IL2 is a secreted cytokine involved in the operation and regulation of immune system. IL2 plays a pivotal role in T-cell activation and effector functions, including T cell proliferation, interferon-γproduction and cytotoxicity. IL2 can stimulate the propagation of lymphocytes and induce the cytotoxic T lymphocytes and lymphokine-activated killer cells for tumor cells. IL2 also influences memory T cell homeostasis through the regulation of memory T cell numbers and enhances major histocompatibility complex II (MHC II) expression on tumor cells.