Increase of proliferative activity of leukaemic blast cells from human peripheral blood in liquid culture.

The proliferative behaviour of leukaemic cells from the peripheral blood of 12 patients suffering from acute leukaemia was investigated in short term liquid culture. In 3 cases of AML an increase of the blast cell number was observed exceeding the initial value whereas in 9 other cases the cell number decreased more or less rapidly. In 9 of these patients the proliferation kinetics of the cultured leukaemic blast cells were studied with 3H-thymidine labelling. In all these cases the labelling index increased during the first days of culture, in 3 cases to values of 48%, 45% and 38% on day 3. Only in 5 cases, however, did an absolute increase of the blast cells incorporating 3H-thymidine occur. Here the doubling times of the proliferating leukaemic blast cells were estimated to be 12, 13, 14, 28 and 55 h. Since a doubling time of 12 to 14 h seems to be too short to be explained only by an exponential growth of the initially proliferating cells it is postulated that leukaemic blast cells in a G0- or long G1-phase were present in the peripheral blood of these patients and that these entered the cell cycle during liquid culture.