30 October 2018
In the field of gene therapy, CRISPR/Cas9 is one of the most important discoveries of recent years. It raises high hopes because it can improve cell therapy and potentially cure genetically-mediated diseases. However, the method is not yet sufficiently researched to make a solid risk-benefit assessment for human use. The team around Dr. Michael Schmück-Henneresse from the Berlin-Brandenburg Center for Regenerative Therapies (BCRT) of the Charité – Universitätsmedizin Berlin has now partially closed this gap by examining the immune reactions against the CRISPR/Cas9 system. They found that there is broad immunity to the Cas9 protein in humans. In order to make the prospective clinical applications safe, the researchers propose and demonstrate first solutions. They report on the opportunities and risks of CRISPR/Cas9 in the renowned journal Nature Medicine.
CRISPR/Cas9 is a new, promising method that allows targeted and reliable modification of DNA. It is particularly suitable for two different therapeutic approaches: either cells are specifically modified outside the body to carry out a desired function in the patient after the injection. Or diseased body cells are modified directly in the patient, for example, to cure genetic diseases. In both cases, animal studies show the superior efficiency and ease of use of CRISPR/Cas9. Initial clinical trials have already started in China and are also in preparation in Europe and the USA.
"An integral part of CRISPR/Cas9 is the protein molecule Cas9, which comes from bacteria called streptococci. Because humans often become infected with these bacteria, we suspected that an immunological memory against Cas9 might already exist," explains Dimitrios Laurin Wagner, first author of the research paper and PhD student in the team of Dr. Michael Schmück-Henneresse and Professor Hans-Dieter Volk at the BCRT. In fact, their team showed that almost all healthy adults have T cells that react against Cas protein molecules. Also Cas molecules from other bacterial strains, such as staphylococci and intestinal bacteria, illicit such immune responses, which could be due to the high similarity of the enzymes. "The T cells we found could lead to unwanted immune responses in gene therapy, which could compromise their safety and efficacy. Since we now know that CRISPR/Cas9 is at risk, we are prepared," says Wagner.
For the modification of cells outside of the body these observations means, that patients should not be injected with cells while CRISPR/Cas9 is still active in them. "To make sure that cells can be safely used, we have developed a test, which can reliably indicate that the risk of an immune response is low", explains Dr. Schmück-Henneresse. However, some genetic disorders cause defects in tissues (such as muscle) that cannot be grown and modified outside the body. Therefore, new solutions have to be found to prevent dangerous immune reactions against the gene scissors.
To treat genetically-related diseases directly and safely with CRISPR/Cas9, the researchers propose an innovative approach. "We have developed a technology to isolate and propagate regulatory T cells that control unwanted immune responses. Initial clinical trials in patients undergoing kidney transplantation or serious complications following bone marrow transplantation are very hopeful," says Professor Petra Reinke, founding director of the Berlin Center for Advanced Therapies (BECAT). “We took advantage of this technology and are working on it to isolate and amplify specific regulatory T cells that selectively inhibit the unwanted immune response to Cas. Such a project is precisely what the BECAT is about: to develop practicable therapeutic approaches from strong basic research. We are confident that we will again be able to create a feasible treatment option with regulatory T cells, this time for CRISPR/Cas9."
Dr. Michael Schmück-Henneresse
Charité – Universitätsmedizin Berlin
Phone: +49 (0)30 450 539 495