CRISPR-Cas13 can fight off our viruses

We envision Cas13 as a research tool to explore many aspects of viral biology in human cells. It could also potentially be a clinical tool, where these systems could be used to diagnose a sample, treat a viral infection, and measure the effectiveness of the treatment – all with the ability to adapt CARVER quickly to deal with new or drug-resistant viruses as they emerge.

Catherine Freije

In nature, CRISPR plays the role of a miniature immune system – bacteria fight off viruses by tearing down foreign genes. A team from MIT leveraged the antiviral side of CRISPR to tackle mammalian ssRNA viruses (such as influenza) in mammalian cells.

Scientists developed a platform called CARVER: Cas13-assisted restriction of viral expression and readout. In contrast to popular Cas9 protein, Cas13 targets RNA molecules. This property allowed researchers to successfully detect and destroy three RNA viruses: influenza A viruses, lymphocytic choriomeningitis viruses, and vesicular stomatitis viruses.

CRISPR-Cas13 can target over 350 out of 396 known ssRNA viruses associated with humans. Two variants of the protein, LwaCas13a (from Leptotrichia wadeii) and PspCas13b (from Prevotella sp. P5-125), have significant antiviral activity.

CARVER is guided by multiple crRNA elements – programmed to target sequences present only in viruses. Initially, the team designed 11 crRNAs for LCMV, which resulted in up to 14-fold reduction of viral RNA. Then, they demonstrated up to a 22-fold decrease of influenza viral RNA with 5 crRNAs. Finally, in the case of VSV, the study reached up to a 43-fold reduction of viral RNA thanks to a few designed crRNAs. Further increase of the number of crRNAs enhanced efficiency of the approach.

The study was performed in cells. Currently, CRISPR-Cas13 can work with viruses for explicitly research purposes, such as investigation of viral cycles. Possible utilization in the clinical setting will require developing a delivery strategy and animal studies.

Publication: Catherine A. Freije, Cameron Myhrvold, Chloe K. Boehm, Aaron E. Lin, Nicole L. Welch, Amber Carter, Hayden C. Metsky, Cynthia Y. Luo, Omar O. Abudayyeh, Jonathan S. Gootenberg, Nathan L. Yozwiak, Feng Zhang, Pardis C. Sabeti (2019). Programmable Inhibition and Detection of RNA Viruses Using Cas13. Doi:10.1016/j.molcel.2019.09.013.
Photo: Dan Higgins, Douglas Jordan, USCDCP

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