“Among the general population, many may want to know how well they are protected,” said Hojun Li, Clinical Investigators Charles W. and Jennifer C. Johnson at MIT’s Koch Institute for Integrative Cancer Research. how. “But I think where this test can make the biggest difference is for anyone who’s on chemotherapy, anyone who’s on immunosuppressive medication for rheumatic disorders or autoimmune diseases. epidemic and for any elderly or non-immune responders in general. These are all people who may need to be boosted earlier or receive more doses to achieve adequate protection.”
The test is designed so that different mutant proteins can be swapped, allowing it to be modified to detect immunity against any existing or future variant, the researchers say. of SARS-CoV-2, the researchers said.
Li, and a practicing physician at the Dana-Farber/Boston Children’s Cancer and Blood Disorders Center, is lead author of the study, which appears online today in Cell Reporting Methods. Guinevere Connelly, a former Koch Institute research technician who is now a graduate student at Duke University, and Orville Kirkland, a research associate at the Koch Institute, are the lead authors of the paper.
Simple COVID test
Li, who joined the Koch Institute in the fall of 2019, studies blood cell development and how blood cells become cancerous. When SARS-CoV-2 appeared, he started thinking about ways to help fight the pandemic. Many other researchers have worked with diagnostic tests for infections, so he was interested in developing a test that could reveal a person’s level of immune protection against COVID-19.
Currently, the gold standard approach to measuring immunity involves mixing a blood sample with a live virus and measuring how many cells in the sample are killed by the virus. That procedure is too dangerous to perform in most laboratories, so the more commonly used approaches involve modified “pseudoviral” particles that are non-infectious, or they based on a test called an ELISA (enzyme-linked immunosorbent assay), which can detect antibodies that neutralize a fragment of a viral protein.
However, these approaches still require trained personnel to work in laboratories with specialized equipment, so they are impractical to use in a doctor’s office to get immediate results. . Li wanted to think of something that could easily be used by a healthcare provider or even by people at home. He was inspired by home pregnancy tests, which are based on a type of test known as a lateral flow test.
Lateral flow testing typically involves strips of paper embedded with test lines that bind to a specific target molecule if it is present in the sample. This technology is also the basis of most rapid at-home tests for COVID-19.
Li had no experience working with this type of test, so he contacted two MIT faculty members with expertise in making a diagnosis based on lateral flow tests: Hadley Sikes, an associate professor professor of chemical engineering, and Sangeeta Bhatia, John and Dorothy Wilson Professor of Health Sciences and Technology and Electrical Engineering and Computer Science, and members of the Koch Institute.
With their help, his lab developed a device that can detect the presence of antibodies that prevent the SARS-CoV-2 receptor-binding region (RBD) from binding to ACE2, the receptor of humans that viruses use to infect cells.
The first step of the test is to mix a human blood sample with the viral RBD protein that has been labeled with tiny gold particles that are visible when glued to a strip of paper. After allowing time for the antibodies in the sample to interact with the viral protein, a few drops of the sample are applied to a test strip impregnated with the two test lines.
One of these pathways attracts viral free RBD proteins, while the other attracts any RBD that has been captured by neutralizing antibodies. A strong signal from the second line indicates high levels of neutralizing antibodies in the sample. There is also a control line that detects free gold particles, confirming that the solution has flowed over the entire range.
To develop the reagents needed for the test, members of Li’s lab worked with the lab of Angela Koehler, an associate professor of biological engineering, and Michael Yaffe, a David H. Koch, both members of the Koch Institute.
Along with the test box containing the paper test strips, this test kit also includes a finger prick that can be used to collect a small blood sample, less than 10 microliters. This sample is then mixed with the reagents required for the test. After about 10 minutes, the sample is exposed to the test cartridge and the results are displayed after 10 minutes.
The output can be read in two different ways: One, just look at the lines indicating whether neutralizing antibodies are present. Or, the device can be used to measure antibody levels more precisely, using a smartphone app that can measure the strength of each line and calculate the ratio between neutralizing RBD protein and infectious RBD protein. infected. When this rate is low, it may be suggested that another booster is needed, or that the individual should take additional precautions to prevent infection.
The researchers tested their device with blood samples collected in December 2020 from about 60 people who had been infected with SARS-CoV-2 and 30 who were not. They can detect neutralizing antibodies in samples from people who have been previously infected with the virus, with the same accuracy as existing laboratory tests. They also tested 30 mass samples from two people before they received the Covid-19 mRNA vaccine and at some point after the vaccination. Neutralizing antibody levels in vaccinated individuals peak about seven weeks after the first dose, then begin to decline slowly.
Previous studies on SARS-CoV-2 and other viruses have shown a strong correlation between the amount of neutralizing antibodies circulating in an individual’s blood and their infectivity.
The test can be easily adapted to different variants of SARS-CoV-2 by swapping out the RBD-specific reagent from the variant of interest, Li said. The researchers now hope to work with a diagnostics company that can mass-produce the tests and get FDA approval for their use.