Sigrid Fu Skjelbostad

• Mikkelsen, Nanna S.; Ravendran, Sujan; Broksø, Amalie D.; Skjelbostad, Sigrid Fu; Pedersen, Maya G. & Fang, Hongyu [Show all 9 contributors for this article] (2025). Orthogonal CRISPR systems for targeted integration and multiplex base editing enable nonviral engineering of allogeneic CAR-T cells. Molecular Therapy. ISSN 1525-0016. 33(12), p. 6100–6100. doi: 10.1016/j.ymthe.2025.08.032. Full text in Research Archive Show summary

  Multiple genomic modifications, including targeted transgene integrations and knockouts, may be required to develop potent, allogeneic chimeric antigen receptor (CAR)-T cell therapies. Conventional CRISPR-Cas systems generate double-strand breaks (DSBs) associated with genomic rearrangements and genotoxicities. DSB-free base editing reduces these risks. Here, we facilitate multiplex editing by combining Staphylococcus aureus Cas9 (SaCas9) mRNA base editors for DSB-free knockout of B2M and REGNASE-1 with Streptococcus pyogenes Cas9 nucleases for targeted integration of an anti-CD19 CAR transgene at the T cell receptor α constant locus. Combined, these edits have been reported to generate safer allogeneic CAR-T cells with enhanced activity and persistence. We demonstrate multiplex gene editing in primary human T cells with B2M and REGNASE-1 base editing frequencies reaching 66% and 84%, respectively, while integrating the anti-CD19 CAR transgene in up to 36% or 71% of cells using nonviral single-stranded DNA repair templates or viral vector templates (AAV6), respectively. Importantly, no detrimental effects on CAR-T cell function were observed in vitro or in vivo, and knockout by base editing reduced rates of balanced chromosomal translocations by 210-fold. This orthogonal CRISPR-Cas engineering approach represents a novel and safer strategy for nonviral, multiplexed genetic engineering of CAR-T cells.

• Kopcil, Pavel; Ervik, Carolina W.; Reint, Ganna; Mamia, Katariina; Szymanska, Monika & Dahal-Koirala, Shiva [Show all 17 contributors for this article] (2025). Editing of ADA2 Point Mutation in Human Hematopoietic Stem Cells. bioRxiv (preprint article). doi: 10.1101/2025.08.14.670303. Full text in Research Archive Show summary

  Abstract Background The homozygous ADA2 : c.506G>A (p.Arg169Gln; p.R169Q) variant accounts for majority of Deficiency in Adenosine Deaminase 2 (DADA2). This monogenic disorder may be amenable to ex vivo gene therapy by correcting the pathogenic mutation in CD34+ hematopoietic stem and progenitor cells (HSPCs). Objective To apply CRISPR-Cas9 and homology-directed repair (HDR) as a surrogate strategy to model correction of the pathogenic ADA2 c.506G>A variant in healthy cord blood HSPCs. Methods HSPCs were electroporated with optimised CRISPR-Cas9 editing reagents, and editing outcomes, including HDR and on-target deletions, were quantified by ddPCR. Cell functionality was assessed through colony-forming unit (CFU) assays and by xenotransplantation into NOD SCID Gamma (NSG) mice. Two HDR enhancement strategies were tested: (1) genetic inhibitors of p53 and non-homologous end joining (NHEJ) pathways, and (2) pharmacological NHEJ inhibition. Results Small-molecule NHEJ inhibitors increased HDR efficiency approximately two-fold (from ∼40 % to ∼80 %). Edited HSPCs retained normal CFU capacity and successfully engrafted in NSG mice. However, up to 8 % of edited cells exhibited on-target chromosome loss, though this declined over time. Up to 40 % of T cells and fibroblasts demonstrated similar losses under NHEJ inhibitors treatment. In contrast, genetically encoded inhibitors did not improve HDR. Conclusion The ADA2 p. c.506G>A variant can be effectively edited employing surrogate strategy in HSPCs without impairing functionality. Although pharmacological inhibition of NHEJ enhances HDR efficiency, it also increases the risk of on-target chromosome aberrations, highlighting the need for careful consideration of the associated risks and benefits in therapeutic gene editing. Key messages 1) The ADA2 p.R169Q variant can be efficiently corrected via HDR, and the edited CD34+ HSPCs retain their engraftment capability in NSG mice. 2) Pharmacological inhibition of NHEJ using small-molecule inhibitors increases HDR efficiency but is associated with significant on-target deletions and chromosomal arm loss, particularly in differentiated cell types, and in a donor-dependent manner. Capsule summary The ADA2 p.R169Q variant is a viable target for precision gene editing in hematopoietic stem cells. Although inhibition of NHEJ improves HDR efficiency, it concomitantly increases the risk of large on-target deletions, particularly in differentiated cells.

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• Skjelbostad, Sigrid Fu (2026). Engineering T-cells with optimized TCR knock-in and enhanced tumor-killing capacity. Full text in Research Archive
• Skjelbostad, Sigrid Fu (2026). Creating stronger cancer-fighting immune cells. Full text in Research Archive

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