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OR19

Mimicking FA mutations in hematopoietic stem and progenitor cells by gene editing approaches

I Peña(1,2) L Ugalde(1,2) L Álvarez(1,2) E Karasau(3) S Siegner(3) L García(1,2) B Olalla(1,2) J Corn(3) J Bueren(1,2) P Río(1,2)

1:Division of Hematopoietic Innovative Therapies. Centro de Investigaciones Energéticas Medioambientales y Tecnológicas and Centro de Investigación Biomédica en Red de Enfermedades Raras (CIEMAT/CIBERER), Madrid 28040, Spain; 2:Advanced Therapies Unit, Instituto de Investigación Sanitaria Fundación Jiménez Díaz (IIS-FJD, UAM), Madrid 28040, Spain; 3:Department of Biology, ETH Zurich, Zurich 8092, Switzerland.

New therapeutic approaches based on CRISPR/Cas9 gene editing tools are being developed to correct multiple Fanconi Anemia (FA) mutations. Nevertheless, the intrinsic defect in hematopoietic stem and progenitor cells (HSPCs) from these patients limits their availability to validate these tools. The generation of FA-like HSPCs from healthy donor CD34+ cells will diminish the bottleneck of accessing FA HSPCs with specific mutations. Using adeno-associated viral vectors carrying the most prevalent mutation in Spain (FANCA c.295 C>T) as a donor template, we obtained up to 65% substitution of the FANCA WT sequence. These edited cells showed a marked proliferative disadvantage, resembling the impaired expansion capacity of FA HSPCs. Moreover, we observed the characteristic hypersensitivity of FA cells to interstrand crosslinking agents such as Mitomycin C (MMC), as deduced by the marked decrease in the clonogenic capacity of FA-like HSPCs treated with it. Furthermore, when FA-like HSPCs were transplanted into immunodeficient mice, an 85% reduction of human hematopoietic engraftment was observed compared to mock HSPCs. To increase the efficiency obtaining FA-like HSPCs, adenosine base editors were used to generate a model of the FANCA c.1083+2T>C mutation. In this case, up to 90% editing efficacy in HSPCs was observed, along with decreased in vitro expansion properties and MMC hypersensitivity. Taken together, our results demonstrate that gene editing allows the generation of HSPCs harboring specific mutations described in FA patients mimicking FA-HSPCs. These approaches will facilitate the evaluation of novel gene editing and delivery systems to target FA-HSPCs in vitro and in vivo

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