The CRISPR-Cas9 gene editing tool has been successfully used to correct clotting abnormalities in newborn and adult mice, demonstrating potential of the CRISPR system for the treatment of hemophilia in humans.
The CRISPR-Cas9 gene editing tool is still experimental, although it has shown considerable potential over other gene editing techniques for treating a wide range of genetic diseases. The system is much easier to use to make gene changes than other gene-editing techniques. It is cheaper, faster, more flexible and more accurate.
The CRISPR-Cas9 gene editing tool involves using guide RNA to bind to a specific section of DNA, then Cas9 enzymes to perform cuts. The DNA can be repaired with sections removed or added as necessary to correct a genetic defect.
Since hemophilia is caused by mutations in DNA sequences, the CRISPR-Cas9 gene editing tool could potentially be used to make the required changes, thus curing the disease. Researchers at the University of Pennsylvania’s Perelman School of Medicine believe they have done just that. They have successfully used their CRISPR-Cas9 gene editing tool to treat adult and newborn mice with induced hemophilia B.
Hemophilia B is caused by mutations in DNA which stop the synthesis of a clotting protein or causes that clotting protein to be defective. The protein in question is called clotting factor IX.
The researchers altered the DNA of the mice to prevent the synthesis of clotting factor IX, then used their CRISPR-Cas9 gene editing tool to insert the human DNA sequence responsible for factor IX into the mouse genome.
To do this the team used a two-vector RNA sequence. The first vector was used to specifically target the gene-editing machinery on liver cells where factor IX is synthesized. The second vector targeted the 5-prime end of exon 2 – the section of the mouse gene involved in clotting factor IX synthesis. A partial cDNA sequence from the human factor IX gene was then inserted into the mouse genome using the CRISPR-Cas9 system.
The team injected the mice with increasing doses of the two vectors which, after a period of around four months, showed factor IX activity at normal or increased levels. The team reported that after eight weeks mice were subjected to partial liver removal and factor IX activity continued at similar levels.
According to first author Lili Wang, PhD, “The targeted insertion leads to the expression of a chimeric hyperactive factor IX protein under the control of the native mouse factor IX promoter.”
The pre-clinical trial clearly showed the potential uses of the CRISPR-Cas9 gene editing tool for the treatment of hemophilia in humans.