Scientists at the Uniformed Services University of the Health Sciences (USU) have discovered a new way to render a microbe non-infectious while preserving its immune system-boosting properties after exposure to gamma radiation.
The discovery could have profound implications for the development of vaccines for deadly diseases like human immunodeficiency virus (HIV), explained USU Pathology Professor Dr. Michael Daly, whose research team led the study.
Daly has devoted more than 20 years to studying Deinococcus radiodurans, a microorganism the Guinness Book of World Records dubbed “the world's toughest bacterium.” Nicknamed “Conan the Bacterium,” it is known for its ability to withstand several thousand times the radiation levels that would kill a human being, and can be found nearly anywhere from your kitchen counter to the middle of a desert.
Deinococcus survives these extreme environments by accumulating high concentrations of manganese a metal element similar to iron and peptides, which protect its proteins from destruction when exposed to high levels of radiation or extremely dry conditions.
“I had been thinking there must be something very, very important we can do with this, and it just came to me, suddenly as a flash: vaccine development might be the way to go,” said Daly.
Vaccines are usually made up of 'bits and pieces' (epitopes) of disease-causing viruses or bacteria, he explained. When injected into a human or animal, these provoke an immune response that includes the production of antibodies, which can defend against future infection.
“However,” Daly explained, “the 'bits and pieces' sometimes aren't enough, and vaccines against many deadly diseases haven't worked.” He added that live vaccines using a weakened version of an intact virus or bacterium are most effective, but not an option when it comes to an otherwise untreatable disease like HIV because they carry an unacceptable risk of infection.
Radiation renders a virus or bacterium non-infectious by destroying the organism's genetic material, but can also damage its protein structures, which the immune system needs to recognize for a vaccine to be effective. Daly's team was able to get around this problem by isolating the manganese complex from Deinococcus and using it to protect a different bacterium's proteins from destruction by radiation.
“The simplicity of it is what's so amazing,” said Daly. “With radiation, their genomes are destroyed, sterilized. But all the proteins and all the structures on their surfaces remain, so you then can take these lethally-radiated pathogens and use them in making vaccines. The immune system then thinks it's encountering the real bugs, which are now just lifeless shells, and mounts a full protective response.”
USU researchers, led by Daly, teamed up with scientists from the National Institutes of Health to test a vaccine for drug-resistant Staphylococcus aureus bacteria in mice. It worked. The breakthrough study was published in the July edition of the scientific journal, “Cell Host and Microbe.” Daly said it could take years to get approval for human trials, but he's optimistic this discovery will be a big help in fighting deadly diseases like HIV and influenza.
“This could speed up the whole process of producing vaccines instead of biochemists spending years trying to clone one aspect of a microbe's protein structure, it could take only a matter of weeks to radiate all the different strains of a disease and create one vaccine to protect against all of them.”
“We've shown this approach can work on Staphylococcus, which kills about 18,000 people per year,” said Daly. “Now it's only a matter of time before we can apply it to other bugs.”
For more information about USU research, please visit: www.usuhs.mil.