Antigen Discovery
Antigens are substances that promote an immune response when introduced into the body. In small amounts, they are useful in the production of vaccines. Currently, there are many global diseases for which there are no vaccines. IDRI’s Antigen Discovery team actively searches for and produces antigens, typically proteins or complex sugars called “polysaccharides,” that can be used to diagnose and vaccinate against these diseases.
THE ANTIGEN DISCOVERY TEAM uses many techniques to identify potential vaccine antigens. Among them is screening DNA expression libraries with serum antibodies to find which antigens are recognized by the immune system of infected individuals. The DNA libraries (representing all of the genes within the pathogen) are made using standard molecular biology techniques. Once a DNA library is made, the techniques used for screening the libraries rely on typical interactions between the immune system and pathogens. Because we know that one immune response to a pathogen is the production of antibodies that recognize specific pathogen proteins, serum antibodies from infected individuals are used to screen the genomic libraries.
Likewise, DNA libraries can also be used to screen T cells. Not only do T cells have the ability to recognize antigens, once they do they multiply and release cytokines (molecules that allow communication between different cell types). Specific recognition of antigens by T cells can be used in the laboratory to identify targets of the immune response. When these antigens are used in a vaccine, they are likely to initiate a protective immune response against the infecting pathogen.
Likewise, DNA libraries can also be used to screen T cells. Not only do T cells have the ability to recognize antigens, once they do they multiply and release cytokines (molecules that allow communication between different cell types). Specific recognition of antigens by T cells can be used in the laboratory to identify targets of the immune response. When these antigens are used in a vaccine, they are likely to initiate a protective immune response against the infecting pathogen.
Another approach is bioinformatics, a field of biology concerned with analyzing DNA databases of organisms. Because the complete DNA sequences of several pathogens are available in these databases, this information can be searched to identify, isolate, and express certain genes for further testing. IDRI's scientists use PCR (polymerase chain reaction) as a rapid way to directly isolate genes of interest for further analysis.
Using bioinformatics, genes from the pathogen are inserted into a plasmid (another DNA molecule), allowing these genes and their protein products to be made in an artificial and controllable system. Usually a laboratory bacterium, such as E. coli, is utilized in this "cloning" process. IDRI’s Antigen Discovery team characterizes the proteins expressed from the isolated genes identified by such screening procedures using bioanalytical techniques such as SDS-polyacrylamide gel electrophoresis and Western blotting provide visual indications of the size, complexity, solubility, and purity of the product(s) made from the cloned genes. Based on these and other criteria, IDRI’s Antigen Discovery team liaises with IDRI’s Preclinical Biology group or Process Science team to further test and develop appropriate antigens.
In work funded by the American Leprosy Missions, IDRI’s Antigen Discovery team is employing a variety of techniques to identify specific leprosy proteins with diagnostic or vaccine potential. To reach this goal, M. leprae genes are isolated for the production of potentially useful proteins. The use of recombinant DNA technologies is especially important in the case of the M. leprae bacillus because it cannot be grown in laboratory culture. Similar strategies of antigen discovery have already been successfully used at IDRI to develop and refine vaccines against leishmaniasis and tuberculosis. The Antigen Discovery team is now also considering additional diseases to target using their laboratory capabilities.