Testing a new COVID-19 test: How T-cells beat antibodies in helping to detect past infections - GeekWire
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GeekWire’s Todd Bishop tested the new T-Detect COVID test prior to its official launch this week to learn whether he had COVID-19 last year.

On a cold, clear weekday morning last month, my quest to figure out whether I had COVID-19 in the early days of the pandemic took me to my back porch, where a mobile phlebotomist drew blood from my arm. It had been 10 months since I was sick, and I had already received a negative result on a standard antibody test

That earlier test was designed to detect the presence of the antibodies produced by the body’s immune system to ward off the virus that causes COVID-19. The negative result meant I probably didn’t have COVID back in March.

But given the possibility of a false negative in the antibody test, I wasn’t giving up that easily. And this test was different.

This was a first-of-its kind diagnostic tool from Seattle-based Adaptive Biotechnologies, a company that develops technology to sequence the human immune system for the diagnosis and treatment of disease.

T-cells are specialized cells that determine the human immune system’s response to disease. Adaptive says tell-tale signs of T-cell responses to specific diseases can be detected earlier and longer than antibody responses, and with a higher degree of accuracy.

Adaptive Biotechnologies’ new test, called T-Detect COVID, was developed in partnership with Microsoft. It officially launched this week, under Clinical Laboratory Improvement Amendments (CLIA) regulations. The Food and Drug Administration is reviewing the T-Detect COVID test for Emergency Use Authorization (EUA). The test costs $150 plus lab fees.

On this episode of the GeekWire Health Tech Podcast, we’ll learn exactly how this works, and what it could mean for diagnosing and treating a wide range of diseases. And yes, I’ll finally learn, almost definitely, whether I had COVID or not.

Listen above, subscribe to GeekWire Health Tech in any podcast app, and continue reading for edited takeaways from Lance Baldo, Adaptive’s chief medical officer.

What are T-cells, and how do they work as part of the immune system?

Baldo: There are two key parts to your adaptive immune system: B-cells, which primarily produce antibodies; and T-cells, which have three really important functions. One is that they talk to B-cells, and they give them little cues to go ahead and produce more antibodies. Second, if one of your cells gets infected with coronavirus, they kind of hold up their hand and then the T-cell says, yep, that cell has been infected, and they help to basically eradicate that cell. The third thing that they do, and this is really important for the T-Detect test, is they stick around for some period of time — so-called memory T-cells — and those T-cells are there to jump into action, should you ever encounter that pathogen again.

Lance Baldo, Adaptive chief medical officer. (Adaptive Biotechnologies Photo)

What are the implications of this type of test for diagnosing other types of disease?

Baldo: Your body is is the world’s most finely tuned diagnostic, because most of the time, it knows what you’re facing and helps you to actually clear that threat. And so what we’re doing is reading the body’s natural diagnostic, reading the body’s immune system, to let the immune system tell us what you’re facing or what you’re encountering. Whereas the first T-Detect test is T-Detect COVID, for recent or prior infection with novel coronavirus, you can imagine eventually we can build out dozens and eventually hundreds of tests using the same platform to let the T-cells tell us what they’re facing, or what they faced in the past.

How accurate is T-Detect COVID, and how does it compare to antibody tests?

Baldo: The specificity is about 99.8%. So that means we have very, very, very few false positives. And we also have a very high sensitivity. In fact, in the hundreds of patients that we studied in support of our FDA Emergency Use Authorization, we picked up the disease when it was expected to be present 95% of the time. That compares to antibodies, where in the studies that we’ve seen, antibodies were only picking up past disease anywhere from about 75% to 90% of the time.

My T-Detect test came back negative, so does that mean I definitely never had COVID-19?

Baldo: Because of that 99.8% specificity, a positive test is incredibly, incredibly powerful in terms of telling you had it, but the absence of proof is not the proof of absence. It’s still possible you had it, though in your case — not having a PCR test, not having antibodies, and now not having T-cells — the likelihood is that you probably did not have novel coronavirus and you probably had some other virus. There are many viruses that cause similar symptoms.

If someone does test positive in the T-Detect COVID test, does that mean they’re immune?

Baldo: The short answer is, we don’t yet know. This is the million-dollar question, or the Holy Grail. There’s a number of things that protect us from future infection. And we’ve described a few of these: memory B-cells, just like memory T-cells, can kick into action, and then produce antibodies specific for coronavirus. You could still have antibodies that are floating around, getting ready to neutralize the virus. We also talked about T-cells, memory T-cells, for instance, that can hang around and jump into action. And it’s that orchestra of all these different components of the immune system that are going to help you thwart future infection. We call that combination a correlative protection. We’re beginning to invest in the research right now to be able to look and see, do T-cells help to serve as a correlative protection.

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