CD40 is a member of the tumor necrosis factor receptor superfamily and is primarily involved in regulating immune responses. It is highly expressed on cells such as B cells, dendritic cells (DCs), and monocytes, and plays a crucial role in linking innate and adaptive immunity. CD40 signaling is a key trigger in the maturation process of monocytes, mainly driving differentiation into M1-type macrophages and DCs. On DC surfaces, CD40 is involved in promoting the production of cytokines and chemokines, inducing the expression of costimulatory molecules, and enhancing antigen cross-presentation. CD40 is also expressed on various types of cells, including fibroblasts, endothelial cells, and certain hematopoietic and epithelial tumor cells. In the context of CAR-T cell therapy, the expression of CD40L on the surface of CAR-T cells has been explored to enhance their anti-tumor functions.