Vaccines are the most effective measures to prevent infectious diseases, and most of these infections occur through the mucous membranes that cover the surfaces of the vital organs of our body.Mucosal vaccination is, however, challenging. The numerous natural defense mechanisms at mucosal surfaces, including the acidic and enzyme-rich environment and the thick and firm mucus layer make the delivery of vaccines across these natural barriers challenging.
Probiotic-grade B. subilis spores could be utilized by the surface display technology as a mucosal vaccine delivery system and simultaneously as an adjuvant for mucosal immunity for the following reasons:
1. B. subtilis spores are resistant at ambient temperatures but remain viable.
2. B. subtilis spores are safe enough for consumption by humans as food components, probiotics, or therapeutics.
3. B. subtilis can be genetically manipulated, making it possible to engineer bacteria that express and display immunogens on the spore surface or in vegetative cells.
4. B. subtilis spores can serve as non-invasive vaccine delivery systems.
As a vaccine with ‘needle-free’ administration that is easy to store and transport under extreme conditions and does not require injection, the need for development is deemed to be high, as it has high application value for mass vaccination such as in a widespread disease outbreaks. A high-efficiency expression system on Bacillus spore, the control of proteolytic enzymes and redesign of genes encoding target proteins have been rapidly advanced.
It would be interesting to explore whether there are any particular spore types or Bacillus strains that show enhanced immunity with antigens displayed on the spore surface. Further discussion should be dedicated to other promising specific antigens and immunization routes that may lead to longer-lasting and moreefficacious vaccines with available technology.