|May 15, 2013|
Inside the lab racing to make vaccine for deadly flu
|Suited and masked, in the secure environment of a biosafety level 3 containment lab at St Jude Children's Hospital in Memphis, Tennessee, Jim Allay and Mike Tillman are lifting culture plates above their heads, peering towards the fluorescent lighting. They're looking for robust "plaques" -- clumps of chicken embryo kidney cells infected with an engineered flu virus.|
The stakes could scarcely be higher. This virus is a vaccine strain carrying genes from the H7N9 bird flu that has killed more than 30 people in China.
If H7N9 acquires the mutations it needs to pass from person to person, the "seed strain" that the St Jude team is racing to produce could be the main line of defence against a flu pandemic that would threaten millions of people.
Just a handful of labs are set up to do this work. Two other labs in the UK and US have recently created initial seed strains. It is vital to give manufacturers a choice of vaccine strains so they can select one that grows well and provokes a strong immune response and then scale it up for full production.
"There's a lot of pressure to get this done," says Richard Webby, the affable head of the WHO Collaborating Center for Studies on the Ecology of Influenza in Animals at St Jude.
Clad in sterile overalls and a hairnet, I peer through two sets of locked doors into the BSL-3 lab as Allay and Tillman get down to work. Soon, they've identified four suitable plaques, each of which will inoculate about 40 fertilised chicken eggs.
The whole process began in April, when Webby's team ordered synthetic DNA to match the RNA genes for haemagglutinin and neuraminidase from one of the first sequences of H7N9 -- taken from a patient in China. These genes code for surface proteins that provoke an immune response. The DNA was added to cell cultures, together with six other components making up the genetic backbone of a vaccine strain known as PR8, which does not itself cause disease.
That was all that was needed to assemble new viral genomes. The viruses have already been grown in one batch of eggs, before two rounds of culturing in chicken embryo kidney cells. By diluting the solution containing the viruses before each round, the team hoped to produce plaques that come from a single virus strain. This means each egg can be injected with as close to a pure strain as possible -- given flu viruses' rapid mutation rates.
Before inoculation, Allay and Tillman's eggs were "candled" -- held up to a light to see the position of the embryo. The shell was marked in the place a tiny hole was to be drilled to get the virus into the allantoic fluid that supplies the embryo with oxygen and where it deposits its waste.
Today's production line involves pulling out a clump of cells from the plaques, and dispersing their cargo of viruses in a culture solution. A hole is drilled in each egg, into which a needle injects the virus. The egg is sealed with paraffin wax.
After growing for three days, the viruses will be harvested from the eggs and delivered to a nearby BSL-3 lab. There Webby's team will test the strain to see if it provokes an acceptable immune response. Early signs are that H7N9 is not good at stimulating immunity -- bad news for vaccine producers. The researchers will also confirm that the vaccine strain can't cause disease in ferrets -- the best animal model for human flu.
Only then can the seed strain be taken out of BSL-3 containment and subjected to rigorous quality control. Two weeks of nail biting will follow, as the team waits to see if any samples put into a nutrient medium show signs of microbial growth.
In 2006, this step disrupted work on vaccine against H7N7 flu at St Jude's, when the test revealed contamination with Streptococcus bacteria, probably from the surfaces of eggs used. This is why I'd earlier seen Tillman spraying the eggs with a biocide that can kill even hardy bacterial spores -- previously eggs had simply been swabbed with alcohol.
When the new vaccine passes quality control, it will be made available to vaccine makers. Commercial production would involve further growth in eggs on a larger scale.
As staff at the St Jude Good Manufacturing Practice facility recount the 2006 incident, their sense of responsibility is clear. The buck stops with Michael Meagher, who heads the facility. "Failure is not an option," he says.