CD194, also known as CCR4 （C-C chemokine receptor type 4）, is a G protein-coupled receptor with seven transmembrane domains. It is expressed on various immune cells, including CD4+ T cells （especially Th2 cells）, regulatory T cells （Tregs）, basophils, monocytes, and natural killer （NK） cells. CCR4 binds to chemokines such as CCL17 （TARC） and CCL22 （MDC）, playing a crucial role in the recruitment of memory T cells and immune responses in conditions like atopic dermatitis and asthma. Additionally, CCR4 is involved in tumor biology, with high expression levels associated with tumor infiltration and prognosis in both hematological malignancies and solid tumors, making it a potential target for cancer immunotherapy.