Professor disputes cancer-virus connection

Hopkins scientist finds inconsistencies in studies linking SV40 and tumors

February 05, 2000|By Gary Dorsey | Gary Dorsey,STAFF WRITER

Despite the suggestions of a growing number of studies, there is little evidence linking human cancer to a monkey virus that once contaminated polio vaccines, according to findings by a Johns Hopkins University researcher.

Keerti V. Shah, professor of mo lecular microbiology and immunology, reviewed existing research for this month's issue of Reviews in Medical Virology and concluded that many of the studies should be treated skeptically because of numerous inconsistencies in the work.

National public health officials have been embroiled in a controversy about the virus, known as SV40, for several years. In 1994, a cancer researcher discovered that the virus, which contaminated polio vaccines between 1955 and 1963, produced a deadly cancer in lab animals. In subsequent studies, scientists have found traces of SV40 in human tumors, including certain forms of brain cancer, bone cancer and lung cancer.

Because of implications that the virus was planted in human populations by the vaccine, the potential for SV40 studies to shake public confidence in vaccines has been a serious concern among public health officials.

"The questions have been: Is the virus in these tumors, and if it is, what is it doing, and is it contributing to cancer and how are people becoming infected?" Shah said yesterday at his office in the School of Public Health. "My review [of existing studies] shows that none of the suggested associations have been established."

The person most commonly affiliated with the controversy, University of Chicago pathologist Michele Carbone, has written more than 20 studies since 1994 concluding that SV40 is a significant human carcinogen.

When questioned about Shah's article yesterday, Carbone said he had read only a short abstract of the analysis and would not comment.

However, he did point to two research papers published in December by scientists at the National Cancer Institute and the University of Texas supporting his idea that there is a significant but mysterious relationship between the virus and cancer.

The author of one of those studies, Adi Gazdar, deputy director of the Hamon Cancer Center at the University of Texas Southwestern Medical Center, said his work indicated that SV40 exists in some human cells long before they become malignant. The most likely explanation for the appearance of the virus, he said, is the contaminated polio vaccine.

There is a growing body of evidence, he said, that points to SV40 as "a very important public health issue."

Shah has studied the virus since the 1960s, when he published the first paper questioning whether SV40 had been passed from monkeys to a human population in India.

From 1955 to 1963 the polio virus used in vaccines was grown in macaque kidney cell cultures, some of which were contaminated with SV40. However, Shah said, the largest manufacturer used a culture system that would have made it difficult for the virus to survive, so a significant portion of the vaccine lots were probably free of SV40.

Further, he said, many people found to have SV40-positive tumors were born many years after 1963, when the contaminated vaccine was no longer in use.

The controversy is far from settled, Shah said, pointing to a lengthy article in this month's Atlantic Monthly magazine that highlights the struggle between Carbone's supporters, the NCI and skeptics like himself.

"I think it is very important that we clarify all this," he said.

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