The immune system isn’t always perfect. On the rare occasion, the immune system fails to recognise a pathogen (or disease-causing organism), or doesn’t properly respond to it, allowing the pathogen to run rampant in the body. Other times, the immune system may inaccurately label something harmless (such as a food particle, pollen, even normal cells) as dangerous, causing things like allergies and autoimmune disease. Environmental and genetic factors also can influence whether the immune system behaves ‘correctly’.
Immunotherapy is often thought of as ‘tipping the balance’ – helping to nudge the immune system in a direction that is beneficial rather than harmful. This might mean helping the immune system identify a pathogen (like a cancer cell), or help suppress an aggressive immune reaction to a harmless peanut. Almost all human diseases are immune-mediated in some way, which means that the majority of human disease may one day be cured or managed through immunotherapy.
Vaccines are a common and effective way we can train our immune system to recognise and respond to infectious agents such as bacteria or viruses, before our bodies encounter them.
Vaccines are one of the most effective tools we have at fighting infectious diseases. They have been around for a long time, and their benefits and side-effects are well understood. Thanks to vaccines, our society has eradicated deadly diseases like polio, smallpox, measles and rubella, to name a few. These diseases once presented a huge threat to human health, with thousands dying from them every year. Today, only tiny pockets of such diseases remain around the world, almost exclusively in places where there isn’t wide-spread vaccination.
Vaccines work by replicating the immune system’s own method of identifying and eradicating infectious agents, without exposing the body to the actual disease. There are many ways scientists can do this.
The most common method involves introducing the body to harmless components of the pathogen in question. This could be something as simple as a protein found on its surface. In this way, the immune system can learn enough about the pathogen to recognise the real thing should it come along. To date, all of our most effective vaccines use this method to combat infectious diseases like influenza, polio, mumps and more. These vaccines are relatively simple and easy to manufacture, and their safety is well understood as we have been using them for decades.
However, the limitations of many vaccines is that pathogens regularly mutate and change their structure – often in a short space of time, which renders the vaccine ineffective. In this case, a new vaccine is needed to retrain the immune system. Influenza is an example. Because the flu virus changes seasonally, we need a new vaccine every year to combat it.
Vaccines for infectious diseases like influenza work best when everybody gets them. When enough people are vaccinated against a disease, eventually the disease runs out of new people to infect and dies out. We have seen this in the case of diseases such as polio – once a common disease – which has now been eradicated from our planet.
Having enough of the population vaccinated against a disease is what’s called ‘herd immunity.’ Herd immunity also helps protect people who are immunocompromised and are unable to receive vaccinations themselves.
Cancer vaccines are an emerging type of immunotherapy. They work in much the same way as other vaccines, except rather than targeting a foreign pathogen like a virus, cancer vaccines target human cells that have become cancerous.
As cancers are typified by uncontrolled cellular division, the cells that make up a tumour are all copies of each other and often present physiological features that distinguish them from normal, healthy cells. This presents the opportunity for vaccines to educate the immune system on what exactly a specific cancer cell looks like, to help the body fight and destroy the cancer.
While cancer vaccines are a relatively new form of therapy, there is promising evidence that – like a regular vaccine – the immune system retains a memory of the cancer and can prevent it from coming back.
However, like a vaccine, if the cancer mutates, the immune system might no longer recognise the cancer, so a new vaccine needs to be developed. Additionally no two cancers are identical between individuals – whereas a viral disease is the same across a population – many emerging cancer vaccines need to be tailor-made for the patient.
There are other ways we can influence the immune system to benefit human health. While things like vaccines work to train the whole immune system, often we want to stimulate or suppress a specific part of immune response to fight a disease, and leave the rest of the immune system unchanged.
Molecular therapies can target one branch of the immune system, or even one type of immune cell, stimulating or suppressing its function whilst leaving the rest of the immune system unchanged.
Additionally, our diet and environment influences the health and function of all our cells – immune cells included. There is growing understanding of this complicated relationship, and in the not too distant future we may be able to improve the function and response of our immune system with the foods we eat.