Phenotypic Diversity of Immunosuppressive B Cells Associated in Urothelial Carcinoma of the Bladder

Background: Urothelial carcinoma of the bladder presents a complex tumor microenvironment, with tumor-infiltrating B cells (TIL-Bs) playing a significant role in disease progression. Although their presence is acknowledged, the phenotypic diversity of regulatory TIL-Bs in bladder cancer remain underexplored. Materials and Methods: In this study, we evaluated core B cell subsets and their immunosuppressive phenotypes in both peripheral blood (n=40) and bladder tumor tissues (n=40) to evaluate their relationship with disease severity. Results: Our findings revealed that high-grade bladder tumors are enriched with B cells and their subsets, particularly transitional B cells and plasmacytes (plasmablasts and plasma cells). However, total memory B cells were reduced in the tumor microenvironment compared to non-tumor tissues. It was further revealed that the high-grade tumors demonstrated significant infiltration of regulatory B cells (Breg), with elevated levels of IL10+ and TGFβ+ Breg cells as well as IL-10+TGF-β+ dual-cytokine-secreting Breg cells, suggesting their role in fostering an immunosuppressive microenvironment. Memory B cells demonstrated the highest frequency of Breg phenotypes among the B cell subsets. Additionally, Tertiary Lymphoid Structure formation and frequency were associated with disease severity, the differentiated B cells and IL10+ Breg cell counts, emphasizing the importance of these structures in bladder cancer progression and the potential involvement in Breg cells formation. Conclusion: This study demonstrates the enrichment of the bladder cancer tumor microenvironment with diverse B cell subsets, including functional Breg cells, which correlates with disease severity.