Stromal LAG-3+ cells infiltration defines poor prognosis subtype muscle-invasive bladder cancer with immunoevasive contexture.

Background Lymphocyte activation gene 3 (LAG-3) is a promising immune checkpoint therapeutic target being evaluated in clinical trials. We assessed the LAG-3+ cells distribution, its association with clinical outcomes and immune contexture and its role in the landscape of muscle-invasive bladder cancer (MIBC) treatment. Methods 141 patients with MIBC from Zhongshan Hospital were included for survival and adjuvant chemotherapy (ACT) benefit analyses. 32 fresh resected samples of MIBC were collected to detect CD8+ T cells functional state. The molecular classification analyses were based on 391 patients with MIBC from The Cancer Genome Atlas. Immunohistochemistry and flow cytometry were performed to characterize various immune cells infiltration. Results In Kaplan-Meier analyses and Cox regression models, stromal LAG-3+ cells enrichment was consistently associated with inferior overall survival and disease-free survival, and indicated suboptimal responsiveness to ACT. Patents with high stromal LAG-3+ cells possessed increased protumor cells, immunosuppressive cytokines and immune checkpoint expression. The phenotypic analyses of CD8+ T cells correlated its dysfunctional state with LAG-3+ cells. Besides, LAG-3 mRNA level was linked to luminal and basal subtypes of MIBC. LAG-3-high tumors exhibited limited FGFR3 mutation and signaling signature, and displayed activated immunotherapeutic and EGFR-associated pathway. Conclusions Stromal LAG-3+ cells abundance indicated an immunoevasive contexture with dysfunctional CD8+ T cells, and represented an independent predictor for adverse survival outcome and ACT resistance in MIBC. LAG-3 expression could potentially be a novel biomarker for FGFR3-targeted and EGFR-targeted therapies and immunotherapy. The crucial role of LAG-3+ cells in the therapeutic landscape of MIBC needs further validation retrospectively and prospectively.