KIT blockade is sufficient for donor hematopoietic stem cell engraftment in Fanconi anemia mice

Selective hematopoietic stem cell ablation using CD117-antibody-drug-conjugates enables safe and effective transplantation with immunity preservation

“…Subsequently, we showed that host HSCs in this model could be depleted using an antagonistic anti-murine CD117 monoclonal antibody (ACK2), resulting in an effective, safe, alternative single-agent conditioning approach enabling high donor HSC engraftment 11 . However, this naked antibody conditioning approach only functions as a stand-alone agent in certain disease models; such as immune deficiency 11,13 and Fanconi anemia 14 . In other settings, it has been found necessary to combine ACK2 with agents such as low-dose irradiation 15 or CD47 antagonism 13 to increase potency, making clinical translation of this approach challenging.…”

Hematopoietic chimerism and donor-specific skin allograft tolerance after non-genotoxic CD117 antibody-drug-conjugate conditioning in MHC-mismatched allotransplantation

“…Biotinylated monoclonal antibodies directed against mouse CD117/c-kit (clone 2B8, Biolegend, San Diego, CA; Lot # 170777–31) were coupled to streptavidin-linked saporin toxin (Advanced Targeting systems, San Diego, CA; Lot # 94-31) as detailed in Czechowicz et al 8 leading to generation of CD117-antibody-drug conjugate (CD117-ADC). Each mouse was injected with 1.5 mg/kg of ADC (~12 µg of streptavidin-saporin) in a total volume of 300 µl of PBS as was previously optimized in Palchaudhuri et al 6 and Czechowicz et al 8 . A biotinylated rat IgG2b kappa isotype control antibody (RTK4530, Biolegend, San Diego, CA) conjugated to saporin and mouse CD117/c-kit-specific antibodies (clones 2B8 & ACK2) unconjugated to saporin served as controls and were dosed at 500 µg per animal (~25 mg per kg) as previously reported 1 .…”

“…Monoclonal antibody (mAb)-based approaches for depleting recipient hematopoietic stem cells (HSCs) have shown promise as non-genotoxic conditioning agents in bone marrow (BM)/HSC transplantation (BMT/HSCT) 1–6 . mAb targeting of CD117 (c-Kit) 7 , a receptor tyrosine kinase that is highly expressed on HSCs and that binds the cytokine stem cell factor (SCF), was first shown to enhance HSC engraftment after syngeneic HSCT in immunodeficient mice; however, this stand-alone approach was unsuccessful in adult wild-type, immunocompetent mice 2 .…”

“…mAb targeting of CD117 (c-Kit) 7 , a receptor tyrosine kinase that is highly expressed on HSCs and that binds the cytokine stem cell factor (SCF), was first shown to enhance HSC engraftment after syngeneic HSCT in immunodeficient mice; however, this stand-alone approach was unsuccessful in adult wild-type, immunocompetent mice 2 . Subsequent improvements have included (1) combining an antagonistic anti-CD117 mAb with CD47 blockade, which promoted engraftment after syngeneic BMT and allogeneic BMT across a minor MHC mismatch 5 , and (2) saporin−conjugated anti-CD45.2 immunotoxin conditioning, which achieved robust syngeneic chimerism in immunocompetent animals but was never shown to be effective in allogeneic settings 6 .…”

Safer conditioning for antigen-encoding bone marrow transfer to induce immune tolerance

“…It is only expressed on the surface of HSPC and some other cell types such as mast cells [276,277]. Initially, anti-c-kit (CD117) antibody was used to achieve host HSC depletion which subsequently facilitated donor chimerism in various immunodeficient mouse models [248,278,279] but failed in immunocompetent mice [250]. However, combination of anti-c-kit with anti-CD47 or low-dose total body irradiation was successful and allowed donor chimerism in immunocompetent mice [227,250].…”