Photo by Aaron Logan
A new gene-editing strategy may be able to cure thalassemia, according to preclinical research published in Nature Communications.
The technique—which involves a combination of nanoparticles, synthetic pieces of DNA, and an intravenous injection—was able to alleviate symptoms of thalassemia in mice.
The strategy also decreases the risk of off-target mutations, when compared to other gene-editing techniques, according to researchers.
The new technique involves biocompatible nanoparticles containing peptide nucleic acids (PNAs), which are small, nano-sized, synthetic molecules in which a protein-like backbone is combined with the nucleobases found in DNA and RNA.
PNAs are designed to open up double-stranded DNA and bind near the target site in a highly specific manner. The PNAs fit inside a nanoparticle delivery system that is approved by the US Food and Drug Administration (FDA) and has already been used to treat neurodegenerative diseases in humans.
“We have developed a system that uses FDA-approved nanoparticles to deliver our PNA molecule along with a donor DNA to repair a malfunctioning gene in living mice,” said study author Danith Ly, PhD, of Carnegie Mellon University in Pittsburgh, Pennsylvania. “This has not been achieved with CRISPR.”
Dr Ly and his colleagues designed a PNA to target the malfunctioning gene in beta-thalassemia, the hemoglobin subunit beta (HBB) gene.
The researchers then loaded the nanoparticles with the PNAs, a donor strand of DNA encoding the sequence for a functional HBB gene, and a stem cell factor that enhances gene editing.
When the PNA binds to the target site in the DNA, it forms a PNA-DNA-PNA triplex, leaving a displaced DNA strand. Formation of such a complex enables the donor DNA to bind to the faulty DNA site within the vicinity.
Taken together, this altered helix engages the cell’s own DNA repair pathways to correct the malfunctioning HBB gene.
In addition to testing this system on mouse and human hematopoietic stem cells, the researchers used an intravenous injection to deliver the gene-editing package in mouse models of beta-thalassemia.
The results showed up to 6.9% successful gene-editing in hematopoietic stem cells. The mice showed elevated levels of hemoglobin—into the normal range—for several months after treatment, a reduction in reticulocytosis, and reversal of splenomegaly.
The researchers said this represents a striking increase in efficacy over typical gene-editing methods, which produce a 0.1% success rate.
“The effect may only be 7%, but that’s curative,” Dr Ly said. “In the case of this particular disease model, you don’t need a lot of correction. You don’t need 100% to see the phenotype return to normal.”
In addition, this gene-editing strategy had “extremely low off-target effects,” according to study author Peter Glazer, MD, of Yale University in New Haven, Connecticut.
The overall off-target modification frequency was 0.0032%.
If this strategy proves effective in clinical studies, it could lead to the development of gene therapy for patients with thalassemia, sickle cell disease, and other inherited blood disorders, Dr Glazer said.
“We might get enough cells corrected that individuals are not anemic anymore,” he added. “We could achieve a symptomatic cure.”
