It's truly astonishing how quickly the scientific community can identify and solve a problem. In April 2012, the first victims of an unknown infectious disease died. By October, the causative agent was identified as a new coronavirus, related to the virus which causes SARS. In August 2013, the microbe, now known as MERS (Middle East Respiratory Syndrome) virus, was traced to both bats and camels, suggesting a possible route of infection to humans.
And now, Spanish scientists have announced another leap: The development of a candidate vaccine strain.
For vaccines, live viruses are often preferable because they are better at eliciting a mucosal immune response. But, the virus needs to be weakened in some way.
To create a weakened virus, the researchers first created a DNA copy of the original MERS virus which has an RNA genome. This DNA copy, known as "complementary DNA (cDNA)," was inserted into an artificial chromosome. This genetic construct was itself infectious; if it was given to cells in culture, the cells produced infectious viral particles.
To weaken the virus, the authors deleted its E gene, which produces the E protein. This protein is essential for creating new virus particles. Without it, the virus can only infect and replicate inside the cell, but it cannot leave. For a MERS virus, that is not good news; a successful coronavirus needs to infect, replicate, produce new particles and exit the cell.
As an analogy, imagine an automobile manufacturing plant that has all of the parts necessary to put together brand new cars, but a glitch in the manufacturing process prevents that from happening. All the parts are there, but no finished cars are built, and nothing leaves the plant. That is similar to what happens to MERS without its E protein. When the authors gave the virus back its E protein, it was once again able to produce viral particles, confirming that the mutant virus is "replication-competent" but "propagation-defective."
In other words, it's a perfect virus for a vaccine. That's because the virus can induce an immune response, but it cannot sustain an infection. Additionally, the authors cite other research showing that SARS without its E protein elicits a protective immune response.
Hopefully, the MERS virus outbreak will fizzle out. But if it does not, a potential vaccine strain is waiting in the wings.
Source: Fernando Almazán, Marta L. DeDiego, Isabel Sola, Sonia Zuñiga, Jose L. Nieto-Torres, Silvia Marquez-Jurado, German Andrés, Luis Enjuanes. "Engineering a Replication-Competent, Propagation-Defective Middle East Respiratory Syndrome Coronavirus as a Vaccine Candidate." mBio 4 (5): e00650-13. 10-September-2013. doi: 10.1128/mBio.00650-13