How cancer vaccines work – and what it means for the future
Vaccine research has been heralded as a bright spot in 2012's medical advances against cancer and related diseases – with potential for yielding even more progress in 2013. But although many people have experienced getting vaccinated, not everyone understands how the shots work to protect them against disease.
So here’s a primer on how vaccines work with the immune system to keep people healthy:
For starters, vaccines fall into two main categories – prevention of disease and treatment of disease – and the immune system is made up of white blood cells, or leukocytes.
There are many types of leukocytes, but most cancer vaccines work with a type known as lymphocytes. Lymphocytes come in two main versions:
-B cells, which create antibodies that flag viruses or defective cells for destruction.
-T cells, which find those flags and are responsible for the actual destruction.
Prevention vaccines – such as the ones for HPV, chickenpox and polio – prepare the immune system to combat a virus before infection even occurs by prompting B cells to create antibodies against the targeted virus. This allows the immune system to take immediate action should it encounter the virus.
The HPV vaccine, for example, wipes out the human papillomavirus before it can take root in the body, preventing the development of HPV-related cervical and throat cancers. The vaccine has not been shown to clear the virus in a person already infected.
Chickenpox vaccinations enable the immune system either to stop the disease from happening or to manage the infection so that it doesn't fully develop.
Treatment vaccines such as CMVPepVax and MVA-p53 – currently being tested at City of Hope – enlist lymphocytes to treat a disease.
Known as immunotherapeutic vaccines, they enlist a neutered version of viruses to infect healthy T cells and genetically modify them to target the disease. As the New York Times reports, an investigational leukemia treatment developed by the University of Pennsylvania uses a version of HIV to spread its genetically modified payload.
CMVPepVax combats cytomegalovirus, an opportunistic infection. The virus is easily spread and many people carry it, but a healthy immune system can keep the virus in check. When a person is immunocompromised – for example, by cancer or AIDS – the virus can easily overwhelm the system.
A clinical trial of CMVPepVax aims to determine whether it can prompt patients' immune systems to fight the virus; if so, patients would have an alternative to the toxic chemicals known as antivirals that are now used to combat the infection.
Similarly, MVA-p53 vaccine is targeted at the p53 protein, a tumor suppressor that contols how cells divide and replicate. Mutations in the p53 protein can lead to uncontrolled cell duplication – essentially cancer.
The vaccine delivers a genetic payload that can churn out T cells. These T cells already recognize the mutant p53 cancer cells, and the vaccine leads to the production of antibodies that flag the cancer for new T cells created by the immune system.
One problem with many vaccines is that they don’t provide lifetime immunity and thus require booster shots. However, City of Hope researchers are testing an immunotherapy treatment with a specific lymphocyte, called a central memory T cell, that may potentially provide lifetime immunity.
Central memory T cells do what their name implies, providing the immune system with a long-term memory so that, even if a person is cancer free, the immune system can respond immediately should the disease develop.
Just as chickenpox can be controlled, and polio has almost been eradicated, cancer vaccines – such as the HPV vaccine and others in development – may spur a revolution against the disease.