The experimental infusion doctors have given to President Trump seeks to counter a problem affecting many older Covid-19 patients: an ineffective immune response.
Among other treatments, Mr. Trump has taken a drug cocktail from
that hasn’t been approved for broad use but aims to jump-start an immune defense by supplying antibodies to help fight the coronavirus that causes Covid-19. The company says its results suggest the infusion can help people infected with the coronavirus who haven’t yet produced their own antibodies.
The approach makes sense in elderly patients, whose bodies are often less able to fight off pathogens, said Janko Nikolich-Zugich, an immunologist and gerontologist who is a professor at the University of Arizona. “You don’t control the virus as quickly as you should” with older patients, he said.
A growing body of research points to the immune system as a key reason why the elderly are so susceptible to serious cases of Covid-19. As a person ages, the system undergoes “immunosenescence,” gradually losing its ability to mount a response to infection as robustly as it once did. The complicated mechanisms of the immune system don’t work together as well, leading to a slower and less-powerful defense.
In addition to his age, 74, Mr. Trump’s weight also may raise concerns about his immunity, as obesity has been tied to impaired response. And a study published in the journal Nature this August also highlighted the possibility that older men, in particular, might tend to mount a less-robust immune response to the virus.
The President’s Medical Treatment
About 80% of deaths in the U.S. have been among those 65 and older, and about 31% of deaths are among people aged at least 85 years, according to death-certificate data from the Centers for Disease Control and Prevention. This is partly because the elderly are often frailer, and they also have higher rates of conditions such as heart disease and diabetes that are risk factors for severe impact from Covid-19.
But their immune systems are another important factor, researchers say. “When you challenge a body with a virus or a vaccine, there’s just not the vigorous response,” said Cari Levy, a geriatrician who is a professor at the University of Colorado.
Older people often produce fewer, and less-effective, antibodies. These y-shaped proteins are supposed to bind to invading pathogens, neutralizing them and signaling to the body to destroy them.
“It’s slower, it’s unreliable—you probably don’t make as many” antibodies, said Peter Chin-Hong, a professor of medicine at the University of California, San Francisco. The hope is that treatments like Regeneron’s experimental cocktail might help fill that gap early in the infection process, potentially slowing the initial spread of the virus.
Elderly immune systems also often have problems generating the powerful soldiers known as T-cells, which supply a main line of defense against invaders. Production of these cells, from a gland in the chest known as the thymus, drops sharply over the course of a person’s life. They can also lose some of their function.
One recent study suggests that older men have a harder time getting their T-cells into action. New research published this August in Nature looked at 98 patients infected with the coronavirus and found evidence that the immune response varied by gender.
“Especially men of older age were very impaired with respect to T-cell activation,” said Akiko Iwasaki, a professor of immunobiology at Yale University who led the study. Those men who had the least T-cell response tended to have worse Covid-19 outcomes, she said.
There is no treatment currently available that would help with Covid-19 patients’ T-cells, she said. Potentially a future vaccine might do this, but vaccines are often less effective in older patients.
But even as vital parts of an elderly person’s immune system are performing sluggishly, another response can cause trouble by firing up too much. As the body fails to contain the virus quickly, the immune system may produce too many of a type of protein called cytokines. These can damage blood vessels and allow fluid to seep into the lungs.
It isn’t clear why this “cytokine storm” effect is triggered in some patients but not others. But elderly people tend to have a higher level of inflammation, and cytokines, said Amber Mueller, a molecular biologist who is a postdoctoral research fellow at Harvard Medical School.
This greater baseline level of inflammation is one reason the soldier T-cells are less effective, and it sets the stage for the dangerous overproduction of cytokines, she said.
President Trump remained hospitalized early Monday, after doctors offered conflicting signals about how he is faring with Covid-19. The president sought to project confidence and vigor over the weekend.
—Jon Kamp contributed to this article.
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