Genetically modifying immune system cells to combat autoimmune diseases or attack cancer cells could one day be a powerful immunotherapy treatment option; however, attempts to edit cells in the innate immune system cells has proven problematic.
The innate immune system is the first line of defense against pathogens. The innate immune system includes immune system cells such as macrophages and dendritic cells that recognize foreign cells and attack them, as opposed to the adaptive immune system that responds to specific molecules present of the surfaces of viruses and bacteria.
Researchers have used CRISPR-Cas9 to make changes to cells of the adaptive immune system, but efforts to use the same techniques on the innate immune system cells have failed. The problem has been the virus used to deliver the CRISPR-Cas9 gene editing tool is recognized as foreign and is attacked by the innate immune system before CRISPR-Cas9 can be delivered.
A team of researchers at UCLA has made a breakthrough. They identified a way that innate immune system cells can have DNA edits performed without activating them and trigging them to attack the harmless viruses used to deliver CRISPR. The technique used by the researchers involves a pulse of electricity, which makes the covering of the cells slightly more porous, but otherwise does not harm the cells. The electricity does not harm the virus carrier nor CRISPR-Cas9, which is delivered into the innate immune system cells through their newly porous membrane. Once inside the cells, the guide RNA (gRNA) binds to a specific section of the DNA and the Cas9 enzyme performs the required edit.
To demonstrate the new technique, the researchers engineered the CRISPR system to target a specific gene in the dendritic cells of mice. The MyD88 gene plays an important role in combatting viruses. Without the gene, the researchers showed that a virus which would normally be attacked by the dendritic cells was not recognized as foreign. As a result, the virus killed the mice. The researchers report that they were able to make the required edit with 95% efficiency and that the process was completed in less than a week.
The researchers also delivered CRISPR-Cas9 to natural killer cells to investigate the role certain genes play in natural killer cell proliferation during viral infections. Natural killer cells are white blood cells that can target cancer cells. If researchers can trigger the proliferation of these cells, it could potentially be used as a treatment for certain types of cancer.
The new approach could be used to deliver CRISPR-Cas9 to immune cells harvested from the blood of patients, which could then be reintroduced into the same patient to train the innate immune system to attack cancer cells or many different pathogens. The technique could also be used to identify the role certain genes play in the immune response.
The researchers, led by Tim O’Sullivan, an assistant professor of microbiology, immunology and molecular genetics at UCLA, are currently using their new approach on human innate immune system cells from human blood samples.
You can read more about the study in the paper – CRISPR-Cas9 Ribonucleoprotein-Mediated Genomic Editing in Mature Primary Innate Immune Cells – which was recently published in the journal Cell Reports. DOI: 10.1016/j.celrep.2020.107651