Viral Mimetic Bacterial Outer Membrane Vesicles for Targeting Angiotensin-Converting Enzyme 2

Purpose: Outer membrane vesicles (OMVs) derived from Gram-negative bacteria naturally serve as a heterologous nano-engineering platform, functioning as effective multi-use nanovesicles for diagnostics, vaccines, and treatments against pathogens. To apply refined OMVs for human theranostic applications, we developed naturally exposed receptor-binding domain (RBD) OMVs grafted with antigen 43 as a minimal modular system targeting angiotensin-converting enzyme 2 (ACE2).

Methods: We constructed E. coli-derived OMVs using the antigen 43 autotransporter system to display RBD referred to as viral mimetic Ag43β700_RBD OMVs. Based on this, Ag43β700_RBD protein were expressed onto Escherichia coli (E. coli) membrane. Artificial viral mimetic Ag43β700_RBD OMVs were fabricated by self-assembly through membrane disruption of the Ag43β700_RBD E. coli using a chemical detergent mainly containing lysozyme. Through serial centrifugation to purify fabricated OMVs, spherical Ag43β700_RBD OMVs with an average diameter of 218 nm were obtained. The confirmation of the RBD expressed on OMVs was performed using trypsin treatment.

Results: Our viral mimetic Ag43β700_RBD OMVs had an impact on the theranostic studies: (i) angiotensin-converting enzyme 2 blockade assay, (ii) enzyme-linked immunosorbent assay for the OMVs, and (iii) intracellular uptake and neutralization assay. As serodiagnostic surrogates, Ag43β700_RBD OMVs were applied to ACE2 blockade and OMVs-ELISA assay to quantify neutralization antibodies (nAbs). They reduced the robust immune response in vitro, especially IL-6 and IL-1β. Experiments in mice, Ag43β700_RBD OMVs was successfully proven to be safe and effective; they produced a detectable level of nAbs with 39-58% neutralisation and reduced viral titres in the lungs and brain without weight loss.

Conclusion: The developed viral mimetic Ag43β700_RBD OMVs may therefore be applied as a nanovesicle-theranostic platform for further emerging infectious disease-related diagnosis, vaccination, and treatment.