Long-lasting gene therapy
Hereditary diseases are currently most effectively treated by methods of gene therapy. But the main problem remains – the replacement of a defective gene with a healthy one is temporary. Often, after a few weeks, the altered gene ceases to function.
Researchers from Washington University School of Medicine in St. Louis combined the CRISPR gene editing method and viral vectors to accurately deliver a healthy gene in an experiment on live mice. A relative long–term effect was demonstrated - a healthy gene functioned for at least 6 months, after which the observation was discontinued. The authors do not exclude that the gene could remain active throughout the life of mice.
A new method of combined gene therapy was tested on mice with hereditary pulmonary emphysema associated with a deficiency of alpha-1-antitrypsin, a protein produced in the liver and necessary for the inactivation of a number of enzymes. Currently, the method is being tested on models of hemophilia, a hereditary blood clotting disorder.
The idea of delivering genes to target cells by viruses is not new. Scientists used the natural ability of viruses to embed their genotype into host cells, having previously inactivated their pathogenic properties and "loaded" with the necessary genes.
For example, a recent study of 10 patients with hemophilia showed that viruses (without CRISPR) successfully delivered a healthy gene to cells. Such therapy has led to a relief of the course of the disease. The problem is that the technique of viral vectors is not accurate enough, and it is impossible to fully control the process. At some stage, it remains to rely on chance and hope that no undesirable mutations will occur in the process of embedding the gene.
The advent of CRISPR technology, which is also called genetic scissors, has made it possible to bring the result of gene therapy as close as possible to the desired level. It determines the target DNA site containing the defective gene most accurately from existing methods, cuts off the mutant site and inserts a healthy one in its place. The main issue when using CRISPR is its delivery to the target cell.
The researchers combined both methods of gene therapy so that they compensate for each other's shortcomings. They used inactivated adenovirus as a means of delivery to cells, and CRISPR for controlling and editing DNA.
The adenovirus was not chosen by chance. The authors proved that its use as a vector leads to a more persistent effect. Previous studies of combined CRISPR virus therapy in other laboratories have been conducted with adeno-associated viruses (AAV) on a Duchenne muscular dystrophy model. This type of delivery is inferior to adenoviruses: AAV is more difficult to produce, besides they have less "load capacity", although it was enough for the treatment of Duchenne dystrophy. But, for example, the treatment of hemophilia requires a virus capable of transporting larger sections of DNA. Adenovirus is ideal for this purpose, although we must not forget about its safety issues.
Viruses carrying a healthy gene were targeted by CRISPR at the so–called "safe haven" of DNA - sites remote from the most active genes, interference in which would not entail undesirable consequences.
The mice participating in the experiment were healthy throughout the observation, no side effects of therapy were noted. However, immune system reactions to both CRISPR and adenoviruses cannot be ruled out. The authors of the study continue to study the safety and efficacy of combining adenovirus delivery and CRISPR for hemophilia gene therapy.
Article by C. J. Stephens et al. Targeted in vivo knock-in of human alpha-1-antitrypsin cDNA using adenoviral delivery of CRISPR/Cas9 is published in the journal Gene Therapy.
Aminat Adzhieva, portal "Eternal Youth" http://vechnayamolodost.ru based on WUSTL materials: CRISPR enhances gene therapy to fight inherited diseases.