GP130 AND C-KIT SIGNALINGS SYNERGIZE FOR EX-VIVO EXPANSION OF HUMAN PRIMITIVE HEMATOPOIETIC PROGENITOR CELLS

gp130, a signal-transducing receptor component of interleukin 6 (IL-6) , associates with an IL-6 and IL-6 receptor (IL-6R) complex and transd uces signals. To examine the role of gp130 signaling in the expansion of human hemopoietic progenitor cells, we tested the effects of a reco mbinant soluble human IL-6 receptor (sIL-6R) and/or IL-6 in combinatio n with other cytokines on purified human umbilical cord blood CD34(+) cells, using methylcellulose clonal assay and suspension culture in th e presence or absence of serum. A combination of sIL-6R and IL-6 (sIL- 6R/IL-6), but not sIL-6R or IL-6 alone, was found to dramatically stim ulate expansion of hemopoietic progenitor cells as well as CD34(+) cel ls in the presence of stem cell factor. Significant generation of mult ipotential hemopoietic progenitors over a period of 3 weeks in suspens ion culture and efficient formation of colonies, especially multilinea ge and blast cell colonies, in methylcellulose assay supplemented with a combination of sIL 6R/IL-6 together with stem cell factor were obse rved in serum-containing and serum-free culture. Addition of anti-gp13 0 monoclonal antibodies or anti-IL-6R monoclonal antibodies to the abo ve cultures dose-dependently inhibited the expansion of progenitor cel ls in suspension culture and also completely blocked the formation of multilineage colonies in methglcellulose culture. These findings demon strated that the significant expansion of human primitive hemopoietic progenitors could be achieved with the gp130 and c-Kit signalings init iated by the sIL-6R/IL-6 complex in the presence of stem cell factor a nd suggested the possible application of this method for ex vivo expan sion of CD34(+) cells for bone marrow transplantation.