Abstract
Leukaemic cells taken from the blood of patients with acute myelogenous leukaemia (AML) frequently proliferate in suspension culture without the addition of growth factors for a limited period only. After a 6--10-fold increase in total cells, cell numbers remain constant for a time and finally decline. The main cause for this limited growth in vitro is not, initially at least, cell death leading to a steady state, but maturation associated in its final stages with cessation of DNA synthesis. Two populations of AML cells from Patients St and Wi respectively were studied, and progressive maturation towards mature leucocytes was demonstrated by the gradual acquisition in culture by the growing blast cells of intracellular enzymes (lysozyme, arginase, acid phosphatase and esterase being measured), surface markers (Fc and C3 receptors), of lactoferrin by Wi cells and of colony-stimulating activity by St cells, as well as changes in Ia antigens, phagocytic properties, morphology and adhesiveness to plastic. With St cells, which carried a characteristic chromosome marker, maturation terminated in cells with the characteristic properties of macrophages. At an intermediate stage, non-adherent and still-dividing St cells acquired Fc and C3 receptors and enzymes characteristic of monocytes. Wi cells progressively became neutrophil-like, and again there was an intermediate population of dividing cells which had Fc and C3 receptors and proteins such as lactoferrin and esterases. characteristic of neutrophils.