Do you remember getting last year's flu shot? What about your childhood measles vaccination, your birthday party-ruining bout of chicken pox, or the last time you were bed-bound by some nasty, unknown virus? Even if you can't recall them all, a newly developed blood test will.

Using just a single drop of blood, a single swoop of the VirScan test will do what would otherwise take hundreds of expensive, time-consuming examinations: It can chronicle your past (and current) battles with any of thousands of different virus strains.

"Instead of testing for viruses one at a time, we're able to perform a full-viral scan."

A team of scientists from eight research institutes (including Harvard and the Max Planck Institute in Germany) have just devised the new test, made possible by advancements in robotics and DNA sequencing technologies. As they explain today in the journal Science, VirScan can offer an unmatched window into your personal viral history. Not only that, but by comparing VirScan results across wide swaths of the population, the technology may also "give us deeper insights into the human immune response, with prospects for designing new therapeutics and vaccines," says Timothy Lu, a biological engineer at MIT who was not involved in the research.

Ben Larman, a biomedical scientist at Johns Hopkins University with who helped design the test, says that "for the first time, instead of testing for viruses one at a time, we're able to perform an inexpensive, full-viral scan. And the viruses we detect are found with very high specificity and sensitivity."

Fishing For Viruses

At its core, Larman says, VirScan works by using "donors' antibodies like a fishing lure, [which is] cast into a pond of all known human viruses." The machine-automated VirScan starts its scan by mixing a small drop of blood with a library of roughly 100,000 harmless viruses—those that attack only bacteria. Each of these viruses has been disguised as a human-attacking virus, such as HIV or the flu—the researchers genetically engineer them to wear one of roughly 100,000 viral masks. These masks are chains of simple molecules, called peptides, which attach to the outer shell of a virus. That's what our own immune system's antibodies use to ID viral invaders.

Once they enter the "library," the antibodies in your drop of blood grapple with any viruses that are wearing masks they recognize. At this point, VirScan immobilizes the blood sample, and washes away any unrecognized viruses that hadn't been attacked by your antibodies. From there, VirScan rips out the DNA from each grappled virus and reads it via DNA sequencing—thus learning which masks set off an immune response. Finally, the scientists put that mask data through a computer algorithm to garner its snapshot of your viral history.

"The power of this technology stems from the scope of the immune profiling that can be done."

According to Larman, this process is robotized using liquid handling robotics. That dramatically lowers the cost of the test—the scientists say it could be performed for only $25 and in just a few days.

Not Every Virus

Larman readily admits that VirScan, as the first incarnation of a brand new technology, isn't perfect yet. While it can catalog thousands of different virus strains, from HIV to Herpes to Hepatitis C, it won't catch them all. That's because while the fishing-lure method excels in finding large viruses, such as the common Epstein-Barr virus, the test has a tendency to let very small viruses (such as Norovirus) slip by. To oversimplify the problem, this is because the smaller viruses are decked out with fewer viral masks.

One other challenge: VirScan can conflate two viral infections you've suffered in your life if the viruses are related. For example, two closely related strains of flu could appear to the test to be the same. And if a viral infection happened long ago (multiple decades), your immune system has essentially forgotten to be on the lookout (it no longer recognizes the correct mask), so VirScan will miss that.

Future research should be able to fix some of those problems, says Lu at MIT. And even with a less-than-perfect profile of viral history, he says, "I think the power of this technology stems from the scale and scope of the immune profiling that can be done." For example, Larman says, scientists already could use VirScan data to investigate questions like how the human virome—that is, the collection of all the viruses in the human body—affects our susceptibility to future viral infections or other diseases, such as cancer.

"It's a new tool unlike anything else," he says.

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