Some uninfected, unexposed patients may be resistant to COVID-19

Even more surprising is the fact that this was also seen in blood samples taken years before the coronavirus pandemic even began, meaning some people have pre-existing resistance against the virus.

A healthy human T cell. (photo credit: Wikimedia Commons)
A healthy human T cell.
(photo credit: Wikimedia Commons)
An enigmatic type of white blood cell could be the key to acquiring immunity to the novel coronavirus, the BBC has reported.
While widespread research efforts have focused on studying antibodies in recovered COVID-19 patients in order to find a potential treatment for the ongoing pandemic, many of these efforts have been stonewalled by how quickly they can be lost.
However, some researchers have found out that a certain form of white blood cell could be the key to fighting the virus.
Known as a T cell, it's a specific type of immune cell that essentially finds and kills infected cells and pathogens. These cells are also highly specific, able to identify specific targets. Essentially, these cells form a core part of the "long-term memory" of the immune system, the BBC reported.
It is not surprising that recovered COVID-19 patients have T cells that target the virus, with multiple studies highlighting this. What is surprising, however, is that there are people who do not possess COVID-19 antibodies but do possess T cells that target the virus.
Even more surprising is the fact that this was also seen in blood samples taken years before the coronavirus pandemic even began, meaning some people have pre-existing resistance against the virus. In fact, according to one study published in the academic journal Cell in May, these T cell responses were found in 40%-60% of unexposed individuals.
It is unclear why exactly this is, but many suspect that it has to do with exposure to other, milder coronaviruses, such as the common cold – although there has yet to be any verification that there are T cells against the various coronaviruses that could cause the common cold.
This is especially important for vaccine development, as showing how the immune system reacts and functions can help direct the development of effective vaccines and treatments. Indeed, the vaccine candidate being developed by AstraZeneca and Oxford University works by specifically encouraging the production of both antibodies and T cells.
“Looking at COVID-19 patients – but also I’m happy to say, looking at individuals who have been infected but did not need hospitalization – it’s absolutely clear that there are T cell responses,” Adrian Hayday, a King's College London immunology professor and Francis Crick Institute group leader, told the BBC. “And almost certainly this is very good news for those who are interested in vaccines, because clearly we’re capable of making antibodies and making T cells that see the virus. That’s all good.”
Studies showed that patients who recovered from the original SARS virus in 2002 still had T cells for the virus years after recovery, showing that T cell responses last much longer than antibodies. In addition, the fact that T cells can become less active in old age could explain why the elderly are much more vulnerable to the virus.
However, there is also a downside to this discovery, as many hospitalized COVID-19 patients have not had a proper T cell response to the virus.
“Vast numbers of T cells are being affected,” Hayday explained. “And what is happening to them is a bit like a wedding party or a stag night gone wrong – I mean massive amounts of activity and proliferation, but the cells are also just disappearing from the blood.”
His team reasons that this is because the cells are actually dying.

“Autopsies of COVID-19 patients are beginning to reveal what we call necrosis, which is a sort of rotting,” he told the BBC, specifying areas where the T cells can normally be found, such as lymph glands and the spleen.
This is especially worrying, because, as Hayday explained, spleen necrosis is a hallmark of diseases that target T cells, specifically, like HIV and AIDS.
It's not entirely the same – HIV targets and infects the T cells directly, which COVID-19 does not seem able to do – but it does further add to the overall confusion many experts have regarding the virus.
“There are potentially many explanations for this, but to my knowledge, nobody has one yet,” Hayday told the BBC. “We have no idea what is happening. There’s every evidence that the T cells can protect you, probably for many years. But when people get ill, the rug seems to be being pulled from under them in their attempts to set up that protective defense mechanism.”