M. Feuring-buske et al., Variable cytotoxicity of diphtheria toxin 388-granulocyte-macrophage colony-stimulating factor fusion protein for acute myelogenous leukemia stem cells, EXP HEMATOL, 28(12), 2000, pp. 1390-1400
Objective. In this study, the utility of DT388-granulocyte-macrophage colon
y-stimulating factor (GM-CSF) for the ex vivo purging and direct administra
tion to patients with acute myeloid leukemia (AML) is tested using clonogen
ic assays, long-term cultures (LTC), and NOD/SCID mice as assays for leukem
ic progenitors.
Materials and Methods. We compare the ability of 24-hour exposure to 0.3 mu
g/mL (4 nM) DT388-GM-CSF to kill AML colony forming cells (CFC) and the mor
e primitive AML progenitors detected after 6 weeks in stromal cocultures (A
ML LTC-initiating cells or AML LTC-IC) and after 8 weeks in NOD/SCID mice.
Results. AML samples (n = 10), expressing a mean of 35 to 1466 GM-CSF recep
tors/blast, showed mean (range) percent kills of AML CFC and LTC-IC of 61 (
17-98) and 46 (0-94) respectively with a direct correlation (r = 0.69) betw
een the % kills detected in the in vitro assays. Among 5 evaluable samples
the percent reduction in AML cell engraftment in NODI SCID marrow following
ex vivo DT388-GM-CSF treatment varied from 38% to 100%. 40% to 56% of norm
al bone marrow CFC and 31% to 45% of normal ETC-IC survived the same ex viv
o treatment (n = 3). In subsequent experiments, NOD/SCID mice received AML
blast cell injections intravenously followed in 24 hours by 1.5 mug DT388-G
M-CSF daily intraperitoneally for 5 days. A reduction of marrow blast cells
was seen with 7 of 9 samples tested 4 to 12 weeks post one course of toxin
. Repeating the 5-day course of toxin 2 or 3 times at 4-week intervals did
not improve the response, while delaying administration until 4 to 8 weeks
post AML cell injection reduced the toxin's effectiveness (n = 5).
Conclusion. This fusion toxin may prove useful for in vitro purging of stem
cell harvests from selected AML patients and far direct administration to
such patients. (C) 2000 International Society for Experimental Hematology.
Published by Elsevier Science Inc.