Memory B cells in mature follicle-like tertiary lymphoid structures predict BCG response in non-muscle-invasive bladder cancer

Response to intravesical Bacillus Calmette-Guérin (BCG) varies among patients with intermediate/high-risk non-muscle-invasive bladder cancer (NMIBC). We investigated whether tumor-infiltrating memory B cells (MBCs) and tertiary lymphoid structures (TLSs) are associated with BCG response. RNA-sequencing data from GSE176178 served as the discovery cohort for identifying immune-cell subsets associated with BCG response via CIBERSORT deconvolution. In an independent validation cohort of 79 BCG-treated NMIBC patients, pre-BCG transurethral resection of bladder tumor (TURBT) specimens were evaluated by hematoxylin and eosin staining and multiplex immunohistochemistry to quantify MBC infiltration and TLS features. Paired post-BCG recurrent TURBT specimens from 16 non-responders were used for exploratory analyses of immune changes after BCG failure. Pretreatment intratumoral MBC abundance was higher in responders than in non-responders ( P = 0.0009), as was TLS density ( P = 0.0026). In paired samples from non-responders, post-BCG recurrent tumors showed reduced MBC levels ( P = 0.0250) and a numerical increase in primary follicle-like TLSs. Higher MBC proportion and the presence of secondary follicle-like TLSs (S-TLSs) were associated with longer recurrence-free survival (RFS), with the optimal response observed when MBCs were spatially embedded within S-TLSs. In multivariable analyses, T1 stage, high MBC infiltration, and S-TLS presence independently predicted RFS. Enrichment of MBCs within mature S-TLSs is associated with improved BCG responsiveness and longer RFS in NMIBC, supporting MBC/S-TLS features as candidate biomarkers to predict BCG benefit and refine patient stratification.