IL7, also known as interleukin 7, is a hematopoietic growth factor that belongs to the IL-7/IL-9 family. It is secreted by stromal cells in the bone marrow and thymus. It is also produced by keratinocytes, dendritic cells, hepatocytes, neurons, and epithelial cells, but is not produced by lymphocytes. Human IL?7 cDNA encodes 177 amino acids （aa） that include a 25 aa signal peptide. 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, and porcine IL-7. IL7 stimulates the proliferation of lymphoid progenitors. It is important for proliferation during certain stages of B-cell maturation. Like other common gamma-chain cytokines like IL-2 and IL-15, IL-7 and its receptor, IL-7R, have been used in a variety of immunotherapy applications, often in fluid tumors and in some instances of solid tumor models.