Rate and time of DNA synthesis of human leukaemic blasts in bone marrow and peripheral blood.

We have evaluated DNA synthesis rate (S rate) and time (Ts) and tritiated thymidine labelling index (LI) of peripheral blood (PB) and/or bone marrow (BM) leukaemic blasts (Bl) in nineteen cases of acute leukaemia (twelve non-lymphoblastic, AnLL, and seven lymphoblastic, ALL), in one case of non-Hodgkin's leukaemic lymphoma and in a case of plasma cell leukaemia. The LI of PB-Bl was significantly lower than that of BM-Bl (range 0.1-6.2% and 1.9-19.5%, respectively; P less than 0.01). The S rate was higher for PB-Bl than for BM-Bl (range 3.5-11.3 and 2.5-9.5 mol X 10(-18)/min; P less than 0.02) and the Ts of PB-Bl was shorter than that of BM-Bl (range 7.6-22.1 and 10.8-34.7 hr, respectively; P less than 0.02). In eight cases where S rates of both BM-Bl and PB-Bl were available, a linear correlation (r = 0.82; P less than 0.01) was found between the two parameters. This suggests that the DNA synthetic rate is a property of the leukaemic cell line in individual patients and differs from case to case. It further indicates that the environmental influences on the DNA synthesis rate in BM or PB are always of the same order of magnitude. From the results of this study we speculate that the DNA synthesis rate of leukaemic blasts is slowed down in the BM by environmental factors such as cell density.