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The idea of cancer-killing viruses is slowly moving from science fiction pages into practical reality. The promise is high, but technical implementation of this approach is remarkably difficult.

The term “oncolytic viruses” refers to the modified viruses that are able to selectively infect and destroy cancer cells in the body. The idea is wonderful. The exciting part is that, in theory, there are no principal problems that could prevent the development of such technology. But can it be done in practice?

Not so many years ago, this rather specialized scientific topic suddenly became a subject of broad public debates. Hollywood’s blockbuster I am Legend graphically depicted how humankind turned into blood-thirsty monsters, thanks to the newly developed virus-based anticancer therapy. In this cinematographic scenario, very soon after the therapy was introduced the virus mutated with the most lethal consequences imaginable.

Good movie (and this one was good, at least well made) does increase the public awareness about the dangerous toys the scientists out there might be playing with. Unfortunately, it is extremely unlikely that any viral therapy would be as effective in curing cancer as the movie suggested. On the positive side, it’s even more unlikely that such therapy would lead to global pandemic of vampirism.

The idea of using viruses to treat cancer is not new

The idea exists for at least a century, actually. Since the early 1800s there have been frequent reports of correlation between viral infection and tumor shrinkage. There was, for instance, a classic example of 42 year old woman who was suffering from myelogenous leukaemia. Her disease went into remissions after she contracted influenza. This and other observations were not properly investigated at the time. As a matter of fact, biomedical science has reached the level of development sufficient for proper investigation of such cases only in the second half of the last century.

The oncolytic viruses are able to replicate within the tumor cells only. They can cause the lysis of the host tumor cells thereby releasing a number of progeny viruses to kill more cancer cells.

How oncolytic viruses recognize cancer?

But how oncolytic viruses create this distinction between the normal and cancerous cells? Generally when any virus infects a host, it hijacks the cellular machinery and makes it to produce more viruses. A number of virus-induced changes are very similar to the conditions required for the growth and proliferation of the tumor cells. As a result, viruses prefer to infect cancer cells.

More robust and more cancer-selective viruses can be made through genetic engineering. These viruses, ideally, would ignore healthy cells of the host altogether. Potential candidates for such genetic manipulations include Adenovirus, Herpes Simplex Virus (HSV), Vaccinia virus, Polio virus and Influenza virus.  

In addition to their ability to recognise cancer cells, oncolytic viruses also produce an immuno-stimulating effect on the recipient. Virus-modified cells get recognized and eliminated by immune system thus further promoting elimination of tumor.

Continue reading after recommendations

  • Everts B and van der Poel HG. (Feb 2005) Replication selective oncolytic viruses in the treatment of cancer. Cancer Gene Ther. 12: 141-161
  • Kelly E, Russell SJ. (Apr 2007) History of oncolytic viruses: genesis to genetic engineering. Mol Ther. 15: 651-659
  • Lee JH, Roh MS, et al. (Feb 2010) Oncolytic and immunostimulatory efficacy of a targeted oncolytic poxvirus expressing human GM-CSF following intravenous administration in a rabbit tumor model. Cancer Gene Therapy. 17, 73-79
  • Adair RA and Roulstone V. (June 2012) Cell carriage, delivery, and selective replication of an oncolytic virus in tumor in patients. Sci Transl Med. 4: 138ra77
  • Le Bœuf F, Batenchuk C et al. (2013) Model-based rational design of an oncolytic virus with improved therapeutic potential. Nat Commun. 4: 1974
  • Kim MK, Breitbach CJ et al. (May 2013) Oncolytic and immunotherapeutic Vaccinia induces antibody-mediated complement-dependent cancer cell lysis in humans. Sci Transl Med. 5: 185ra63.
  • Photo courtesy of Phil and Pam Gradwell (to be) by Flickr : www.flickr.com/photos/philandpam/223015379/
  • Photo courtesy of melanie cook by Flickr : www.flickr.com/photos/wiccked/4054681731/

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