Pneumococcal membrane vesicles as cell-free vaccine avenue to pneumonia infections

• Applicants: Professor Dr. Gregor Fuhrmann, Ph.D.; Dr. Franziska Voß
• Subject Area: Medical Microbiology and Mycology, Hygiene, Molecular Infection Biology ; Pharmacy
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 556453571

The World Health Organisation has classified Streptococcus pneumoniae as one of the pathogens, for which the development of new antimicrobial strategies is of highest priority. Pneumococcal infections could lead to pneumonia, meningitis, and septicemia. In vulnerable groups such as young children, the elderly and immunocompromised individuals, this Gram-positive bacterium induces high mortality rates. While antibiotics such as beta-lactams are currently used in therapy, rising resistance numbers – particularly in developing countries – pose an increasing healthcare threat. Vaccine approaches introduced in the 1970s are based on capsular polysaccharides, which determine the serotype of the bacterium, with over 100 serotypes identified to date. However, current vaccines only cover a subset of the known serotypes. Although they have reduced invasive diseases, they suffer from shortcomings, including 1) increased incidence of non-vaccine-type infections, 2) incomplete serotype coverage, and 3) persisting high pediatric morbidity and mortality. These issues underline the need to evaluate alternative vaccine strategies. Membrane vesicles represent an interesting class of bacteria-derived nanoparticles which carry certain bacterial properties without the ability to replicate. These vesicles are shed from the bacterial membrane and are generally composed of a phospholipid membrane with surface and membrane proteins. Pneumococcal MVs carry antigenic virulence factors, such as pneumolysin, various enzymes, transporters, and host-adhesion proteins. Our preliminary results show that pneumococcal MVs interact with host cells, including epithelial cells, macrophages, and dendritic cells. They induce the production of inflammatory cytokines such as IL-6, IL-8, and TNF-α by human dendritic cells, which makes them interesting entities to comprehend their immunomodulatory potential. We furthermore found that lipidation of pneumococcal proteins enhances their immune response. Finally, a preliminary protocol for the incorporation of membrane vesicles into microparticles of 2.34 µm was established. Such size is required for inhalation into the deep lung, where alveolar macrophages are encountered for mucosal vaccination. Here, we want to further expand our knowledge on pneumococcal vesicles and better comprehend their immunomodulatory properties to pave the way towards a cell-free vaccination platform. We will study how genetic manipulation of pneumococci and culture optimization alters their vesicle yield. We aim to understand how composition and biocompatibility affect the immunogenicity of bacterial vesicles and we will study the ability of pneumococcal vesicles to stimulate innate and adaptive immune responses in vitro and in vivo. By optimizing a microparticle delivery system for lung application, we finally assess how protection against pneumococcal colonization and pneumonia is conferred in vivo.

• DFG Programme: Research Grants