The metabolic roles of immune checkpoint molecules.

Immune checkpoint molecules (ICMs) are a class of surface proteins predominantly expressed on immune cells that play a key role in maintaining immune homeostasis by regulating the functions of T cells and other immune cells. Beyond their established immunoregulatory roles, emerging evidence indicates that ICMs are also involved in metabolic regulation. Within the tumor microenvironment (TME), tumour-derived ICMs have been shown to modulate glucose, amino acid, and lipid metabolism in infiltrating T cells, thereby influencing their metabolic reprogramming and functional states. Certain ICMs expressed on immune cells may directly regulate systemic metabolism through cell-intrinsic, immune-independent mechanisms. Moreover, specific ICMs are constitutively expressed in key metabolic tissues, such as pancreatic islets, liver, and adipose tissue, where they are thought to contribute to the maintenance of systemic metabolic homeostasis. Clinically, host metabolic status can affect the efficacy of immune checkpoint inhibitor (ICI) therapies. Conversely, ICI treatment can lead to metabolism-related adverse effects, such as ICI-associated diabetes (ICI-DM), which may extend beyond classic autoimmune insulin-dependent diabetes. Accumulating evidence suggests that ICMs can exert direct regulatory roles in metabolism independent of their canonical immune functions. Elucidating how ICMs regulate metabolism could, on the one hand, improve ICI therapy by maintaining metabolic homeostasis and preventing T cell exhaustion, and on the other hand, facilitate the development of novel therapeutic strategies for metabolic diseases that simultaneously target metabolic and inflammatory pathways. This review synthesises current knowledge on the metabolic roles and regulatory mechanisms of ICMs.