Novel Antigens

Identify bacterial cell surface sugars

Each bacterial pathogen has a layer of cell surface carbohydrates – sugars – that protect the organism. It is called the natural capsular polysaccharide (“CPS”). The CPS is the antigen in a bacterial-targeted vaccine.

Determine repeating units

A CPS contains a limited number of one or more different sugars arranged in a specific sequence. This is called a repeating unit. There can be hundreds of repeating units in a CPS.

For example, if a CPS contains three different sugars, A, B, and C, the repeating unit would be ABC. The entire capsular polysaccharide could be a structure with 100 linked repeating units of ABC or 300 sugars in total.

The sugars and their sequence make the structure unique to each bacteria species.

Synthesize antigen library (length, terminal sugar)

Once the repeating unit its known, chemists build a library of smaller structures based on two variables: terminal sugar and length.

The terminal sugar is the last sugar in the repeating unit. If the repeating unit is ABC then there are three possible structural combinations of structures, each with a different terminal sugar: ABC, BCA, or CAB.

The number of repeating units is also important to induce an immune response, so chemists synthesize multiple lengths such as ABC-ABC-ABC to create a trimer (3 repeating unit carbohydrate).

Screen library in vitro with Glycan array

After a library has been created, the structures are then tested in vitro (on glass). Using a glass plate coated with antibodies, the structures from the library are mixed in small wells on the plates. The strength of binding between the antigen and the antibodies can then be assessed.

Select optimal antigen

After measuring the strength of binding, scientists select the optimal antigen, typically the one with the best binding effect.

Conduct animal study

Finally, the optimal antigen is used to create a complete vaccine by conjugating it to a carrier such as CRM197 or α-galactosylceramide.

An in vivo (in animals) study is then conducted typically in mice. The mice are given either a fake vaccine or a real vaccine and. then infected with the target bacteria.

Scientists assess the difference between the mice which received the real vaccinated and the other group to understand the safety and efficacy of the new vaccine.

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