However, considering the recent study that indicated that Treg is chemoattracted to the tumor microenvironment by chemokine gradients such as C-C motif chemokine receptor 4 (CCR4)-C-C motif chemokine ligand 17 (CCL17)/CCL22, CCR8-CCL1, CCR10-CCL28, and CXCR3-CCL9/10/11, it is demonstrated that Treg cells are activated and inhibit antitumor immune responses, suggesting that strategies to deplete Treg cells and the control of Treg cell functions to increase antitumor immune responses are required in cancer immunotherapy (29), which demonstrates the multifaceted role of Treg in cancer. The gene discussed is CCL17; the disease is cancer.