Submitted April 3, 2006
Accepted July 6, 2006
Expression of Interleukin-3 receptor subunits on defined subpopulations of acute myeloid leukemia blasts predicts the cytotoxicity of diphtheria toxin Interleukin-3 fusion protein against malignant progenitors which engraft in immunodeficient mice
Leman Yalcintepe, Arthur E Frankel, and Donna Hogge*
Terry Fox Laboratory, British Columbia Cancer Agency, Vancouver, Canada
Scott and White Memorial Hospital, Temple, TX, USA
* Corresponding author; email: dhogge{at}bccancer.bc.ca.
The interleukin-3 receptor (IL-3R) subunits are overexpressed on acute myeloid leukemia (AML) blasts as compared to normal hematopoietic cells and are thus potential targets for novel therapeutic agents. Both FACS analysis and quantitative Realtime RT-PCR (QRT-PCR) were used to quantify expression of the IL-3R
and
c subunits on AML cells. QRT-PCR for both subunits was most predictive of killing of AML colony forming cells (AML-CFC) by diphtheria toxin-IL-3 fusion protein (DT388IL3). Among 19 patient samples, the relative level of the IL-3R
was higher than the IL-3R
c and highest in CD34+CD38-CD71- cells, enriched for candidate leukemia stem cells, as compared to cell fractions depleted of such progenitors. Overall, the amount of IL-3R
c subunit did not vary among sorted subpopulations. However, expression of both subunits varied by >10-fold among different AML samples for all subpopulations studied. The level of IL-3R
c expression vs GAPDH (set at 1000) ranged from 0.14 to 13.56 in CD34+CD38-CD71- cells from different samples and this value was correlated (r=0.76, p=0.05) with the ability of DT388IL3 to kill AML progenitors which engraft in
2-microglobin-deficient NOD/SCID mice (n=7). Thus, quantification of IL-3R subunit expression on AML blasts predicts the effectiveness IL-3R-targeted therapy in killing primitive leukemic progenitors.