TALEN-based gene editing was able to correct mutations in the HBB gene of hematopoietic stem and progenitor cells (HSPCs) taken from patients with sickle cell disease (SCD), as presented at the 63rd American Society for Hematology Annual Meeting & Exposition.

The researchers found that TALGlobin01, an autologous HSPC-based gene therapy, was able to achieve up to a 70% (mean 56%) correction of the HBB genes in homozygous (HbSS) sickle cell disease patient HSPCs.

Treatment with TALGlobin01 also resulted in only 20% of nonhomologous end joining-dependent insertion/deletion events. Cell viability, hematopoietic stem/progenitor immunophenotype, and differentiation potential of the HSPCs were not affected by the gene therapy.

“These results are the first demonstration that a TALEN-based engineering process could be used to efficiently correct the SCD mutated HBB gene in HbSS patient-derived [hematopoietic progenitor cell antigen] HSPCs,” the authors said.

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During the experiment, the corrected HSPCs were differentiated into late-stage erythroid cells in vitro and the hemoglobin A (HbA) protein production was measured using high-performance liquid chromatography. The HbA protein made up as much as 60% (mean, 49%) of the total hemoglobin produced.

The sickle hemoglobin percentage dropped from 93% in unedited cells to only 13% in the corrected cells. Edited cells were also injected into immunodeficient NOD scid gamma mice where they were able to engraft and reach roughly a 40% allelic correction. The cells were still detectable 16 to 17 weeks after transplantation.

Through an unbiased genome-wide approach and high-throughput sequencing screening, the TALGlobin01 cleavage activity was only found at 1 off-target site. The site was located on the HBD gene locus and the cleavage activity at this site was much lower (1.2%) compared to the on-site cleavage activity (50.7%).

“Taken together, the high level of HbA expression and reversion of sickling phenotype, the efficient in vivo long-term engraftment potential of TALGlobin01 edited cells and the low levels of HBB KO or off-target cleavage generated by our gene correction process, warrant the clinical evaluation of TALGlobin01 to treat SCD patients,” the authors concluded.

Reference

Moiani A, Hong P, Letort G, et al. Pre-clinical development of a highly efficient TALEN®-based correction of the β-globin gene in patient-derived hematopoietic stem and progenitor cells (HSPCs) to treat sickle cell disease. Poster presented at: 63rd American Society for Hematology Annual Meeting & Exposition: December 11, 2021; Atlanta, Georgia.