Modified Smallpox Vaccine Targets Cancer Cells, Study Says

A genetically modified smallpox vaccine was able to target and shrink tumors in some cancer patients while leaving healthy cells unharmed, in the first study to show the potential of using a virus to fight human malignancies.

Almost two-dozen patients with advanced cancers were injected with varying amounts of the virus, called JX-594, and six participants in the highest dose group had their tumors stabilize or shrink, according to the report released today by the journal Nature.

The trial demonstrated that a virus injected into the blood stream could infect and spread within tumors without harming other cells, said John Bell, one of the study’s authors and a cancer research scientist at Ottawa Hospital Research Institute. Results were from the first of three testing stages generally required for regulatory approval.

“It’s never been shown before that we could do this in humans,” Bell said in an interview. “We even see in some patients a modest therapeutic benefit.”

Researchers used the same strain of virus that’s used in the smallpox vaccine, called vaccinia virus, because of its natural ability to replicate itself in cancer cells, the report said. They then modified it to enhance its cancer-fighting properties.

While vaccinia virus is similar to smallpox, it doesn’t contain smallpox and can’t cause the disease, according to the U.S. Centers for Disease Control and Prevention.

New Approach

The approach differs from so-called cancer vaccines, such as Merck & Co.’s Gardasil shot that targets a virus that causes cervical cancer or Dendreon Corp.’s Provenge, which stimulates an immune response against prostate cancer cells.

The therapy, developed by closely held San Francisco-based Jennerex Inc., will be tested in a broader trial, said Bell, who co-founded Jennerex and is its chief scientific officer. If successful, the method could help patients whose cancer has spread beyond one area.

“The big problem with cancer is not people showing up with one tumor you can excise with a scalpel, the problem is metastatic disease that you can’t even see where it is,” he said. “By putting the virus in the blood system, it allows the virus to go around and potentially find all the fertile ground for it to grow in, all the places tumors are, and once it does that, it can affect them all and destroy them.”

Some patients in the trial had side effects such as mild to moderate flu-like symptoms that lasted less than one day, according to the report. Jennerex, the Terry Fox Foundation, the Canadian Institutes of Health Research and the Ontario Institute for Cancer Research and others financed the study.

Jennerex has enough cash to run the next set of experiments, and will likely look for additional funds later, Bell said. The company’s name is based on Edward Jenner, an 18th century English scientist who developed the first vaccination with an inoculation against the related cow-pox virus.

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