Leukocyte Kinetics in Chronic Myeloid Leukemia: I. DNA Synthesis Time in Blood and Marrow Myelocytes

A FRACTION of the leukocytes circulating in the blood of patients with chronic myeloid leukemia ( CML) is synthesizing DNA.#{176} This paper presents data to show that the DNA synthesis time (Ts) of these cells is similar to that found in normal bone marrow by Stryckmans et al.1’ Despite the presence of cells in DNA synthesis ( S) , mitoses are rarely seen in the peripheral blood in CML. Since the ratio of the number of cells in S to the number in mitosis should be the same as the ratio of Ts to the mitotic time ( Tm) , this means either that cells must leave the blood before dividing, or that Ts is very much longer in the blood than in the marrow. In myeloid metaplasia the relative frequency of mitoses in the blood permits estimation of Ts from the curve of labeled mitoses, whereas the rarity of mitoses in the blood in CML makes this impractical. For this reason a double-labeling tech-nic’2 has been used, in which in vivo labeling with tritiated thymidine (3H-TdR) is followed by in vitro incubation of the sample with ‘4C-thymidine (14C-TdR)