Program: Oral and Poster Abstracts
Session: 508. Bone Marrow Failure: Poster I
Objective:To develop a safe KIT blocking antibody (KIT-Ab) based HSCT conditioning regimen for FA that does not involve chemotherapy or irradiation.
Method: High purity KIT-Ab was made from the ACK2 hybridoma and its specificity to KIT binding was validated using mast cell assay. Baseline peripheral blood cells and the bone marrow hematopoietic stem and progenitor cell (HSPC) compartment (Lin-Kit+Sca+ and Lin-Kit+Sca+CD150+CD48- cells) of FANCA-/- and FANCD2-/- murine models were analyzed. Mechanistic studies using sorted FA bone marrow HSPC were performed ex vivo. This was followed by definitive primary and secondary transplants experiments following injection of KIT-Ab.
Results: Several features of FA hematopoietic stem/progenitor cells (HSPC) suggested their susceptibility to KIT-Ab blockade-mediated killing: (a) Expression of KIT was significantly lower in FANCA-/- HSPC, while expression of its ligand was higher in bone marrow stroma; (b) Moreover, genes associated with apoptosis/senescence, stress and inflammatory signaling that were upregulated in WT-HSPC following KIT-Ab blockade, were upregulated in FANCA-/- HSPC at baseline; (c) Furthermore, FANCA-/- HSPC demonstrated increased susceptibility to KIT-Ab mediated apoptosis and had a reduced proliferative capacity. In-vivo studies following ACK2 injection showed a marked reduction of colony-forming units (CFU-C) from both FANCA-/- and FANCD2-/- mice one week following injection, when compared to WT mice (48% and 76% decrease in CFU-C, respectively). Based on these findings, we evaluated the role of ACK2 as a sole HSCT conditioning regimen in FANCA-/- and FANCD2-/- mice. Indeed, definitive HSCT in both FANCA-/- and FANCD2-/-mice using KIT-Ab based conditioning resulted in donor HSC engraftment with multi-lineage chimerism, which progressively increased to 22-24% by 4-months, and was sustained in secondary transplants. Overall, we show that KIT-blockade alone is an adequate non-genotoxic HSPC-targeted conditioning in FA mice, and its clinical translation could circumvent the extensive transplant-related morbidity/mortality in this disease.
Disclosures: No relevant conflicts of interest to declare.
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