Targeted hematopoietic stem cell depletion through SCF-blockade.

Area of Science:

• Immunology
• Hematology
• Oncology

Background:

• Hematopoietic stem cell transplantation (HSCT) is a vital curative treatment for blood and immune disorders.
• Current HSCT conditioning methods (chemotherapy, TBI) cause significant toxicity and long-term side effects.
• Monoclonal antibody (mAb)-based HSC depletion presents a less toxic alternative conditioning strategy.

Purpose of the Study:

• To elucidate the mechanism of action for αCD117 mAbs in HSC depletion.
• To compare the efficacy of different αCD117 mAb clones and fragments.
• To explore combination regimens for enhanced HSCT conditioning.

Main Methods:

• In vitro and in vivo comparison of αCD117 mAb clones (ACK2, 2B8, 3C11) and fragments.
• Assessment of HSC proliferation inhibition and SCF binding antagonism.
• Evaluation of HSC depletion and donor engraftment in severe combined immunodeficiency (SCID) and wildtype (WT) mouse models.

Main Results:

• ACK2 fully inhibited SCF binding and HSC proliferation in vitro, leading to HSC depletion and engraftment in SCID mice.
• αCD117 mAb fragments retained HSC depletion capacity in SCID models.
• Combination of αCD117 mAb ACK2 with αCD47 mAb was essential for robust donor HSC engraftment in WT mice, demonstrating the Fc region's importance in immunocompetent settings.

Conclusions:

• αCD117 mAb-mediated HSC depletion mechanisms were clarified.
• Effective strategies for HSCT conditioning in both SCID and WT settings were identified.
• This research supports the development of non-genotoxic HSCT conditioning approaches for broader clinical application.