Release date: 2018-01-10
2017 is a year of gene therapy. In the terminally ill such as sickle cell disease, spinal muscular atrophy, and hemophilia, gene therapy has been a lot of success, and it has to be expected. In the gene therapy family, CRISPR is a high hope for scientists.
The expectations of scientists are not difficult to understand. CRISPR is fast, accurate, small in size, and highly flexible. Whether it is used as a research tool or a treatment, it is very effective, and it is worthy of the title of "Genetic Devil". In just ten years, CRISPR has stood on the custod, and numerous researchers and companies keep up with the trains of the times. Domestic researchers are not far behind. In the clinical field of CRISPR treatment of cancer, even clinical trials have been carried out in the United States [1]. .
However, is this burning torch really as strong as it seems?
Recently, a team of professors of the University of Stanford, Professor Matthew H. Porteus, found that Cas9 protein homologs were found in 70% of healthy people, and nearly half of them had antigen-specific T cells with Cas9 protein homologs [2]. Cas9 is currently the most widely used tool protein for CRISPR technology. The results of this study imply that humoral and cellular immunity against Cas9 protein is present in most humans. The application of CRISPR/Cas9 in real humans will be difficult to guarantee and may even trigger a serious immune response. .
CRISPR/Cas9 is a microbial-based gene editing system. The most widely used Cas9 protein is SaCas9 from Staphylococcus aureus and SpCas9 from Streptococcus pyogenes.
These two can be said to be old friends of our humanity, but not good friends. Their appearance often means a serious infection. Studies have shown that 40% of humans have Staphylococcus aureus [3], 20% of school-age children have S. pyogenes [4], and antibodies against both bacteria, almost 100% of adults have [5] 7].
This can't help but make people think, is the Cas9 protein from these two bacteria also rejected by our body?
The researchers tested 22 umbilical cord blood samples and 12 healthy adult peripheral blood samples and tested them by immunoblotting. The antibody can penetrate the placental barrier, and the cord blood can represent the maternal immune level to a certain extent.
The results were surprising. In cord blood, 86% of SaCas9 antibodies were detected and 73% of SpCas9 antibodies were detected. In adult peripheral blood, 67% of SaCas9 antibodies were detected and 42% of SpCas9 antibodies were detected. Overall, 79% have SaCas9 antibodies and 65% have SpCas9 antibodies!
Given the differences in the treatment of cord blood and peripheral blood samples, Cas9 protein antibodies may be sensitive to treatment, and the two types of samples have slightly different results. The actual number of detections may be higher.
The researchers further tested Cas9 antigen-specific T cells in blood samples using the Cytokine Capture System (CCS). In three peripheral blood samples from healthy adults, 46% of SaCas9 antigen-specific T cells were detected, 71% of which also had SaCas9 antibodies; SpCas9 was not detected. But this does not mean that SpCas9-specific T cells are not present. In the experiment, the researchers have detected the clues of SpCas9-related T cells, but given the limited sensitivity of the CCS system, the experimental results cannot be repeated and can only be recorded as undetected.
Cord blood was used as a negative control group in the experiment. The newborn has not been exposed to the antigen and there are no relevant specific T cells. In the CCS assay, no specific T cells were produced in contact with the Cas9 protein. This also demonstrates that the SaCas9 antigen-specific T cells detected in human blood samples were originally present, rather than being produced by the first exposure to antigen during the assay.
The current CRISPR/Cas9 technology has both in vitro editing and in vivo editing. In vitro editing, electroporation transfection is typically used to introduce editing systems into cells; in vivo editing often uses viral vectors or nanoparticle-embedded forms. In this case, the Cas9 protein is not directly exposed to the corresponding antibody.
However, entry of Cas9 into cells does not mean safety. The cells can still notify the immune system of internal enemies by means of MHC antigen presentation. This allows the immune system to actively clear cells that have been engineered through Cas9, resulting in no treatment. Considering the scope of treatment, if the cells are modified throughout the body, this killing behavior will cause serious systemic immunity problems.
This means that human adaptive immunity will become a huge barrier to CRISPR gene therapy, and this risk cannot be easily ruled out in non-human systems [8].
As soon as this article comes out, the prospects for CRISPR technology are once again questioned by the market. Even though there may be new technologies to solve this potential problem in the future, in the short term, pioneering technology companies in this field will be affected. After the publication of the paper on Friday, Editas shares fell 0.7%, Intellia fell 2.7%, and the positive Thesis Therapetutics has been slightly stunned [9].
As for how to solve this problem, Professor Porteus proposed three ideas. Accelerate the depletion of Cas9, immunosuppression, and search for new sources of Cas9 protein. No matter which one can really break, the road ahead must be full of hardships.
In 1999, American boy Jesse Gelsinger died of a severe immune response during gene therapy, and since then, the industry has been enthusiastically pursuing gene therapy for ten years. In 2017, CRISPR has repeatedly published top journals, and many of the clinical projects expected to be launched in 2018 seem to have a lot to offer.
A life is enough to make the development of technology stagnant or even backward. I hope that researchers will be cautious and cautious on the road of science. I hope that the fire will illuminate the future for a long time.
Reference materials:
[ 1 ] https://gizmodo.com/in-2018-we-will-crispr-human-beings-1821540150
[ 2 ] https://
[3] FD Lowy, Staphylococcus aureus Infections. New England Journal of Medicine 339, 520-532 ( 1998 ) .
[4] AL Roberts et al., Detection of group A Streptococcus in tonsils from pediatric patients reveals high rate of asymptomatic streptococcal carriage. BMC Pediatrics 12, 3 ( 2012 ) .
[5] P. Colque-Navarro, G. Jacobsson, R. Andersson, J.-I. Flock, R. M ö llby, Levels of Antibody against 11 Staphylococcus aureus Antigens in a Healthy Population. Clinical and Vaccine Immunology : CVI 17 1117-1123 ( 2010 ) .
[6] A. Dryla et al., Comparison of Antibody Repertoires against Staphylococcus aureus in Healthy Individuals and in Acutely Infected Patients. Clinical and Diagnostic Laboratory Immunology 12, 387-398 ( 2005 ) .
[7] R. Mortensen et al., Adaptive Immunity against Streptococcus pyogenes in Adults Involves Increased IFN- γ and IgG3 Responses Compared with Children. The Journal of Immunology 195, 1657 ( 2015 ) .
[8] WL Chew et al., A multifunctional AAV-CRISPR-Cas9 and its host response. Nat Meth 13, 868-874 ( 2016 ) .
[ 9 ]https://
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