Development of a yeast-based immunoassay for SARS-CoV-2 serologic testing amenable to inexpensive local production

Mcmillen, David R | $179,140

Ontario University of Toronto 2020 CIHR Operating Grant

To monitor the spread of the COVID‑19 pandemic and test individuals for potential immunity, we need antibody detection tests, where a blood sample is checked for the presence of antibodies induced by past exposure to the virus. These tests are often expensive, requiring either a fully-equipped laboratory with highly trained technical staff, or costing many dollars per test for field-deployable “strip tests”. Sending tests to a lab or paying a few dollars per test does not perhaps seem like a problem, here in Canada, but in our partner nation of the Philippines, both of these present significant barriers: public health dollars are sharply limited, and remote areas have very limited access to lab facilities and technical staff. Our goal is to create an antibody detection test that can be “grown” locally, here in Canada and in the Philippines. By modifying baker’s yeast (S. cerevisiae), we can put antibody-binding proteins (antigens) on their surfaces, able to capture disease-induced antibodies found in blood samples. We test for the presence of these antibodies with an agglutination test: when the yeast cells settle to the bottom of a round well, in the absence of antibodies they form into a tight button that looks like a dot to the naked eye; or in the presence of antibodies they form larger clumps that stay more spread out and look like a flat sheet to the naked eye. A minimally-trained user can thus obtain a positive or negative result with no expensive instruments. The yeast (once designed) can be grown in a simple sugar solution, at a raw material cost that we estimate to be something less than 0.01 cents per test. We have demonstrated lab-bench success at detecting Chagas’ disease and dengue fever antibodies, and now we propose to adapt the technique to detect COVID‑19 antibodies and develop it in a fully deployable kit for use in under-resourced areas. Our first target is the Philippines, with the help of our collaborators at UP Manila.

With funding from the Government of Canada

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