Interleukin-7 (IL-7) is encoded by the IL7 gene and secreted by stromal cells in the red marrow and thymus. It binds to the IL-7 receptor, a heterodimer consisting of IL-7 receptor alpha and IL-2 receptor gamma chain. IL-7 stimulates the differentiation of hematopoietic stem cells into lymphoid progenitor cells and also stimulates proliferation of B cells, T cells and NK cells. Murine IL-7 has approximately 65 % amino acid sequence identity with human IL-7 and both proteins exhibit cross-speciesactivity. IL-7 as an immunotherapy agent has been examinedin many human clinical trials for various malignancies and during HIV infection.