The Crispr gene scissors give many people with hereditary diseases hope for future treatment options. The revolutionary technology can change genetic material in a targeted manner by cutting out parts of the DNA and replacing them with other genetic material.
American biologists have now successfully tested a finer variant of gene scissors on flies, which promises more precise and safer interventions with better results. The team led by researcher Sitara Roy from the University of California San Diego published the results of the gene experiment in the journal Science Advances in early July.
The new approach benefits from the natural mechanism of DNA repair and forms the basis for novel gene therapies. In many cases, people with hereditary diseases have specific mutations in the genes inherited from their parents.
The latter come in the form of a total of 46 chromosomes in every human cell nucleus. A mutation in one part of a chromosome often has a healthy counterpart on another chromosome.
“Once the mutant DNA is cut, the cell’s own repair can use the healthy counterpart to correct the pathological mutation,” says co-author Annabel Guichard. “Surprisingly, the same result can be achieved even better with a harmless cut.”
The researchers came to this conclusion through the following experiment: they first bred mutant fruit flies with white eyes.
When the biologists used the gene scissors Crispr on the same mutant flies, large red spots appeared on the previously completely white eyes. This was a sign that the cell’s own DNA repair had reversed the mutation and resorted to the healthy counterpart on another chromosome.
The success of the artificially generated DNA repair can be measured by the pigmentation of the eyes. The researchers then tested the finer gene scissors, which use a so-called nickase enzyme to target only one affected DNA strand instead of both.
The success rate with this finer variant of the gene scissors, measured by the red spots on the white eyes of the fruit flies, was 50 to 70 percent. The conventional variant, on the other hand, only achieved a success rate of around 20 to 30 percent and often led to unintended mutations in the fruit fly’s genome elsewhere.
“I couldn’t believe how well the nickase worked – it was totally unexpected,” shared Sitara Roy, the study’s lead author. Co-author Annabel Guichard noted, “We don’t yet know how this process translates to human cells and whether we can apply it to such genomes.” A few tweaks may be needed to adapt DNA repair to disease-causing mutations in human cells apply chromosomes.
According to a co-author, another advantage of the finer gene scissors is their simplicity – they only rely on a few components and the DNA cuts are finer than with the Cas9 gene scissors, the use of which leads to complete DNA breaks and mutations.
For this reason, Sarah Hedtrich also considers the tested method to be elegant. As a professor at the Berlin Institute of Health (BIH) in the Charité, she researches gene therapies based on Crispr gene scissors and was not involved in the study.
“The tested gene scissors are not groundbreaking – there are already approaches that, in contrast to classic gene scissors, do not lead to complete DNA breaks,” she says. In addition, experience has shown that high success rates of 70 percent, as observed in fruit flies in the study, are not to be expected in humans.
Nevertheless, the discovered approach is possibly one that could expand the “toolbox” of researchers in genetic engineering. “The experiment also shows once again how much is happening in the research field of Crispr – new approaches to gene scissors appear almost daily. “
Hedtrich is confident that within the next year or two, U.S. regulators will allow Crispr-based gene therapies — and people with congenital conditions like sickle cell disease can expect treatment. Above all, those affected would benefit from this, whose illnesses have so far been difficult or impossible to treat.
Hedtrich doubts that approval could happen so quickly in Germany. “Germany is rather reluctant when it comes to Crispr and approaches research and development with more concerns than the USA or Canada.”
Research into gene therapy options remains important because in Germany alone it is estimated that more than three million people suffer from hereditary diseases that fall under the “rare disease” category. Some of these diseases, such as cystic fibrosis, greatly reduce the life expectancy of those affected.
The institutes in Germany that are researching gene therapies based on Crispr technology include the University of Regensburg, the BIH in the Charité and the Max Delbrück Center for Molecular Medicine in Berlin.
