All-trans retinoic acid enhances the long-term repopulating activity of cultured hematopoietic stem cells.

The retinoic acid receptor (RAR) agonist, all-trans retinoic acid (ATRA), is a potent inducer of terminal differentiation of malignant promyelocytes, but its effects on more primitive hematopoietic progenitors and stem cells are less clear. We previously reported that pharmacologic levels (1 micromol) of ATRA enhanced the generation of colony-forming cell (CFC) and colony-forming unit-spleen (CFU-S) in liquid suspension cultures of lin- c-kit+ Sca-1+ murine hematopoietic precursors. In this study, we further investigated the effects of ATRA as well as an RAR antagonist, AGN 193109, on the generation of transplantable cells, including pre-CFU-S, short-term repopulating stem cells (STRCs), and long-term repopulating stem cells (LTRCs). ATRA enhanced the ex vivo maintenance and production of competitive repopulating STRCs and LTRCs from lin- c-kit+ Sca-1+ cells cultured in liquid suspension for 14 days. In addition, ATRA prevented the differentiation of these primitive stem cells into more mature pre-CFU-S during the 14 days of culture. In marked contrast, lin- c-kit+ Sca-1+ cells cultured with AGN 193109 for 7 days had virtually no short- or long-term repopulating ability, but displayed an approximately 6-fold increase in the pre-CFU-S population. The data suggest that the RAR agonist ATRA enhances the maintenance and self-renewal of short- and long-term repopulating stem cells. In contrast, the RAR antagonist AGN 193109 abrogates reconstituting ability, most likely by promoting the differentiation of the primitive stem cells. These results imply an important and unexpected role of retinoids in regulating hematopoietic stem cell differentiation. (Blood. 2000;95:470-477)