Treg cells expressing chemokine receptors CCR4, CCR5, CCR10, and CXCR3 migrate to tumor sites through chemotaxis, induced by a gradient of chemokines released by tumor-associated immune cells such as tumor-associated macrophages (TAMs) and suppressor cells of myeloid origin, myeloid-derived suppressor cells (MDSC) that produce various chemokines such as C-C chemokine ligands 17, 22, 5, 6, or 28 (CCL17, CCL22, CCL5, CCL6, or CCL28) according to the tumor or its location [57,60]. The gene discussed is CCL5; the disease is neoplasm.