Adjuvant effect of bacterial outer membrane vesicles with penta-acylated lipopolysaccharide on antigen-specific T...

Area of Science:

• Immunology
• Microbiology
• Vaccinology

Background:

• Outer membrane vesicles (OMVs) from Gram-negative bacteria are used in vaccine development.
• Lipopolysaccharide (LPS) acylation influences OMV properties, including endotoxicity and immunogenicity.
• Modifying LPS acylation offers a strategy to enhance OMV safety and efficacy as vaccine adjuvants.

Purpose of the Study:

• To compare the T cell adjuvant activity and endotoxicity of OMVs with penta-acylated LPS (mOMV) versus hexa-acylated LPS (wOMV).
• To investigate the underlying mechanisms of mOMV's adjuvant effect, focusing on innate immune responses and Toll-like receptor 4 (TLR4) dependency.

Main Methods:

• Generation of mOMV from a ΔmsbB/ΔpagP mutant Escherichia coli strain with penta-acylated LPS.
• Comparison of mOMV and wOMV in vitro and in vivo toxicity assays.
• Evaluation of T cell priming in mice immunized with KLH protein or SIINFEKL peptide using mOMV as an adjuvant.
• Assessment of mOMV's effect on bone marrow-derived dendritic cells (BMDCs), including co-stimulatory molecule expression and cytokine production.
• Analysis of TLR4 dependency using TLR4 knockout (K/O) mice.

Main Results:

• mOMV exhibited significantly lower endotoxicity compared to wOMV in both in vitro and in vivo models.
• mOMV demonstrated robust T cell adjuvant activity, comparable to wOMV and LPS, in KLH protein and SIINFEKL peptide immunization models.
• The adjuvant effect of mOMV was dependent on Toll-like receptor 4 (TLR4), as it was abrogated in TLR4 K/O mice.
• mOMV stimulated BMDCs to upregulate co-stimulatory molecules and produce pro-inflammatory cytokines in a TLR4-dependent manner, but to a lesser extent than wOMV.

Conclusions:

• OMVs with penta-acylated LPS (mOMV) possess significant T cell adjuvant properties.
• mOMV represents a safer vaccine adjuvant candidate due to its reduced endotoxicity compared to wild-type OMVs.
• mOMV holds potential for vaccine development against viral diseases and cancer, particularly for enhancing T cell responses.