In vitro expansion of hematopoietic stem cells.

We have investigated the effects of interleukin 3 (IL-3) and IL-1 on in vitro expansion of murine hematopoietic progenitors and stem cells using a highly purified progenitor population. Lineage negative, Ly-6A/E+, c-kit+ bone marrow cells from male mice were cultured in suspension in the presence of stem cell factor, IL-6, IL-11 and erythropoietin with or without IL-3 or IL-1. An exponential increase in total nucleated cell counts and about a 10-fold enhancement of nucleated cells by IL-3 were observed during the initial 10 days. Addition of IL-3 hastened the development but significantly suppressed the peak production of colony-forming cells. Addition of IL-1 also significantly suppressed the numbers of progenitors. We then tested the reconstituting ability of the cultured cells by transplanting cells together with "compromised" marrow cells into lethally irradiated mice. The cells expanded from enriched cells in the absence of IL-3 or IL-1 revealed engraftment at two, six and 10 months, while addition of IL-3 or IL-1 to the cultures significantly reduced the reconstituting ability. IL-3 and IL-1 may have negative modulatory effects on the self-renewal of stem cells.