Immune cell responses in COVID-19 patients far from optimal
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Melbourne researchers have discovered that killer T cells, key immune cells in fighting viral infections, are present at much lower levels in people with COVID-19, compared to influenza or glandular fever.

Publishing their findings today in PNAS, the team looked at 22 COVID-19 samples from patients who experienced asymptomatic, mild or moderate illness.

Researchers said their research concentrated on CD8 T cells (killer T cells), which are integral to mounting an effective and rapid recovery from viruses such as influenza.

The team looked at T cells in people who express a protein called human antigen leucocyte (HLA) serotype HLA-A2. HLA proteins are important for T cell recognition and vary across individuals.

They found that key immune cells weren't stimulated optimally for rapid proliferation and expansion to fight SAR-CoV-2.

The magnitude of the killer T cells was only five times higher than those of the naïve immune cells. To give that perspective, it's 10 times lower than what we see during an influenza or glandular fever response.

In addition to magnitude, the team also looked at the activation profile of these immune cells and found that not only was activation poor, but in some cases these cells remained largely naïve, as if they hadn't been exposed to the virus at all.

"Knowing the specific T cells and proteins to target will inform the design of an effective vaccine," researchers said. "This research shows that potentially, if a vaccine was able to prime the immune system of killer T cells and then boost them a short time later, the immune response is likely to be much more robust to fight SARS-CoV2."

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