and a normal one
Image by Betty Pace
Gene editing via zinc-finger nucleases (ZFNs) shows early promise for treating sickle cell disease (SCD), according to preclinical research published in Blood.
Investigators used ZFNs to correct the SCD mutation in CD34+ hematopoietic stem and progenitor cells (HSPCs) derived from the bone marrow of SCD patients.
And these modified cells were able to produce normal red blood cells in vitro.
“This is a very exciting result,” said study author Donald Kohn, MD, of the University of California, Los Angeles.
“It suggests the future direction for treating genetic diseases will be by correcting the specific mutation in a patient’s genetic code.”
For this research, Dr Kohn and his colleagues took ZFNs designed to flank the SCD mutation and delivered them with a homologous donor template (either an integrase-defective lentiviral vector [IDLV] or a DNA oligonucleotide).
The investigators first tested this gene-editing system in CD34+ HSPCs derived from healthy donors and observed “high levels” of gene modification at the beta-globin locus. They also discovered off-target cleavage in the delta-globin gene but noted that this gene is “functionally dispensable.”
Additional experiments revealed that the modified CD34+ HSPCs could differentiate into erythroid, myeloid, and lymphoid cell types in vitro and in NSG mice.
So the investigators tested ZFN messenger RNA and the IDLV donor in CD34+ cells derived from the bone marrow of SCD patients. The team cultured cells in erythroid expansion medium and, after expansion but before enucleation, harvested the cells.
Genomic analysis revealed correction of the SCD mutation in 18.4±6.7% of the reads, and with that came the production of wild-type hemoglobin.
The investigators said these results show that ZFNs can provide site-specific gene correction and lay the groundwork for a potential therapy to treat SCD. The next steps will be to make the gene correction process more efficient and conduct additional research to determine if the method is effective and safe enough to move to clinical trials.
“This is a promising first step in showing that gene correction has the potential to help patients with sickle cell disease,” said Megan Hoban, a graduate student at UCLA. “The study data provide the foundational evidence that the method is viable.”
Another research group has reported similarly promising early results using induced pluripotent stem cells and CRISPR/Cas9 to correct the SCD mutation.
