Antibodies - a potentially powerful tool for detecting and treating COVID-19?
By Dr Lara Marks, Visiting Research Fellow, Department of Medicine, University of Cambridge and Managing editor of WhatisBiotechnology.org
Publication date: 7 April 2020
One of the most powerful tools we have today for tackling the COVID-19 (SARS-CoV-2) pandemic potentially lies within our bodies in the form of antibodies. These tiny Y-shaped molecules are continuously produced by specific white blood cells (B cells) to identify and help eliminate foreign invaders like viruses, bacteria, fungi, pollen and other particles considered alien by the body. Millions of different types of antibody can be found in the blood of humans and other animals. Each antibody is highly specific, in that they recognise and bind to a particular signature molecule, known as the antigen, found on the surfaces of all biological substances, including pathogens. Once bound to the antigen, the antibody assists in generating further immune responses that eliminates the intruder.
Figure 1: Diagram of antibody binding to an antigen.
The use of antibodies for medical purposes is not new and they have a long history of being applied to fight against disease. Their deployment as tools emerged out of early medical and scientific efforts to understand the nature of immunity to infections, and also to combat infectious diseases. Right from when the Black Death struck in the fourteenth century, perceptive observers noticed that some people who contracted but ultimately survived one episode of infectious disease were immune the next time it resurfaced. Such observations ultimately paved the way for the development of vaccines. This originally involved injecting individuals with a weakened form of an infectious organism to induce immunity. The first such vaccine was against smallpox, which was adopted on a wide scale in the seventeenth century.
Despite the success of the early vaccines, no one quite understood the precise mechanism of immunity. The first evidence only began to surface following the discovery by Emil von Behring and Kitasato Shibasaburo in 1890 that injections of serum from animals that had survived diphtheria and tetanus conferred immunity in animals with no previous exposure to such diseases. Notably, the serum also cured animals with diphtheria and tetanus. Soon after, Paul Ehrlich, a physician with expertise in structural chemistry, identified a substance in blood/serum that appeared to provide immunity against plant toxins. He called the new substance an antibody.
For the greater part of the twentieth century the only source of antibodies were those that could be obtained from serum extracted from the blood of previously immunised animals. This required extensive preparation and purification, which was time-consuming and expensive. The major challenge was that serum contains a plethora of different antibodies, each differing in their binding capacity and specificity. Moreover, batches from individual animals vary over time and their supply is dependent on the lifetime of particular immunised animals. This made standardised production of antibodies impossible, thereby limiting their formal use for medical applications. The situation changed as a result of the work of César Milstein, an Argentinian immunologist, and Georges Köhler, a German biologist, at the Laboratory of Medicine in Cambridge. In 1975 they published a technique to quickly produce endless quantities of identical antibodies to a specific target. These were generated by fusing a myeloma cancer cell with a spleen cell taken from an immunised animal. The new antibodies were called 'monoclonal antibodies' (mAbs) because each one was the product of a genetically identical clone of B cell.
Figure 2: This diagram illustrates the basic protocol developed by Milstein and Köhler for making monoclonal antibodies. It was first published in G. Galfré and C. Milstein, 'Preparation of monoclonal antibodies: Strategies and procedures', Methods in Enzymology, 75 (1981), p.15.
Awarded the Nobel Prize in 1994, Milstein and Köhler’s invention rapidly provided the means to develop simple, cost-effective, fast and accurate diagnostics suitable for the mass screening of infectious diseases. Such tests were built on the back of existing immuno-based diagnostic tests, the first of which was introduced for detecting cases of typhoid back in 1894. The primary means of detection for such tests, also known as serological testing, is the antibody-antigen binding reaction. The key advantage of the immuno-based tests is that they enable the determination of disease directly from a clinical sample, eliminating the need for the time-consuming process of culturing a causative agent. This dramatically reduces the time required for generating a result (1).
Figure 3: Milstein (1927-2002) with Köhler (1946-1995) at the time of their receiving the Nobel Prize in 1984. Photo credit: MRC, Laboratory of Molecular Biology.
There are two types of tests. The first, known as an antigen test, is performed at the time of illness to determine if a person is actively infected with the specific pathogen. It detects the presence or absence of antigens. These are proteins found on the surface of the pathogen that trigger the production of antibodies by the immune system. The second, known as antibody tests, are used to work out the degree to which a person has developed immunity. Such tests detect two different antibodies produced by the immune system. The first, called immunoglobulin M (IgM), is one of the primary types of antibody the body produces early in the course of many infections. The second, called immunoglobulin G (IgG), is an antibody which increases throughout the course of infection, peaks during convalescence, and is a marker of existing immunity.
Figure 4: The mechanism behind antigen and antibody tests.
The creation of mAb technology enabled immuno-diagnostic tests to be produced on an industrial scale that was previously inconceivable due to the previous inability to standardise production. Some of the first tests were developed for the mass screening of hepatitis B, a highly infectious virus which often remains hidden because people can be infected for many years without experiencing noticeable symptoms. Those infected with hepatitis B face the risk of dying prematurely from scarring and cancer of the liver. The virus is spread through contact with infected blood. Mother-to-child at birth is one of the most important points for transmission. But spreading the virus can also occur through sexual contact and the sharing of contaminated needles for intravenous drug use. The first mAb-based tests for hepatitis B were approved in the early 1980s. In addition to offering more effective diagnosis of patients, the new tests provided the means to screen for the virus in blood on an unprecedented scale, which greatly improved the safety of blood banking and transfusions.
Antibody-antigen based tests could well be a ‘game-changer’ for COVID-19. Firstly, they provide a means to determine if a person is actively infected with the virus. Secondly, they can detect whether an individual has been infected in the past. They therefore offer a means to identify those in the population who are actively infected and need to avoid contact with others and seek medical help, as opposed to those who have already gained immunity so can go back to work safely.
Just how valuable such tests are, may be gauged from China where they were rolled out for the rapid detection of cases as the epidemic was gathering momentum. Going forward, such tests will allow us to assess the true extent of the coronavirus pandemic in a specific human population. Meaning, we can detect how fast it is spreading and whether it has been contained. This is difficult to do with other tests, such as those using the polymerase chain reaction (PCR), which only give a positive result when the virus is still present (2). These antibody based tests and the additional information they provide about past infection when the virus is no longer detectable are therefore pivotal to efforts to contain and slow down the spread of the virus.
The information provided by antibody tests is not only important for reviving the economy, but will help us understand the course of immunity to the virus. Presently, we have limited data as to how long immunity may last after a person has been exposed to the virus or whether such immunity would be relevant for protection against similar viruses.
Antibody targeting tests to detect the presence of viral antigen have the advantage that, unlike gene-based tests such as PCR, they do not need complex laboratory facilities to be processed. They are also not reliant on the use of swabs and other reagents, which may be in increasingly short supply. In addition, they produce results in a matter of minutes which can be read easily without any special training. Working in a similar way to pregnancy tests - except that the tests require a drop of blood instead of urine - any viral antigen contained in the sample triggers the appearance of a coloured line. This would make it possible for individuals to undertake the test within their own home without the need to visit a clinic. Both Public Health England and other healthcare bodies across the world are now investigating this possibility with the help of companies. One idea is to have the test distributed by online retailers like Amazon and high street pharmacies.
Despite their promise, rolling out antibodies tests on such a large scale cannot be done quickly. Optimising and validating the antibody tests will take time and cannot be rushed. It relies on access to a gold standard test to ensure you know the correct answer. In addition it needs a number of other tools. Firstly, sera is needed from patients who recovered from COVID-19 infection approximately 28 days before. Secondly, blood is needed from people who donated before the outbreak of the pandemic so that you can check for false positives which are in fact the detection of other coronaviruses in the sample.(3)
Once developed the test will need to undergo careful evaluation which could take months to complete. The process involves checking that the tests can accurately detect an antigen that is unique to COVID-19 and not one associated with other coronaviruses responsible for the common cold and other mild diseases. Most people at one time or another in their lifetime come into contact with such coronaviruses. A test for COVID-19 could thus provide a false positive. Similarly, it is important to ensure that the tests do not give false negative results. This would give individuals a false sense of security to go out into the community with potentially dire consequences.
The major difficulty at present is not constructing a test that works, but one that can be made available to the public at large. For this reason antibody testing is likely to be rolled out first with A&E and intensive care healthcare workers.(4) Once the tests have successfully completed assessment, however, they can be very cheaply and quickly produced on an industrial scale which will enable rapid testing of thousands of people. The next hurdle will be working out how to certify people have had the test and the mechanism to ensure their results are passed on to their doctors.
Antibodies may not only provide useful diagnostic tools for COVID-19. They also offer a potentially important therapeutic avenue in the way of giving an important boost to immunity. This approach is unlike vaccination, which relies on an individual generating an immune response to a component of the pathogen that provides immunity without the infection, which takes time. The foundation for passive antibody therapy originated out of the work of Behring and Ehrlich who rapidly applied the knowledge they acquired from animals to develop a new form of treatment. First provided to diphtheria patients in 1894, the treatment, known as serum therapy, involved giving infected individuals serum taken from animals immunised against the disease. Subsequent therapy used serum from recovered human patients. So successful was serum therapy that it had become the mainstay of treatment for multiple infectious diseases by the 1930s, including pneumonia, whooping cough, measles, poliomyelitis, influenza meningitis, dysentery and chickenpox.
Despite its benefits, almost all patients, however, manifested some type of allergic reaction to serum therapy. These reactions included fever, rashes, joint pains, and sometimes anaphylactic complications. These side effects stemmed from the fact that the serum preparations contained a variety of different components, which the body treated as foreign particles and therefore generated an immune response against them. Not surprisingly, serum therapy fell out of favour following the introduction of sulphonamides in the 1930s and further antibiotics in the 1940s. In part this was because the new antimicrobial drugs were easier to produce and less toxic to patients than serum therapy.
The invention of mAb technology helped to rekindle interest in antibody therapy. Progress was initially slow, however, because the early mAbs were derived in mice and rats. This meant that they were likely to trigger the similar side effects as observed with serum therapy. What was really needed was a method for producing more human-like antibodies, that were less likely to trigger undesirable immune responses in patients. From the mid-1980s new mAb formulations began to emerge, with the help of genetic engineering, which were more acceptable to the human immune system. Such advances dramatically improved the potential of mAbs to be used as drugs. The first mAbs that was approved for human therapy was in 1986. Since then more than 100 mAb based drugs have been licensed in Europe and the US to treat multiple indications and the rate of approvals is rapidly increasing.
Most of the focus until now has been directed towards developing mAbs for treating cancer and autoimmune disorders. While some work has been undertaken on the development of mAbs for the treatment of infectious diseases, only a handful of anti-infective mAb drugs have so far been licensed. The first was approved in 1998 for respiratory syncytial virus in high-risk premature babies, which is linked to infections of the lungs and respiratory tract.
Slow progress in infectious disease mAb therapeutics chiefly stems from the current high reliance on antibiotics, which are cheap to produce and easier to administer to patients. Antibiotics, however, are not suitable for the treatment of COVID-19 because they are anti-bacterial. Vaccines are also a useful tool, but it could take at least 18 months before a vaccine has been developed and gone through testing and regulatory approval to the point where it can be rolled out into the general population. By this point the pandemic will likely have passed its peak and already claimed thousands of lives.
Several antibody-based approaches are already being investigated for combatting COVID-19. One of the most promising is the use of concentrated pathogen-specific antibodies, known as polyclonal hyperimmune globulin, which is prepared from plasma collected from individuals who have recovered from the infection. Such therapy aims to boost a person’s ability to respond to an infection and enhance their ability to recover from an infection. This approach is not new and has been used for decades to treat individuals exposed to rabies and hepatitis B, or poisoned with venom from snake bites. In more recent years this approach has found use, with some success, to treat the victims of two previous coronavirus epidemics, SARS1 in 2003 and the Middle East respiratory syndrome in 2012. Polyclonal hyperimmune globulin was also helped improve the chances of survival for those infected with Ebola in 2013 (5).
Serum from people who had recovered from COVID-19 was tested in China in early February 2020, with seriously ill patients reported to improve within 24 hours. Many experts around the world are now looking to introduce the same type of therapy elsewhere. This includes Takeda, one of Japan’s largest pharmaceutical companies, which has long-established expertise in the production of immunoglobulin for thousands of people with rare and complex diseases.
Polyclonal hyperimmune globulin has the key advantage that it is much quicker to develop than a vaccine or a new drug. Isolating serum or plasma from recovered patients and ensuring it is not contaminated with other dangerous pathogens is a very well-established procedure. Moreover, most hospitals and blood-banking centres already have the equipment to ensure purity. Supply from potential donors also stands to increase over time as more and more individuals contract and recover from COVID-19. Yet, the treatment is not a total panacea. This is because it is most effective when administered shortly after the onset of symptoms. Where it will prove most useful is as a stopgap measure to keep patients out of intensive care units, which is critical to helping hospitals overwhelmed by the increasing flood of cases (6).
Beyond the use of hyperimmune globulin, a number of mAb drugs already approved for other conditions are also being investigated for treating COVID-19. This includes sarilumab, a fully human mAb originally licensed by US and European regulators in 2017 for the treatment of rheumatoid arthritis. The mAb works by blocking IL-6, a protein that plays a key role in chronic inflammation and believed to be critical in driving the overactive inflammatory response in the lungs of patients who are severely or critically ill with COVID-19. Developed by Regeneron Pharmaceuticals and Sanofi, sarilumab is now being tried out in a number of multi-centre, double-blind trials in a number of different countries (6).
In the past mAb drugs were considered to be unsuitable for infectious diseases. This is because they are highly expensive and they need to be administered intravenously. However, mAb therapy for COVID-19 has several advantages over other approaches. Firstly, patients who are severely ill with COVID-19 are already being treated in intensive care units and are receiving intravenous infusions. In this situation it would be comparatively straightforward to give them a mAb drug. Secondly, a number of advances have been made to mAb drugs in recent years which has increased their affinity for their target and their specificity. This has reduced the dose that needs to be given to patients, which provides a means to also reduce the cost.
If mAb drugs can be made to work with COVID-19, we might find this a useful approach to treating other infectious diseases. To date, mAb drugs have attracted little commercial investment. In part this is because infectious diseases are short-lived and therefore have a limited market. This is in contrast to chronic conditions like cancer and autoimmune diseases which require regular treatment and therefore offer greater profit potential. COVID-19 is likely to make both the public and private sector re-examine the development of mAb drugs for infectious diseases, including those that are becoming more prominent as a consequence of increased antibiotic resistance.
With the emergence of the new coronavirus and its wretched disease COVID-19, once again we reach to mAb technology to provide us with urgent therapeutic and diagnostic tools. They are part of the global response to identify and contain the pandemic, while measures to develop vaccines and antiviral medications take their course. Both Kohler and Milstein, two immigrants into UK science, are less well known than James Watson or Francis Crick, but thanks to their pioneering work into immunity and infection, their legacy touches almost every household in the nation and beyond.
Figure 5: Argentinian stamp, dated 2005, celebrating Milstein's Nobel Prize. Conscious of his own difficulties as a scientist in Argentina, throughout his career Milstein devoted himself to assisting science and scientists in less developed countries. In March 2000, he wrote trenchantly, 'Science will only fulfil its promises when the benefits are equally shared by the REALLY poor of the world'.
I would like to thank Stephen Baker for his insightful comments in the preparation of this article and for the support of Gordon Dougan and his team at the Department of Medicine, Cambridge University. Many thanks also go to Stephen Sacks at King’s College London, who greatly helped me strengthen the final draft.
(1) LV Marks, The Lock and Key of Medicine: Monoclonal antibodies and the transformation of healthcare (Yale University Press, 2015).
(2) D Normille, ‘Singapore claims first use of antibody test to track coronavirus infections’, Science Magazine, 27 Feb 2020, https://www.sciencemag.org/news/2020/02/singapore-claims-first-use-antibody-test-track-coronavirus-infections.
(3) J Bell, 'Trouble in testing land', 5 April 2020, https://www.research.ox.ac.uk/Article/2020-04-05-trouble-in-testing-land.
(4)'In the Lab: Rupert Beale and Thomas Jones', London Review of Books, April 2020, https://www.lrb.co.uk/podcasts-and-videos/podcasts/lrb-conversations/in-the-lab.
(5) A Casadevall, L-A Pirofski, ‘The convalescent sera option for containing COVID-19’, The Journal of Clinical Investigation, 2020, https://doi.org/10.1172/JCI138003.
(6) A Maxmen, ‘How blood from coronavirus survivors might save lives’, Nature, 24 March 2020, https://www.nature.com/articles/d41586-020-00895-8
(7) V Rees, ‘Global trial to evaluate Kevzara® (sarilumab) as COVID-19 therapy initiated’, European Pharmaceutical Review, 30 March 2020, https://www.europeanpharmaceuticalreview.com/news/116003/global-trial-to-evaluate-kevzara-sarilumab-as-covid-19-therapy-initiated.