INTERLEUKIN-6 RECEPTOR-INTERLEUKIN-6 FUSION PROTEINS WITH ENHANCED INTERLEUKIN-6 TYPE PLEIOTROPIC ACTIVITIES

An sIL-6R/IL-6 chimera, directly fusing the natural forms of soluble I L-6 receptor and IL-6, as found in human body fluids, was produced in transfected human cells, The secreted p85 glycoprotein was active at a concentration of 120 pM to produce growth-arrest and spindleoid diffe rentiation of murine melanoma F10.9 cells, which do not respond to IL- 6 alone. This fusion protein was as active as the yeast-produced p56 f usion protein containing a shortened sIL-6R, linked through a flexible peptide chain to IL-6 (Hyper IL-6), The concentration of Hyper IL-6 n eeded to arrest the growth of F10.9 cells was much lower than that nee ded of a combination of IL-6 and sIL-6R, added separately, Hyper IL-6 was also more active than IL-6 in stimulating growth of murine plasmac ytoma T1165 cells, the half maximal stimulation being obtained at 2 pM Hyper IL-6 versus 23 pM for IL-6. In order to evaluate the effect of the fused sIL-6R/IL-6 proteins on human hematopoietic primitive progen itor cells, they were added to suspension cultures of CD34(+) cells fr om human cord blood in addition to both flt3/flk2 ligand (FL) and stem cell factor (SCF). Fused sIL-6R/IL-6 produced a marked stimulation of cell expansion and a marked increase in the number of colony forming units when subsequently plated in semi-solid medium with IL-3, GM-CSF, SCF and erythropoietin. Ex-vivo maintenance and expansion of early pr ogenitor cells in bone marrow transplantation protocols may be a poten tial application for the sIL-6R/IL-6 chimeric glycoproteins.