LIVE BACTERIAL VACCINES

What is meant by live bacterial vaccines?

• Two types:

– Those that combat the disease causing organism itself• An immune response induced against the bacteria itself

– Those that assist in combatting another disease causing organism• An immune response induced against a carried heterologous antigen

LIVE ATTENUATED BACTERIAL VACCINES

RECOMBINANT BACTERIAL VACCINE VECTORS

Live Attenuated Bacterial Vaccines

• Currently three of this type of vaccine exist:

Typhoid Vaccine – Ty21a

Cholera Vaccine - CVD 103-HgR

Tuberculosis - BCG

• Contains a live attenuated form of Salmonella typhi

Shigella – Proposed Vaccine

• Brand name is Dukoral• Contains both a live attenuated version of Vibrio cholerae serotype O1

plus a recombinant cholera toxin B subunit (rCTB)

• Contains a live attenuated strain of the bovine strain of tuberculosis – Mycobacterium bovis

MUST ENCOMPASS BOTH:

REACTOGENICITY

IMMUNOGENICTY

P

P

Virulence Attenuation

• Used to be achieved by laboratory passage but is now achieved by recombinant DNA technology methods:

Gene Deletions

• Affect the way virulence genes are regulated• Salmonella spp. deletions in phoP or phoQ genes.

Auxotrophs

• Require metabolites that are not present in host tissues

• Gene deletions within the aro biosynthetic pathway

Recombinant Bacterial Vaccine Vectors

• Using live attenuated bacteria to carry heterologous antigens– Either protein or DNA

Chromosomally Encoded Antigens

Plasmid Encoded Antigens

• Cassettes integrated into the chromosome• Genetically stable• Multiple antigen genes can be expressed• Low copy number – only one per bacterial cell

• This may not be enough to elicit a suitable immune response

• Antigen genes encoded on plasmids• Unstable – can be lost• Amount of antigen expressed can be varied

• low copy and high copy plasmids• Control of antigen expression via inducible promoters

dmsA dmsB dmsCIP

Getting Noticed

• Exploit invasive bacterial pathogens

• Vector type key to immune response – MHC Class I

Shigella spp. and Listeria monocytogenes

• Both are intracellular pathogens able to transverse directly into the cytoplasmic region of the cell to deliver antigens to MHC Class I pathway

• Auxotroph deletion asd – in vivo lysis due to low DAP

Salmonella spp.

• Delivery to MHC Class I is inefficient as antigens remain localised to the membrane

• Exploiting the T3SS allows for efficient secretion of antigens to antigen presenting cells

Immune responses can be achieved through efficient invasion of mucosal cells of intestinal tract.

Positives, Negatives and Future

• No injection – more compliance

• Easy, cheap to manufacture

• Potentially stable without refrigeration

• Multiple antigens in a single vector

• Can be destroyed with antibiotics

• Reversion to virulence

• Unwanted immune responses

• Environmental contamination

• Pathogens: HIV, those that attack GI, Respiratory and Genital tract

• Currently no licensed bacterial vaccine vectors – several currently in clinical trial

Positives

Negatives

Future

References

Carleton, H. A. (2010). Pathogenic bacteria as vaccine vectors: Teaching old bugs new tricks. Yale Journal of Biology and Medicine, 83(4), 217-222.Detmer, A. & Glenting, J. (2006). Live bacterial vaccines - a review and identification of potential hazards. Microbial Cell Factories, 5.Fiorentino, M., Levine, M. M., Sztein, M. B. & Fasano, A. (2014). Effect of wild-type Shigella species and attenuated Shigella vaccine candidates on small intestinal barrier function, antigen trafficking, and cytokine release. Plos One, 9(1).Gunn, B. M., Wanda, S.-Y., Burshell, D., Wang, C. & Curtiss, R., III (2010). Construction of recombinant attenuated Salmonella enterica serovar Typhimurium vaccine vector strains for safety in newborn and infant mice. Clinical and Vaccine Immunology, 17(3), 354-362.Jong, W. S., Daleke-Schermerhorn, M. H. & Luirink, J. (2014). An autotransporter display platform for the development of multivalent recombinant bacterial vaccine vectors. Microbial Cell Factories, 13(162).Kotton, C. N. & Hohmann, E. L. (2004). Enteric pathogens as vaccine vectors for foreign antigen delivery. Infection and Immunity, 72(10), 5535-5547.Orr, N., Galen, J. E. & Levine, M. M. (2001). Novel use of anaerobically induced promoter, dmsA, for controlled expression of fragment C of tetanus toxin in live attenuated Salmonella enterica serovar Typhi strain CVD 908-htrA. Vaccine, 19(13-14), 1694-1700.Porwollik, S. (2010). Salmonella : from genome to function. Poole: Caister Academic Press.Vecino, W. H., Morin, P. M., Agha, R., Jacobs, W. R. & Fennelly, G. J. (2002). Mucosal DNA vaccination with highly attenuated Shigella is superior to attenuated Salmonella and comparable to intramuscular DNA vaccination for T cells against HIV. Immunology Letters, 82(3), 197-204.Wang, S., Kong, Q. & Curtiss, R., III (2013). New technologies in developing recombinant attenuated Salmonellavaccine vectors. Microbial Pathogenesis, 58, 17-28.