New coronavirus new therapy! CRISPR gene can deal with various virus variants

White Dew Since the outbreak of novel coronavirus (SARS-CoV-2), with the competitive research of experts, some therapeutic drugs have been discovered, including nucleoside analogues, Reed, remdesivir, anti malaria and autoimmune diseases, chloroquine (chloroquine), anti HIV drug, and ritonavir / ritonavir (lopinavir / However, the effect of these drugs on sars-cov-2 is limited, and whether they can effectively fight against different variants of the virus is still unknown On February 18, researchers from Harvard Medical School published an article in cell research to introduce a potential therapy based on CRISPR technology to fight against sars-cov-2 and other RNA viruses and their variants [1] The researchers analyzed the sars-cov-2 RNA genome of 19 patients from China, the United States and Australia, and found that there were differences in the sequence of these viruses (figure a), which were mainly single nucleotide variations The article also shows an example of single nucleotide variation (Fig b) that resulted in changes in amino acid 62 and 84 positions of ORF8 (related to driving the migration of coronavirus from bats to humans) in sars-cov-2 Data from these patient samples indicate that sars-cov-2 is actively acquiring new mutations that may enable it to evade antiviral drugs This poses a serious challenge to the development of traditional drugs and vaccines Other deadly RNA viruses, such as SARS or mers, face the same problem CRISPR / cas13d is a RNA directed RNA targeting CRISPR system Here, the researchers suggest using the system to "chew" the RNA genome of sars-cov-2 specifically to limit its ability to regenerate Cas13d protein and guided RNAs (gRNAs) containing complementary spacer specific to viral RNA genome were selected to cut the RNA genome of sars-cov-2 (Figure C) In order to destroy the function of the virus, the researchers will specially use the gRNAs targeting both orf1ab and s genes of the virus Orf1ab gene encodes orf1ab polypeptide, participates in the transcription and replication of virus RNA, and has many functions such as protease and methyltransferase; s gene encodes the surface glycoprotein of coronavirus, also known as spike Protein), which is distributed on the envelope of the virus like a crown, hence the name "coronavirus" They directly mediate the infection and fusion of the virus to the host cells by binding with ACE2 protein in the human body These functional proteins play an important role in the infection and replication of the virus If they interfere with the function of one or more of the proteins individually or at the same time and inhibit their activity, they can block the process of virus infection or self replication in the host cell, so as to play a therapeutic effect One of the advantages of CRISPR / cas13d system is the flexibility of gRNA design, because the RNA targeted cleavage activity of cas13d does not depend on the existence of specific adjacent sequences (such as the NGG sequence of DNA Editing effector cas9) This feature meets the requirements of rapid development of gRNA for different virus variants that can evolve and possibly escape traditional drugs The researchers designed 10333 gRNAs that specifically targeted 10 peptide coding regions of the RNA genome of sars-cov-2 virus without affecting the human transcriptome (Figure d) Adeno-associated virus (AAV) has good safety, and can be used as a carrier to transmit cas13d effector to sars-cov-2 infected patients The smaller size of cas13d effector is also suitable for "integrated" AAV delivery with gRNA array, because the maximum loading capacity of AAV is only about 4.7kb Specifically, as many as three gRNAs targeting different peptide coding regions of the sars-cov-2 RNA genome can be packaged into an AAV vector (Figure E), which enables the system to more effectively eliminate the virus and prevent drug resistance In addition, the lung is the main organ of sars-cov-2 infection AAV has a highly specific serotype for the lung, so it can be used for targeted delivery of CRISPR system The expression of cas13d can be driven by tissue-specific promoters to achieve the precise treatment of infected organs Similar strategies can be applied to other types of RNA viruses In conclusion, CRISPR / cas13d system is proposed as a simple, flexible and rapid potential method to treat and prevent RNA virus infection However, before using the system in patients' treatment, further studies are needed in animal models to determine the safety and effectiveness of the system in eliminating sars-cov-2 and other RNA viruses If proven to be effective, this treatment will provide patients around the world with more options to fight life-threatening viruses that could rapidly evolve and develop resistance.