Neoplastic macrophages grown from human leukaemic monocytes.

Leucocyte suspensions from some cases of acute myelogenous leukaemia produced large numbers of macrophages when cultured in vitro. The macrophages increased steadily in number during the first 1-2 wk of culture. The increase was partly derived from division of the macrophages themselves, partly from augmentation from supernatant cells not adherent to the surface of the culture flask. This augmentation occurred mostly in the first 24 hr of culture. The leukaemic macrophages had many features of normal macrophages as regards light microscopy, surface receptors, phagocytic activity and cytochemistry. Under the electron microscope, however, they had many abnormal characteristics, all of which have been recorded previously as features of malignant transformation. Cultures containing the abnormal macrophages and their precursor cells caused local solid tumours when injected into immune-deprived mice. The tumours were composed of rather uniform cells many of which resembled neoplastic reticulum cells. It is concluded that human leukaemic monocytes or promonocytes can develop into macrophages with ultrastructural features of malignancy. This appears to be the first demonstration of the development of neoplastic macrophages. It is suggested that some lymph node tumours of man may be composed of similar neoplastic macrophages and their precursor cells.