CD304, also known as neuropilin-1, is a 140 kD type I transmembrane protein. Its extracellular region contains two CUB, two FV/FVIII, and one MAM domain. It is expressed by natural regulatory T cells (nTreg), a subset of invariant natural killer T cells (iNKT), endothelial cells, and neurons. Neuropilin-1 stabilizes the interaction between Tregs and dendritic cells, contributes to the recruitment of tumor-infiltrating Tregs in response to tumor-derived VEGF, and influences the process of angiogenesis and axon guidance. The ligands of CD304 are VEGF165 and semaphorin-3A.