Among the proposals advanced to explain the effect are enhanced levels of monocyte chemoattract protein-1 (MCP-1) [119]; elimination of sinks for homeostatic cytokines, such as interleukin-2 (IL-2), IL-7, and IL-15 [120]; and downregulation of indoleamine 2,3-dioxygenase in tumor cells [121]. This evidence concerns the gene CCL2 and neoplasm.