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WASHINGTON (Reuters) - A common virus that is harmless to people can destroy cancerous cells in the body and might be developed into a new cancer therapy, U.S. researchers said on Tuesday.

The virus, called adeno-associated virus type 2, or AAV-2, infects an estimated 80 percent of the population.

"Our results suggest that adeno-associated virus type 2, which infects the majority of the population but has no known ill effects, kills multiple types of cancer cells yet has no effect on healthy cells," said Craig Meyers, a professor of microbiology and immunology at the Penn State College of Medicine in Pennsylvania.

"We believe that AAV-2 recognizes that the cancer cells are abnormal and destroys them. This suggests that AAV-2 has great potential to be developed as an anti-cancer agent," Meyers said in a statement.

He said at a meeting of the American Society for Virology that studies have shown women infected with AAV-2 who are also infected with a cancer-causing wart virus called HPV develop cervical cancer less frequently than uninfected women do.

AAV-2 is a small virus that cannot replicate itself without the help of another virus. But with the help of a second virus it kills cells.

For their study, Meyers and colleagues first infected a batch of human cells with HPV, some strains of which cause cervical cancer.

They then infected these cells and normal cells with AAV-2.

After six days, all the HPV-infected cells died.

The same thing happened with cervical, breast, prostate and squamous cell tumor cells.

All are cancers of the epithelial cells, which include skin cells and other cells that line the insides and outsides of organs.

"One of the most compelling findings is that AAV-2 appears to have no pathologic effects on healthy cells," Meyers said.

"So many cancer therapies are as poisonous to healthy cells as they are to cancer cells. A therapy that is able to distinguish between healthy and cancer cells could be less difficult to endure for those with cancer."

AAV-2 is being studied intensively as a gene therapy vector -- a virus modified to carry disease-correcting genes into the body. Gene therapy researchers favor it because it does not seem to cause disease or immune system reaction on its own.

I was wondering if the science inclined people of this board could explain to me why this wouldn't work, or why it would work.

It would seem to me--since it's a virus an all--that someone could gain a natural immunity to it and thus make the virus unable to do its job? Or does it just kill cancer cells outright? Because the article says that it doesn't touch healthy cells?
not enough info to know if it will or wont.

There are two possible ways in which this thing could work;

1) just normal viral/body interactions, infects cells, goes into lytic cycle, forces cell to make many copies of the virus, then destroy the cell and release the virus particles so that they infect more cells. This is still a complicated process, firstly because of the way the virus targets cells. For a virus to be selective for certain types of cells it must have receptors on its surface which only interact with that cell. Otherwise it would infect every cell in the body, remember that a virus has one aim in life, infect and multiply, from an evolutionary standpoint its not served by being super selective.

2) this is amore interesting approach, assumes that the virus is able to select between cancerous and non cancerous cell. Normally when a virus infects a cell, the cell releases chemicals called infractions, infr-alpha, and infr-beta which are detected by CD4+ helper T-cellsl which then order the CD8+ cytotoxic killet T cells to kill the infected cell. Additionally antibodies begin to bind with virus particles that havent yet infected cells and destroy them. Its through this process that we dont have a life long flu infection. This process is not exact for all viruses for example HIV, marburg and e-boli can evade the immune response, usually by infecting the immune cells themselves. But lets say this virus infects cancer cells, these cells release the infraction chemical signals and the T-cells then kill the cancer cells.

But this process is also a major reason as to why the virus wont work, because the immune system will dystroy it long before it destroys all cancer cells. Hence it may reduce the size of tumours, maybe even considerably but these will eventually regrow and continue on. And because T-cells are the adaptive immunity system , this virus could only be used effectivly once, essentially when T and B cells kills some new organism, memory cells are created which will recognise this organism/virus in the future and prevent infection.

This process *might* work if used in conjunction with some pretty strong immune repressive drugs that would inhibit the immune response.

Hope this helps
I personally expect most of the progress in this arena from the cosmetics industry. For example, there were some presentations on some really neat anti-aging stuff at a conference I attended recently. They don't totally understand why different things work, they just make stuff that does. Good enough. The silly biologists can figure out why afterwards.

I'm currently running a project under a world leader in this field that will help build a very robust development model of the next generation materials (nanosciencey, you might say) that will far outstrip what you currently think is possible. In a few months, i'll be moving to another project that is currently developing the, uhm, "manufacturing systems" which will produce our next generation of materials. Forget biology, nanoscience is where it's at... smile.gif
Yes, that helped. It's better than me googling it and reading four pages of something that I won't understand.

Nanoscience. I know all about you nanoscience freaks. I've run into a couple of you before and you guys are... fanatics.
Deus Ex Machina
If nanoscience is as good as some people say it is (I have some 40 odd scanned/xeroxed pages from various sources as to why it will save humanity from nuclear war, environmental damage, AIDS, cancer, alien invasion, holocaust, genocode, or, alternatively, turn the universe into a grey goo), I can understand the fanaticism.
its not that great, just a new fad amongst physicists.

In 20 years time it will be like genetics today. Interesting but too well established to get excited about.
I have a follow up to Coffee's initial question based on Russian's answer. If the virus would be wiped out as easily as you think it will how do you explain this part of the article?

The virus, called adeno-associated virus type 2, or AAV-2, infects an estimated 80 percent of the population.

It would seem to me that in order to infect that large of a percent of the population it would need to be hard for the immune system to fight or have multiple varieties like the cold virus or something else. Am I wrong or is there some other reason that I don't know about?
i missed that part of the article. The only answer i have is that they are able to evade the immune system, for example the HIV virus can hide inside the macrophage cell without infecting it. I base this on the fact that;

1) it's impossible for it to go into the lysogenic cycle; whereby it integrates its dna with the dna of the cells, without causing the cell to start producing new virions. If that was to happen there would be lots of mutations and instead of killing cancer cells the virus would cause them.

Perhaps it is able to hide within the healthy cells without infecting them and that could explain why it differentiates between cancer cells and noncancerous ones? I know I'm not big on biology so feel free to prove my completely wrong about this idea. Or perhaps I'm misreading what you posted and you're saying that this alternative would cause it to create more cancer cells.
its possible.

Cancer cells occur for many reasons and all of them revolve around damage t the dna. When viruses infect cells their dna recombines with the dna of the cell, from there 1 thing will always happen, and 1 thing might happen depending on the virusl.

1) The cell stop its normal processes and begin to manufacture new virus particles. it does this at the expense of all other operations such as membrane synthesis. Eventually the amount of viruses become so large, or the membrane becomes so weak that the cell burts (lyses/dies) and the viruses are released into the body to infect other cells. In HIV the virus particles are released continously with the cell being destroyd over a period of time.

2) sometimes when the dna of the virus recombines with the dna of the cell, nothing happens. The virus dna is still there, the cell dna continues on as before, the cell might replicate and in which case the daughter cell has inherited the viral dna from its mother. Eventually however the viral dna will be activated, ( we dont know why, we can only speculate at how) and the cell enters the (1) phase i just described.

As an aside, this process is used in gene manipulation in microorganisms and plants.

However when the viral dna recombines with cell dna it can cause mutations, especially if its transcribed in the middle of a gene. Remember that 90% of our dna is 'junk' dna which isnt encoded into anything. So the probability of a mutation occuring, assuming transciption is a random event (which it isnt), there's a one in 10 chance of a mutation. Not all mutations cause the cell to rapidly replicate, changes due to mutation might not be noticeable. However when a cell begins to replicate due to dna mutation, the daughter cells inherit the mutation and themselves begint to devide. Hence tumours form.
a host/parasitic type virus? it may be able to differentiate between healthy and non-healthy prey due to a difference in the cell makup, and therefore infects/kills the weaker cell for nourishment, and reproduces or whatnot.
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