The correlation between LAG-3 expression and the efficacy of chemoimmunotherapy in advanced biliary tract cancer

In our previous phase II T1219 trial for advanced biliary tract cancer (ABTC), the combination of nivolumab with modified gemcitabine and S-1 exhibited promising efficacy, while the programmed-death-ligand-1 (PD-L1) expression did not predict chemoimmunotherapy efficacy. Lymphocyte-activation-gene-3 (LAG-3), a negative immune checkpoint, is frequently co-expressed with PD-L1. This study assessed the predictive value of LAG-3 expression in ABTC patients who received chemoimmunotherapy. We analyzed 44 formalin-fixed ABTC samples using immunohistochemical staining for PD-L1 and LAG-3 and correlated them with the clinical efficacy of chemoimmunotherapy. Digital spatial profiling was conducted in selected regions of interest to examine immune cell infiltration and checkpoint expression in six cases. Three public BTC datasets were used for analysis: TCGA-CHOL, GSE32225, and GSE132305. LAG-3 positivity was observed in 38.6% of the ABTC samples and was significantly correlated with PD-L1 positivity (P < 0.001). The objective response rate (ORR) was significantly higher in LAG-3-positive tumors than in LAG-3-negative tumors (70.6% vs. 33.3%, P = 0.029). The LAG-3 expression level was associated with an increased ORR (33%, 58%, and 100% for LAG-3 < 1%, 1-9%, and ≥ 10%, respectively; P = 0.018) and a deeper therapeutic response (20.1%, 38.6%, and 57.6% for the same respective groups; P = 0.04). LAG-3 expression is positively correlated with the expression of numerous immune checkpoints. Enrichment of CD8⁺ T cells was observed in LAG-3-positive BTC, indicating that LAG-3 expression may serve as a biomarker for identifying immune-inflamed tumors and predicting the therapeutic response to chemoimmunotherapy in ABTC.