Primary human acute myeloblastic leukaemia: an analysis of in vitro granulocytic maturation following stimulation with retinoic acid and G-CSF.

Acute myeloid leukaemia (AML) is characterized by the inability of myeloid cells to reach terminal maturation. We examined to what degree granulocytic maturation could be achieved by stimulating AML blast cells in an in vitro serum-free system with a combination of granulocyte-colony stimulating factor (G-CSF) and all-trans-retinoic acid (RA). Specimens from 41 AML patients were cultured for 7 d and then examined for cytochemistry (myeloperoxidase, Sudan Black, naphthyl-ASD-chloracetate esterase, periodic acid Schiff) an nitroblue tetrazolium reduction. The expression of CD11a, CD11b, CD11c, CD15, CD18, CD10, CD24 and B13-3 membrane antigens was also evaluated. Morphological and cytochemical studies were also performed after AML colony culture and culture of normal bone marrow cells (NBM). The comparative analysis of the panel of parameters was indicative of granulocytic maturation although to different degrees. The cells from 25/41 cases showed morphologic maturation (May-Grünwald-Giemsa). A positive correlation was evident between morphological maturation and CD11b expression (11/22 patients) as well as that of CD11c and CD15 (6 patients). Napthyl ASD chloroacetate esterase and PAS stainings also correlated with morphology (in 10/22 and 10/24 patients respectively). Nevertheless, the pattern of granulocytic maturation was remarkably variable among the 41 cases examined. The cells from only a few patients acquired the full spectrum of granulocytic markers. The comparison with normal bone marrow blasts indicates that serum-free culture conditions can, per se, limit granulocytic maturation, but it also confirms the intrinsic inability of AML cells to attain complete maturation in response to two potent granulocytic inducers.