Beschreibung
Bacterial membrane vesicles (BMV's) represent a promising approach for vaccination. Secreted by bacteria at any time of growth, they perform a number of diverse valuable tasks for them. Through their release, BMV‘s form a long-range transport system of bacteria by protecting their contents from degradation and dilution. In this way, they enable bacterial cells to transfer a range of biomolecules such as RNA and DNA fragments, autolysins, cytokines, plasmids as well as virulence factors, and ultimately enable communication between bacterial cells and influence host cells. One obstacle in working with BMV's is their endotoxicity, caused by the lipopolysaccharides (LPS) present in large amounts in their outer membranes. However, work with the strain ClearColi® with modified LPS structure is promising in this regard. Due to the deletion of seven genes that are involved in LPS synthesis in ClearColi®, these bacteria have a modified LPS structure that is not recognized by Toll-like receptor 4 (TLR4). As a result, BMV's derived from ClearColi® exhibit virtually no LPS based endotoxicity.
In the present work, bacterial strains with increased vesicle production were successfully generated by chromosomal integrating hlyF and deleting nlpI. Since these were generated based on the strain ClearColi®, the BMV's obtained from these strains have been shown to have very low endotoxicity. In addition, modified BMV's with the S1 subunit of the SARS-CoV-2 spike protein were successfully generated. Thereby, the targeted induction of S1 protein expression succeeded in enriching the S1 protein in the vesicles.
Increasing production levels is prerequisite for industrial production of BMV-based vaccines and reducing endotoxicity is necessary for the safety of future vaccines. The detection of the SARS-CoV-2 S1 surface protein in the vesicles shows how adaptable the method can be for new pathogens. Thus, ultimately, this work demonstrated and further developed the potential of the BMV-based vaccination strategy. Further animal experiments are needed to investigate the ability of the produced BMV's with respect to the production of neutralizing antibodies against SARS-CoV-2.
