression also significantly correlated with CD3ε expression (p = < 0.0001). Conclusions: Esophageal cancer with high IDO1 and PD-L1 levels is associated with significantly decreased survival. The expression of IDO1 and PD-L1 is significantly enhanced by the coincident intratumoral increase of T cells. These data suggest that combinatorial approaches for combination therapies that simultaneously inhibit IDO1 and PD-(L)1 may enhance T-cell mediated control of esophageal cancer in patients.