March 01, 2015
In the event of an impending global flu pandemic, vaccine production could quickly reach its limits, as flu vaccines are still largely produced in embryonated chicken eggs. Udo Reichl, Director at the Max Planck Institute for Dynamics of Complex Technical Systems, and his colleagues have therefore been working on a fully automated method for production in cell cultures that could yield vaccines in large quantities in a crisis.
Text: Tim Schröder
The weapons against influenza include the egg – the plain old chicken egg. The egg is, after all, a biotechnology laboratory in miniature. In 1931, pathologist Ernest W. Goodpasture at Vanderbilt University in Nashville made a momentous discovery. He pricked an incubated egg with a fine needle and infected it with influenza viruses. The viruses reproduced prodigiously in the egg. When Goodpasture drew a bit of liquid out of the egg and examined it a few days later, he found that the number of viruses had skyrocketed. Goodpasture immediately realized that eggs are an ideal host for growing influenza viruses and, since vaccines require viruses, the perfect tool for producing vaccines.
The trick is to carefully inoculate the body with viruses without making it ill. The immune system then learns to recognize the pathogen and is able to mount a defense against it. Medicine uses three basic immunization methods for this. The first is to inject a large number of killed viruses; the second is to inject smaller numbers of attenuated and therefore non-infective viruses; and the third is to inject fragments of the virus shell or individual viral proteins. In any case, all three methods require viruses.
Goodpasture’s method is now 80 years old and has been continuously refined. Nevertheless, the egg remains the method of choice for manufacturing flu vaccines. Ninety-five percent of all flu vaccine doses still contain egg-grown viruses. However, this method is nearing its limits: for a single vaccine dose, one or two eggs have to be embryonated in a temperature-controlled cabinet, and many millions of eggs are needed to produce enough vaccine to supply an entire country.
In the European Union, it has so far been possible to provide a sufficient stockpile of vaccine for the next flu epidemic using this method. “But what happens if an epidemic breaks out in China or India, countries with a combined population of more than two billion? Production couldn’t keep up,” says Udo Reichl, Director of the Department of Bioprocess Engineering at the Max Planck Institute for Dynamics of Complex Technical Systems in Magdeburg.
The biologist and process engineer has been working with his team on developing alternatives to vaccine production in eggs. Like vaccine manufacturers and other research groups around the world, he is pinning his hopes on animal cells cultivated in laboratory vessels and bioreactors. However, it is expensive to replace an established method of pharmaceutical production, and the industry is very reluctant to do so. Udo Reichl is therefore seeking to make the production of vaccines in cell cultures so efficient that companies will see it as a viable alternative.
The cells that come into question for virus production were, for the most part, extracted from various animals and organs many years or even decades ago – from monkeys, hamsters and dogs, for example. Many of these cell lines are immortal, meaning that they can propagate indefinitely. There are also some new cell lines that research institutions and biotech companies have rendered genetically immortal. These, too, would be suitable for use in pharmaceutical production.
Udo Reichl’s team has identified several such cell lines that are particularly suitable for growing viruses. “It’s ironic,” says Reichl. “Other scientists are busy fighting viruses and keeping their numbers as low as possible, while we’re trying to stimulate a cell to produce as many viruses as possible. Our work isn’t anti-, but pro-viral.”
It is both fascinating and frightening how a virus infects a cell and reprograms it to release thousands of copies of itself. An influenza virus resembles a spiked ball. The spikes consist of the proteins hemagglutinin and neuraminidase. At the tip of the hemagglutinin spike is a lock-like structure that enables the virus to bond to the surface of animal or human cells. The fine structure of this site determines whether the structures on the cell surface fit the viral hemagglutinin like lock and key, thus allowing the virus to enter the cell.
If the lock on the virus surface finds a corresponding key on the cell surface, the influenza infection begins to run its fateful course. The membrane of the host cell opens up, and the virus penetrates into the cell and releases its genome inside the nucleus. The viral RNA then reprograms the cell to act as a virus factory. The cell blithely synthesizes viral components, which are then assembled into hundreds or even thousands of new viruses. The assembled viruses bud off from the cell surface, a process that requires the viral protein neuraminidase. For humans and other animals, it is disastrous when the viruses start to replicate so prolifically – that’s when influenza really takes hold. For vaccine production, however, it is ideal.
While influenza viruses are, for the most part, still being produced in eggs, other types of viruses have long been grown in cell cultures. But the aim of vaccine developers in both cases is the same: to produce large quantities of viruses in a short time so as to have sufficient vaccine on hand in the event of an epidemic or global pandemic. Unfortunately, it is pointless to stockpile some vaccines because many viruses – particularly the influenza virus – readily mutate, giving rise to new pathogens against which the available vaccine is useless.
The fight against influenza viruses is thus a race against time. Will scientists be able to identify a new virus variant and adapt the composition of vaccines before the pathogen is able to trigger a flu epidemic? More often than not, pharmaceutical manufacturers and researchers win the race. But all too often, the viruses are quicker. Things then get tricky, because the virus may spread rapidly and trigger a pandemic. In such cases, it would be good to have a fully automated breeding machine for influenza viruses that could be ramped up quickly and churn out the viruses in large quantities – a production line such as Reichl is hoping to develop.