Enhancement of human granulopoiesis in vitro by biosynthetic insulin-like growth factor I/somatomedin C and human growth hormone.

The effect of biosynthetic recombinant insulin-like growth factor I/somatomedin C (IGF-I/Sm-C) and human growth hormone (hGH) on the in vitro growth and maturation of human marrow myeloid progenitors was investigated. Myeloid colony formation was maximally enhanced by 60 ng/ml IGF-I/Sm-C and by 250 ng/ml hGH, resulting in an increase in colony numbers of 41 +/- 7 and 38 +/- 4%, respectively (P less than 0.001). Both peptides induced a 1.5-2.5-fold increase in the frequency of colonies composed of granulocytes alone, but did not alter the numbers of monocyte/macrophage or mixed granulocyte/macrophage colonies. IGF-I/Sm-C and hGH were also found to enhance myeloid maturation towards mature granulocytes in suspension cultures of human marrow cells. The effect of both peptides on human marrow granulopoiesis was similarly demonstrable in serum-free cultures stimulated with human recombinant granulocyte/macrophage colony-stimulating factor. Enhancement of human marrow granulopoiesis in vitro by hGH required the presence of marrow adherent cells and was abrogated by specific monoclonal antibodies directed against IGF-I/Sm-C receptors. The effect of hGH on marrow myeloid progenitors thus appears to be mediated by paracrine IGF-I/Sm-C.