Scientists have been able to show for the first time that the body's immune defences can destroy the common cold virus after it has actually invaded the inner sanctum of a human cell, a feat believed to be impossible.
The discovery opens the door to the development of a new class of antiviral drugs that work by enhancing this natural virus-killing machinery of the cell.
Scientists believe the first clinical trials of new drugs based on the findings could begin within two to five years.
The researchers said many other viruses responsible for a range of diseases could also be targeted by the new approach. They include the norovirus, which causes winter vomiting, and rotavirus, which results in severe diarrhoea and kills thousands of children in developing countries.
Viruses are mankind's biggest killers, responsible for twice as many deaths as cancer, essentially because they can get inside cells where they can hide away from the body's immune defences and the powerful antibiotic drugs that have proved invaluable against bacterial infections.
However, a study by a team of researchers from the Laboratory of Molecular Biology in Cambridge has shown that this textbook explanation of the limits of the human immune system is wrong because anti-viral antibodies can enter the cell with the invading virus, where they are able to trigger the rapid destruction of the foreign invader.
"In any immunology textbook you will read that once a virus makes it into a cell, that is game over because the cell is now infected. At that point there is nothing the immune response can do other than kill that cell," said Leo James, who led the research team.
But studies at the Medical Research Council's laboratory have found that the antibodies produced by the immune system, which recognise and attack invading viruses, actually ride piggyback into the inside of a cell with the invading virus.
Once inside the cell, the presence of the antibody is recognised by a naturally occurring protein in the cell called TRIM21, which in turn activates a powerful virus-crushing machinery that can eliminate the virus within two hours - long before it has the chance to hijack the cell to start making its own viral proteins. "This is the last opportunity a cell gets because after that it gets infected and there is nothing else the body can do but kill the cell," James said.
It was thought that the antibodies of the immune system worked entirely outside cells.