Intervacc´s novel vaccines are based on research carried out at the Karolinska Institute and the Swedish University of Agricultural Sciences. Below follows a brief summary of this technology which forms a basis for Intervacc´s development program.
Mechanism of protection
In order for a bacterium to be infectious, it must be able to adhere to a tissue surface. This is done by surface-localised bacterial proteins, called adhesins, which have a specific binding affinity to e.g. collagen, fibrin, fibronectin and numerous other tissue structures.
The principle of Intervacc’s vaccine development is to identify such surface-localised bacterial adhesins and to produce these in a large scale by recombinant technology. When the adhesins are used as vaccine components, specific antibodies are formed that have two functions:
1) bind to the adhesins and block the bacterial adhesion to the tissue thereby impeding the infection process.
2) bind to the adhesins and thereby provide a signal to the white blood cells to internalise and kill the bacteria.
Intervacc’s vaccine development
The proteins that make up the adhesins have been identified by bioinformatic analysis of DNA sequences from Streptococcus equi and can be compared with previously known virulence factors from e.g. Streptococcus pyogenes, a human pathogen with similar pathogenesis as strangles. Other proteins have been identified, whose effect is of importance to the infection process, for instance by impairing the horse’s immune system. Antibodies against these have a neutralising effect and deprive the bacteria of this “weapon” and thereby attenuating the infectious ability of the bacteria.
The effect of a vaccine increases substantially if multiple components are included in the vaccine. In order to reduce production costs Intervacc have fused the genes coding for various proteins so that multiple proteins are included in the same polypeptide. For example Strangvac® contains three polypeptides that are derived from eight different proteins.
The same approach to vaccine development has been selected for vaccine candidates against Streptococcus suis and against Staphylococcus aureus.
Strains of Streptococcus equi isolated from strangles outbreaks from different parts of the world are very similar to each other, which means that only one version of the vaccine is necessary to provide global coverage.
Conventional vaccines against bacterial infections generally consist of live attenuated or killed bacteria or specific components, such as capsular polysaccharides and toxoids. When attenuated bacteria are used as vaccines a sub-clinical infection is induced, often with mild or no symptoms, but antibodies are formed which have a protective ability. The risk is, however, that the sub-clinical infection of the vaccine strain develops into a more serious infection. When using bacteria-containing vaccines against strangles, there have been reports on horses that have suffered from strangles infection instead of being protected from the disease. These vaccines against strangles are used only to a small degree. Intervacc have therefore chosen not to develop these types of vaccines.
To summarise, Intervacc possess the technology, expertise and strategic collaborations to take a project from the research stage to the finished product.