Tumor-Infiltrating Immune Cells in Non-Muscle-Invasive Bladder Cancer: Prognostic Implications, Predictive Value, and Future Perspectives

Non-muscle invasive bladder cancer (NMIBC) accounts for the majority of bladder cancer diagnoses and remains a clinical challenge due to its high recurrence and progression rates despite intravesical Bacillus Calmette–Guérin (BCG) therapy. In recent years, tumor-infiltrating lymphocytes (TILs) have emerged as promising biomarkers, reflecting the interplay between the tumor and host immune system. However, the evidence regarding their prognostic and predictive role is still conflicting, largely due to methodological heterogeneity, lack of standardized evaluation criteria, and limited prospective validation. This narrative review summarizes the current knowledge on TILs in NMIBC, focusing on their compartmental distribution (stromal, intraepithelial, and tumor–stroma interface), compositional diversity (CD4+, CD8+, Treg, B cells), and spatial dynamics. Special attention is given to their role in predicting response to BCG immunotherapy, the contribution of tumor-associated macrophages and tertiary lymphoid structures, and the emergence of immune escape pathways, including Programmed Death-Ligand 1 (PD-L1) and the HLA-E/NKG2A axis. Advances in digital pathology, spatial transcriptomics, and integrated immunoscore models provide more accurate metrics compared to simple cell counts, highlighting the importance of functional and spatial signatures. Despite encouraging progress, TILs are not yet ready for routine incorporation into histopathological reporting. Future directions include standardized assessment, integration with molecular biomarkers, and prospective multicenter validation to enable their translation into risk stratification and personalized therapeutic decision-making.