Written by Zia Chan
Illustrated by Sania Bahman
Diseases have shaped societies, economies, and nations for as long as they have existed. Epidemics hold the power to halt trade, decimate populations, and force communities to adapt. In response, humans developed early methods of protection, such as a practice known as inoculation, which laid the groundwork for modern vaccination¹ ². Inoculation, used in parts of Asia, Africa, and the Middle East, was the process of deliberately exposing healthy individuals to material from an infected individual. Although these practices were flawed, they reinforced a fundamental concept of immunity: people who recovered from a particular disease are generally not susceptible to the same disease again¹.
In the past two centuries, vaccines have become a cornerstone of public health. Vaccines are commonly prophylactic, meaning they prime the immune system before infection so the body is prepared to respond quickly and effectively if it encounters the virus naturally. However, scientists are also exploring a different type of vaccine: one designed not to prevent but to treat existing diseases³. These are known as therapeutic vaccines, and one of their most promising applications is in cancer treatment.
Cancer is characterised by the abnormal growth and division of cells. Mutations in the DNA, whether inherited or caused by environmental factors, can disrupt routine processes that control how cells grow, divide, and use energy⁴. Interestingly, the immune system is not entirely unaware of these abnormal cells. Cells of the immune system constantly patrol the body, identifying and eliminating what they perceive as threats. However, danger arises when cancer cells develop mutations that allow them to evade or suppress immune responses. Cells then begin to multiply uncontrollably, all the while remaining undetected by the body’s immune system.
As cancer progresses, these mutated cells can invade nearby tissues and spread to other parts of the body, disrupting organ function and other normal biological processes. Because of the complexity of these behaviours, cancer remains one of the leading causes of death worldwide⁴ ⁵. Therapeutic cancer vaccines address this challenge by training the immune system to recognise cancer cells more effectively³.
Advances in gene sequencing have played a crucial role in this effort, allowing scientists and researchers to analyse in detail the specific genetic mutations that tumour cells develop. These mutations can produce abnormal proteins, or antigens, on the surface of cancer cells, which act as tiny molecular flags that the immune system can potentially recognise. Researchers can link these specific mutations to tumour cell growth and development, which has been significantly improved with the development of high-throughput genomic data sequencing and analysis technologies⁴ ⁵.
These flags generally fall into two broad categories: tumour-associated antigens (TAAs) and tumour-specific antigens (TSAs). TAAs are proteins that are present in normal tissues but produced at significantly higher levels in cancer cells. One example is the HER2 protein, which is found at elevated levels in cancer cells but is still present in normal tissues³. Because TAAs are not entirely unique to cancer cells, targeting them can lead to less precise immune responses and may have unintended effects on healthy tissues⁴.
On the other hand, TSAs are only found on cancer cells. Because they often arise from mutations that create entirely new, unique proteins, they are known as neoantigens. TSAs do not exist on normal cells, so they can serve as highly specific targets for the immune system. Vaccines designed to target these neoantigens can potentially trigger stronger immune responses against tumour cells while sparing healthy tissues⁶. In some cases, these neoantigens are even unique to an individual patient’s tumour. This feature has led to the development of cancer vaccines tailored to the specific mutations found in a particular patient. In other cases, certain mutations are common between many patients. These “public” neoantigens are particularly promising, and some are the focus of developing “off-the-shelf” therapeutic cancer vaccines³ ⁶. Since “off-the-shelf” vaccines target shared neoantigens, they do not need to be customised for individual patients before they can be used for treatments³.
Despite its potential, developing effective vaccines for cancer treatment is extremely challenging. One major obstacle is the tumour microenvironment (TME), the complex ecosystem surrounding cancer cells. It is composed of immune cells, blood vessels, and other structural components that interact with the tumour. Rather than helping the immune system destroy the cancer, many elements of the TME can actively suppress immune responses⁷. This makes it difficult for immune cells to recognise and effectively attack tumour cells.
Tumours are made up of many different types of cells and can vary considerably, both physically and in their underlying genetic makeup. Their variation makes identifying consistent targets for vaccines more difficult. Age of the individual with cancer further contributes to this challenge. Most cancers occur in older adults, with the median age of diagnosis in the United States being 67 years⁸. As people age, the immune system gradually becomes less responsive and effective, which can make it more difficult for vaccines to generate a robust and lasting immune response in the patients who may need it most⁷.
Researchers are working towards overcoming these challenges. One strategy is combination therapy, in which these cancer vaccines are used alongside other treatments. These vaccines can be used alongside chemotherapy or radiotherapy, immune checkpoint inhibitors, or other drugs that modulate immune activity. Current studies show that combining these approaches appear to strengthen the immune response and improve the effectiveness of cancer treatment⁷.
Rapid advances in genomics, immunology, and biotechnology are accelerating progress in this field. As sequencing technologies become faster and more affordable, scientists are gaining unprecedented insight into the genetic changes that drive cancer. Although cancer remains an extraordinarily complex disease, each breakthrough brings researchers closer to treatments that work with the body’s own defences. Cancer vaccines offer a powerful new strategy: one that transforms cancer treatment into more personalised, precise, and effective care.