High-throughput screening assays of candidate synthetic peptides that drive cellular proliferation help speed the rate of antigen
discovery. Reverse vaccinology combines knowledge of the pathogen’s genome sequence with known protein sequences via computer analysis, to predict protein expression and post-translational modifications and identify likely vaccine candidates (see Chapter 3 – Vaccine antigens; Figure 3.5). The development of epitope-based vaccines is one example of reverse vaccinology selleck compound where computer software combines prediction algorithms to suggest sequences similar to those for pathogenic components. Epitope mapping, combined with the creation of more stable poly-epitope vaccines, may lead to the successful translation of this technology into products. MHC molecules exhibit widely varying binding specificities; a vaccine expressing a single peptide antigen would therefore only target a few MHC molecules and thus only be recognised by the T cells of individuals carrying a specific MHC phenotype. Thiazovivin cell line Poly-epitope technology could be used to generate a synthetic protein carrying antigenic epitopes from multiple strains or pathogens. This would overcome the MHC restriction and afford protection in individuals carrying different MHC types. The screening of pathogen peptide libraries is another example of new approaches to antigen discovery.
Screening methods are used to identify antigens that can stimulate CD4+ or CD8+T cells, or which bind to antibodies from humans known to have been infected with the relevant pathogen.
Where peptide screening uses antibodies, an additional consideration is the synthesis of antigens that contain the tertiary (folding/three-dimensional) structure of the native immunogen, since vaccine efficacy can be impacted by infidelities in the structure of the final product. Incorrect protein folding may result in a less immunogenic antigen or an Farnesyltransferase antigen that induces an immune response that differs from that of the native immunogen. The mimicking of the three-dimensional structure of the native immunogen is important during the synthesis of antigens that are being used to target B-cell responses. Conversely, the requirement for folding is reduced for T cells since T cells bind only processed peptides, from degraded proteins. Likewise, DNA expression libraries using the pathogen genomic DNA have been screened using animal model systems to identify genes encoding proteins that afford protection against infection or disease caused by the pathogen. One example is Genocea’s vaccine development programmes that are built around a broad platform for the rapid discovery of T-cell antigens. The process is explained in Figure 6.3. T-cell antigens, specifically antigens that stimulate CD4+ and CD8+ T cells, are critical to generating disease-specific cellular immune responses and long-term T-cell memory. Stability of the final product is another important consideration.