ICOS and pancreatic neoplasm: The high relative frequency of regulatory T cells in PDAC is consistent with previous observations in mouse models and human, and in agreement with the notion that regulatory T cells, together with myeloid cells, are key immunosuppressive components in PDAC.42–45 More importantly, the regulatory T cells in pancreatic tumors expressed high levels of ICOS, which highlights the potential use of ICOS antagonists to inhibit Treg interactions with ICOSL (such as NCT03829501).