Insulin-like growth factor 1 (IGF-I) is a polypeptide which belongs to the family of insulin-like growth factors that are similar in molecular structure to proinsulin. IGF-I binds to the IGF-I receptor and is a potent activator of the PI3K/AKT pathway; it also activates ERK1/2 signaling. IGF-I is required for embryonic development, and it is produced mainly in liver in response to a hepatocyte growth hormone. In the absence of insulin, IGF-I is necessary for the maintenance of human pluripotent stem cells (Wang et al.). Together with interleukin 3 (IL-3), IGF-I stimulates differentiation and proliferation of myeloid cells, and has been shown to regulate lymphopoiesis by stimulating proliferation and differentiation of T and B cells in lymphoid organs (Heemskerk et al.).