Vaccines are usually given before we actually get infected, as a form of preventative medicine.

But cancer researchers are also developing vaccines that could be used as treatments after cancer has been found.

The idea is to teach the body's immune system to recognise the cancer cells and then kill them. There are several ways to do this.

Every cell in the body is surrounded by a cell membrane with proteins embedded in it.

Inside cells, there are proteins too.

Cancer cells make proteins found nowhere else in the body.

Think of them like a barcode.

The simplest type of cancer vaccine takes a single protein commonly found in one type of cancer and teaches the immune system to react to it.

The protein, or antigen, is injected into the body where an immune cell called a dendritic cell ingests it.

The dendritic cell then activates another class of immune cells called T-cells, and these attack the cancer.

This method is straightforward, and hospitals could have a supply of vaccines in the fridge for the most common types of cancer.

But in trials, these vaccines haven't always worked. So researchers are now trying to target patients' tumors more specifically.

As tumors grow, they mutate, which means they change.

The unique proteins that each patient's tumor acquires as it mutates are known as neoantigens.

And these neoantigens are being tested as the basis for personalized vaccines.

First, a sample of the patient's tumor is taken.

The tumor cells contain messenger RNA, which carries the genetic instructions for making proteins.

The mRNA is extracted and sequenced along with the cell's DNA to identify the instructions for the tumor's unique proteins, its neoantigens.

The ones predicted to most powerfully stimulate the immune system are selected and injected into the body for the dendritic cells to find.

This kind of bespoke mRNA vaccine is showing exciting promise for treating melanoma and pancreatic cancers. There's another way to make personalized vaccines that doesn't involve genetic sequencing.

Again, a tumor sample is taken.

But this time, the proteins are extracted from the cancer cells and then, without identifying the proteins, introduced to a sample of the patient's dendritic cells in a Petri dish.

When the dendritic cells are injected back into the body, they stimulate T-cells to recognize and attack the cancer. Personalized vaccines may be very powerful, but making them anew for every patient is costly and time-consuming.

So scientists are also working on off-the-shelf treatments where the vaccination process occurs completely within the patient's body.

Patients are given drugs that activate dendritic cells, as well as a treatment like radiotherapy that kills cancer cells.

The dying cancer cells release their proteins, which are mopped up by the switched-on dendritic cells.

These cells then present the cancer proteins to T-cells, stimulating the T-cells to attack the cancer.

All of these approaches are still being developed and tested.

If trials continue to go well, vaccines that boost the body's own immune defenses look set to become another tool in our efforts to defeat cancer.