Changes in Indoleamine 2,3-Dioxygenase 1 Expression and CD8+ Tumor-Infiltrating Lymphocytes after Neoadjuvant Chemoradiation Therapy and Prognostic Significance in Esophageal Squamous Cell Carcinoma.

Despite good preclinical evidence, clinical data on the effect of neoadjuvant chemoradiation therapy (CRT) on expression of immune markers in esophageal cancer are limited. This study aimed to evaluate the changes in indoleamine 2,3-dioxygenase 1 (IDO1) expression, programmed cell death-ligand 1 (PD-L1) expression, and CD8+ tumor-infiltrating lymphocyte status after neoadjuvant CRT and the prognostic significance in esophageal squamous cell carcinoma (ESCC). Between 2003 and 2017, 138 patients with ESCC who underwent neoadjuvant CRT and esophagectomy without achieving pathologic complete response were included for analysis. Both pre-CRT biopsies and post-CRT surgical specimens were available in 82 patients. Immunohistochemistry of IDO1, PD-L1, and CD8 density were analyzed. Among 82 paired samples, the expression levels of IDO1 and PD-L1 and CD8 density increased significantly after neoadjuvant CRT (P < .01 for all). Patients with high IDO1 expression after CRT had poorer overall survival (P = .001) and recurrence-free survival (P < .001) than those with low IDO1 expression. High post-CRT CD8 density was significantly correlated with more favorable overall survival (P = .01) and recurrence-free survival (P = .008). Neither pre- nor post-CRT PD-L1 expression was an independent prognostic factor for survival. Stratification analysis revealed that patients with combined low IDO1 expression and high CD8 density after CRT were significantly associated with better survival than other subgroups. The major findings were reproducible in an independent validation cohort. IDO1 and PD-L1 expression and CD8 density increased significantly after neoadjuvant CRT in ESCC. The post-CRT IDO1 expression and CD8 density could serve as prognostic biomarkers for survival.