An HMBA-resistant and heme-synthesizing variant clone of Friend leukemia cells

A clone of Friend leukemia (FL) cells has been isolated which, in the presence of hexamethylene bisacetamide (HMBA) as inducer, is capable of growing and producing heme for long periods of time. The differentiation program expressed by this clone is very similar to that observed in the 5-86 parent, that, however, is arrested in its growth. The expression of the differentiated state in this clone depends on the continuous presence of an inducer; if the inducer is removed from a culture containing a high percentage of B+ (benzidine-positive) cells, the cells rapidly (5-7 days) revert to an undifferentiated state and appear to lose their differentiated character consecutively rather than simultaneously. The clone described in this paper is unstable; when grown for more than two months in the presence of an inducer it shifts toward a population containing a low percentage of heme-synthesizing cells. This instability seems to be due to the accumulation of a faster growing and more undifferentiated cell population.