Interleukin-7 (IL-7) is required for the development and survival of T cells and plays a critical role in modulating T-cell homeostasis.IL-7 is a limiting resource under normal conditions, but it accumulates during lymphopaenia, leading to increased T cell proliferation.Human IL-7 shares approximately 60-63% aa sequence identity with mouse, rat, canine and feline IL-7, and 72-76% with equine, bovine, ovine, porcine, feline and canine IL-7. IL-7 as an immunotherapy agent has been examinedin many human clinical trials for various malignancies and during HIV infection. Furthermore, IL-7 induces the arming of effector functions and enhances the sensitivity of MAIT cells.