Leukaemogenic potency of WEHI-3B cells grown in vitro or in leukaemic mice

In order to quantify contaminating leukaemia inducing cells in blood or bone marrow from WEHI-3B bearing BALB/c mice (injected with 10(5) WEHI-3B suspension culture cells), in vitro colony forming leukaemia cells (CFU-L) and survival rate and/or survival time of mice transplanted with cells from WEHI bearing mice or suspension culture were correlated. ED(50) (inoculum inducing leukaemia in 50% of the animals) was 109 CFU-L (33-361) from suspension culture cells. Three weeks after initiation of leukaemia 2 x 10(5) BM or 0.5-2.0 x 10(6) blood cells induced 100% mortality of recipients. After mobilisation with CY or CY and G-CSF, the same amount of blood or BM cells did not induce leukaemia in recipients. A significant negative correlation was found between the survival time of leukaemic mice and the log number of CFU-L inoculated from in vivo sources. In terms of CFU-L cells, leukaemia induction to BM or WBC obtained 3 weeks after leukaemia induction were more potent; those from BM or WBC also obtained at 3 weeks but after mobilisation were less potent inducers than those from suspension culture. These data suggest that CFU-L and leukaemogenic cells are associated, but not identical.