Efforts to overcome COVID-19 have focused as much on prevention as on treatment and cure. As well as the emphasis on increased hand washing and social distancing, there have also been huge efforts to develop a vaccine. To celebrate Biomedical Science Day (11 June 2020), we wanted to explore how biomedical science is contributing to this work. We spoke to Tara Hurst, a lecturer in Biomedical Sciences, about the importance of understanding the virus and the road towards finding a vaccine.
Your best frenemy in the fight against coronavirus
The immune system. No doubt you have been hearing a lot about it during the pandemic. It is our friend, protecting us from such dangerous diseases as COVID-19. But did you know it is likely to be to blame when people develop severe symptoms?
We all know that the immune system consists of cells that help to fight infection. They do this by producing antibodies that can coat a pathogen, such as a virus or bacterium, making it an easier target for destruction by other cells called phagocytes. Alternatively, there are the T cells and Natural Killer cells that can seek and kill virally-infected cells directly.
What co-ordinates the actions of these cells? Can they communicate with each other? The answers to these questions are molecules known as cytokines. Cytokines are messengers between cells of the immune system, frequently called interleukins (abbreviated IL). This is because the white blood cells (or leukocytes) contain the cells of the immune system. So cytokines communicate between (inter) leukocytes.
One of these interleukins, IL-6, is responsible for producing inflammation in response to the virus. This is a necessary early warning system to start to deal with the infection and to recruit the other cells needed to fight it. The trouble is IL-6, like many of its fellow interleukins, is too good at its job. And so it is not just a little inflammation but a lot. In some COVID-19 patients, disease progression is due to a so-called cytokine storm in which excess IL-6 and other pro-inflammatory cytokines are produced and trigger additional inflammation and the recruitment of other immune cells and molecules. This tips the balance from immune protection to immune-mediated damage, leading to the serious respiratory problems observed in COVID-19. Thus, the protective immune response can become a bigger problem than the initial viral infection that initiated it.
That said, in the long term, our safe return to a so-called normal life will depend upon making the immune system work for us. We need to potentiate it against SARS-CoV-2 with an effective vaccine and immunise a large enough proportion of the population to keep the virus in check.
An effective vaccine is most likely one that will allow people to develop sustained and neutralising immunity to the virus. Neutralising immunity simply means that our immune systems can prevent the virus from entering our cells and producing copies of itself. This blocks infection at the earliest step. One such vaccine that is entering phase II/III clinical trials at the University of Oxford shows promise to be available for distribution globally within as little as six months. This vaccine uses a carrier virus (called a vector) to transmit the sequence of the SARS-CoV-2 spike protein into the body. The carrier virus will stimulate the immune system but won’t cause an infection in and of itself. Indeed, it is specifically limited by molecular alterations to prevent it from reproducing. But it will make copies of the SARS-CoV-2 spike protein which will then be detected by the immune system and used to stimulate antibody and cytotoxic T cell production. Ultimately, the hope is that neutralising antibodies will be produced that can block infection and thereby prevent the virus from gaining a foothold in the body.
Such a vaccine could allow us to safely develop herd immunity. If the majority of the population has been vaccinated, the virus will struggle to find susceptible hosts and so will not be able to spread as easily through the population. Herd immunity can replace the need for social distancing since, like distancing, it prevents virus spread to susceptible individuals. It can also protect those who cannot be vaccinated and who the COVID-19 pandemic has shown to be most vulnerable to the infection. While herd immunity can be achieved through natural infection, our recent experience clearly shows that it is a potentially dangerous approach and a vaccine is therefore highly sought after.
The number of cases and fatalities is declining and lockdown is being eased. But it is worth being aware that the virus has emerged and now circulates among humans so is unlikely to go away any time soon. Our best hope for managing this situation at the moment continues to be social distancing and other hygiene measures until such a time as the vaccine is in widespread use and/or an effective treatment is identified.
Interested in learning more?
Immunology is one of many topics covered in our Biomedical Sciences degree. If you would like to know more, visit our website or come to an open day.