The methods are evolving from the standard polymerase chain reaction (PCR) test to the gene-editing CRISPR-based tests and next-generation rapid diagnostic tests (RDTs) that single out a protein existing only in the COVID-19 virus.
Celltrion recently said it was working on a next-generation rapid detection for COVID-19. The conventional RDTs detect the N protein commonly shown in various types of coronaviruses, so patients need reverse transcription-polymerase chain reaction (RT-PCR) test to confirm COVID-19 infection, said Seo Jung-jin, chairman of Celltrion Group, in a live YouTube news conference on Monday.
However, Celltrion’s experimental diagnostic kit detects the S protein that exists only in the COVID-19 virus, which will show similar performance compared to the standard PT-PCR test, he said. “We will be able to get the test result in 15 or 20 minutes,” he added.
Usually, rapid diagnostic tests use an antigen or an antibody so that the test results can come out faster than the standard PCR test. However, their accuracy is only about 50 to 70 percent of the standard test. However, Celltrion’s new diagnostic kit will be a new rapid diagnostic test with high precision, Seo noted.
“The next-generation rapid diagnostic test kits will be able to replace PCR tests,” he said.
Celltrion said it planned to complete producing prototype products by April, finish a clinical trial by May, and get CE certification to export them to Europe.
Local and U.S. biotech firms are also using the gene-editing tool, CRISPR, to detect the viral infection.
CRISPR-based diagnostic kits use techniques similar to those of the PCR test, such as the extraction and amplification of RNA. After extracting and amplifying the RNA from the patient's sample, examiners add the guide RNA to find the sequence of the COVID-19 genome. When CAS12 with the guide RNA arrives at the corresponding sequence, it gives off a molecule that changes color, which shows the positive result of the viral infection.
One biotech firm in the U.S. tested the kit with a COVID-19 patient’s sample, and it showed a similar accuracy to the standard PCR test, news reports said. Using “Loop-Mediated Isothermal Amplification” (LAMP) in the CRISPR-based test can detect the virus in about 30 minutes, they said.
However, it is still questionable whether such experimental tests could replace the standard RT-PCR test, experts said.
Lee Hyuk-min, director of infection control affairs at the Korean Society for Laboratory Medicine, was skeptical about Celltrion’s next-generation COVID-19 detection. “Even though they say they would detect the S protein to raise sensitivity, the S protein is easily mutated,” Lee said. “Antigen/antibody tests produce many variants, thus difficult to control, compared to PCR tests.”
Lee pointed out that CRISPR-based tests could raise sensitivity even higher than the PCR test, but it would hinge on how they would be designed. As the current PCR tests do not have sensitivity issues, companies would have to have the right strategy because people need a test with the right level of sensitivity so that the patient could get an urgent surgery, he added.
“Loop-mediated isothermal amplification does not need complex equipment as PCR tests do, so the method would be helpful to raise sensitivity and simplify equipment,” Lee said.
Just like GeneXpert that obtained urgent use approval in the U.S., emergency tests could be possible depending on how companies design the “packaging” for the PCR test, he noted.
“Even when companies have the same technique, they can produce very different kits depending on their strategies. So, it is important to use the right strategy.”
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