Normal Differentiation of Myeloid Leukaemic Cells induced by a Differentiation-inducing Protein

VARIOUS types of cells release an inducer for the formation of colonies in vitro with mature differentiated macrophages and granulocytes from single normal undifferentiated haematopoietic cells^1–8. Using purified inducer from a cloned line of mouse fibroblasts, we have shown that this induction requires a protein (MGI) with a molecular weight of 65–70,000 and a low molecular weight co-factor, both secreted by the fibroblasts⁹. Adenine or adenine-containing nucleotides can substitute for the co-factor^9,10. We have also shown that non-purified conditioned medium produced by human cells can induce undifferentiated cells from patients with acute myeloid leukaemia to differentiate into mature granulocytes¹¹.