Bladder cancer immune microenvironment: immune-cell distribution, disease associations, treatment remodeling, and baseline immune features associated with treatment response and prognosis

Bladder cancer is characterized by substantial heterogeneity in the tumor immune microenvironment (TIME), which influences recurrence, progression, treatment resistance, and responses to Bacillus Calmette–Guérin (BCG), neoadjuvant chemotherapy, immune checkpoint inhibitors, and radiotherapy. This narrative review critically synthesizes evidence on immune-cell distribution, disease-state associations, treatment-associated remodeling, and baseline immune features linked to treatment response and prognosis. Current evidence indicates that the clinical meaning of immune infiltration depends not only on cell abundance but also on localization across histological compartments, functional state, tumor compartment, and therapeutic context. Cytotoxic lymphocyte infiltration may indicate antitumor immune activity when tumor-accessible and functionally active, whereas regulatory T cells, myeloid-derived suppressor cells, and M2-like tumor-associated macrophages often reflect suppressive or treatment-resistant immune states. Treatments can reshape the bladder cancer TIME, but the strength of evidence varies across modalities: BCG has relatively stronger human support for treatment-associated immune changes, whereas evidence for chemotherapy-, immunotherapy-, and radiotherapy-associated remodeling remains more heterogeneous. Baseline or pretreatment immune architecture may provide a more informative basis for biomarker development than single immune-cell markers. Future longitudinal studies with matched pre- and post-treatment specimens are needed to determine whether treatment-induced TIME changes provide additional treatment-response-associated or prognostic information beyond baseline immune features, whereas establishment of predictive utility will require comparative treatment designs with formal biomarker-by-treatment interaction testing.