Ontario researchers have launched the first clinical trial that will use two, custom-made, cancer-fighting viruses to stimulate the immune system into attacking and destroying tumours.

The use of viruses in cancer treatment is part of a growing field of research called immunotherapy. The idea is to use genes, antibodies and viruses to help the immune system recognize and attack cancer on its own.

In this study, researchers will use an engineered cold virus called Adenovirus and an engineered Maraba virus, which comes from Brazilian sandflies.

Both viruses have been designed to attack cancer cells that express a dangerous protein called MAGE-A3, or melanoma-associated antigen 3. Approximately one-third of tumours express the protein.

The Adenovirus would train the patient's immune system to recognize cancer cells. The Maraba virus would go a step further by replicating inside the cancer cells and killing them directly.

Both viruses have been developed over the last 15 years in specialized facilities at The Ottawa Hospital and McMaster University.

So far, the cancer-fighting viruses have shown good results in mice. The clinical trial will now test the viruses on 79 advanced cancer patients whose disease has resisted conventional treatments.

Of them, 24 will receive only one of the viruses, while the rest will receive both, in doses given two weeks apart. While the study is already underway, the research team is still looking for more patients who are appropriate for the study.

The clinical trial is scheduled to run until 2017, though full results may not be published until several months later.

It's too soon to say whether the viral therapy is proving successful in the first patients enrolled. But the treatment is easier on patients than conventional chemotherapy and radiation, as it produces fewer side effects.

Christina Monker, 75, is one of the first patients treated in the trial. She has stage 4 cancer that has spread to both her lungs but that has resisted treatment despite 30 rounds of chemotherapy. She was treated with the viral therapy in June, 2015, and says it produced few side effects.

"The nausea of chemotherapy was worse than I ever could have imagined. But with the viral therapy I just felt like I had the flu for a couple of days, and the symptoms were easily managed," she said in a statement.

Dr. John Bell, a senior scientist at the Ottawa Hospital says these viruses will be tested on solid tumours, such as melanoma, lung and colorectal cancer. But he says the hope is to eventually be able to use the same approach on other cancer types.

"We have other viruses that we're developing that we'll also bring to the table and hopefully get something that can treat any type of cancer," he told reporters.

"In the long term, we would have a sort of menu of viruses that we would use in combination with other therapies such as immune-stimulating therapies."

The study is being funded by the government of Ontario through the Ontario Institute for Cancer Research.

Other organizations supporting the research include The Ottawa Hospital Foundation, CHEO Foundation, Canadian Cancer Society, Terry Fox Research Institute, Canadian Institutes of Health Research, and several other donors.