Expression of the membrane tetraspanin claudin 18 on cancer cells promotes T lymphocyte infiltration and antitumor immunity in pancreatic cancer

Tumors weakly infiltrated by T lymphocytes poorly respond to immunotherapy. We aimed to unveil malig- nancy-associated programs regulating T cell entrance, arrest, and activation in the tumor environment. Dif- ferential expression of cell adhesion and tissue architecture programs, particularly the presence of the membrane tetraspanin claudin (CLDN)18 as a signature gene, demarcated immune-infiltrated from im- mune-depleted mouse pancreatic tumors. In human pancreatic ductal adenocarcinoma (PDAC) and non- small cell lung cancer, CLDN18 expression positively correlated with more differentiated histology and favor- able prognosis. CLDN18 on the cell surface promoted accrual of cytotoxic T lymphocytes (CTLs), facilitating direct CTL contacts with tumor cells by driving the mobilization of the adhesion protein ALCAM to the lipid rafts of the tumor cell membrane through actin. This process favored the formation of robust immunological synapses (ISs) between CTLs and CLDN18-positive cancer cells, resulting in increased T cell activation. Our data reveal an immune role for CLDN18 in orchestrating T cell infiltration and shaping the tumor immune contexture