Vaccines play a key role in fighting disease
A common immunosuppressive drug may have the ability to boost the power of vaccines, research suggests.
Rapamycin is commonly give to transplant patients to stop their bodies rejecting donor organs.
In tests on mice and monkeys, scientists found it enhanced the response of their immune system to experimental vaccines.
The Emory University study, featured in the journal Nature, also raises hopes of a new generation of potent vaccines.
Rapamycin seems to work by inhibiting a protein called mTOR, which plays a key role in controlling cell growth.
The researchers found that when they switched off mTOR using rapamycin in virus-infected mice, the animals produced a better immune response.
In particular, the treatment seemed to boost the number of 'memory' T cells - the cells that are responsible for remembering infections they have encountered before.
The Emory team went on to show that rapamycin could improve memory T-cell responses to experimental vaccines in both mice and monkeys.
The study suggests that mTOR plays a key role in regulating the generation of memory T cells.
Harnessing this knowledge could potentially help vaccine manufacturers find a way to create memory T cells, which in theory may lead to more powerful vaccines against chronic infections and tumours.
Researcher Dr Koichi Araki said: "Many vaccines need multiple vaccinations to obtain enough immunity to overcome infections because immunity after a single shot of vaccination is often too weak to fight with infection.
"So, researchers are looking for the way to boost vaccine-induced immunity.
"Our approach might become one strategy to enhance vaccine efficacy.
"We believe that rapamycin could be administered at the same time as a vaccine to boost its potency."
Professor Adrian Hill, director of the Jenner Insitutute, said the study was valuable because it enhanced understanding of T cells.
He stressed very few currently licensed vaccines worked through the type of immune responses studied in the research - but new vaccines under development for diseases such as HIV, cancer and malaria potentially would.
"It might be complicated to use an immunosuppressive drug for widespread prophylactic vaccination but this could certainly be tried with some experimental cancer vaccines," he said.
But he stressed that drugs that successfully modify the immune system in animals fail to work in humans.