That Sciencemag blog you linked on the Brazilian regulators choosing to reject the Sputnik vaccine was fascinating.
OK, now we need to talk about how you make big piles of virus if you’ve kept them from replicating. That’s an interesting question that has a slick solution: you’re going to be using human cells (often the HEK293 line) to expand your virus production, and what you do is engineer those human cells so that they make the missing E1 protein that the virus needs to replicate. So as long as you’re growing up virus in these engineered cells, you’ll make more, but if they infect normal human cells that haven’t been jiggered to make a key viral protein (as in when you inject them as a vaccine) they’ll stall out on replication immediately. Problem solved!
Mostly. There are still places where this can go wrong. Double-stranded DNA breaks, which can happen more or less randomly, are generally repaired by processes called “homologous recombination” and “nonhomologous end joining”, and these can lead to mix-and-match behavior between DNA from different sources. This process can be deliberately harnessed for gene editing – that’s what the classic CRISPR enzyme Cas9 does – but it can also be a source of trouble in a system like this one. There is a chance that the occasional viral particle might be able to regain the DNA sequence for the E1 protein by picking it up from the human-cell background. If that goes right (well, wrong), then that will turn it back into a replicating virus, and that’s just what it will do in your cell culture tanks.
According to the rest of the article, there are existing engineering solutions to make these types of undesirable recombinations less likely and to screen for them after the viral particles are produced. But somehow the producers still let the replicating virus slip through. Sounds like sloppy work to me.
That Sciencemag blog you linked on the Brazilian regulators choosing to reject the Sputnik vaccine was fascinating.
According to the rest of the article, there are existing engineering solutions to make these types of undesirable recombinations less likely and to screen for them after the viral particles are produced. But somehow the producers still let the replicating virus slip through. Sounds like sloppy work to me.