Will T-cells or antibodies beat Covid-19?

You could have both, but Harry de Quetteville investigates which is proving more effective in the race against coronavirus

In late March, Mark Lamb, a businessman from north London, and his wife Emma, began to feel unwell. She had pain in her kidneys and heart palpitations. He had “classic chest compression, shards of glass in the lungs”.

Their symptoms were so clearcut that a doctor friend diagnosed them with Covid-19 and told them to wear oxygen monitors on the tip of a finger. There were, Lamb recalls, scary moments, even for a fit man in his mid-50s: “I was getting worse and worse, going to sleep, then waking up at 2am with massive shortness of breath. We heard about day eight or nine being critical. I wondered, which path would I go down?”

Fortunately, Lamb, who might have been infected when he attended the now notorious Champions League match between Liverpool and Atletico Madrid on March 11, slowly recovered. Then, at the beginning of this month, he paid £180 for a private Covid-19 test manufactured by the American company Abbott which was, like another test made by Roche, approved by Public Health England.

Used by the Government on key workers, such tests detect antibodies specific to Covid-19, generated by the body’s immune system. Clinics boast of 99 per cent or 100 per cent accuracy, and the results are doubly critical – first, offering peace of mind to those who suspect they may have had the disease, and secondly, extending the tantalising prospect of immunity from future infection.

“The blood test is for IGG antibodies to the virus and therefore, tests for immunity to this virus,” says the website for Samedaydoctor, which charges £190. “Having

IGG antibodies can mean that you are potentially immune to future illness,” notes the Harley Street Health Centre, which charges £165, though it does add the caveat that “we don’t really know yet”.

Yet to Lamb’s astonishment, his test came back negative, suggesting that he had never had the disease. “And yet I know

I had it,” he says.

It turns out, however, that test efficacy is not always what it seems. Both Abbott and Roche tests allegedly miss positives.

PHE’S own data shows that from 93 confirmed Covid samples, Roche found 78, missing 16 per cent, while Abbott scored 90 from 94, missing 4 per cent. “They certainly cannot be described as 100 per cent accurate,” noted Jon Deeks, professor of biostatistics and head of the Test Evaluation Research Group at the University of Birmingham.

Assuming Lamb had indeed had Covid, there is also another possibility to explain his result – but it is one flagged by few of the clinics offering expensive private tests. Samedaydoctor is an exception: “Please note that some people do not develop antibodies even after proven infection with Covid-19.”

“[Most clinics] don’t make that clear,” says Lamb. “They are continuing to sell these tests, because they’re making money. And they shouldn’t be doing it, because it doesn’t prove anything.”

Some experts agree. Prof Karol Sikora, the well-known oncologist, suggests “many people will be disappointed” by antibody tests that cost several hundred pounds because of this question mark over antibody production even in Covid-positive patients. “For an individual, [testing] is not worth doing,” he says.

But if recovered patients do not always develop antibodies specific to today’s virus, it raises another question: how are they fighting off the disease it causes?

The most likely other candidate leading the body’s fight back against the virus is the T-cell. T-cells are part two of a three-phase response to infection. If you are unlucky enough to encounter the virus, it begins to bind to receptors in the mucus membranes at the back of your nose and throat. At that point, with the detection of a foreign protein in the body, the first immune phase kicks in.

So-called “non-specific” immune cells, which respond to any invader instantly, set about tackling it. If they cannot, backup is summoned: T-cells. The involvement of T-cells in the body’s response to Covid-19 was not clear until a pair of recent studies, one German and one American, confirmed their presence in recovering patients.

They take two forms: “helper”

T-cells and

“killer”

T-cells. The latter attack the virus directly and, says Sikora, “usually gobble it up”.

“If they don’t,” he adds, “the virus gets into the blood system.” It is then that the third line of defence (which “helper” T-cells play a part in activating) kicks in. “It is called the ‘B-cell system’,” says Sikora “and it is this which makes antibodies.”

He says it is entirely possible that the initial two layers of the immune response deal in some cases with the Sars-cov-2 virus without the production of antibodies, leading to useless tests and disappointed customers.

One of the “disappointed”, in fact, is Sikora himself. Because, he says, he was convinced until only recently that antibody tests would be critical to social and economic recovery from Covid – effectively splitting the population into three groups: the susceptible; the infected; and the recovered, with the third group part of an immuno-elite protected from reinfection by their antibodies and able to live and work normally.

Today, now that scientists are not sure if antibodies confer immunity, or even if they are always produced in Covid patients at all, such dreams have faded. “I believed we would have a nice simple test to get the workforce back…”

In the meantime, however, other hope has arisen, based on those T-cells. A fascinating new study from Singapore (which remains to be peer-reviewed) suggests, like the German and US studies, that T-cells play an important part in the immune response of patients with Covid-19.

But, critically, it goes on to look at patients infected with Sars-cov-1 – the strikingly similar coronavirus to that of today which emerged in 2002-3, causing the disease Sars. Two findings emerge: first, the T-cells generated back then are still active 17 years on. And secondly, those old T-cells offer protection against the new coronavirus.

Even more extraordinary, the study looks at another group who hadn’t been exposed to the Sars virus back in 2003 and found that half of them also had T-cells which were, in the jargon, “cross-reactive” to the virus of today, attacking it.

The researchers described the finding as “remarkable”, and theorised that coronaviruses which we don’t yet know about have been knocking about blamelessly, generating a T-cell response in many of us which turns out to be a powerful weapon against Sars-cov-2.

How powerful? That is not clear. The WHO’S Michael Ryan said recently that “there is certainly some evidence, with regard to T-cells, that if you have had a previous coronavirus infection you may be able to mount a more rapid response to Covid-19.

“But there’s no empirical evidence that previous coronavirus infections protect you from infection with Covid-19. The jury is still very much out.”

That means testing to see if you might have T-cell protection is not imminent. But it is theoretically possible – HIV patients have long tested T-cell counts to quantify the strength of their immune systems, and cells can be cultured in labs to see which specific antigens prompt them to grow and attack.

What is clear today, however, is the centrality of the T-cell response.

“One take-home message,” noted François Balloux, the director of the Genetics Institute at the University College of London, “is that infection with coronaviruses induces strong and long-lasting T-cell (cross-) immunity.

“T-cell immunity is probably far more important for our immune response to Sars-cov-2 infection than antibodies.”

‘There is some evidence that a previous infection may help mount a more rapid response’