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

Abstract

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.

Targeted therapy aimed at cancer stem cells: Wilms’ tumor as an example

“…This discovery was followed by several efforts aimed at targeting the hematopoietic cancer stem cell markers, such as CD44 and CD123 in AML [64][65][66][67][68]. Further studies have since been performed by targeting CSCs in several solid tumors such as pancreatic, breast, prostate and colon cancers, melanoma, glioma, hepatocellular carcinoma, and others.…”

Human acute myelogenous leukemia stem cells are rare and heterogeneous when assayed in NOD/SCID/IL2Rγc-deficient mice

“…A recent report demonstrates that treatment of AML mononuclear cells with anti-CD38 antibodies prior to transplantation inhibits engraftment in NS mice, suggesting that CD38 + subsets may contain LSCs (21). Also, several groups have shown that treatment of mice with anti-CD44, anti-CD47, or anti-CD123 can inhibit growth of LSCs or their engraftment in NS mice (22)(23)(24). It is not clear whether these antibodies interfere with BM homing or stimulation of intracellular signaling or through Fc-mediated clearance of antibody-labeled cells (22).…”

“…Also, several groups have shown that treatment of mice with anti-CD44, anti-CD47, or anti-CD123 can inhibit growth of LSCs or their engraftment in NS mice (22)(23)(24). It is not clear whether these antibodies interfere with BM homing or stimulation of intracellular signaling or through Fc-mediated clearance of antibody-labeled cells (22). Furthermore, Taussig et al have observed that both CD34 -and CD34 + fractions from the majority of primary NPM1-mutated AML contained LSCs (25).…”

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

“…A number of therapeutic agents with similar molecular formats as those described for CD33 have been developed, including immunoglobulins, 47–49 a radio-immunoconjugate, 50 ADCs and a fusion protein between the cytokine IL-3 and a fragment of diphtheria toxin, 51–54 bi-specific T cell-recruiting agents (BiTEs) and Dual-Antigen Recruiting T-cell engagers (DARTs), 55–58 dual-targeting triplebodies, 59,60 and CAR-transfected T cells. 61–64 Expression of CD123 is largely restricted to hematopoietic cells, but expression on endothelial cells has been reported.…”