In this study, we evaluated the in vitro growth of normal hematopoietic progenitors (CFU-GM, BFU-E, CFU-GEMM, CFU-meg) stimulated by optimal sources of colony stimulating activity in the absence or presence of 10(-6) M all-trans retinoic acid (ATRA). ATRA alone did not show any colony-stimulating ability when added in culture to partially purified bone marrow populations. On the other hand, it significantly increased the number of CFU-GM (p = 0.003) and both the number (p = 0.009) and size (p = 0.002) of CFU-meg in the presence of appropriate colony-stimulating activity. Since ATRA had only modest stimulatory effects on purified CD34+ cells, the megakaryocyte colony-stimulating activity of ATRA was mainly due to an increased production of endogenous cytokines by bone marrow accessory cells. In parallel experiments, the in vitro growth of the different hematopoietic progenitors was evaluated in 28 patients affected by acute non-lymphoid leukemia (ANLL), mainly acute promyelocytic leukemia (APL). Bone marrow cells were harvested after remission induction obtained: (i) in ten APL patients treated with ATRA followed by one chemotherapy cycle (CHT) (3/7: Daunorubicin+Ara-C): group A ('ATRA/CHT'); (ii) eight APL patients treated with one CHT cycle alone (3/7 as above): group B ('APL-CHT'); (iii) in ten ANLL-non-APL patients after one CHT cycle (3/7 as above): group C ('ANLL-CHT'). The number of the different hematopoietic progenitors, and in particular CFU-GM and CFU-meg, was significantly higher in APL patients treated with ATRA plus CHT (group A) compared to APL (group B) or ANLL-non-APL (group C) patients treated with CHT alone (CFU-GM: p = 0.01; CFU-meg: p = 0.03). Our data demonstrate that ATRA is able to potentiate both normal and APL megakaryocytopoiesis and suggest that the in vivo administration of ATRA could be beneficial in other pathological conditions, where the megakaryocyte progenitor cell compartment is impaired.
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