Recombinant outer membrane vesicles carrying Chlamydia muridarum HtrA induce antibodies that neutralize chlamydial
Erika Bartolini1, Elvira Ianni, Elisabetta Frigimelica
1Novartis Vaccines and Diagnostics, Siena, Italy.
Background:
Outer membrane vesicles (OMVs) are spheroid particles released by all Gram-negative bacteria as a result of the budding out of the outer membrane. Since they carry many of the bacterial surface-associated proteins and feature a potent built-in adjuvanticity, OMVs are being utilized as vaccines, some of which commercially available. Recently, methods for manipulating the protein content of OMVs have been proposed, thus making OMVs a promising platform for recombinant, multivalent vaccines development.
Methods:
Chlamydia muridarum DO serine protease HtrA, an antigen which stimulates strong humoral and cellular responses in mice and humans, was expressed in Escherichia coli fused to the OmpA leader sequence to deliver it to the OMV compartment. Purified OMVs carrying HtrA (CM rHtrA-OMV) were analyzed for their capacity to induce antibodies capable of neutralizing Chlamydia infection of LLC-MK2 cells in vitro.
Results:
CM rHtrA-OMV immunization in mice induced antibodies that neutralize Chlamydial invasion as judged by an in vitro infectivity assay. This was remarkably different from what observed with an enzymatically functional recombinant HtrA expressed in, and purified from the E. coli cytoplasm (CM rHtrA). The difference in functionality between anti-CM rHtrA and anti-CM rHtrA-OMV antibodies was associated to a different pattern of protein epitopes recognition. The epitope recognition profile of anti-CM HtrA-OMV antibodies was similar to that induced in mice during Chlamydial infection.
Conclusions:
When expressed in OMVs HtrA appears to assume a conformation similar to the native one and this results in the elicitation of functional immune responses. These data further support the potentiality of OMVs as vaccine platform.
Insights
Outer membrane vesicles (OMVs) carrying a Chlamydia antigen elicited neutralizing antibodies in mice, unlike the antigen expressed in E. coli cytoplasm. This demonstrates OMVs
Area of Science:
- Bacteriology and Immunology
- Vaccine Development
- Protein Engineering
Background:
- Outer membrane vesicles (OMVs) are bacterial nanoparticles with inherent adjuvant properties, making them suitable for vaccine applications.
- OMVs can be engineered to display specific antigens, offering a platform for developing recombinant and multivalent vaccines.
- Chlamydia muridarum DO serine protease HtrA is a promising antigen for inducing robust immune responses.
Purpose of the Study:
- To investigate the immunogenicity and functionality of Chlamydia muridarum HtrA antigen when expressed within OMVs.
- To evaluate the capacity of OMV-displayed HtrA to elicit neutralizing antibodies against Chlamydia infection.
- To compare the immune response induced by OMV-borne HtrA with that of cytoplasmically expressed HtrA.
Main Methods:
- Chlamydia muridarum HtrA was expressed in Escherichia coli with an OmpA leader sequence for OMV targeting.
- Purified OMVs displaying HtrA (CM rHtrA-OMV) were generated.
- Mice were immunized with CM rHtrA-OMV, and antibody responses were assessed using an in vitro Chlamydia infection neutralization assay.
Main Results:
- Immunization with CM rHtrA-OMV induced antibodies that effectively neutralized Chlamydia invasion in vitro.
- Antibodies generated against OMV-borne HtrA recognized epitopes similar to those targeted during natural Chlamydia infection.
- In contrast, antibodies against cytoplasmically expressed HtrA showed different epitope recognition and reduced neutralizing capacity.
Conclusions:
- HtrA expressed within OMVs adopts a native-like conformation, leading to functional immune responses.
- OMVs serve as an effective platform for presenting antigens in a conformationally relevant manner for vaccine development.
- These findings support the potential of engineered OMVs as a versatile vaccine platform.
