IL2RA and neoplasm: The lack of JAK1 phosphorylation, the activation of JAK3 and STAT5 in response to low doses of IL-2, and the opposite effect in response to high doses of IL-2 indicate different mechanisms for the IL-2R transduction pathway that may explain the presence of tumour cells in an environment where cytotoxic lymphocytes also exist and compete for IL-2 [64].