On the cover: Immunohistochemical staining for programmed death ligand 1 (PD-L1, B7-H1) in human placenta. The section cuts across several placental villi. PD-L1 was strongly expressed on syncytiotrophoblasts, the cells found at the maternal-fetal interface. Expression was lower on the underlying cytotrophoblasts that fuse to give rise to the layer of syncytiotrophoblasts on the surface of villi. Brown et al. Blockade of programmed death-1 ligands on dendritic cells enhances T cell activation and cytokine production. 1257)