Aberrant glycosylation actively contributes to tumor progression and is a key hallmark of cancer. Most of the glycan moieties expressed on the surface of cancer cells are sialic acids that may modulate antitumor immune responses via binding to sialic acid-binding immunoglobulin-like lectins (Siglecs) expressed by immune cells. Here we show that Siglecs may decrease the bladder tumor immune response mediated by natural killer (NK) cells. We observed higher NK cell activity against desialylated bladder tumor cell lines. We therefore determined the expression of nine Siglecs on circulatory NK cells from healthy donors and patients with bladder cancer (BCa). NK cells from blood mainly express Siglec-7, which is highly upregulated in non-muscle-invasive BCa (NMIBC), as well as Siglec-6, albeit at a much lower level. However, both Siglecs are expressed by urinary NK cells from NMIBC patients undergoing bacillus Calmette-Guérin therapy. Ex vivo analysis of Siglec-6 and Siglec-7 expression levels on tumor-infiltrating NK cells (TINKs) from BCa patients showed that only Siglec-7 is expressed by TINKs. Finally, analyses for The Cancer Genome Atlas data set revealed that BCa patients with high expression levels of Siglec-7 have a poor survival rate. This work indicates that Siglec-7 may restrain NK-mediated antitumor immunity in BCa.
We investigated the expression of proteins called Siglecs in natural killer (NK) cells from patients with bladder cancer. We showed that levels of the protein Siglec-7 in blood, urine, and tumors from patients with bladder cancer are associated with poor clinical outcomes. Thus, Siglec-7 may be involved in the regulation of antitumor immunity mediated by NK cells in bladder cancer.