Resistance to immune checkpoint inhibitors has hampered their clinical success. Thus, there has been an impetus to find new targets acting on tumour-specific T cells. One set of potential targets are the CD33-related sialic acid-binding immunoglobulin-like lectins (Siglecs), which function as pattern recognition immune receptors. Siglecs bind to a variety of sialoglycan ligands, which serve as self-associated molecular patterns. Stanczak et al. identified that Siglec-9 is upregulated on tumour-infiltrating T cells from patients with non-small-cell lung cancer (NSCLC) and colorectal and ovarian cancer compared with the low-level expression on normal T cells. Moreover, in patients with NSCLC its expression was correlated with decreased survival. The sialoglycan–Siglec pathway was shown to mediate immune evasion in vivo and, importantly, could be targeted both in vitro and in vivo to improve anticancer immune responses.