Discriminating 93 serotypes takes a lot of beads
Ger Rijkers and the Pneumococcal Consortium are working to develop standardized multiplex assays for S. pneumoniae antibodies. For this project, Rijkers, Head of the Department of Science at University College Roosevelt in The Netherlands, is designing a custom multiplex assay to efficiently identify the 93 antibodies against specific serotypes of S. pneumoniae responsible for infection. We caught up with him to learn more.
Why does S. pneumoniae present a challenge?
S. pneumoniae comes in 93 different serotypes, i.e., there are 93 different polysaccharide capsules. This also presents a challenge for vaccine development, and vaccine manufacturers to formulate a vaccine that covers the most common serotypes. In the early days, before there was any multiplex immunoassay, the way to determine the serotype was by enzyme-linked immunosorbent assay. Ideally, you would do 93 different ELISAs to detect all serotypes, which of course was not logistically possible. When xMAP® Technology launched, I immediately realized that we could use it to detect those multiple serotypes simultaneously, which would provide massive benefits to our laboratory.
Why is the measurement of serotype-specific antibodies important?
There are some assays on the market that are nonspecific and measure a mixture of all the polysaccharides. However, these give you limited information about the infection. The latest S. pneumoniae vaccine is made up of 13 serotypes. Discriminating between the serotype-specific antibodies enables you to identify whether the infection is due to a vaccine failure or a non-vaccine serotype.
How does the Pneumococcal Consortium fit into this work?
We started the Pneumococcal Consortium in 2013 because laboratories all over the world were struggling with the same problem of identifying the different S. pneumoniae serotypes, as there was no ready-to-use diagnostic kit available. Since then, we’ve harmonized the protocols, agreed on common standards, and standardized results. We are working to publish a harmonized protocol so that other laboratories around the world can benefit from this technology. Our panel currently contains 25 serotypes, but our aim is to create an all-inclusive 93 serotype panel.
What limits the number of serotypes you can detect at one time?
Theoretically, the only limiting factor to the multiplex system would be the number of different color-coded beads available, but in reality, there are other hurdles. You can get unexpected cross-reactions, where one antibody can react with multiple polysaccharides or vice versa. When this happens, it is difficult to solve; you might have to go back to the drawing board and select completely different antibodies. So, the higher the complexity of your multiplex system, the higher the risk that you’ll run into a problem with specificity. We remain optimistic and hope that we’ll end up with the full 93 serotypes, but I would be satisfied if we could get 80 to 85.
How will pneumococcal research progress in the future?
Our aim is to create an immunoassay that can be used in hospitals around the world to identify antibodies against all 93 serotypes of S. pneumoniae. Such an assay would aid effective patient treatment, inform vaccine development, and improve understanding of the disease.
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