PREPARATION OF A RECOMBINANT CHIMERA OF INSULIN-LIKE-GROWTH-FACTOR-IIAND INTERLEUKIN-3 WITH HIGH PROLIFERATIVE POTENCY FOR HEMATOPOIETIC-CELLS

We have found that a slightly modified insulin-like growth factor II ( IGF II) consisting of a chimaera of bombyxin and human IGF II (BOMIGF) is properly secreted in insect cells by using the baculovirus express ion system. Human interleukin 3 (IL-3) was attached to the C-terminal amino acid residue of BOMIGF with peptide linkers containing five or t welve residues. Only the chimaera with the 12-residue linker had biolo gical activities of both IGF II and IL-3, The chimaera had a significa ntly higher mitogenic activity than IL-3 in cell cultures of the human haemopoietic cell line TF-1 and its effect could be observed even at femtomolar concentrations. It was also able to stimulate thymidine inc orporation in ICF II-dependent bovine fetal erythroid cells. The chima era significantly increased the number of macroscopic haemopoietic col onies in cultures of human peripheral blood in comparison with IL-3 or mixtures of IL-3 and BOMIGF in vitro. Subcutaneous injection of a BOM IGF-mouse IL-3 chimaera in normal C57BL/6 mice resulted in a significa nt increase of the number of spleen stem cells producing macroscopic h aemopoietic colonies. This new system for the biosynthesis of IGF-cyto kine fusion proteins in insect cells might prove advantageous for the low-cost and high-yield production of molecules with complementary or synergistic biological activities.