Design of Bacterial Inclusion Bodies as Antigen Carrier Systems

Abstract

Synthetic subunit vaccines hold great promise to prevent infectious diseases, but they often induce only weak immune responses. Here bioengineering techniques to develop immunogenic antigen particles comprised of self‐assembling antigenic peptides are exploited. A bioparticle platform is developed to present repetitive copies of subunit antigens, which mimic the host‐pathogen surface interaction to provide enhanced immunogenicity. Herein, mycobacterial fusion proteins H4 (consisting of Ag88B‐TB10.4) and H28 (containing Ag88B‐TB10.4‐Rv2660c) are bioengineered to assemble H4 and/or H28 antigens into particulate vaccines inside an endotoxin‐free Escherichia coli strain, to serve as a novel vaccine against tuberculosis (TB). A bioprocess for particle isolation is developed. The physicochemical properties of the particles are investigated. Antigen particles formulated with the adjuvant dimethyl dioctadecyl ammonium bromide are used to subcutaneously immunize C57BL/6 mice. Both soluble and particulate vaccines elicit production of functional and specific antibodies, which only interact with target antigens and not production host cell proteins. Particulate vaccines induce strong production of interferon gamma (IFNγ) and interleukin 17A (IL17A) cytokines. When compared to soluble antigens, the antigen particle vaccines show increased immunogenicity. Overall, this study provides proof of concept that selected antigens can be engineered to self‐assemble into inclusion bodies to serve as particulate vaccines with improved immunological properties compared to the respective soluble antigens.