Antigen Identification Program (AIP®)
The design and development of novel subunit vaccines is highly dependent on the identification and characterization of the proper antigens. Through AIP® we successfully have identified and refined a large number of antigens of several bacterial pathogens.
The process of defining the antigenome of bacterial pathogens
The selected antibodies are derived from infected or healthy exposed individuals and therefore directly mirror the presence, accessibility and antigenicity of relevant proteins from the particular microorganism in its human host.
The first step in the process is a random fragmentation of the DNA isolated from the microorganism of interest. The encoded peptides are then displayed in vivo on the surface of E. coli by a set of outer membrane proteins, a process called bacterial surface display. Thereafter, biotinylated antibodies isolated from infected or healthy exposed individuals are added to the bacterial cell population. This will result in a display of all possible peptide fragments encoded by the genome of the respective pathogen. Finally, paramagnetic beads are used to capture the antibody-cell complex (via biotin-streptavidin interaction) with the aim to identify those epitopes interacting with the human antibodies.
The antigenome of a defined pathogen typically consists of about 100 to 200 antigens. These are analyzed in order to select the most promising candidates for vaccine development.
Validating the most promising candidates
The validation procedure involves several steps, including PCR studies to confirm the conservation of the encoding gene in multiple clinical isolates, peptide ELISA assays to prove the immunogenicity in humans and FACS analyses to show that the antigen is localized on the surface of the pathogen. Bactericidal assays are performed to test the functionality of the antibodies directed against a particular antigen in animal models. A total of about 20 antigens are selected for recombinant protein expression, purification and further studies.
A successful approach
AIP® has successfully been applied to identify a large number of novel antigens from several pathogenic organisms including S. aureus, S. epidermidis, S. pneumoniae, S. agalactiae, S. pyogenes, Enterococcus faecalis, K. pneumoniae, Borrelia spp., ETEC, Shigella, Campylobacter jejuni, non-typable Haemophilus influenzae and Moraxella catarhalis. It has resulted in promising in-house product candidates and generated strategic partnerships.