All-trans-retinoic acid effects the growth, differentiation and apoptosis of normal human myeloid progenitors derived from purified CD34(+) bone marrow cells

We have previously shown that all-trans retinoic acid (ATRA) increases the number of CFU-GM colonies grown from unseparated human bone marrow cells wi th crude sources of colony stimulating factors. In this study, we further c haracterized the effect of ATRA on the growth of CFU-GM stimulated by indiv idual cytokines from multiple samples of CD34(+) enriched or purified human bone marrow cells. The number of IL-3- or GM-CSF-induced CFU-GM with 3 x 1 0(-7) M ATRA was 3.25 +/- 1.13, and 2.17 +/- 0.8-fold greater respectively, compared to controls without ATRA, while G-CSF had no effect and the ratio of colony-induced with or without ATRA was 1.06 +/- 0.17 (P = 0.00012). No colonies grew with ATRA + IL-6 or ATRA without a cytokine. Maximum enhanci ng effect on IL-3-induced CFU-GM occurred when ATRA was added on day 2, gra dually diminished when delaying ATRA, and in cultures of day 9 or older add ing ATRA had no effect. In 14 days liquid cultures of purified CD34+ cells with IL-3, ATRA increased the number of myeloid differentiated cells to 91- 95%, compared to 37-70% with IL-3 alone. In addition, the number of apoptot ic cells using the annexin V method increased after 14 days from 5.1% with IL-3 to 17.1% with IL-3 + ATRA and by the TUNEL in situ method from 10-26% to 60-95%, respectively. This study demonstrates that ATRA consistently enh ances the growth of myeloid progenitors from CD34+ cells. This effect is de pendent on the stimulating cytokine, suggesting the myeloid cells respondin g to ATRA are the less mature CFU-GMs that are targets of IL-3 and GM-CSF a nd not the G-CSF-responding mature progenitors. The growth stimulation by A TRA and IL-3 is also associated with granulocyte differentiation and increa sed apoptosis. These studies further suggest a potential role of pharmacolo gical doses of ATRA on the development of normal human hematopoietic cells.