MS4A4A‐positive tumor‐associated macrophages associate with poor prognosis and T‐cell exhaustion in patients with urothelial carcinoma of the bladder

Abstract Tumor‐associated macrophages (TAMs) have multiple potent functions in cancer representing important therapeutic targets. MS4A4A is a functional TAM marker with controversial implications for prognosis. This study aimed to evaluate the association between MS4A4A + TAM infiltration and clinical outcomes in urothelial carcinoma of the bladder (UCB), as well as their impact on the immune landscape. A total of 400 UCB patients from cohorts at Sun Yat‐sen Memorial Hospital were analyzed. Immunohistochemistry was used to quantify MS4A4A + TAMs and assess their spatial distribution alongside various immune components, evaluate the benefit of Bacillus Calmette‐Guérin (BCG) immunotherapy, and analyze survival outcomes. Additionally, matched UCB tissues were examined before and after recurrence or progression. We observed that MS4A4A + TAMs were present at higher levels in the stromal region compared to the intratumoral region, and correlated with advanced tumor stage and poor prognosis in both regions. No significant difference was observed in the number of MS4A4A + TAMs before and after recurrence/progression in the same patient. Stromal MS4A4A + TAMs were negatively correlated with BCG efficacy and recurrence‐free survival. These TAMs were positively associated with CD8 + T cells, Foxp3 + regulatory T cells, immune checkpoints (PD‐1, LAG‐3, HAVcr‐2, TIGIT), and anti‐inflammatory molecules (TGF‐β1, IL‐4) in the same respective regions. Additionally, MS4A4A + TAMs expressed high levels of TGF‐β1 and HAVcr‐2 in UCB tissues. In vitro , IL‐4 induced MS4A4A expression in mouse bone marrow‐derived macrophages, while Ms4a4a knockdown reduced the anti‐inflammatory molecule Arg1 and increased pro‐inflammatory molecule Nos2 expression. These findings demonstrate that MS4A4A is a reliable prognostic marker and predictor of BCG response in UCB, highlighting its role in shaping the immune landscape and immunotherapy outcomes. © 2025 The Pathological Society of Great Britain and Ireland.