Poor clinical outcomes and immunoevasive contexture in SIRPα+ tumor-associated macrophages enriched muscle-invasive bladder cancer patients

Objectives In tumor immune microenvironment, the functions of tumor-associated macrophages (TAMs), including phagocytosis and immunomodulatory, have attracted increasing attention recently. With the discovery of CD47–signal regulatory protein-α (SIRPα) as “don't eat me” signaling pathway, the role of novel subpopulation of TAMs expressing SIRPα has not been fully elucidated in a wide spectrum of solid tumors including bladder cancer. In this study, we investigated the prognostic and predictive implication of SIRPα+ TAMs regarding clinical outcomes and adjuvant chemotherapeutic benefit in muscle-invasive bladder cancer (MIBC), and preliminarily characterized the phenotypic features of SIRPα+ TAMs and its relationship with immune contexture. Materials and methods A total of 141 histochemical MIBC samples from Zhongshan Hospital (ZS), 45 fresh tissue samples, and 391 MIBC patients from TCGA database were enrolled in this study. SIRPα+ TAMs was evaluated by immunohistochemical staining of CD68 and SIRPα, and flow cytometry fluorescence staining. Results Our results illustrated that SIRPα+ TAMs were enriched in MIBC specimens. Patients with high SIRPα+ TAMs infiltration suffered significant poor overall survival and recurrence-free survival (P = 0.0030 and P = 0.0282). SIRPα+ TAMs infiltration was an independent prognosticator in multivariate Cox model. Moreover, adjuvant chemotherapy (ACT) application showed significantly survival benefit in patients with low SIRPα+ TAMs infiltration (P = 0.0135). SIRPα+ TAMs with suppressive phenotype exhibited a positive correlation with immune tolerance and dysfunctional CD8+ T cells in MIBC. Conclusions SIRPα+ TAMs infiltration indicated poor prognosis and ACT resistance in MIBC. Immunosuppressive SIRPα+ TAMs is closely related to immune evasion with exhausted T cells states, suggesting the prospect of SIRPα+ TAMs as a potential therapeutic target in MIBC.