CCL19 (C-C motif chemokine ligand 19) is a critical chemokine that primarily functions to direct lymphocyte trafficking and immune cell organization through binding to CCR7 receptor 1. The protein plays essential roles in tertiary lymphoid structure (TLS) formation, where CCL19-producing fibroblasts facilitate lymphocyte trafficking and create specialized immune microenvironments 23. In cancer contexts, CCL19 demonstrates dual therapeutic potential: it promotes anti-tumor immunity by enabling TLS formation that generates tumor-targeting antibodies in colorectal cancer liver metastasis 2, and CCL19-expressing fibroblastic reticular cells create protective T cell environments in lung cancer 3. Therapeutically, engineered immune cells co-expressing IL-7 and CCL19 show enhanced anti-tumor activity against solid tumors, with clinical trials demonstrating complete tumor regression in hepatocellular carcinoma patients 45. The chemokine also functions in autoimmune pathogenesis, where fibroblast-derived CCL19 promotes pathogenic TLS formation in hidradenitis suppurativa through TNF-α-CCL19 feedback loops 6. During inflammation, CCL19 becomes critical for maintaining naive lymphocyte recruitment into lymph nodes when CCL21 is downregulated 1. CCL19+ dendritic cells serve as biomarkers for favorable immune checkpoint inhibitor responses in breast cancer 7.