A breakthrough in vaccination technology, which could speed up the production of vaccines for epidemics like Ebola, Zika or the Flu, has been announced by researchers in the US this week.
Traditionally vaccines are made by growing infectious disease agents in culture and then deactivating and purifying them, which can take months.
In outbreak situations, such delays can be a major obstacle to successfully curbing disease threats.
Now MIT scientist Omar F Khan, writing in PNAS, has taken a different approach. He's invented a nanoparticle that can deliver into the body small pieces of genetic information, in a form called RNA, that encode for parts of the disease-causing microbe.
This enables the body to read those instructions and rapidly churn out both protective antibodies and infection-fighting white blood cells.
"We've turned the patient's own cells into vaccine factories," says Khan. "These cells make the vaccine components and educate the immune system to fight off the threat."
The nanoparticles are made by mixing a bulky, highly-branched polymer called a dendrimer with polyethylene glycol molecules linked to a pair of fatty acid chains, and then the cocktail of RNA "instruction" molecules.
This mixture self-assembles into tiny spherical particles, each about 1/20,000th of a millimetre across, with the RNA at the core surrounded by the dendrimer material and the whole thing encased by a polyethylene glycol lipid shell.
The particles are highly stable and preserve the RNA intact for at least a month. They are biologically inert meaning that they do not trigger an inflammatory reaction in the body and can be injected safely, whereupon they can deliver their RNA cargo to a range of cell types.
The RNA instructions are also "self-replicating", meaning that they can copy themselves within the cell for a limited period of time, leading to the production of large amounts of proteins normally made by the infectious agent represented by the vaccine.
Such an arrangement provokes a powerful and long-lasting immune response that includes making both antibodies capable of neutralising the infection and white blood cells capable of attacking the agent.
An added bonus is that the particles are sufficiently large to carry RNA instructions relevant to a mixture of different infectious diseases, so one shot could drive immunity against multiple diseases at once.
In tests, mice given a single dose of the particles were protected within 2 weeks against otherwise lethal doses of influenza, ebola and even the parasitic infection Toxoplasma gondii.
"That is proof-positive that this works," says Khan.