Novel insights into immune checkpoints in psoriasis and atopic dermatitis: From expression and function to treatments.

Psoriasis and atopic dermatitis (AD) are both chronic inflammatory skin diseases, which are common and difficult to cure. Currently, the emerging biologics have demonstrated outstanding efficacy, but not all patients are able to benefit from them, and traditional systemic treatments come with many severe side effects. The emergence of immune checkpoints brings new hope to solve this problem. Immune checkpoints regulate T cell activation. Upon damage to the co-inhibitory molecules, the inhibition on T cells is removed, leading to the excessive activation of T cells. In this review, we delineate and highlight the expression and function of immune checkpoint molecules (CTLA-4, PD-1, TIM-3, TIGIT, VISTA, LAG-3, OX40, GITR) in psoriasis and AD. We provide preclinical and clinical studies supporting a potential therapeutic approach of targeting these checkpoints for inflammatory skin diseases. Moreover, the complexity of immune checkpoints and safety of clinical application are discussed.