CCL2 and neoplasm: For instance, in preclinical HCC models, an adenovirus engineered to express both HSV-TK and a membrane-bound chemokine gene fusion [monocyte chemoattractant protein-1 (MCP-1) fused with the membrane-spanning domain of C-X3-C motif chemokine ligand 1 (CX3CL1)] significantly enhanced immune cell infiltration into the tumor, thereby amplifying the cytotoxic effects of GCV treatment [32].