The Cya A vector
The CyaA vector (AC-) is a technological antigen delivery platform developed by the Institut Pasteur and the Academy of Sciences of the Czech Republic. Bordetella bronshiseptica Adenylcyclase (CyaA) protein has been genetically engineered to allow antigen insertion to activate the immune system against cells with the inserted antigen. This activation is carried out by means of specific cells of the immune response, the dendritic cells (DC), using signaling pathways which allow to initiate a cellular and humoral response (Th1 type response). This type of response is ideal for the development of prophylactic but also therapeutic vaccines.
The vaccines produced with the CyaA vector are chimeric recombinant proteins consisting of the CyaA protein and the selected antigen, inserted by genetic engineering.
When injected into the animal, the CyaA vector naturally delivers the antigen inserted directly into the DC inducing the cytotoxic T lymphocytes CD8 + (T Killer) and CD4 + (T Helper) specific for these antigens. These T Killer cells then circulate in the body and destroy only the cells carrying the antigen inserted into the CyaA. This technology therefore works by targeting and selective eradication of infected cells bearing the same antigen as that inserted in the CyaA.
Biological mechanism of action
CyaA has a unique mechanism of penetration into eukaryotic cells. CyaA is capable of internalizing its N-terminal domain directly through the cytoplasmic membrane of the target cells, from the extracellular to the cytosol (1, 2, 3, 4, 5, 6, 7, 8).
The adenylcyclase has been modified to inactivate its enzymatic activity and to be capable of harboring a variety of polypeptide or antigenic vaccine sequences. This was obtained without altering its strong affinity with the target sentinel cells (called dendritic cells (DC)) or its translocation capacity in the DC cytosol (10).
CyaA targets animal dendritic cells (DC) extremely efficiently. Indeed, the CyaA protein binds specifically to cells that carry CD11b / CD18 αm / β2 integrin. This complex is expressed only in DC, neutrophils / granulocytes, macrophages, Natural Killer cells (NK), and CD8 + B and T cell subsets (11). After binding of molecules to antigen presenting cells (APCs), two sets of events occur:
1. Presentation in association with MHC-I molecules
Some CyaA molecules insert the terminal fraction of amino acid 400 into the cytosol where it is then treated by the proteasome. The released peptides bind to the transporter associated with antigen treatment (TAP) for routine delivery of the endoplasmic reticulum (ER) and presentation in association with the MHC class I neosynthesized complex at the APC surface. The epitopes presented in the MHC class I context are recognized by CD8 + T lymphocytes via their TCR receptor. This interaction can induce activation of the CD8 + T lymphocyte in cytotoxic T lymphocytes (1).
2. Presentation in association with MHC-II molecules
Some CyaA molecules are absorbed via the endosomal route via endocytosis. Once captured inside a lysosome, the CyaA protein is subjected to acid degradation into peptides which can then associate with the MHC class II molecules, transported across the cell membrane for its external presentation. These complexes are recognized by CD4 + T lymphocytes, which are activated and begin to secrete interferon-gamma (IFN-γ) (12, 13).
Finally, the CyaA vector also has the ability to provide maturation signals to the DC.
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