Immune response finding offers new hope in fight against COVID

Our bodies own natural immune response could offer a new hope in fighting the COVID-19 pandemic and help underpin the success of future vaccines, a team of scientists have said.

In an editorial to the British Medical Journal (BMJ), the researchers, led by Emeritus Professor of Immunology Herb Sewell at the University of Nottingham, highlight that a section of the population appears to have some natural cellular immune responses to the coronavirus, SARS-CoV-2 virus which causes COVID-19 disease.

Currently, most studies focus on antibodies in the fight against SARS-CoV-2 and assume that neutralising antibodies (NAbs), which prevent virus binding to human cell receptors, the essential requirement for successful infection, will prove effective in protecting against the virus – although their ability to prevent clinical infection or reinfection have not yet been proven.

Natural immune responses

However, national surveys of populations badly hit by the Covid-19 pandemic including the UK, Spain and US, have shown that only between five and 15 per cent of people have developed antibodies against the virus. Many people therefore remain susceptible to infection.

Equally worrying are findings that have shown that over a period of four to six months after infection, antibody levels appear to drop off, leading to further concerns that populations will not have enough antibody immunity to fight off COVID-19.

T cells are a type of white blood cell known as a lymphocyte which are produced by the body’s thymus gland and are divided into different types (including T helper and killer cells) which play key roles in the body’s immune system.

Killer T cells have the ability to directly target and kill virus infected cells, as well as cancer cells, while helper T cells also support the work of the body’s B cells, which produce the NAbs effective against SARS-CoV-2, and also help to stimulate the production of more killer T cells.

New T cell findings have shown very high percentages (80 to 100 per cent of participants) T cells which fight SARS-CoV-2 in most of the COVID-19 patients. Surprisingly and encouragingly, significant numbers of these T cells were also found in members of the population who had repeatedly swabbed negative for the virus, as well as in blood stored from before the pandemic. This shows that some people have ‘natural T cell immune responses’ that may help to protect them if they encounter the virus. It is assumed these natural T cell responses arises because of cross reactions to other closely related but much less harmful coronaviruses that circulate in the community, such as some common cold viruses.

Protecting the population

Early phase clinical trials of Covid-19 vaccines, including those being developed by scientists at Oxford University and in China, have revealed the presence of virus neutralising antibodies and anti-viral helper and killer T cells (agents responsible for cellular immune responses), in the vaccinated healthy volunteers, giving new hope that the vaccines will be successful in protecting the population from infection.

As killer T cells can directly kill virus infected cells and other T cells can also help B cells to produce good anti-viral antibodies, there is renewed excitement that we may well get successful vaccines because of the possible head start that may be given to vaccine induced immune responses by the pre-existing “natural T cell” effects.

He added: “If enough of the public were to take up such vaccines, then herd immunity, which effectively protects all of society against the disease, could become possible.”

The BMJ editorial was co-authored by Raymond M Agius, Emeritus Professor of Occupational and Environmental Medicine at the University of Manchester, Marcia Stewart, lay member and emeritus academic at De Montford University and Denise Kendrick, general practitioner and professor of primary care research at the University of Nottingham.

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