Effect of PTX on engraftment. PTX attenuates short-term engraftment. (A) Lethally irradiated hosts were injected with 250 000 BM cells, incubated for 20 hours with SCF in the absence or presence of PTX. This cell dose, equivalent to 740 ± 37 control CFU-Cs and 783 ± 58 PTX-treated CFU-Cs, was sufficient to radioprotect 10 of 10 lethally irradiated recipients of control cells, whereas 8 of 10 of the recipients of PTX-treated cells died between days 11 and 15 (recipients of control cells, gray diamonds; recipients of PTX-treated cells, black squares). (B) Lethally irradiated hosts received 1.5 × 106 BM cells, equivalent to 5940 ± 127 control CFU-Cs and 5880 ± 119 PTX-treated CFU-Cs, incubated for 20 hours with SCF in the absence or presence of PTX. At 8 days after transplantation, the recipients were killed. CFU-Cs were enumerated in BM, peripheral blood, and spleen and depicted as CFU-Cs per tissue (mean ± SEM). CFU-C contents were dramatically reduced in all 3 tissues of recipients of PTX-treated cells (control cells, ▦; PTX-treated cells, ▪). *P < .005 compared with control.