CCL17, also known as Thymus and Activation-Regulated Chemokine (TARC), is a protein that belongs to the C-C chemokine family. It is primarily produced by dendritic cells, endothelial cells, keratinocytes, and fibroblasts, and is highly expressed in the thymus. CCL17 plays a crucial role in immune regulation by recruiting lymphocytes and modulating immune function. It acts as a ligand for the C-C chemokine receptor type 4 (CCR4), which is highly expressed on helper T cells. This chemokine is involved in various biological processes, including T-cell development, trafficking, and activation of mature T cells. Additionally, CCL17 has been implicated in several diseases, such as chronic kidney disease, where it may promote renal fibrosis by inducing epithelial-mesenchymal transition. In the context of cancer, CCL17 can influence the tumor microenvironment by recruiting regulatory T cells and affecting tumor progression.