SV40, polio vaccine, and cancer: Now beyond coincidence?
9 April 2002 10:40 EST
by Apoorva Mandavilli, BioMedNet News [caption and credit]San Francisco - At the American Association of Cancer Research meeting here today, controversy continued to swirl around accusations that contaminated polio vaccine stocks are to blame for certain cancers, based on the publication a month ago of two high-profile papers linking the simian virus SV40 to human lymphomas.
Less than a week after the papers were published in March, the US National Cancer Institute contacted the researchers to establish plans to send blinded results to three independent labs, lead researcher Adi Gazdar told BioMedNet News today.
But Gazdar seems unconvinced of the NCI's intentions. "They just want to prove us wrong," he said.
Gazdar and his colleagues scanned 99 lymphomas, 235 epithelial tumors and 40 control tissues for the virus. They found the virus in 43% of non-Hodgkin's lymphomas, 9% of Hodgkin's lymphomas, and in none of the control tissues. A second team independently found the virus in 42% of non-Hodgkin's lymphomas, "almost unbelievable agreement," said Gazdar, who is professor of pathology at the University of Texas Southwestern medical center.
"These are very respectable labs with basically identical results," said Michele Carbone, associate professor of pathology at Loyola University in Chicago. The "clear clustering of positives" is "no accident," he told BioMedNet News.
This is not the first time scientists have linked SV40 to human cancers. Researchers suggested for years that millions of vials of polio vaccine, contaminated with SV40, infected individuals between 1953 and 1963 and caused human tumors. Until recently, they were inevitably met with skepticism, even contempt - and some NCI researchers published directly contradictory results.
In 1997, the US National Institutes of Health, with other organizations, organized an international conference to review the SV40 literature and address the possibility that the virus causes human tumors. At the meeting, Carbone, presented his then-controversial data linking the virus to mesotheliomas. (Since then, more than 30 independent reports have confirmed his results).
After the meeting, Carbone says, a conscientious Chicago public health official contacted Carbone and gave him the last remaining stocks of polio vaccine from the 1950s. In her paper, Butel isolated a strain of SV40 from three patients that closely matches the strain Carbone sequenced from the polio vaccine vials.
The evidence proves Butel's results are no artifact, Carbone says. "You cannot contaminate with something that doesn't exist," he said. "This thing only exists in my freezer."
Since publication of their research in the Lancet last month, Gazdar and his colleagues have been investigating rarer subtypes like leukemia and multiple myelomas. The experiments have not been proceeding as fast as they would like, Gazdar says, partly because "there's no government funding" for the research. "The lymphoma story might force them to [fund it]."
An important next step, Gazdar says, is to prove that the SV40 virus causes lymphomas and isn't just a "passenger" in the cells. That is no easy task, since researchers have only been able to isolate the virus in rare instances. For the most part, they believe, the virus launches a "hit-and-run" attack, initiating a cascade of tumorigenic events before it is destroyed by the body.
Still, it is critical that this research continue, Gazdar says, because molecular and immunologic data suggest those born after 1963 have also been exposed to the virus, via horizontal or vertical transmission, or through sexual contact.
The rates of mesotheliomas, lymphomas and brain tumors have also all gone up "dramatically" in the last 30 years. "Coincidence or not, we have to find out," he said. "It's something to think about."
Picture caption and credit:
Transmission electron micrograph of polyomavirus SV40, CDC/Dr. Erskine Palmer.
Click here for more from AACR.