In-vitro effect of retinoic acid on normal and chronic myeloid leukemia granulopoiesis.

The effect of increasing concentrations of retinoic acid (RA) on the in-vitro proliferation of normal and chronic myeloid leukemia (CML) granulo-monocyte precursors (CFU-GM) was studied. 10(-7)M RA added to semisolid cultures stimulated the growth of day 14 but not of day 7 normal CFU-GM, whereas in CML the growth of both populations was either unchanged or inhibited. Five-day and 10-day preincubation of normal bone marrow cells with RA augmented the number of day 14 CFU-GM (by up to 187% with 10(-6) M RA), whereas there was a marked decrease when CML cells were used. Total cellularity was not much affected, though a slight increase in liquid normal bone marrow cultures and a slight fall in CML cultures could be detected. These data point to a difference in the response to RA of normal and CML precursors. They may offer of preclinical basis for its employment to delay the blastic progression of CML.