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Happy Hour

June 27, 2012

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By Alisa Kim

Can vaccines be used to treat cancer?

That is the question Dr. Jean Gariépy, a senior scientist at Sunnybrook Research Institute (SRI), addressed at a café scientifique held on June 27, 2012 at the Duke of York Pub, in downtown Toronto. He and fellow SRI scientist Dr. Neil Berinstein were guest speakers at the event, which provides a forum for scientific experts to engage the public in an informal, interactive setting. They spoke about the role of vaccines in cancer prevention and their research into developing a vaccine against metastatic cancer (cancer that spreads to the rest of the body).

Berinstein gave an overview of clinical trials on cancer vaccines that have been done to date. Gariépy will discuss the progress made in cancer prevention through vaccination and the scientific challenges in developing vaccines against metastatic cancer.

Gariépy points to vaccines that prevent stomach cancer and cervical cancer as two success stories. These vaccines are effective because they help the immune system fight a foreign pathogen, such as a bacterium or virus, that is implicated in these cancers. In the case of stomach cancer, preventive vaccines target the Helicobacter pylori bacteria; likewise, vaccines that fight infection from specific types of the human papillomaviruses can avert cervical cancer.

"If you make a vaccine against bacteria such as Helicobacter pylori, the body will make an immune response that will block or destroy such bacteria, making the patient less predisposed to developing stomach cancer in the future. It 's a preventive vaccine strategy that cures both the patient of stomach ulcers caused by the infection and predisposition to stomach cancer. The same goes for [vaccines to prevent] cervical cancer. You're targeting the virus, not the cancer," Gariépy says.

Vaccines that help the body defend itself against foreign invaders work, but infectious disease-related cancers account for only 20% of all cancers, notes Gariépy. Directing an immune response at "enemy" molecules expressed directly on cancer cells is far more of a challenge.

"Most cancer cells display your own molecules. A cancer cell expresses more of one particular molecule than your normal cells. When you try to mount an immune response to that, you're never going to get it. Your body says, ‘No. This is not foreign. This is you.' If you have an immune response to ‘you,' you'll get an autoimmune disease," says Gariépy.

And therein lies the rub: cancer cells grow unchecked because they are "self," but a vaccine that tricks the body into thinking they are "non self" can incite a misguided immune attack.

His lab is working on a way to make CEA (carcinoembryonic antigen), a molecule that is a tumour marker, look foreign to the body to generate a strong immune response against metastatic cancer. He is making a shortened version of CEA that is not sugar-coated like the original one. The result is a very focused immune response that blocks cancer cells from sticking to each other and forming large metastatic clumps.

"As we get better at making normal molecules look ‘non-normal,' we may elicit such a good response that the body may see some signs of autoimmune disease. We're trying to balance that, but haven't reached it yet," says Gariépy.

The café scientifique was sponsored by the Canadian Institutes of Health Research and the Ontario Institute for Cancer Research.

Dr. Jean Gariépy