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[Updated] Fast Paper Strip Covid-19 Test Devised with Crispr

Sherlock paper test strips

Sherlock paper test strips (Zhang Lab, Broad Institute)

Update 11 May 2020. Sherlock Biosciences says it received an emergency use authorization from the U.S. Food and Drug Administration for its Crispr-based SARS-CoV-2 detection kit.

6 May 2020. A simple, fast test for Covid-19 infections with treated paper dipped in specimens is being created with the gene-editing technology Crispr. The test is developed by a team from the McGovern Institute for Brain Research at MIT and Broad Institute, a genetics research center affiliated with MIT and Harvard University.

Simple, inexpensive, and easy-to-deploy diagnostic testing for SARS-CoV-2 viruses responsible for Covid-19 infections is an urgent need in the U.S. and elsewhere to find individuals with virus and to assess the state of public health. Advances in testing technology are happening quickly, with new methods recently introduced for point-of-care and even at-home testing.

But most of those techniques require extracting RNA from the specimen and conducting a reverse transcription – polymerase chain reaction, or RT-PCR, test to amplify DNA in specimens for detecting SARS-CoV-2. RT-PCR tests use a specialized, sophisticated, and expensive genetics technology, usually in a remote lab. Current tests are also hampered by a shortage of chemical reagents to extract RNA from specimen samples and even swabs to collect samples.

A team led by McGovern and Broad researchers Feng Zhang, Omar Abudayyeh, and Jonathan Gootenberg applied a diagnostic technology to Covid-19 testing, using the gene editing technology Crispr — short for clustered, regularly interspaced short palindromic repeats — designed to create simple diagnostics. That technology known as Sherlock, short for specific high-sensitivity enzymatic reporter unlocking, employs Crispr to edit RNA rather than DNA.

Sherlock uses Crispr editing enzymes that seek out specific genetic sequences in a specimen sample, and if detected in the sample, bind to and cut the RNA in nearby locations. Sherlock adds a reporter sequence to the RNA, a specific piece of synthetic RNA, which also gets cut by the editing enzyme, releasing a signal identifying the presence of the original target sequence. When coupled with a companion technique (and acronym) Inspectr, short for internal splint-pairing expression cassette translation reaction, reporter sequence signals are converted into a bioluminescent visual display that can appear on an everyday material like paper and at room temperature.

The McGovern-Broad team applies Sherlock with an editing enzyme called Cas12b to detect SARS-CoV-2 in a platform called STOPCovid, described in a paper for publication. The researchers say STOPCovid can detect the virus from saliva or nose-throat samples on paper strips with equal true-positive sensitivity and true-negative specificity as RT-PCR analysis. Visible results on the strips are returned in about 70 minutes, while using a fluorescent reading device reduces that time to 40 minutes. A proof-of-concept assessment shows STOPCovid accurately detected SARS-CoV-2 in 12 individuals already testing positive for the virus, while not detecting virus in 5 persons testing negative.

“The ability to test for COVID-19 at home, or even in pharmacies or places of employment, could be a game-changer for getting people safely back to work and into their communities,” says Zhang in a statement. “Creating a point-of-care tool is a critically important goal to allow timely decisions for protecting patients and those around them.”

As reported by Science & Enterprise in March 2019, the Sherlock technology is licensed to the spin-off enterprise Sherlock Biosciences, but in this case, STOPCovid is made openly available under a technology sharing arrangement established by Harvard, MIT, and Stanford University. Those terms allow for sharing STOPCovid under a non-exclusive royalty-free license, as long as it’s used to prevent, diagnose and treat COVID-19 infections during the pandemic and for a short period after. Resulting products must also be distributed as widely as possible and at low cost.

The researchers point out the STOPCovid technology has not yet been submitted to FDA for authorization, and is still limited to research.

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