PD-1⁺CD8⁺ T cell infiltration complements PD-L1 to predict first-line chemo-immunotherapy outcomes in advanced ESCC

Only a subset of patients with esophageal squamous cell carcinoma (ESCC) benefits from first-line immunochemotherapy, and PD-L1 alone has limited predictive value, underscoring the need for complementary biomarkers. We analyzed pretreatment FFPE biopsies from 147 ESCC patients treated with PD-1 inhibitors plus chemotherapy using multiplex immunofluorescence (CD4, CD8, CD20, CD68, PD-1, PD-L1, DAPI). PFS and OS were assessed by Kaplan-Meier and Cox models; cut-offs were derived by ROC/Youden analyses. With a median follow-up of 32.2 months, median PFS and OS were 6.7 and 17.0 months. PD-L1 was predominantly expressed on tumor cells, whereas PD-1 was localized mainly to tumor-infiltrating immune cells. In multivariable analysis, high PD-L1 expression independently associated with longer PFS (HR 0.210, 95%CI: 0.060-0.731; p = 0.014), whereas high PD-1⁺CD8⁺ T cell infiltration predicted shorter PFS (HR 2.694, 95%CI: 1.162-6.246; p = 0.021). Combined stratification identified the longest PFS in high PD-L1 expression and low PD-1⁺CD8⁺ T cell infiltration (8.8 months) and the shortest in low PD-L1 and high PD-1⁺CD8⁺ T cell infiltration (3.5 months), supporting PD-1⁺CD8⁺ T cell infiltration might as a complementary biomarker to PD-L1. For OS, intratumoral CD8⁺ T cell density (HR 0.896; p = 0.011), clinical stage (HR 1.570; p = 0.025), and BMI (HR 0.935; p = 0.015) were independent factors.