Bacterial Vector Vaccine Design

The strategy of using live bacterial cells as vehicles to deliver recombinant antigens has emerged over the past 20 years as an interesting alternative for the development of new vaccines. With the development of genetic engineering techniques, recombinant microorganisms and pathogens are capable of expressing heterologous proteins in different cell compartments, thereby increasing their antigenic potential for vaccines against viruses, bacteria, and parasites. To date, Creative Biolabs has developed vaccine delivery vectors based on live bacteria from different species through a variety of strategies, such as a bacterial surface display. As a service provider, our goal is to provide the highest level of service, confidentiality and customer support.

Introduction of Bacterial Vectors

An ideal vaccine vector should not only be able to trigger potent innate but adaptive immune response in the inoculated host. The use of live bacteria as a vector to deliver heterologous antigens is an effective and original alternative to the development of new vaccines. Living bacteria, including attenuated bacteria and probiotics, can be engineered to deliver target antigens to stimulate the host immune system. The intrinsic characteristics of these microorganisms, such as lipopolysaccharide in Gram-negative bacteria or lipoteichoic acid in Gram-positive bacteria, and the innate immune response of bacterial pathogens and their effects on the adaptive immune system makes attenuated live microorganisms extremely effective vector for stimulating specific and long-term immune responses against antigens. The bacteria commonly used to deliver antigens are genetically modified recombinant bacteria, and most of their pathogenic components have been removed to attenuate bacteria toxicity, thereby ensuring the safety of the host. Currently, heterologous antigens are expressed in bacteria primarily through chromosomal integration of the antigen-coding cassette or by a plasmid-based antigen expression system.

The Delivery Strategies of Heterologous Antigen in Bacterial Vectors

The form of heterologous antigen expression has a crucial impact on the type and efficiency of the immune response of live bacterial vaccines. The antigens are typically fused into bacterial host by plasmid or specifically integrated into the host genome. Although most recombinant plasmids exhibit stability in vitro under antibiotic selection pressure, antibiotic residues would be transferred to the environment, resulting in more environmental pollution worldwide. Therefore, future work should aim to integrate heterologous antigens into the host's genome (chromosomes) to develop more stable and long-term recombinant bacteria. At present, many techniques can improve the efficiency of chromosome integration, such as clustered regularly interspaced short palindromic (CRISPR/Cas9). Creative Biolabs offers a variety of heterologous antigen delivery strategies, such as bacterial surface display systems, bacterial secretion systems, and balanced lethal vector systems to achieve efficient delivery of antigen.

Balanced Lethal Vector System

Balanced lethal vector system, based on auxotrophic genes for elements of biosynthetic pathways necessary for growth or metabolism, has been proved to be an effective strategy for providing an alternative to antibiotic-resistance selection markers and enhancing the expression level of heterologous antigen. Creative Biolabs provides a balanced lethal vector system based on multiple genes such as asd, dal, and glmS.

Bacterial Surface Display System

In this system, the target antigen is usually expressed and displayed on the surface of living bacteria. In most cases, the target antigen is fused to the outer membrane protein in Gram-negative bacteria. Therefore, anchoring motifs are a major factor affecting the stability of heterologous antigen expression in bacterial surface display systems. Creative Biolabs establishes bacterial display systems by using different kinds of anchoring motifs, including N-terminal lipoprotein anchors or C-terminal cell wall anchors and S-layer proteins. In addition, some proteins with LPXTG anchoring motifs have been processed to display target antigens on the surface of Gram-positive bacteria.

Bacterial Secretion System

The secretion of the foreign antigen could raise the immune efficiency of a vaccine used against corresponding pathogens. The type I secretion system (T1SS) and the type III secretion system (T3SS) are mainly used in certain Gram-negative bacteria for the development of live vector vaccines. For example, attenuated pathogenic bacteria, E. coli, Salmonella and Shigella have been used to deliver foreign antigens in a type III secretion system. T3SS is an important delivery platform for various Gram-negative pathogenic bacteria for delivering effector proteins (exotoxin or foreign antigen) to the outside of the cell.

Other Systems

In addition to these delivery strategies for heterologous antigens in live bacteria, Creative Biolabs has developed other bacterial control systems that can also be used for live bacterial vaccines, including bacterial post-segregational killing system based on antitoxic proteins and bacterial lysis systems, all of which can deliver foreign antigen to the host cell safely and efficiently.

The Advantages of Bacterial Vectors

Compared to other types of vaccine carriers, bacteria-based antigen delivery vectors exhibit multiple advantages:

• The possibility to control its intrinsic infectious power (a variety of well-characterized virulence-attenuating mutations and available antibiotherapy)
• Non-integrative properties
• The ability to regulate the amount and in vivo localization of antigen expression
• The potential for multiple vaccine delivery routes
• Potent stimulation of the innate and adaptive immune systems
• Relatively low manufacturing costs and suitable for large-scale administration

Bacterial Vectors Provided by Creative Biolabs

Genetically attenuated microorganisms, pathogens, and some commensal bacteria can be engineered to deliver recombinant heterologous antigens to stimulate the host immune system, while still offering good levels of safety. Creative Biolabs is the world's leader in vaccine vector development and we offer you the best and highest quality vaccine vector design services. If you need any help, please feel free to contact us.

All of our products can only be used for research purposes. These vaccine ingredients CANNOT be used directly on humans or animals.