The interleukin-3 receptor alpha chain is a unique marker for human acute myelogenous leukemia stem cells

Abstract

Recent studies suggest that the population of malignant cells found in human acute myelogenous leukemia (AML) arises from a rare population of leukemic stem cells (LSCs). LSCs have been documented for nearly all AML subtypes and have been phenotypically described as CD34 + /CD38 − or CD34 + /HLA-DR − . Given the potentially critical role of these primitive cells in perpetuating leukemic disease, we sought to further investigate their molecular and cellular characteristics. Flow cytometric studies using primary AML tissue showed that the interleukin-3 receptor alpha chain (IL-3R␣ or CD123) was strongly expressed in CD34 + /CD38 − cells (98 ± 2% positive) from 16 of 18 primary specimens. Conversely, normal bone marrow derived CD34 + /CD38 − cells showed virtually no detectable expression of the CD123 antigen. To assess the functional role of IL-3R␣ positive cells, purified CD34 + /CD123 + leukemia cells were transplanted into immune deficient NOD/SCID mice. These experiments showed that CD123 + cells were competent to establish and maintain leukemic populations in vivo. To begin to elucidate a biological role for CD123 in leukemia, primary AML samples were analyzed with respect to signal transduction activity in the MAPK, Akt, and Stat5 pathways. Phosphorylation was not detected in response to IL-3 stimulation, thereby suggesting CD123 is not active in conventional IL-3-mediated signaling. Collectively, these data indicate that CD123 represents a unique marker for primitive leukemic stem cells. Given the strong expression of this receptor on LSCs, we propose that targeting of CD123 may be a promising strategy for the preferential ablation of AML cells.

Dual-targeting triplebody 33-16-123 (SPM-2) mediates effective redirected lysis of primary blasts from patients with a broad range of AML subtypes in combination with natural killer cells

“…CD34pos CD38neg cells, which are enriched in AML-LSCs for patients with CD34-positive AML, from 16 of 18 primary AML samples showed strong expression of CD123. 40 Another prominent study also reported CD123 expressed on the surface of CD34pos CD38neg AML cells, but in this study the antigen was also present on the corresponding cellular subsets from healthy bone marrow (BM) and cord blood (CB), although expression levels on the enriched normal BM cells were at least 10-fold lower than on on the corresponding AML cells. 12 CD123 is also expressed on normal HSCs from AML patients in follow-up after induction therapy.…”

“…7,10–12,40,46 We are not aware of any published reports indicating that they should differ from AML blasts in their intrinsic susceptibility to RDL by antibodies or antibody-derived agents in combination with NK cells. For most patients with CD34-positive AML, the relapse-relevant AML-LSCs are contained predominantly in the compartments of CD34-positive and (CD34-positive CD38-negative) cells.…”

“…For most patients with CD34-positive AML, the relapse-relevant AML-LSCs are contained predominantly in the compartments of CD34-positive and (CD34-positive CD38-negative) cells. 12,40,43–46,73 Therefore, we have first enriched CD34-bearing cells from 2 patients with CD34-positive AML, for whom sufficient cell numbers were available (patients 9 & 11; Table 3), by immuno-magnetic sorting with a commercial kit. Both samples carried intermediate combined densities of CD33 plus CD123 on their blasts (MNCs; approx.…”

“…8,40–45 In a landmark study, fewer than 1% of CD34pos CD38neg progenitor cells from a normal human bone marrow (BM) expressed CD123, while 99% of the corresponding cells from a patient with CD34-positive AML showed high grade expression. CD34pos CD38neg cells, which are enriched in AML-LSCs for patients with CD34-positive AML, from 16 of 18 primary AML samples showed strong expression of CD123.…”

“…We anticipate that SPM-2 will be able to discriminate at least to a degree between AML-LSCs and remaining normal HSCs of a patient, due to its dual-targeting capacity and the greater combined surface density of CD33 and CD123 on AML-LSCs than on normal HSCs. 11,12,24,27,40,46 A preferential elimination of AML-LSCs over normal HSCs would be a distinct advantage, if it could be reached, because the surviving HSCs may be able to reconstitute the patient’s hematopoietic system after the end of therapy at least in part, possibly even without the need for a stem cell transplant. Here we have studied, whether SPM-2 in conjunction with activated human NK cells was capable of eliminating blasts from patients with a very broad range of AML subtypes, as predicted, 8 and found the prediction to be fulfilled.…”