How could a vaccine fight cancer?

Hook

Why and how could a vaccine fight cancer? Not prevent it, the way a flu shot does, but teach your immune system to hunt down cancer cells left behind after surgery. In October, Merck and Moderna reported that a personalized mRNA cancer vaccine cut the risk of melanoma coming back. Here's how it works.

Problem

Your immune system already kills a lot of abnormal cells. But tumors grow from your own cells, so they can look normal enough to slip past, and even switch the attack off. The trick is to point out what makes them different.

Mutations

That difference is mutations. As a cancer grows, its DNA picks up errors, and some of those errors make proteins no healthy cell has. Scientists call these neoantigens. Every patient's tumor has its own set.

Recipe

So the vaccine is built for one person. Doctors sequence the tumor's DNA and compare it with healthy tissue. Software predicts which mutations the immune system is most likely to recognize, and picks up to thirty four of them.

Mrna

Those targets are written into a strand of mRNA, the same kind of technology used in some COVID vaccines. Wrapped in a tiny fat bubble and injected, it tells the body's cells to make pieces of those neoantigens, training T cells to find and attack anything carrying them.

Combo

In the trial, the vaccine was given with Keytruda, a drug that takes the brakes off the immune system. Together they work like a wanted poster plus a stronger police force.

Results

The phase three trial enrolled more than eleven hundred people whose melanoma had been surgically removed. After two years, about eighty two percent of those on the vaccine plus Keytruda were alive with no relapse, compared with about seventy percent on Keytruda alone. That's a forty two percent lower risk of relapse or death than Keytruda alone. It isn't approved yet. The companies are taking the data to regulators.

Close

So this experimental vaccine works by reading your tumor's unique mutations and training your immune system to recognize them. ThatsWhyHow.