Virotherapy: Definition & Uses

Instructor: Angela Hartsock

Angela has taught college microbiology and anatomy & physiology, has a doctoral degree in microbiology, and has worked as a post-doctoral research scholar for Pittsburgh’s National Energy Technology Laboratory.

In this lesson, we will discusses virotherapy, which is the use of viruses in therapies to treat disease. We will identify the three main categories of virotherapy and review the basics of how these approaches work.

Viruses Reinvented

Everybody loves a good story. And a good writer knows the literary tricks to pull in readers and really get them hooked. A classic trick is the reinvention of a main character. The weak and downtrodden emerge as the strong and victorious. The corrupt and selfish transform into the ethical and philanthropic. Or, how about the murderous and violent villain becomes reinvented as the savior of the sick and dying?

You might be surprised to learn that we can cast viruses in the role of the reinvented villain. When we think of viruses, we think of illness, damage to the body, death, and outbreaks. It's hard to imagine a more villainous creature. But what if we could reimagine viruses?

Virotherapy is the use of viruses in therapies to treat diseases - a sort of reinvention of the virus. Scientists are taking these infectious agents and using some of their features, like how viruses can find specific cells in the body to target and destroy cancer cells or how they can stimulate the immune system. Basically, scientists are turning a villain into a savior. Before we talk about the different kinds of virotherapy, let's review the basics of how a virus works.

Virus Basics

Viruses are tiny little packages of protein and genetic material (DNA or RNA). They seek out our cells then invade, hijack, and convert them to miniature virus factories churning out thousands upon thousands of new viruses.

The viral proteins act as a shell that surrounds the genetic material, protecting it when the virus is not infecting a host. Some of the viral proteins also stick out from the surface of the virus and can attach to specific cells within the body. This is why doctors call a virus like influenza a respiratory virus; it has proteins that only allow it to grab onto and infect our respiratory cells. When a viral protein hooks to a human cell, it can dump the genetic material into that host cell and hijack it.

Okay, now back to virotherapy. There are currently three main areas of virotherapy: oncolytic virotherapy, viral gene therapy, and viral immunotherapy. While they all use viruses to treat disease, they do so by different strategies. Let's look at the key features of each.

Oncolytic Virotherapy

Oncolytic virotherapy uses viruses to target cancer cells and destroy them. We can break down the term oncolytic into onco which refers to cancer and lytic which refers to destruction.

Remember that viruses have surface proteins that attach to specific human cells. In addition to the normal human cells that are targeted by a virus, the proteins on many viruses will also preferentially attach to and invade tumor cells. Once a virus invades a tumor cell, it can still force the tumor cell to make more viruses, but when it is done making new viruses, the tumor cell dies. This is a good thing! The defining characteristic of cancer or tumor cells is the ability to continue growing and dividing out of control. The viral infection can break that cycle and limit the spread of the cancer.

Beside the 'natural' viruses that invade tumor cells, scientists are also trying to engineer or design viral proteins that can attach to specific tumor cells. This could make the process more targeted and more efficient.

Viral Gene Therapy

Viral gene therapy uses viruses to deliver beneficial or therapeutic genes into human cells, where the genes can be used to change the cell in some way. In this form of virotherapy, the virus is just a shuttle to get the cargo (the therapeutic gene) to where it is needed.

Remember we said that a virus was just a protein shell that surrounds the viral genetic material. Normally, the viral genetic material gets delivered to the host cell, where it causes problems (damage, disease, etc.). But, if we replace the viral genetic material with a beneficial gene, the protein shell will still deliver that cargo to human cells. If we have a human cell that has a defective gene that is causing the cell to misbehave, the virus can deliver a new, non-defective copy of the gene to replace the bad one.

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