About the Cover
T cells are critical components of the antitumor response but are constrained from action by multiple mechanisms. The interaction of the immune checkpoint PD-1 with its ligand PD-L1 will suppresses CD8⁺ T cells, and in some cancers this effect can be abrogated through antibody blockade. However, pancreatic ductal adenocarcinoma remains nonresponsive when blocking antibodies are administered. To investigate the mechanisms of immunological resistance in pancreatic cancer, Stromnes and colleagues showed that PD-L1 (green) is quite rare in pancreatic tumor cells (magenta), but is expressed in stromal cell clusters. Tumoral T cells in pancreatic tumors had marked variation in their abundance, localization, and phenotype, indicating the multiple and distinct mechanisms of immunotherapy resistance at work. Read more in this issue of Cancer Immunology Research starting on page 978. Original fluorescent micrograph from Stromnes and colleagues. Artwork by Lewis Long.