Human placental conditioned medium reverses apparent commitment to differentiation of human promyelocytic leukemia cells (HL60).

Using a system of sequential daughter cell transfers in semisolid medium, we have analyzed self-renewal and differentiation of human promyelocytic leukemia cells (HL60) in presence of all-trans retinoic acid and human placental conditioned medium (HPCM). We find that retinoic acid induces coordinated losses of self-renewal potential which are followed by phenotypic differentiation. The latter occurs as an all-or-none event and is reversible in the presence of HPCM. Thus, HL60 cells that apparently had terminally differentiated (as estimated by the ability to reduce nitroblue tetrazolium [NBT]) can lose their differentiation marker and reenter the proliferative pool.