Live bacterial vectors for mucosal immunization

Construction of an artificial recombinant bicistronic plasmid DNA vaccine against porcine rotavirus

The attenuated Salmonella typhimurium χ4550 strain was used to harbour a reconstructed bicistronic DNA vaccine against porcine rotavirus, which carried the rotavirus nonstructural protein 4 (NSP4) and VP7 genes simultaneously. Using a balanced lethal system, the kanamycin resistance gene of expressing eukaryotic plasmids pVAX1 and pVAXD were replaced by the aspartate β-semialdehyde dehydrogenase (asd) gene. The NSP4 cleavage product (259-525) of rotavirus OSU strain and VP7 full-length genes were amplified by reverse transcription polymerase chain reaction and then inserted into the eukaryotic single-expression plasmid, pVAX1-asd, and the eukaryotic dual-expression plasmid, pVAXD-asd, respectively. The recombinant plasmids pVAX1-asd-NSP4, pVAX1-asd-VP7 and pVAXD-asd-NSP4-VP7 were transformed into the attenuated S. typhimurium χ4550 strain by electrotransformation. An indirect immunofluorescence assay of the expressed COS-7 cell suggested that the recombinant S. typhimurium χ4550 strain was constructed successfully. The recombinant S. typhimurium χ4550 strain was orally administered to BALB/c mice. The group immunised with dual- expression plasmids produced a significantly higher level of serum Immunoglobulin G (IgG) and intestinal Immunoglobulin A (IgA) than the group immunised with single-expression plasmids. These results indicated that eukaryotic bicistronic plasmid DNA vaccines could be successfully constructed to enhance humoural, mucosal and cellular immune response against rotavirus infection.

Intragastric administration of attenuated Salmonella typhimurium harbouring transmissible gastroenteritis virus (TGEV) DNA vaccine induced specific antibody production

Attenuated Salmonella typhimurium was selected as a transgenic vehicle for the development of live mucosal vaccines against transmissible gastroenteritis virus (TGEV). A 2.2kb DNA fragment, encoding for N-terminal domain glycoprotein S of TGEV, was amplified by RT-PCR and cloned into eukaryotic expression vector pVAX1. The recombinant plasmid pVAX-S was transformed by electroporation into attenuated S. typhimurium SL7207, the expression and translation of the pVAX-S delivered by recombinant S. typhimurium SL7207 (pVAX-S) was detected in vitro and in vivo respectively. BALB/c mice were inoculated orally with SL7207 (pVAX-S) at different dosages, the bacterium was safe to mice at dosage of 2x10(9)CFU and eventually eliminated from the spleen and liver at week 4 post-immunization. Mice immunized with different dosages of SL7207 (pVAX-S) elicited specific anti-TGEV local mucosal and humoral responses as measured by indirect ELISA assay. Moreover, the immunogenicity of the DNA vaccine was highly dependent on the dosage of the attenuated bacteria used for oral administration, 10(9)CFU dosage group showed higher antibody response than 10(8)CFU and 10(7)CFU dosages groups during week 4-8 post-immunization. The results indicated that attenuated S. typhimurium could be used as a delivery vector for oral immunization of TGEV DNA vaccine.

Homologous recombination with linear DNA to insert antigenic protein in the flagellin: improvement of the Th1 immune response

Bacterial flagellin is a surface protein with numerous advantages for the presentation of exogenous peptides. However, the production of recombinant bacteria and the expression of fusion proteins is laborious and time consuming. Here, we present a simple way to produce modified bacteria. Partially deleted, non-functional, chromosomal flagellin gene (fliC ) was changed using homologous recombination by a functional linear fliC gene in which we introduced an exogenous oligonucleotide encoding for the peptide of interest. The modified fliC gene was produced by polymerase chain amplification. Linear amplicons were introduced into the non-motile E. coli by electroporation. The formation of functional flagellar filaments allowed the discrimination of motile transformants from non-motile, non-transformed cells. Thus antibiotic selection and gene expression inductors are not required since transformed bacteria can be easily isolated and used as a vector and adjuvant for immunization. To validate this hypothesis, we studied the immune response against the N-terminal peptide of Clostridium tyrobutyricum flagellin fragment. BALB/c mice were immunized either with the protein displayed as flagellin fusion protein on the surface of E. coli, with the recombinant protein in Freund's adjuvant (FA), or with the pcDNA3 vector bearing the DNA fragment encoding this protein. Immunization with the flagellin recombinant bacteria induced a strong Th1 response as measured by high level of IFN-gamma production and the lack of IL-4 production. The results indicate that the flagellar filament protein carrying a specific epitope can be a potent inducer of the Th1 cellular response.

Vaccines for fertility regulation of wild and domestic species

The application of fertility control technologies for the management of animal populations is still a relatively new concept and remains to be proven on a large scale. While there have been demonstrations of its utility using crude antigenic preparations of porcine zona pellucida, refined, cheap and easily delivered vaccines are still in the early phases of development, especially those required for remote delivery to free-ranging wild animal populations. The relative slow emergence of such technologies for practical application clearly reflects the complexity of the science and the requirement for a multidisciplinary research approach when attempting to develop such technologies for wild animal management. In many cases, one of the areas where further information is required is the immunobiology of such target species. Effective immunocontraceptive vaccines will also be critically dependent upon the design of the delivery systems. These will be unique to each species under study. A major challenge for free-ranging species will be to ensure that the vaccine can induce a long-lasting immune response to a high percentage of the target population, thus reducing the frequency and, hence, the cost of vaccine application. Many of the delivery systems being considered will utilise recombinant organisms. Hence, considerations on the use of such organisms needs to take into account the political, ethical and safety constraints prior to any environmental release. Also of prime importance is the issue of species specificity. In some instances, this will be a major challenge and careful thought will need to be given to ensure that specificity can be built into the vaccine at several levels. These might include the target antigen or epitopes, the microbial or other delivery vector, and, where applicable, the bait matrix and any target-specific attractive properties it may require. If these caveats can be satisfied and the public is able to accept the use of such vaccines, the potential for their application to manage animal populations and their impact is most certainly assured.