Vaccine Research: Then and Now
If life expectancy has greatly increased in the past century, this is largely due to vaccines, which, according to the WHO, save 6 million people from death each year. This terrific success, unfortunately, has led many to forget about the devastating consequences of viruses such measles, polio, and smallpox, to the point of embracing some, mostly irrational, anti-vaccine campaigns.
Nevertheless, many in the research and medical communities have hopes of one day seeing the application of effective vaccines against the modern viral plagues of HIV, dengue, chikungunya, and others. Unfortunately, efforts to develop a vaccine against HIV are hampered by the high mutation rate of the virus, which rapidly develops new resistant strains. The development of vaccines against dengue are complicated by the existence of four dengue serotypes, and by the fact that immunity against one serotype has the paradoxical effect of enhancing infection by the others, by preventing the development of a specific neutralizing response, and also helping the antibody-bound virus to infect more cells. Often times, a vaccine against other emerging viruses cannot be developed in time or generates little interest from investors.
Despite these difficulties, the history of vaccines is a successful one, and it perhaps goes back further than most people might realize. In the first studies of infectious disease, humanity was the laboratory, and the sick were the test tubes. By observation, trials, and errors, civilizations would gradually learn how best to protect themselves from the disease. There is perhaps no better example of this than the history of smallpox.
Small Pox and the first vaccine
Smallpox (caused by the variola virus) was a devastating disease that plagued humanity from ancient times until its eventual eradication in 1980. During the 17th century, smallpox was infecting 95% of people in Europe and killing up to three in ten. The disease was distinctive because it would leave permanent, recognizable marks and often caused blindness. This made it obvious that, once infected, survivors were safe from re-infection. Indeed, as early as 430 BC, the Greek historian Thucydides observed that the survivors of a small-pox epidemic in Athens were safe from subsequent disease.
This obvious immunity to re-infection led the ancient Chinese to develop a primitive form of vaccination against smallpox that involved inhaling dried, powdered pox scab through the nose. This practice became known as variolation and spread from China across Asia to Persia and Turkey, where it was used for many centuries.
In 1717, variolation was introduced to Britain by Lady Mary Montagu. Lady Montagu was an aristocrat and wife of the ambassador to Turkey. It was when in Turkey that Lady Montagu came across the practice known as ingrafting, where small-pox scabs were inserted in a needle scratch in the skin. When recalled from Turkey, Lady Montagu persuaded leading members of the Royal College of Physicians to support variolation. After initial promising results in small-scale trials, variolation was more broadly applied and was successful at protecting many against smallpox. However, it soon became apparent that variolation was unsafe, with estimates that it was killing as many as one in every eight people treated. The difficulty for the variolation practitioners was selecting an appropriate dose. Variolation using too little virus was insufficient to produce future immunity, whereas introducing too much virus overwhelmed the immune system, producing the full-blown disease.
Almost 80 years after Lady Montagu’s initial reports about variolation in Turkey, Edward Jenner developed the much safer technique of vaccination. The peasants of Jenner’s parish described how milkmaids that had been infected with cowpox (a non-fatal disease producing pustules on the hands and forearms) were protected from smallpox. This led Jenner to his famous experiment, in which he extracted pus from cowpox lesions on a milkmaid’s hand and introduced that fluid into a cut he had made on the arm of a young boy. Jenner supposed that this would provide immunity against smallpox and, after six weeks, tested this by exposing the boy to the deadly disease. Fortunately, the boy did not develop the infection, either then or on 20 subsequent exposures. Jenner had shown that cowpox protects humans from smallpox infection, thus kindling the fields of immunology and vaccine therapy. In fact, in recognition of Janners work and the importance of cowpox to the science virology, the term vaccine is derived from the Latin vaccinus “from cows”.
Pasteur and rabies
Later, Louis Pasteur would unintentionally immunize chickens against the bacterium cholera. Pasteur had isolated and could culture cholera in chicken broth, and used this to infect chickens that would die from the disease. In the summer of 1880, Pasteur observed than an old cholera culture (that had been exposed to oxygen for several days) had lost its virulence; the infected chickens showed only mild signs of the disease and survived. The breakthrough came when Pasteur re-infected these chickens using a fresh batch of cholera culture. This fresh batch was expected to be more potent but, upon inoculation, the chickens did not become ill. Pasteur realized that he had unintentionally repeated Jenner’s principle of vaccination.
Pasteur later turned his attention to rabies. Unlike cholera, which is caused by a bacterium, rabies is caused by a virus. This prevented Pasteur from being able to cultivate the causative agent of rabies in vitro (in the lab). Instead, Pasteur used rabbits to cultivate the causative agent of rabies. By repeated passage of the rabies virus through rabbits, the virus would become more adapted to this host (and, thus, less dangerous to man); the virus became “attenuated”.
Then, by drying the spinal cord of the rabies-infected rabbits, Pasteur was able to produce a vaccine. Together with Pierre Roux, rabies vaccines produced in this way were successfully used to immunize 50 dogs against rabies.
In 1885, Pasteur was presented with a 9-year-old boy, Joseph Meister, that had been badly mauled by a rabid dog. Aware that the disease is fatal in 100% of cases, Pasteur agreed to treat the boy, giving twelve doses of his vaccine in increasing quantity. The boy survived, showing no symptoms of the disease. Pasteur was not a physician and might have been prosecuted had his vaccine failed; he had risked his career to save Joseph’s life.
Joseph Meister would forever remain loyal to Pasteur, and as an adult became the gatekeeper at the Pasteur Institute in Paris. Tragically, in June 1940, when the invading Nazi Germans demanded access to Pasteur’s tomb, Joseph Meister took his own life, rather than surrender the tomb’s keys.
Vaccines Today
Jenner’s initial experiments were carried out in a pre-germ theory era that lacked much knowledge (or even awareness) of the difference between bacterial and viral agents. Nevertheless, their achievements were remarkable, and their legacy continues today.
Relying on the killed-deactivated or live-attenuated virus inoculation approaches pioneered by Jenner and Pasteur, vaccines have changed the course of human history, eradicating smallpox and almost eliminating many other deadly diseases, including diphtheria, tetanus, poliomyelitis, measles, mumps, and rubella.
In an attempt to fully realize the ambitions of the vaccine pioneers and early immunologists, researchers are continually developing novel approaches and technological advances. For example, recombinant DNA technology now enables entire viral genomes or individual viral proteins to be cloned into DNA vectors, allowing safer manipulation of genes and bypassing the need for handling the infectious virus. The advent of recombinant technology has improved the quantity and purity of antigen produced, vaccine safety, and the efficacy of production, as well as minimizing potential side effects. Also, a deeper knowledge of the immune response to infection allows scientists to develop more effective and long-lasting vaccines. And to overcome the viral high mutation rates, annual influenza vaccines are now prepared seasonally.
At Virology Research Service, we understand the importance and the challenges of vaccine research, and we aim to share our expertise and our state of the art resources with those scientists aiming to develop new vaccines and antiviral treatments. We are also constantly expanding our range of assays, and we have recently introduced high-throughput micro-neutralisation tests and antibody-dependent enhancement (ADE) tests. Our assays range from standard plaque reduction neutralization tests (PRNT) to high-throughput analysis of different concentrations of antibodies, sera, or compounds, allowing the simultaneous comparison of several conditions in multiple replicates. For example, beside standard plate readers, we use high-throughput sampler flow cytometers, and the Opera Phenix™ High Content Screening System by PerkinElmer, allowing a single researcher to screen thousands of conditions in a single day. Even Jenner and Pasteur would be impressed!
