Da. Vallera et al., Targeting myeloid leukemia with a DT390-mIL-3 fusion immunotoxin: ex vivo and in vivo studies in mice, PROTEIN ENG, 12(9), 1999, pp. 779-785
The IL-3 receptor was expressed on a high frequency of myeloid leukemia cel
ls and also on hematopoietic and vascular cells. We previously showed that
a recombinant IL-3 fusion immunotoxin (DT390IL-3) expressed by splicing the
murine IL-3 gene to a truncated diphtheria toxin (DT390) gene selectively
killed IL-3R(+) expressing cells and was not uniformly toxic to uncommited
BM progenitor cells (Chan,C.-H,, Blazar,B,R., Greenfield,L., Kreitman,R.J.
and Vallera,D.A., 1996, Blood, 88, 1445-1456), Thus, we explored the feasab
ility of using DT390IL-3 as an antileukemia agent. DT390IL-3 was toxic when
administered to mice at doses as low as 0.1 mu g/day, The dose limiting to
xicity appeared to be related to platelet and bleeding effects of the fusio
n toxin, Because of these effects, DT390IL-3 was Studied ex vivo as a means
of purging contaminating leukemia cells from BM grafts in a murine autolog
ous BM transplantation. In this setting, as few as 1000 IL-3R-expressing, b
cr/abl transformed myeloid 32Dp210 leukemia cells were lethal, An optimal p
urging interval of 10 nM/l for 8 h eliminated leukemia cells from 32Dp210/B
M: mixtures given to lethally irradiated (8 Gy) C3H/HeJ syngeneic mice. Mic
e given treated grafts containing BM and a lethal dose of 32Dp210 cells sur
vived over 100 days while mice given untreated grafts did not survive (P <
0.00001). DT390IL-3 may prove highly useful for ex vivo purging of lethal m
alignant leukemia cells from autologous BM grafts.