21 Mar 2012

Vaccinia Virus
Vaccinia Virus

Those pesky viruses can make us all sick, but one day could be engineered to defeat cancer.  Cancer cells have one trait that may leave them open to attack.  They aren't good at killing off viral infections, hence, at least in theory, you could use a virus to kill cancer cells without affecting the patient.

Some of the efforts to use viruses to defeat cancer date back to 1951.  A 4-year old with leukemia caught chicken pox.  As a result the leukemia went into remission, but later returned once the chicken pox was gone, unfortunately the child later died.  Continued efforts to use these techniques went on until the 1960s and after this point, other methods began to be investigated.  Since the 1960s much has happened in science, with an understanding in the genetics and workings of viruses and cancer.  

Efforts into using the herpes simplex virus (HSV-1) were started back in 1991 by Dr. Robert Martuza, a chief neurosurgeon at the Massachusetts General Hospital and professor at the Harvard Medical School.  A few genes from the virus were injected into mice with brain cancer, the cancer went into remission but most of the mice died from encephalitis.

Years later Dr. Ian Mohr, a virologist at New York University, altered the herpes virus so that it isn't attacked by the immune system and kills cancer cells more efficiently.

Another virus that is proving effective for liver cancer is Vaccinia.  Vaccinia is used to protect against smallpox and so far the results have been promising.  Several groups of patients have had an increase in survival times.  Meanwhile other viruses are being used for things like melanoma, bladder cancer, and head and neck cancer.

Gene therapy to modify the virus uses a vector (virus or retrovirus) inserting new genes into the body's cells.  Since cancerous cells are ignored by the immune system, they use altered viruses that produce T-cell receptors, allowing them to destroy cancerous cells.  They also add a reporter gene that glows under PET scans to follow the progress in real time.

The altered molecule is "instructed" to have T-cells attach and attack cancer cells. The encoding of the T-cell appears to be done with a protein, in one case, called GM-CSF which triggers the attack on cancer cells. The body initially doesn't fight off the virus, but researchers fear that repeated doses may make the cancer virus ineffective.

The Tech-Stew Take Home

We shouldn't get too excited yet, though, as increasing survival time is not the same as a cure.  It is not likely we will ever find a one cure for all types of cancers, as each case is different.

There are also risks with any modification of a virus.  Some are outlandish like that of sci-fi stories, while most are more down to Earth, such as mutating the virus may actually cause harm to areas not infected by cancer cells.

Source:  news.discovery.com


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