T-cell immune response is still high against Omicron despite its many mutations, study says

A new study from researchers in Hong Kong and Australia is suggesting that T-cells — a less discussed aspect of the body’s immune response — are equipped to tackle Omicron, despite the variant’s many mutations.

When we talk about immune response, we often focus on neutralizing antibodies, but there are other facets of the immune system as well. One of those is T-cells, which can be generated both by vaccination and by previous COVID-19 infection.

Previous studies have suggested that Omicron has a greater ability to evade antibodies, potentially increasing its transmission ability.

But this new research, published Sunday in the journal Viruses, found that Omicron may not be able to evade T-cells as easily, potentially allowing T-cells to help limit severe illness in those with the virus.

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“Despite being a preliminary study, we believe this is positive news,” Matthew Mckay, a professor from the University of Melbourne and co-lead of the research, said in a press release. “Even if Omicron, or some other variant for that matter, can potentially escape antibodies, a robust T cell response can still be expected to offer protection and help to prevent significant illness.”

One of the most concerning aspects of Omicron is its increased number of mutations, particularly in the spike protein, which is how SARS-CoV-2 attaches to our cells to attack the human body.

The spike protein’s importance is why our existing vaccines target it so heavily with the intent of producing antibodies.

The T-cell response to COVID-19 infection has not been researched as closely as antibodies, but T-cells assist in the immune response largely by eliminating cells that are infected with viruses.

In order to investigate this T-cell response, researchers examined more than 1,500 T-cell epitopes of SARS-CoV-2. Epitopes are a part of an antigen that antibodies, T-cells or B-cells can recognize and bind to in order to trigger the processes needed to destroy the virus. By focusing on the epitopes that T-cells have been observed to recognize in COVID-19 patients or vaccinated people, researchers were looking to see if Omicron’s mutations interfered with how well T-cells could bind to those epitopes.

They found that only 20 per cent of T-cell epitopes in vaccinated or previously infected individuals had mutations similar to Omicron, which could open a door for the virus. But this doesn’t mean the 20 per cent with those mutations are going to be able to evade T-cells all of the time, researchers said.

“Among these T cell epitopes that have Omicron mutations, our further analysis revealed that more than half are predicted to still be visible to T cells,” Ahmed Abdul Quadeer, research assistant professor at Hong Kong University of Science and Technology's  Department of Electronic and Computer Engineering and co-lead of the study, said in the release. “This further diminishes the chance that Omicron may escape T cells’ defences.”

Outside of mutations on the spike protein, researchers found that more than 97 per cent of non-spike T-cell epitopes did not have mutations similar to Omicron.

“These results overall, would suggest that broad escape from T cells is very unlikely,” McKay said. “Based on our data, we anticipate that T cell responses elicited by vaccines and boosters, for example, will continue to help protect against Omicron, as observed for other variants.”

Researchers noted in the study that they investigated SARS-CoV-2 epitopes that have been determined in previous experiments, meaning there may be other epitopes they are unaware of.

“Further targeted experiments are required to confirm the robustness of T cell responses against Omicron, and also to test the capacity of specific epitope mutations to confer T cell escape,” the study stated.