CXCL1 and gastric cancer: Another study showed that epithelial Smad4 deficiency increased the stemness of gastric cancer cells via CXCL1, which functionally suppressed the function of dendritic cells (DC) and altered the expression of immune checkpoint molecules 4-1BB ligand (4-1BBL) and programmed death-ligand 1 (PD-L1) 49.