A virus that contaminated polio vaccines in the 1950s appears to be associated with non-Hodgkin’s lymphoma, researchers from Dallas and Houston reported last week.
The virus, called SV40, is a monkey virus that contaminated vaccines from 1955 to 1963. It had previously been linked to some brain and bone tumors, but its association with non-Hodgkin’s lymphoma had remained unclear.
Non-Hodgkin’s lymphoma is a malignancy of certain white blood cells. Experts have been puzzled to see the disease move from relative obscurity to become the fifth most common cancer in the United States. It is the disease that killed Jacqueline Kennedy Onassis and King Hussein of Jordan.
The new research suggests that SV40 may be at least partly to blame in some cases. Scientists from the University of Texas Southwestern Medical Center at Dallas found the virus in 43 percent of 68 non-Hodgkin’s lymphoma tumors, but only 9 percent of tumors from patients with Hodgkin’s lymphoma, another type of white-blood-cell cancer. The researchers couldn’t find the virus at all among the white blood cells of healthy volunteers.
“I think it’s a very powerful finding,” says UT Southwestern’s Dr. Adi Gazdar.
When Dr. Gazdar and his colleagues started the research, they didn’t realize that scientists at the Baylor College of Medicine in Houston had embarked on their own hunt for SV40. Working independently, the Baylor scientists came up with almost the exact same result: 42 percent of the 154 non-Hodgkin’s lymphoma tumors tested contained the virus, compared with none of the lymph node and blood samples from people without the disease. The Houston team included in its study people infected with the AIDS virus, who have a much higher risk of developing non-Hodgkin’s lymphoma.
Both studies appeared last week in the British journal The Lancet.
Now that scientists have found the virus huddled in tumors, they have to determine whether SV40 is a culprit or just an innocent bystander as a cell becomes cancerous. And if SV40 does have a role in non-Hodgkin’s lymphoma, how important is it?
“It’s not the only cause; it may not even be the main cause,” Dr. Gazdar says. “It may be an added factor.”
Researchers also have a lot of questions about SV40 itself. No one is sure how many people are infected, or where the virus hides out in the body. Even routes of transmission are uncertain: Although millions were exposed from polio vaccines, scientists have also found the virus in people far too young to have received tainted immunizations.
“My prediction is that it is being transmitted person to person,” says Janet Butel, the senior investigator of the Baylor study. “A number of people with SV40-positive tumors are too young to have been exposed to contaminated polio vaccine.”
The researchers hope the new work will prompt other scientists to investigate SV40, and ultimately, to determine how a monkey virus might prod a normal white blood cell into becoming malignant.
“There’s a lot of work to do,” Dr. Gazdar says. “We have to fill in all the blanks.”