How does the immune system combat coronavirus? Case study brings a vaccine closer

Two of the biggest questions scientists have about the new coronavirus COVID-19 are how to fight it with medication, and how to support the body's own defenses against the virus.

In a case study published Monday, March 16 as a letter in the journal Nature Medicine, researchers finally offer some clues to at least the second question.

By sequencing the immune response of a person with confirmed, mild-to-moderate COVID-19, researchers pinpointed exactly which of the body's own immune cells attack the new coronavirus. If these preliminary results bear out in others with the virus, they could lead to an effective treatment and vaccine.

"This is an incredible step forward in understanding what drives recovery of COVID-19,” Katherine Kedzierska, a co-author on the new study and researcher at the Peter Doherty Institute for Infection and Immunity, said in a statement.

“People can use our methods to understand the immune responses in larger COVID-19 cohorts, and also understand what's lacking in those who have fatal outcomes."

The case study focuses on one person, so the findings cannot be applied to everyone with the infection. But they do offer tantalizing hints as to what happens when the body starts to defend itself against COVID-19.

"This is how we deal with infection whether it is the flu or the seasonal cold virus or COVID-19."

“We have to be careful because the study of one person is very difficult to generalize to a broad population,” Mark Slifka, a microbiologist at Oregon Health and Science University who was not involved in the case study, tells Inverse.

“More studies are needed."

At this stage, these clues to the body's immune response provides a jumping off point for researchers to better predict who might recover from COVID-19, and how fast they'll get better.

Window into recovery

In the new case study, scientists tracked the immune response of a 47-year-old woman who successfully fought off a mild-to-moderate COVID-19 infection. The woman was one of the first coronavirus cases confirmed in Australia. It is thought that she came down with COVID-19 after traveling from Wuhan, China, to Melbourne, Australia.

The otherwise healthy woman's COVID-19 symptoms included lethargy, a sore throat, dry cough, chest pains, trouble breathing, and a fever. She presented to a Melbourne hospital and recovered within two weeks of presentation.

Throughout the woman's illness, researchers observed her symptoms and took blood samples at four different time points during her hospitalization. They then sequenced which immune cells were present in her blood, charting both when they appeared and disappeared.

Their results suggest the immune system launches a similar attack on the new coronavirus as it does on the seasonal flu.

Three days before the woman's symptoms faded, the researchers looked at levels of four types of immune cells that activated to fight COVID-19: antibody-secreting cells, follicular helper T cells, activated CD4+ T cells and CD8+ T cells and immunoglobulin M, and IgG antibodies that bound the COVID-19-causing coronavirus.

"We showed that even though COVID-19 is caused by a new virus, in an otherwise healthy person, a robust immune response across different cell types was associated with clinical recovery, similar to what we see in influenza," Kedzierska said.

“Her immune responses did a great job,” Kedzierska told Bloomberg at the time the case study was published.

Tracking these immune cells, which are often a “tell-tale” sign of recovery during seasonal flu infection, enabled the researchers to predict the patient’s recovery, Oanh Nguyen, a case study co-author and researcher at the Doherty Institute, said in the same statement accompanying the research.

How does COVID-19 compare to other infections?

This immune response resembles how the body responds to other infections, Slifka says.

"We know that people are able to clear this infection and they are mounting strong immune responses — both T cell responses and eventually antibody responses," he says.

"This is how we deal with infection whether it is the flu or the seasonal cold virus or COVID-19."

The researchers on the new study hope to replicate their analysis in other people with COVID-19. Ultimately, they want to understand why certain demographics have trouble fighting COVID-19, while others seem to be protected.

"We hope to now expand our work nationally and internationally to understand why some people die from COVID-19, and build further knowledge to assist in the rapid response of COVID-19 and future emerging viruses," Irani Thevarajan, a co-author on the new case study and researcher at the Doherty Institute, said in a statement.

Abstract: We report the kinetics of immune responses in relation to clinical and virological features of a patient with mild-to-moderate coronavirus disease 2019 (COVID-19) that required hospitalization. Increased antibody-secreting cells (ASCs), follicular helper T cells (T_FH cells), activated CD4⁺ T cells and CD8⁺ T cells and immunoglobulin M (IgM) and IgG antibodies that bound the COVID-19-causing coronavirus SARS-CoV-2 were detected in blood before symptomatic recovery. These immunological changes persisted for at least 7 d following full resolution of symptoms.