Phenotypic characterization of tumor associated macrophages and circulating monocytes in patients with Urothelial carcinoma of bladder.

Objectives: Targeting immune checkpoints has shown clinical efficacy in Urothelial carcinoma of bladder (UBC); however, a substantial percentage of patients remains unresponsive, which warrants the elucidation of novel therapeutic targets to circumvent immune suppression. Tumor associated macrophages (TAMs) are known for their indispensable role in cancer immunosuppression however, their phenotype and functionality in UBC is not yet clear.

Materials and methods: Phenotypic composition and functional markers of TAMs, and circulating monocytes were assessed in surgically resected bladder tumors and PBMC of UBC patients (n = 40). Besides, 40 healthy volunteers were recruited to draw comparisons for peripheral monocytes. Monocytes from patients were treated with autologous bladder tumor conditioned media (TCM) to assess its effects on macrophage-based markers.

Results: The infiltration of TAMs was significantly increased in bladder tumor tissue by 21.2% and which displayed both M1 and M2 phenotypic markers, wherein M2 phenotype exhibited positive correlation with disease severity. Circulating monocytes exhibited an increase in frequency of non-classical monocytes by 17.42% and elevated M2-macrophage markers by 20%. Further, TAMs and circulating monocytes exhibits an elevated expression of IL- 10 and inhibitory immune checkpoints (PD-1, PD-L1, and B7-H4). Stimulation of patient-derived monocytes with TCM further augmented the expression of immune checkpoints, and immunosuppressive markers like IL-10, TGF-β and CX3CR- 1. Lastly, M2 phenotype of TAMs and PD-L1+ and B7-H4 + TAMs displayed positive correlation with clinico-pathological parameters in UBC patients.

Conclusion: This study presents TAMs with an immunosuppressive phenotype that correlates positively with disease severity and suggests TAMs as a potential therapeutic candidate to restore the anti-tumor immunity in UBC.