Monkey Virus May Hold Clue to Blood Cancer

Examination of tumors in patients with newly diagnosed non-Hodgkin's lymphoma (NHL) found that half of them show evidence of monkey virus DNA that may have originated from contaminated polio vaccines, M. D. Anderson researchers say.

These findings suggest that Simian virus 40 (SV40) may "participate" in development of the blood cancer, according to scientists who presented their findings at the annual meeting of the American Association for Cancer Research last month.

There is no known etiology (cause) for most non-Hodgkin's lymphoma, which has doubled in incidence within the past 30 years, the researchers say.

"We found a strong association between the monkey virus DNA and non-Hodgkin's lymphoma in this study, and now the question is whether the virus DNA is an innocent bystander, or if it has a role to play in causing the cancer," says the first author, Felipe Samaniego, M.D., assistant professor in M. D. Anderson's Department of Lymphoma/Myeloma.

Examining viruses

There has been a debate as to whether SV40, which contaminated some batches of polio vaccine in the 1950s and 1960s, could cause human cancer, especially after the virus was discovered in human tumors. Given that, the M. D. Anderson researchers looked to see if either DNA from the virus or associated antigens or antibodies could be found in non-Hodgkin's lymphoma.

One reason they looked for evidence of SV40 in non-Hodgkin's lymphoma is because other viruses have been commonly found in this form of lymphoma, including Epstein Barr virus.

"The assumption has long been that if only some NHL cases showed signs of virus, the rest may have another virus involved in the development of this lymphoma," Samaniego says. "Now we wonder, which one is most important?"

The research team, which included Suizhao Wang, M.D., Ph.D., and Shu Wang, M.D., both postdoctoral fellows in the Department of Lymphoma/Myeloma, examined 55 tumors taken from newly diagnosed patients who had not yet been treated with chemotherapy and isolated DNA from the genomes of the cancer cells.

Researchers found that:

• 33 of the tumors contained DNA sequences from the antigen produced by the virus
• 30 of 57 tumors stained positive with antibody that recognizes the large T antigen of SV40

There is no question that SV40 is a powerful cancer virus in some animals, Samaniego says. In a hamster, for example, the virus causes lymphomas and mesothelioma, as well as tumors in the brain and bones.

People may pick up the virus by:

• Association with infected animals
• Through a polio vaccine
• Though secretions, such as saliva, from an infected person

One study suggested that at least 5% of Americans have signs of monkey virus infection, Samaniego says.

But he theorizes that the body's immune system normally keeps the virus in check until "a transforming event, inflammation or other disease," Samaniego says. "Then the virus may reactivate and cause cancer."

If SV40 does prove to play a role in development of non-Hodgkin's lymphoma, then treatment aimed at destroying the virus could help prevent its development, he says. "The virus could serve as a target in novel immune-based prevention and therapeutic strategies for non-Hodgkin's lymphoma," Samaniego says. "Although this cancer is quite treatable with a 60% cure rate, a new therapeutic strategy would be welcomed."