Dirty Little Secrets
What does it take to do something great? In 2008, an experiment was conducted in which experienced chess players were shown a game that could be won using a well-known sequence of five moves. But there was also a more dramatic, unconventional way to win the same game, in just three moves. When asked for the quickest way to win the game, experts usually pointed out the familiar five-move plan, missing the optimal three. Only the very best chess players – the grandmasters – saw the three-move win; ordinary experts stuck to what they were familiar with.
It's in our nature to try to resolve problems using what has worked before. But knowing what worked before can blind us to the insight required for major leaps forward. Our greatest scientists are those who, despite their expertise, remain free to think differently. By this measure, Charles Janeway, an immunologist working at Yale University, was indeed one of our greatest scientists. He was also said to be 'one of the most exciting, decent, and thoughtful immunologists on the planet'.
Born in Boston in 1943, Janeway studied chemistry and then medicine at Harvard. His path to medicine was influenced by his father, an eminent Harvard paediatrician and a department head at Boston's Children's Hospital, but Janeway felt that 'surgery was going to condemn [him] to a life of routine procedures' and he switched his focus to basic research. He married when young but in 1970, aged twenty-seven, he split up from his wife Sally, when their child was aged one. As a result, he 'felt lonely for many years', but gained time and freedom for his research. In 1977 he joined the faculty of Yale, where he met his second wife, Kim Bottomly, also a well-known immunologist.
In 1989, Janeway puzzled over what he called the 'dirty little secret' in our understanding of immunity. The problem concerned vaccines and the way in which they were thought to work. The basic principle of vaccination follows the familiar idea that an infection, caused by a virus or bacteria, is dealt with much more efficiently if your immune system has encountered that same virus or bacteria previously. So – the dogma goes – vaccines work by exposing you to a dead or harmless version of a germ. By provoking your immune system to build up defences against it, it prepares you to respond rapidly if you encounter the same germ again. This works because the particular immune cells that are activated by a particular germ multiply and persist in the body for a long time, long after the germ has been eradicated, meaning they are ready for action if they encounter the same germ again. And with this, so it seems, one of humankind's greatest medical triumphs can be explained in just a few lines.
But take one step deeper and it turns out that vaccination has a touch of alchemy about it too. The 'dirty little secret' is that vaccines only work well when so-called 'adjuvants' are added. Adjuvants (from the Latin word adiuvare meaning 'to help') are chemicals, such as aluminium hydroxide, which, as discovered by chance, help vaccines be effective. At one level it seems such a small thing – aluminium hydroxide somehow helps vaccines be effective – but to Janeway this small technical tip revealed a crack in our basic understanding, because no one could actually explain why adjuvants did this. Understanding vaccination is unquestionably important – nothing apart from providing safe water, not even antibiotics, has ever saved more lives – and Janeway was determined to understand precisely why adjuvant was necessary. In doing so, he uncovered a whole new way of thinking about how the human immune system really works.
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The use of vaccination as a medical procedure long pre-dates any scientific knowledge of how the process works. The first descriptions of this vital lifesaver can be found in folklore. Deliberate infections to provide protection – inoculations – were practised in China, India and some African countries, long before any formal medical procedure was established. The scientific story begins, however, in 1721, when an epidemic of smallpox made the British royal family anxious, especially for the safety of their children. The royals had heard of rural traditions and stories from other countries about how to inoculate against the disease, but details varied as to how, exactly, the procedure should be performed. Was an application of blister fluid best? Or were hand-squeezed smallpox scabs preferable? It was widely known that people only ever got smallpox once, and so the real issue was whether or not a small dose of smallpox could be given to someone without it killing them. A test was needed to determine the safety and efficacy of inoculation before it was used on the royal family – and prisoners seemed appropriate for the honour.
The first recorded 'clinical trial' in the history of immunity was performed on 'volunteers' who had been recruited on the basis that they could either participate in the potentially deadly trial or face the certain death of judicial execution. On 9 August 1721, incisions were made on the arms and legs of six convicts. Skin and pus from a smallpox patient was rubbed in. Another prisoner was given a sample of skin and pus up her nose – needless to say, to her great discomfort. Twenty-five members of the scientific elite witnessed the event, including fellows of the Royal Society (which had been granted its Royal Charter in 1662 but still only had vague criteria for membership). In accordance with folk wisdom, each prisoner became ill with symptoms of smallpox for a day or two, and then recovered. The woman inoculated nasally became especially ill, but recovered nonetheless. On 6 September 1721, King George I pardoned the convicted volunteers and they were released. Their immune systems had saved them from two death sentences: the gallows and the pox.
A few months later on 17 April 1722, the Prince and Princess of Wales – who in five years would become King George II and Queen Caroline – had two of their own daughters inoculated. The event was covered by all the newspapers and led to considerable interest in inoculation (a reminder that high-profile leaders or celebrities have enormous influence on public attitudes to new scientific ideas). Even so, the procedure remained controversial, in part because, some claimed, the intervention went against Nature or God – a London preacher spoke in 1722 on 'the dangerous and sinful practice of inoculation' for example – but also because around 2% of people died after being deliberately inoculated with smallpox.
Forty-eight years later, a twenty-one-year-old man named Edward Jenner began three years' training at St George's Hospital, London, under John Hunter, one of the most prominent surgeons and anatomists in England. Hunter helped sharpen Jenner's critical faculties and cultivated his passion for experimentation, but he never got to see how his protégé blossomed. Hunter died in 1793, three years before Jenner discovered a way to circumvent the acute danger of inoculation while achieving the same effect.
As a country physician who spent most of his life in his small hometown of Berkeley, Gloucestershire, Jenner was familiar with the fact that milkmaids never get smallpox. His revelatory idea was that perhaps their exposure to cowpox – a mild viral infection that humans could catch from cows – provided protection against smallpox, and that pus from non-fatal cowpox blisters might therefore be used for inoculation instead of pus from smallpox victims, which was far more dangerous. His now-legendary experiment was performed on 14 May 1796. Jenner took pus from dairymaid Sarah Nelmes, who had been infected with cow pox from one of her cows, Blossom, and inoculated his gardener's eight-year-old son, James Phipps. James was then given pus from a smallpox patient and he didn't get ill.
This experiment is often said to mark the birth of immunology but at the time, Jenner had trouble just publishing his findings. The Royal Society said the observation was merely anecdotal – which it was – and suggested that Jenner should first test many more children before making such bold claims. Jenner did repeat the test on others, including his own eleven-month-old son, but even so, he didn't try to publish with the Royal Society again. Instead, Jenner self-published his work in a large-print seventy-five-page book. Initially available in just two London shops, the book was released on 17 September 1798 and became a huge success. The term 'vaccine' was coined a few years later by a friend of Jenner to describe the process he had discovered, from the Latin word for cow, vacca. Smallpox became the first disease fought on a global scale and was officially eradicated in 1980.
Jenner always believed that his work could lead to a global annihilation of smallpox, but he never had a deep understanding of how vaccination worked. By the time of Janeway's epiphany in 1989, the consensus view was that the presence of a germ in the body triggers an immune reaction because the body is primed to detect molecules that it has not encountered before; in other words, that the immune system works by reacting against molecules that are non-self – not from the body. After exposure to molecules alien to the body, the immune system is poised to react rapidly if the same non-self molecules are encountered again. But an experiment performed by two different scientists working independently in the early 1920s (it's unclear precisely when), didn't fit this simple view of vaccination, and this puzzled Janeway deeply.
The experiment was performed by French biologist Gaston Ramon and London physician Alexander Glenny. They each discovered that a protein molecule made by the bacteria which cause diphtheria – diphtheria toxin – could be inactivated by heat and a small amount of the chemical formalin. Potentially this meant it might be used as a safe vaccine against the disease. To their surprise, however, when the inactivated protein molecule was injected into animals, the immunity it produced was only short-lived. The observation was seen as mildly curious at the time, and largely forgotten, but decades later Janeway reasoned that protein from the bacteria was non-self – not part of the human body – and so, according to the consensus view of the 1980s, there was no explanation for why it would not work well as a vaccine. How come the pus from cowpox blisters worked well as a vaccine, Janeway wondered, whereas protein molecules such as diphtheria toxin, which had been isolated from germs, did not?
Glenny was a workaholic, and though extremely shy and not easy to get on with, he was skilled in organising his research, streamlining procedures so that he and his co-workers could perform huge numbers of experiments with great efficiency. He had no time for proper statistical analysis; results were either 'obvious and useful, or doubtful and valueless'. This attitude – go-getting, fast-moving – was an important factor in his lab's ability to screen an enormous number of experimental conditions, seeking a way to make diphtheria toxin work as a vaccine. Eventually, in 1926, Glenny's team found that when diphtheria protein was purified by a chemical process that involved combining it with aluminium salts, it became an effective vaccine. Glenny's explanation was that the aluminium salts helped the diphtheria toxin stay in the body long enough for an immune reaction to develop, but no one knew of any process which could explain how or why this might be. After Glenny, other substances such as paraffin oil were discovered to help vaccines work in the same way that aluminium salts did, and collectively they became known as adjuvants. But still, there was no obvious common feature that explained why they worked.
In January 1989, Janeway and his wife, fellow immunologist Kim Bottomly, were discussing what happens in the body when you get a cut or an infection. They realised that they could not easily explain how an immune response starts: what exactly was the trigger? As Bottomly recalled, they often argued about scientific matters in their car and later simply forgot what had been said, but this time they were attending a conference in Steamboat Springs, Colorado, so they had their notebooks with them. The debate stuck with Janeway. For the next few months, he mulled over the problem – how does an immune reaction start? – as well as the question of how adjuvants work, and it was by thinking about the two problems together that he had a revelatory idea.
An important clue was that a chemical normally found in the outer coating of bacteria (a large molecule with the cumbersome name of lipopolysaccharide, or LPS) had been shown to be an especially effective adjuvant. What if, Janeway reasoned, the presence of something that has never been in your body before was not the sole indication that an immune reaction should occur? What if there has to be something else – a second signal – that's needed to kick off an immune reaction, a second signal that can be provided by an adjuvant, which might in turn replicate the presence of actual germs? This might explain why protein molecules separated from their originating germ were ineffective as vaccines, but a molecule such as LPS, from the outer coating of bacteria, worked well as an adjuvant.
With great gusto, Janeway first presented his idea in a now-famous paper entitled 'Approaching the asymptote? Evolution and revolution in immunology', published in the proceedings of a prestigious meeting at Cold Spring Harbor, New York, held in June 1989. In it he suggested that everyone seemed to be studying the immune system as if the knowledge was approaching 'some sort of asymptote, where future experiments are obvious, technically difficult to perform, and aim to achieve ever higher degrees of precision rather than revolutionary changes in our understanding'. As a result, they had all missed something big: the 'tremendous gap' in our understanding of how immune reactions start. He suggested that distinguishing between self and non-self was not enough: the immune system has to be able to tell when something is likely to be a threat to the body before an immune reaction takes place, and that therefore the immune system must, he reasoned, be able to detect telltale signs of actual germs or infected cells. He predicted that there had to be a whole part of our immune system, yet to be identified, with this very purpose, and he even predicted a way it could work.
As we have seen and as Janeway pointed out, nobody at this time paid much attention to how an immune reaction started, and most (if not all) researchers focused on understanding another aspect of immunity, related to inoculation and vaccination: namely, how the immune system is able to respond to germs faster and more efficiently a second time around. It was known that at the heart of this process are two types of white blood cells called T cells and B cells. These white blood cells have an especially important receptor molecule at their surface, not so imaginatively called the T cell receptor and the B cell receptor. These receptors come from the class of biological molecules known as proteins, which are long strings of atoms that fold up into elaborate shapes well adapted for a specific task in the body. In general, proteins bind or join with other molecules, including other proteins, to complete their tasks, and the precise shape of a protein dictates which types of other molecules it is able to connect with, in the same way that two jigsaw pieces interlock by having complementary shapes. The receptor on each individual T cell or B cell has a slightly different shape, allowing it to interlock with a different foreign molecule. It reaches out from the immune cell's surface into its surroundings, and if it connects with something that hasn't been in your body before, it 'switches on' the immune cell, which then kills the germ or infected cell directly, or summons other immune cells to help. Crucially, the activated immune cell also multiplies, populating your body with more cells that have the same usefully shaped receptor. Some of these cells stay in the body for a long time, which is what gives the immune system a memory for germs that have been encountered before – which is, of course, at the heart of how vaccination works.
Importantly, receptors on T cells and B cells are not made to bind germs per se; these receptors have randomly shaped ends, which allow them to lock onto all kinds of molecules. The way in which the body ensures they only latch onto germs is one of the greatest wonders of the immune system, and works as follows. Each T cell and B cell acquires its receptor while developing in bone marrow. A shuffling of genes as the cell develops gives each cell a uniquely shaped receptor. But before entering the bloodstream, each individual T cell and B cell is tested in case its receptor is able to bind to healthy cells. If it is, then that particular T cell or B cell is killed off, because it would be dangerous to have such an immune cell in the body. In this way, only T cells and B cells that won't attack healthy cells are allowed to defend the body, and by the same logic, if a receptor on a T cell or B cell does bind to something, that something must be a molecule that hasn't been in your body before. In formal language, this is how the immune system is able to distinguish self, the components of your body, from non-self, anything that's not part of you.