Prior Exposure To 'Harmless' Common Cold Coronaviruses Might Make People Immune To SARS-CoV-2: Study

Prior exposure to common cold viruses could make some healthy people immune to the SARS-CoV-2, the virus that causes COVID-19, a new study shows.

Researchers at the Charite-Universitatsmedizin Berlin and the Max Plank Institute for Molecular Genetics found that some healthy individuals’ immune systems can recognize the novel coronavirus. They said that prior infections with common cold coronaviruses might be offering this immunity against SARS-CoV-2.

But it is still unclear as to whether this cross-reactivity will have any protective effects on the clinical course in COVID-19 patients.

While some individuals suffer from severe symptoms following infection with the novel coronavirus, others hardly show any signs of it. This could be due to various factors, but one potentially crucial factor has now been identified by the researchers - prior exposure to harmless common cold coronaviruses.

They identified this factor based on research involving T-helper cells – a type of specialized white blood cells that are key to the regulation of our immune response.

The research team found that one in three individuals without any prior exposure to SARS-CoV-2 has T-helper cells that are capable of recognizing the virus. This could be because the novel coronavirus shares certain structural similarities with coronaviruses which causes the common cold.

The researchers isolated immune cells from the blood of 18 COVID-19 patients. They also isolated the immune cells from the blood samples collected from 68 healthy individuals who had never been exposed to SARS-CoV-2.

They then stimulated these immune cells using small, synthetic fragments of the novel coronavirus’ spike proteins – which enable the attachment to the host cells.

The researchers also tested if the T-helper cells would be activated upon exposure to the new virus’ protein fragments.

In a vast majority (15 out of 18) of COVID-19 patients, the immune cells get activated by contact with the protein fragments. Since T-helper cells cannot be activated outside the human body during an illness, some patients’ samples might not have revealed the cell activation.

But surprisingly, the researchers found memory T-helper cells capable of recognizing fragments of the novel coronavirus in the blood samples of healthy individuals.

• In 35% of healthy individuals, the immune cells could recognize the novel coronavirus
• Immune cells of COVID-19 patients reacted to different fragments of the viral envelope than those of the healthy individuals
• While T-helper cells of COVID-19 patients recognized the spike protein in its full length, those of the healthy individuals were primarily activated by smaller portions of the spike proteins which showed similarity to those found in spike proteins of common cold-causing coronaviruses.

"This suggests that the T-helper cells of healthy individuals react to SARS-CoV-2 because of previous exposure to the endemic 'common cold' coronaviruses. One of the characteristics of T-helper cells is that they are not only activated by a pathogen with an 'exact fit', but also by pathogens with 'sufficient similarity'," said the study author Dr. Giesecke-Thiel.

The study was published in the journal Nature.