Different growth factor requirements for the ex vivo amplification of transplantable human cord blood cells in a NOD/SCID mouse model

The growth factor combination containing early acting cytokines FLT-9 ligan d (FL), Stem Cell Factor (SCF) and thrombopoietin (TPO) is able to maintain , for an extended culture period, early stem cells, defined as long-term re populating NOD/SCID mice (Scid Repopulating Cell-SRC) contained in cord blo od (CB), In this culture system, the role of IL-6 and IL-3 has not been cle arly established, Using a combination of FL+TPO+SCF with or without IL-6, we were able to for m CB CD34(+) cells for 30 weeks. The CB CD34(+) cells cultured in this syst em engrafted NOD/SCID mice after 6 weeks of culture; the cells from primary recipients were also able to engraft secondary NOD/SCID mice. When CB CD34(+) cells were cultured in the presence of IL-3 in the place of IL-6 we observed an even better expansion of cells and a similar clonogeni c progenitor output in the first 8 weeks of culture. However, more primitiv e LTC-IC output increased up to week 6 with the growth factor combination c ontaining IL-3 and then decreased and disappeared, while with the growth fa ctor combination with or without IL-6 increased up to week 23, Cells cultur ed for 4 weeks with the 4-factor combination containing IL-3 engrafted NOD/ SCID mice less efficiently. Repopulation of NOD/SCID mice was no longer obs erved when ex vivo expansion was performed for 6 weeks. This study provides some evidence that no differences could be detected in long-term maintenance and even expansion of human primitive cord blood cell s cultured with FL+TPO+SCF in the presence or absence of IL-6. Under the cu lture conditions employed in this study, the presence of IL-3 reduced the r epopulating potential of expanded CB CD34(+) cells.