GP130 and c-kit signalling, initiated by the sIL-6R/IL-6 complex, is insufficient to expand the primitive adult bone marrow CD34+CD38-pre-CFU cell

It has previously been shown that gp130 and c-kit signalling synergize for the ex vivo expansion of human cord blood (CB) CD34+ haematopoietic progeni tor cells. We were interested in evaluating this synergy within an ontogene tically different haematopoietic tissue [i.e. adult bone marrow (BM)I and o n a more primitive progenitor subset (i.e. CD34 + CD38-cells), which are hi ghly enriched for pre-colony forming unit (CFU) cells. These cells were pla ted out in a primary liquid culture supplemented with either interleukin (I L)-6+stem cell factor (SCF), IL-6+SCF+soluble IL-6 receptor (sIL-6R), IL-6SCF+sIL-6R+IL3 + IL-1 or SCF + IL-3 + IL-6 + IL-1. Cell counting after liqu id culture revealed an absolute expansion of 2.2-, 4.1-, 89.5- and 65.7-fol d compared with initial cell input for the four-cytokine combinations, resp ectively. The secondary read-out assay revealed that this cell expansion in the liquid culture also resulted in CFU generation, with absolute cloning efficiencies of 0.002, 0.024, 12.13 and 7.73 (per cell initially present) f or the respective cytokine combinations. These results indicate that gp130 and c-kit signalling alone (i.e. using IL-6+SCF+IL-6R), in terms of both ce ll number and CFU generation, insufficiently stimulate primitive adult BM C D34+CD38- haematopoietic cells in order to reach a CFU generation comparabl e with that obtained after multifactor stimulation. Adding sIL-6R to the mu ltifactor stimulation and compared with this multifactor stimulation, a 1.7 -fold synergy in terms of cell expansion and a 3.0-fold synergy in terms of CFU generation are obtained. The sIL-6R/IL-6 complex thus has a narrower s pectrum of action on primitive adult BM CD34 + CD38 - cells than on CB CD34 + cells.