CXCR4 and pancreatic ductal adenocarcinoma: It was recently shown that tumors derived from murine pancreatic ductal adenocarcinoma (PDAC) cells respond differently to T cell targeted checkpoint immunotherapy with anti-programmed death receptor 1 (anti-PD1) blocking antibodies on the basis of keratin 19 expression [23] which impairs CXCL12 linkage and CXCR4 mediated T cell exclusion from tumors [24, 25].