Engineered bacteria are designed to produce modified lipid A with reduced toxicity and either polypeptide or polysaccharide antigens, which can be used in vaccines to elicit targeted immune responses.
The challenge of developing effective vaccines against bacterial infections lies in the dual necessity of eliciting a robust immune response while minimizing toxicity. Lipopolysaccharides (LPS), particularly the lipid A component, are potent immunostimulants found on the surface of Gram-negative bacteria. Lipid A’s interaction with the Toll-like receptor 4 (TLR4) on immune cells triggers a strong immune response, which is beneficial for vaccine adjuvants but can also lead to severe endotoxic shock.
Traditional approaches to mitigate lipid A toxicity involve modifying its acylation pattern, such as through genetic inactivation of lipid A biosynthesis genes like lpxM. However, these methods often result in a limited set of lipid A variants, restricting the ability to fine-tune the immune response. Additionally, the production of glycoconjugate vaccines, which combine polysaccharide antigens with protein carriers, is labor-intensive and costly, involving complex chemical synthesis and purification processes. This complexity is compounded by the difficulty in synthesizing certain carbohydrate antigens in vitro. Consequently, there is a need for innovative strategies that can generate a diverse array of lipid A variants and conjugate these with antigens efficiently for better vaccine efficacy and safety, with reduced production costs.
Engineered bacteria are designed to produce modified lipid A and either polypeptide or polysaccharide antigens. These bacteria contain expression vectors encoding lipid A modification enzymes such as lpxE, lpxF, lpxO, lpxR, pagL, and pagP, which alter the lipid A structure to reduce its toxicity while maintaining its immunogenic properties. The bacteria also carry vectors encoding either polypeptide antigens fused to membrane anchor sequences or genes for polysaccharide antigen biosynthesis.
For polypeptide antigens, the system co-expresses antigens like the HA2 domain of the influenza hemagglutinin protein, fused to membrane anchor sequences such as Lpp-OmpA, resulting in surface display on the bacterial outer membrane. For polysaccharide antigens, genes responsible for the synthesis of antigens like the Vibrio cholerae O-antigen are expressed, leading to covalent linkage of the polysaccharide to the modified lipid A. The engineered bacteria can be used to produce outer membrane vesicles (OMVs) containing these antigen-adjuvant combinations, which can serve as vaccine components to elicit targeted immune responses.
This technology is differentiated by its ability to produce both protein and carbohydrate antigens directly on the surface of bacteria, which are then packaged into OMVs. This method allows for the simultaneous production of antigen and adjuvant, reducing the need for laborious chemical synthesis and purification processes. The use of lipid A modification enzymes to reduce toxicity while maintaining immunogenicity is particularly innovative, as it addresses the safety concerns associated with traditional lipid A adjuvants.
Additionally, the versatility of the system allows for the expression of a wide range of antigens, making it adaptable for various infectious diseases. The co‑localization of antigens and adjuvants in OMVs enhances the immune response, offering a more effective and efficient approach to vaccine development. This combinatorial platform provides a cost-effective and scalable solution for producing vaccines, especially valuable in responding to emerging infectious diseases and potential pandemics.
Issued patent US 10,420,833