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The number of viruses that are presumed to exist on the planet exceeds the number of stars in the universe. Of these, more than 300,000 cause diseases in mammals and at least 200 cause ailments in humans. It would be illogical then to think that the same viruses that make us sick can also cure us. But this is the case, and the use of viruses against cancer is not new.
The first documented case of what is now called oncolytic virotherapy dates back to 1897, when a US physician, George Dock, detected a significant remission of leukemia in a woman after she had the flu. A similar case was identified in 1971, both fortuitous and fortunate: a boy in Uganda with Burkitt’s lymphoma who began to get better after contracting measles. Later in time, in the 1990s, researchers in Canada discovered that a common virus called reovirus destroyed infected cancer cells. And in 2005, Grant McFadden, a virologist at Arizona State University, was studying a rabbit virus that he thought had no implications for human health, when he discovered that it also attacked human cancer cells.
Since then, oncolytic viruses are a form of immunotherapy that uses viruses to infect and destroy cancer cells.
But let’s go to the beginning. Viruses are particles that infect or enter our cells and then use their genetic machinery to make copies of themselves and then invade other cells. What is surprising, in this context, is that infection by certain viruses has been linked to the development of certain types of tumors. Hepatitis B virus with liver cancer and human papillomavirus (HPV) with cervical cancer. The problem is that tumor cells are “immortal” since they produce telomerase after each division, guaranteeing their reproduction without errors. How to attack them then? This is where oncolytic viruses come in. These are modified viruses and take advantage of the fact that cancer cells often have impaired antiviral defenses that make them susceptible to infection.
These modified viruses can be designed to give them advantageous properties, including diminishing their ability to infect healthy cells and giving them the ability to deliver therapeutic payloads specifically to tumors and produce molecules that stimulate the immune system once they infect tumor cells. In the same way that vaccines allow the immune system to identify certain viruses, oncolytic technology recognizes cancer cells and attacks them, bypassing healthy ones.
In 2015, the US Food and Drug Administration (FDA) approved the first oncolytic virus immunotherapy for the treatment of cancer: the T-VEC virus to treat melanoma. This treatment involves a herpes virus that has been designed to be less likely to infect healthy cells and to cause infected cancer cells to produce the GM-CSF protein that stimulates the immune system.
In Spain, the onco-hematology laboratory of the Niño Jesús Hospital together with the CNIO (National Center for Oncology Research) are developing a project to use oncolytic technology to treat different types of childhood cancer.
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