T-cells: A fork in the COVID-19 road?

Updated at 2.10 pm 4 January 2022 to include the results of new research.

Vaccination remains one of the best defences we have in the fight against COVID-19, but the efficacy of current vaccines against emerging strains is an ongoing concern.
 
Present vaccines work primarily by stimulating the production of neutralising antibodies by B cells against the SARS-CoV-2 spike protein. The nature of this humoral response is such that vaccine-induced immunity to COVID-19 tends to wane overtime.
 
In a recent UK-based pre-print study, Pfizer’s efficacy against the Delta variant declined to 90% after 30 days, 85% after 60 days and 78% after 90 days. AstraZeneca’s efficacy began at 69% two weeks after the second dose, falling to 61% after 90 days.
 
Another problem is that the SARS-CoV-2 virus can mutate quickly, with new strains often picking up mutations in the spike protein.
 
The newest variant of concern, Omicron, has already proven its ability to evade neutralising antibodies. In an Australian-based pre-print study, researchers observed a 17–22 fold reduction in the in-vitro antibody neutralisation titres to Omicron.
 
Now new research is turning its focus toward T-cells. 
 
In a bid to answer how important T-cells are in the fight against COVID-19, researchers from Peking University China used a mathematical model to analyse clinical data from hundreds of patients infected with COVID-19.
 
Simulations by the team show that a lack of T-cells result in more significant inflammation, leading them to conclude that T cells likely play a critical role in clearing the COVID-19 virus and in controlling disease.
 
This supports what is already known, namely that T-cells are a key part of any viral-induced immune response. They help eliminate virus-infected cells and assist with B-cell activation.

And while the vaccine-induced antibody (humoral) response appears less effective against Omicron compared with previous variants, the T-cell response remains robust.
 
Researchers in South Africa recently looked at Pfizer’s ability to stimulate T cells against Omicron. In samples taken from participants who were double-vaccinated, they found that their T cell response remained 70–80% effective despite Omicron’s ability to evade other defences.
 
This is consistent with findings from another recent study led by researchers in Hong Kong and Australia, which analysed more than 1500 viral proteins called epitopes that are recognised by T-cells. The study found that only 20% of viral epitopes from the spike protein that are targeted by T-cells showed mutations associated with Omicron.
 
The team’s findings suggest Omicron is unlikely to be able to evade the T-cell response, adding to the growing body of evidence that T cells play an important role in the fight against COVID-19.
 
‘These results overall would suggest that broad escape from T-cells is very unlikely,’ co-lead researcher Professor Matthew 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’.
 
Across the globe, researchers in the US are also looking more closely at the T-cell response to COVID-19, potentially paving the way for new T cell-based vaccines. They found that certain T cells could target specific coronavirus proteins which are highly conserved due to their critical role in the virus’ life cycle.
 
New-generation T-cell vaccines taking advantage of this could potentially induce even longer-term immunity against COVID-19, as well as a broader range of coronaviruses.
 
Although the future remains unclear, what is clear is that this new research offers a glimmer of hope as Australians continue to grapple with an Omicron surge that has led to record COVID case numbers across the country.
 
Log in below to join the conversation.

COVID-19 Omicron T cells vaccination