__Update: __On Tuesday, the FDA issued a draft guidance to prevent Zika from spreading through blood transfusions. For areas with active Zika transmission, the FDA recommends using blood from other areas or using this pathogen-reduction technology.
Giving blood is a reminder that human are sacks of microbes, and blood is a very good way to spread the nasty ones. Have you ever used needles to take drugs? the questionnaires probe. Had a tattoo? Lived with a person who has hepatitis? And even if you’ve done none of the above, you could still have some new virus no one ever thought to ask about. Like Zika. Last week, Brazil reported its first cases of Zika transmission via blood transfusion.
But that’s preventable, even the new viruses. The technology to inactivate nearly all pathogens in donated blood exists---and it’s existed for over a decade.
In Europe, blood banks have been using Cerus’s Intercept system for platelets and blood plasma transfusions since the early 2000s. In 2014, the US Food and Drug Administration finally approved the system in the US. And this week, Cerus announced a partnership with the American Red Cross, the single largest supplier of blood products in the US.
In a time of Zika and chikungunya and other once obscure viruses creeping through the Americas, a system that can knock out all pathogens, known or unknown, makes sense. “It is not practical to keep adding a new test every time some emerging disease comes along,” says Jed Gorlin, medical director of Memorial Blood Centers in Minnesota. “We cannot possibly keep up.” The American Red Cross’s battery of current tests, used on all donated blood, includes six viruses, including HIV and hepatitis B and C. Each additional test adds somewhere around several dollars per unit of blood.
The system especially makes sense in places where wide-spread diseases threaten the safety of the blood supply. In Puerto Rico, where the chikungunya virus is prevalent, the Red Cross has already been testing Intercept in the blood supply. And if it's widely implemented in the US, the system would certainly ease the minds of hyper-vigilant blood recipients in mosquito-friendly climates. But the killer app for a system like Intercept may not have to do with viruses but bacteria. It’s all about the money. To understand that, it helps to understand how Intercept works.
Intercept exploits a simple distinction: The useful components of donated blood---platelets, plasma, and red blood cells---do not contain any DNA or RNA. Bacteria, viruses, parasites, and even white blood cells, which are dangerous when transfused into immunosuppressed patients, do. Blood banks add a molecule called amotosalen to bags of platelets or plasma, and the molecule binds to the DNA or RNA when activated with UV light. The amotosalen is like a lock that prevents pathogens from replicating. Any extra amotosalen is then filtered out. The whole process takes just a few minutes.
With a decade-long track record Europe, Intercept certainly works, but blood banks are only going to use it if they can save money by doing so. How much money they save will depend on the FDA, which is in the middle of setting new regulations for bacteria testing in platelets. Because platelets are too delicate to be refrigerated or frozen, they’re stored at room temperature---also the perfect temperature for a bacteria party. According to the CDC, contaminated platelets cause life-threatening illness in 1 in 100,000 transfusion recipients and death in 1 in 500,000. Cerus’s chief medical officer, writing in the journal Blood, recently called bacterial contamination a “silent epidemic.”
Blood banks already take cultures from platelets to look for bacteria, but the screening system clearly doesn't catch every bug. So the FDA may require a second “point of release” culture right before transfusions. That could add another $30 per unit. With a system like Intercept, though, you eliminate all the cumbersome culturing. When the FDA’s enhanced regulations come out later this year, it may become more expensive to screen for the bacteria than to simply kill all of them. Point: Intercept.
It’s worth noting here that Intercept doesn't offer perfect protection either. For example, it can’t get at bacterial spores, whose DNA is surrounded by a thick coating of protective protein. About 5 percent of bacterial contamination in platelets is the result of Bacillus spores, estimates Michael Jacobs, a microbiologist at Case Western Reserve University.
The current system also does not work with red blood cells because of the reliance on UV light. “UV will go through a yellow bag of platelets or plasma. It wouldn’t go through a red bag,” says Gorlin. “You can’t get a sunburn if you’re covered by bags of blood.” (I suppose this is why your organs don’t get sunburned either.) Cerus is currently working on a modified system that uses another molecule, which is pH rather than UV activated. Cerus CEO Obi Greenman says they’re planning to submit an application in Europe later this year. Though it’s anyone’s guess when the FDA will get around to it.
