Recent progress in targeting the sialylated glycan-SIGLEC axis in cancer immunotherapy

Malignant tumors are complex structures composed of cancer cells and tumor microenvironmental cells. In this complex structure, cells cross-talk and interact, thus jointly promoting cancer development and metastasis. Recently, immunoregulatory molecule-based cancer immunotherapy has greatly improved treatment efficacy for solid cancers, thus enabling some patients to achieve persistent responses or cure. However, owing to the development of drug-resistance and the low response rate, immunotherapy against the available targets PD-1/PD-L1 or CTLA-4 has limited benefits. Although combination therapies have been proposed to enhance the response rate, severe adverse effects are observed. Thus, alternative immune checkpoints must be identified. The SIGLECs are a family of immunoregulatory receptors (known as glyco-immune checkpoints) discovered in recent years. This review systematically describes the molecular characteristics of the SIGLECs, and discusses recent progress in areas including synthetic ligands, monoclonal antibody inhibitors, and Chimeric antigen receptor T (CAR-T) cells, with a focus on available strategies for blocking the sialylated glycan-SIGLEC axis. Targeting glyco-immune checkpoints can expand the scope of immune checkpoints and provide multiple options for new drug development.