Building cancer-fighting immunity: How a new therapy is retraining the immune system to identify and attack cancer

Cancer is, unfortunately, a grim reality that many of us (or our loved ones) will face. In Canada, nearly one in two people will be diagnosed with cancer, and one in four will die from it. It’s the leading cause of death worldwide.

Part of the problem stems from the fact that our bodies don’t deal with cancer in the way they handle other threats. If something doesn’t belong in our body, like a flu virus, for example, then our immune system is trained to recognize it as a foreign invader and eventually attack and kill it. Cancer, though, is different. Despite the immune system’s powerful capabilities, it does not recognize or fight off cancer in the same way.

“The biggest difference between cancer and a virus is that cancer comes from within you,” explains Dr. Shashi Gujar, Executive Director, Cancer Immunotherapy, Innovation & Global Partnerships at Faculty of Medicine, Dalhousie University. “Cancer is a deviation of your normal cells. So cancer can fool the immune system into thinking it is normal cells, meaning the immune system doesn’t see those cells as an invader to be dealt with. That’s when the cancer starts to grow and spread.”

But Dr. Gujar’s team is working to change that.

Retraining the immune system

It’s a concept that might have sounded like science fiction not too long ago: What if we could retrain the immune system to not only identify cancer, but to fight it off and prevent it from ever coming back?

“It would be game changing,” says Dr. Gujar, “and that’s exactly where the research is headed.”

The approach is called cancer immunotherapy, a form of precision medicine that teaches our immune systems to fight cancer. The therapy—which uses pills, intravenous drugs, or topical creams to boost the immune system, especially T immune cells (a type of white blood cell),—is already being used in Canada and around the world as an alternative or in addition to surgery, chemotherapy and radiation therapy.

While cancer immunotherapy is still considered to be a new and evolving treatment, it is showing success in more than a dozen cancers including skin, lung, bladder and kidney cancers, with positive results in about 15 to 20 percent of patients.

Scientists are now taking that research one step further. Rather than using pills or topical creams, the next generation of cancer immunotherapy explores a novel and exciting technique that uses oncolytic viruses, which are cancer-killing viruses, to directly target and fight cancer cells in the body.

Cancer-killing viruses

Dr. Gujar’s research uses the cancer-killing virus called reovirus. The reovirus is actually a harmless human virus that most of us have unknowingly had with little or no effects—which is an important point because even a cancer-killing virus wouldn’t be very helpful if it made the patient very sick with an infection.

“We use this benign virus to draw the immune system’s attention to the cancer,” explains Dr. Gujar. His team injects the reovirus directly into cancerous cells, where the virus has the opportunity to replicate and invade even more cancer cells, just by doing what viruses do when they find a host.

“And the thing is, once those cancer cells are infected with the virus, they start to look funny to the immune system,” he continues. “So the immune system gets activated, realizing there is a foreign invader in the body, and takes steps to kill not just the virus, but the cancer cells, too.”

To date, this approach using the reovirus has been effective at fighting almost every type of cancer Dr. Gujar has tested. But it’s the incredible side effect that truly excites him.

“When the reovirus first starts to replicate and begins to break down the cancer cells, it produces these chunks of dying cancer that are coated in the virus, which then travel throughout the body,” he explains. “And this coating means that the cancer is no longer in cognito for the immune system. It will chase after those chunks to fight the virus—and consequently, it will learn to fight the cancer, too. Once your immune system starts to see the cancer as an invader, it can even identify that same cancer in other parts of the body.”

This astounding result suggests that we can virtually retrain the immune system to attack the cancer wherever it goes, so the cancer is not only destroyed—it’s also prevented from coming back.

A promising future

This ability to kill cancerous tumours and subsequently stop them from growing again—a phenomenon called anti-tumour immunity that has been documented in studies—leads Dr. Gujar to push this life-saving potential even further.

“One of the challenges in developing cancer treatments is that there are so many different types of cancer,” he explains. “So, after immunotherapy has taken place and anti-tumour immunity has been established, what happens if that newly trained immune system comes across a different type of cancer? Will it still be able to recognize it, or will these other cancer cells be able to ‘hide’ as normal cells?” 

Finding that answer is the focus of his current research at Dalhousie University.

“We know that different kinds of cancers have diverse characteristics, but they also have some similarities,” he continues. “If we can strip down normal cells and cancerous cells and really, at a molecular level, determine what characteristics could be used to make the cancer cells stand out from normal cells—well, then we can use those characteristics to train the immune system to recognize and attack the cancer. And, because we’re looking for similarities in those characteristics across cancer types, the idea is that we would be training the immune system to identify and kill many kinds of cancer instead of just one.”

If it works, then Dr. Gujar sees the opportunity to not only treat existing cancer but also prevent it using a model like a vaccine. “What if we could take some of your own immune cells, train them to recognize all of these specific cancer characteristics, and then put them back in your body to hunt for cancerous intruders in the years to come? You wouldn’t have to experience cancer and treatment first—your immune system would simply be trained to stop cancer in its tracks if it ever finds it,” he says.

As Dr. Gujar’s lab pursues this research using a cutting-edge platform of their own design, Dr. Gujar himself is very optimistic about where cancer immunotherapies will take us. Cancer-killing viruses are already being tested in clinical trials around the world without any major side effects. One virus, a genetically modified form of the herpesvirus for treating melanoma, has even been approved by the US Food and Drug Administration (FDA). And with the potential he sees in personalized immunotherapies and vaccines to treat and prevent cancer, the biggest dream of all is on his mind.

“It’s hard to find anyone nowadays who is not affected by cancer, and it’s the patients and their loved ones that are the driving forces in our work each and every day,” says Dr. Gujar. “So while I recognize that cure is a big word, I don’t use it lightly. I truly believe that cancer immunotherapy is the answer, and I’m confident that all the research underway here in Canada and around the world will allow us to one day develop cures for many types of cancer.”

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