Streptococcus as Vaccine-vectors

Over the years many commensals or attenuated pathogenic bacteria, used as live vectors of antigen delivery for mucosal immunization against a variety of diseases, have received considerable attention in the field of vaccine research. Creative Biolabs is a world leader in the field of vaccines vector design. With our extensive experience and professional team, we are therefore confident in offering the best bacterial vaccine vector design services.

Streptococcus as Delivery Vehicle

Streptococcus as Vaccine-vectors– Creative Biolabs

The genus Streptococcus contains 104 recognized species, many of which are associated with human or animal hosts, and their interaction with host organisms ranges from commensal to pathogenic. Some of these commensal streptococci have been developed as live vaccine vectors that potentially confer life-long immunization through colonization, of which Streptococcus mitis (S. mitis) and Streptococcus gordonii (S. gordonii) are the most widely used. In recent years, a variety of antigens, of different origin and size, have been expressed in S. mitis and S. gordonii and were found to be immunogenic by the systemic and mucosal routes (oral, vaginal, intragastric).

Streptococcus mitis

S. mitis is the most abundant member of the normal human oral flora and is an excellent colonizer of the mucosal site, inhabiting the human oral cavity as early as 1-3 days postpartum. The induced mucosal immune response of S. mitis has been well documented, and the salivary IgA antibody to S. mitis exists after birth and continues to adulthood. Due to this particular biological association with human hosts, S. mitis is an attractive vaccine vector for inducing mucosal immunity in humans. Creative Biolabs developed a recombinant S. mitis stably expressing a heterologous antigen using homologous recombination technology. The integrating fragment into S. mitis genome contains 250 bp of S. mitis 5 flanking sequence that includes the pullulanase (pulA) gene signal peptide sequence, the foreign antigen, the erythromycin resistance (ermR) gene cassette, and 250 bp of S. mitis 3 pulA flanking sequence (Fig 2). The S. mitis flanking sequence allows for the integration of the foreign fragment into the S. mitis chromosome by homologous recombination.

Schematic representation of the homologous recombination in S. mitis.

Fig 2 Schematic representation of the homologous recombination in S. mitis.

Streptococcus gordonii

S. gordonii is a non-pathogenic Gram-positive commensal bacterium that is part of the normal microbial flora of the human oral cavity and was developed as a candidate for live mucosal vaccine delivery vector. In order to stably express foreign genes, we integrated the foreign genes into the S. gordonii chromosome by genetic engineering techniques.

  • The method for constructing a recombinant live vector vaccine based on S. gordonii is to surface-localize heterologous antigens with the M6 protein from Streptococcus pyogenes. M6 is a fibrous surface protein of Streptococcus pyogenes whose N-terminal signal sequence is exported to the cell surface and the conserved C-terminal domain anchored to the cell wall. In Creative Biolabs' surface display system, translational gene fusions of the heterologous gene with the M6 gene are constructed in an E. coli-streptococci shuttle expression vector. During the transformation, the insertion vector fragment containing the gene fusions and an ermR marker is integrated into the chromosome of S. gordonii by homologous recombination.
  • Thymidylate synthase (ThyA) is an enzyme that catalyzes the conversion of dUMP to dTMP and is essential for DNA synthesis. The thyA mutants are auxotrophs that require exogenous thymidine to grow. Based on this property, we designed a plasmid-free gene delivery system using thyA as a tool. The system consists of a thymidine auxotrophic recipient strain constructed by deleting a portion of thyA, and a linear gene delivery constructs, composed of a functional thyA gene, a vaccine antigen gene, and a DNA fragment immediately downstream of thyA. The construct is assembled through a ligation and polymerase chain reaction strategy. After the introduction of the thyA mutant, the vaccine antigen gene is integrated into the chromosome by a double crossing-over event while avoiding several safety issues caused by some selectable markers, including the risk of transmitting antibiotic resistance genes to pathogenic organisms.

With years of experience and advanced vaccine technology platform, Creative Biolabs offers a variety of vaccine vector design services based on S. gordonii and S. mitis, including the use of selectable markers and more. If you are interested in our services, please feel free to contact us.


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