Evasion of immunosurveillance by the upregulation of Siglec15 in bladder cancer

Abstract

Immunotherapy resistance in bladder cancer (BLCA) is associated with elevated levels of sialic acid-binding immunoglobulin-like lectin (Siglec15). This protein plays a crucial role in fostering a noninflammatory tumor microenvironment (TME), which is conducive to cancer progression. Our study confirmed that the overexpression of Siglec15 led to a reduction in CD8⁺ T cell infiltration. This effect was mediated by the downregulation of pro-inflammatory cytokines and chemokines, which in turn exacerbated BLCA malignancy. Furthermore, Siglec15 inhibited the cytotoxicity of effector T cell, contributing to immune evasion. An in vivo study demonstrated that Siglec15 overexpression induced a non-inflammatory TME and promoted resistance to immunotherapy. These findings highlight Siglec15 as a potential therapeutic target for BLCA. By modulating inflammation in the TME and CD8⁺ T cell function, targeting Siglec15 may offer a novel strategy for overcoming immunotherapy resistance and improving patient outcomes.

Keywords: Bladder cancer; Immunotherapy; Noninflamed tumor microenvironment; Siglec15.

Fig. 1

Evasion of immunosurveillance by the upregulation of Siglec15 in BLCA. A High-throughput liquid-phase protein chip detection shows the effects of different Siglec15 expression levels on the concentrations of 34 cytokines. B The effects of different Siglec15 expression levels on CCL2, CCL3, CCL4, CCL5, CXCL9, and CXCL10 were determined by reverse transcription‒quantitative polymerase chain reaction and enzyme-linked immunosorbent assays. C Transwell chemotaxis assay process diagram. D Natural killer cell, CD4⁺ T cell, and CD8⁺ T cell recruitment decreased with Siglec15 overexpression. E Panoramic scanning was used to analyze the co-expression and spatial distance between each cell. F Spatial distribution of CD8⁺ T cells and Siglec15⁺/CK19⁺ cells. G Schematic diagram of the CD8⁺ T cell and tumor cell coculture killing assay. H Residual tumor cells were stained with crystal violet. I Flow cytometry analysis of the expression levels of TNF-α and IFN-γ in CD8⁺ T cells. J Schematic diagram of the in vivo experimental process. K Tumor tissue photos at the endpoint of treatment. L Tumor growth curves of the mice in the different treatment groups. M Tumor volume statistics at the endpoint of treatment. N Survival curves of the mice in the different treatment groups. O Flow cytometry analysis of the expression levels of TNF-α, GZMB and Ki67 in different groups of tumor tissues. P Expression of cytokines in CD8⁺ T cells within the tumor tissues of different treatment groups. Q Immunofluorescence staining revealed different levels of CD8⁺ T-cell infiltration in the tumor tissues of different treatment groups. R Quantitative statistical analysis of the number of CD8⁺ T cells in Q