SIRPα-αCD123 fusion antibodies targeting CD123 in conjunction with CD47 blockade enhance the clearance of AML-initiating cells

Abstract

Background Acute myeloid leukaemia (AML) stem cells (LSCs) cause disease relapse. The CD47 “don’t eat me signal” is upregulated on LSCs and contributes to immune evasion by inhibiting phagocytosis through interacting with myeloid-specific signal regulatory protein alpha (SIRPα). Activation of macrophages by blocking CD47 has been successful, but the ubiquitous expression of CD47 on healthy cells poses potential limitations for such therapies. In contrast, CD123 is a well-known LSC-specific surface marker utilized as a therapeutic target. Here, we report the development of SIRPα-αCD123 fusion antibodies that localize the disruption of CD47/SIRPα signalling to AML while specifically enhancing LSC clearance. Methods SIRPα-αCD123 antibodies were generated by fusing the extracellular domain of SIRPα to an αCD123 antibody. The binding properties of the antibodies were analysed by flow cytometry and surface plasmon resonance. The functional characteristics of the fusion antibodies were determined by antibody-dependent cellular phagocytosis and antibody-dependent cellular cytotoxicity assays using primary AML patient cells. Finally, an in vivo engraftment assay was utilized to assess LSC targeting. Results SIRPα-αCD123 fusion antibodies exhibited increased binding and preferential targeting of CD123+ CD47+ AML cells even in the presence of CD47+ healthy cells. Furthermore, SIRPα-αCD123 fusion antibodies confined disruption of the CD47-SIRPα axis locally to AML cells. In vitro experiments demonstrated that SIRPα-αCD123 antibodies greatly enhanced AML cell phagocytosis mediated by allogeneic and autologous macrophages. Moreover, SIRPα-αCD123 fusion antibodies efficiently targeted LSCs with in vivo engraftment potential. Conclusions SIRPα-αCD123 antibodies combine local CD47 blockade with specific LSC targeting in a single molecule, minimize the risk of targeting healthy cells and efficiently eliminate AML LSCs. These results validate SIRPα-αCD123 antibodies as promising therapeutic interventions for AML.

The Differential Expression of CD47 may be Related to the Pathogenesis From Myelodysplastic Syndromes to Acute Myeloid Leukemia

“…For example, the humanized anti-CD47 monoclonal antibody CC-90002 enables tumor cells killed by macrophages by blocking the CD47/SIRPα interaction ( 16 ). Similarly, a SIRPα-αCD123 antibody, reported by Siret Tahk et al, intervenes against tumors by blocking local CD47 and binding to a single molecule on specific leukemic stem cells ( 17 ). These studies have revealed the mechanisms of actions of CD47 in MDS or AML from a horizontal perspective, whereas the present study explored the effect and association of CD47 expression on the transformation of MDS to AML from a longitudinal perspective.…”

Targeting CD47 for cancer immunotherapy

“…Most recently, a study demonstrated that SIRPα-αCD123 antibodies combined local CD47 blockade with specific AML LSCs targeting in a single molecule, minimized the risk of targeting healthy cells and efficiently eliminated AML LSCs. This indicates that SIRPα-αCD123 fusion antibodies targeting CD123 in conjunction with CD47 blockade could enhance the clearance of AML-initiating cells, which may be used as promising therapeutic interventions for AML [ 90 ].…”

Targeting macrophages in hematological malignancies: recent advances and future directions

“…SIRPα receptors on macrophages interact with CD47 to inhibit phagocytosis. SIRPα/CD123 BsAb was designed by Siret Tahk et al based on these interactions [ 191 ] . Their results demonstrate that SIRPα/CD123 BsAb yields strong anticancer activity against AML in vitro and in vivo via enhanced NK cell-dependent ADCC and macrophage-mediated ADCP effects.…”