Monoclonal Antibody-Mediated Targeting of CD123, IL-3 Receptor α Chain, Eliminates Human Acute Myeloid Leukemic Stem Cells

Division of Cell and Molecular Biology, University Health Network, Toronto, ON M5G 1L7, Canada.
Cell stem cell (Impact Factor: 22.27). 08/2009; 5(1):31-42. DOI: 10.1016/j.stem.2009.04.018
Source: PubMed


Leukemia stem cells (LSCs) initiate and sustain the acute myeloid leukemia (AML) clonal hierarchy and possess biological properties rendering them resistant to conventional chemotherapy. The poor survival of AML patients raises expectations that LSC-targeted therapies might achieve durable remissions. We report that an anti-interleukin-3 (IL-3) receptor alpha chain (CD123)-neutralizing antibody (7G3) targeted AML-LSCs, impairing homing to bone marrow (BM) and activating innate immunity of nonobese diabetic/severe-combined immunodeficient (NOD/SCID) mice. 7G3 treatment profoundly reduced AML-LSC engraftment and improved mouse survival. Mice with pre-established disease showed reduced AML burden in the BM and periphery and impaired secondary transplantation upon treatment, establishing that AML-LSCs were directly targeted. 7G3 inhibited IL-3-mediated intracellular signaling of isolated AML CD34(+)CD38(-) cells in vitro and reduced their survival. These results provide clear validation for therapeutic monoclonal antibody (mAb) targeting of AML-LSCs and for translation of in vivo preclinical research findings toward a clinical application.

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    • "Paradoxically, monoclonal antibody (mAb) 7G3 recognizes the IL3Ra NTD (Sun et al., 1996; Barry et al., 1997) and completely blocks IL-3 binding and signaling. We recently showed that mAb 7G3 eliminates engrafted human AML stem cells in a mouse model of human AML (Jin et al., 2009). mAb 7G3, now humanized and designated as CSL362 (Busfield et al., 2014), is entering clinical trials for the treatment of patients with AML ( "
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    ABSTRACT: Interleukin-3 (IL-3) is an activated T cell product that bridges innate and adaptive immunity and contributes to several immunopathologies. Here, we report the crystal structure of the IL-3 receptor α chain (IL3Rα) in complex with the anti-leukemia antibody CSL362 that reveals the N-terminal domain (NTD), a domain also present in the granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-5, and IL-13 receptors, adopting unique "open" and classical "closed" conformations. Although extensive mutational analyses of the NTD epitope of CSL362 show minor overlap with the IL-3 binding site, CSL362 only inhibits IL-3 binding to the closed conformation, indicating alternative mechanisms for blocking IL-3 signaling. Significantly, whereas "open-like" IL3Rα mutants can simultaneously bind IL-3 and CSL362, CSL362 still prevents the assembly of a higher-order IL-3 receptor-signaling complex. The discovery of open forms of cytokine receptors provides the framework for development of potent antibodies that can achieve a "double hit" cytokine receptor blockade.
    Full-text · Article · Jul 2014 · Cell Reports
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    • "Strikingly, CD123 shows a fourfold increased expression on AML-LSCs over normal HSCs (Jin et al, 2009). This finding, together with the clinical observations that elevated expression of CD123 in AML is associated with higher blast counts at diagnosis and a lower complete remission rate resulting in poorer prognosis (Testa et al, 2002, 2004; Graf et al, 2004), make CD123 a particularly interesting target for antibody-derived therapeutics (Jin et al, 2009). AML-LSCs are known to possess several remarkable properties including self-renewal potential and increased resistance against chemotherapeutics and DNA damage (Lapidot et al, 1994; Bonnet & Dick, 1997; Guan & Hogge, 2000; Guzman et al, 2001; Hope et al, 2004; Ishikawa et al, 2007; Dick, 2008). "

    Full-text · Dataset · Jun 2014
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    • "It was shown that the targeting of CD123 using the 7G3 mAb impairs leukemic stem cells in vivo[20]. This effect seems to be related to two different mechanisms: one dependent upon inhibition of homing and engraftment of leukemic CD34+/CD38- cells into immunodeficient mice; the other related to the activation of innate immunity into NOD/SCID mice [20]. It is important to note that the inhibitory effects of the 7G3 mAb are not restricted only to the CD34+/CD38- leukemic subpopulation, but are exerted on the whole bulk leukemic cell population [20]. "
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    ABSTRACT: Recent studies indicate that abnormalities of the alpha-chain of the interleukin-3 receptor (IL-3RA or CD123) are frequently observed in some leukemic disorders and may contribute to the proliferative advantage of leukemic cells. This review analyzes the studies indicating that CD123 is overexpressed in various hematologic malignancies, including a part of acute myeloid and B-lymphoid leukemias, blastic plasmocytoid dendritic neoplasms (BPDCN) and hairy cell leukemia. Given the low/absent CD123 expression on normal hematopoietic stem cells, attempts have been made at preclinical first, and then at clinical level to target this receptor. Since the IL-3R is a membrane receptor there are two relatively simple means to target this molecule, either using its natural ligand or neutralizing monoclonal antibodies. Recent reports using a fusion molecule composed by human IL-3 coupled to a truncated diphteria toxin have shown promising antitumor activity in BPDCN and AML patients.
    Full-text · Article · Feb 2014
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