MONDAY, Aug. 2 (HealthDay News) -- Scientists have genetically
tweaked a virus to fashion a therapeutic vaccine that appears to
attack a variety of advanced cancers.
The vaccine has provoked the required tumor-fighting immune
response in early human trials, but only in a minority of patients
And one expert urged caution. "They were able to generate an
immune response [with the vaccine]. That's a good thing but we need
a little more information," said Dr. Adam Cohen, assistant
professor in medical oncology at Fox Chase Cancer Center in
Philadelphia. He was not involved in the study.
"This is the first study in cancer patients with this type of vaccine, with a relatively small number of patients treated so far," Cohen noted. "So while the immune response data are promising, further study in a larger number of patients will be required to assess the clinical benefit of the vaccine."
One vaccine to treat prostate cancer, Provenge, was recently
approved by the U.S. Food and Drug Administration. However, Cohen
noted that many other cancer vaccines have shown early promise and
not panned out.
The theory behind therapeutic cancer vaccines is that people
with cancer tend to have defects in their immune system that
compromise their ability to respond to malignancy, explained study
lead author Dr. Michael Morse, associate professor of medicine at
Duke University Medical Center.
"A vaccine has to work by activating immune cells that are capable of killing tumors and those immune cells have to survive long enough [to] get to the tumor and destroy it," he explained.
For this vaccine, the authors used the Venezuelan equine
encephalitis virus, an "alphavirus" that affects the nervous
systems of equines, including horses and donkeys.
Alphaviruses provide an attractive vector for vaccines because
they naturally seek out dendritic cells, which stimulate the body's
In their work, the authors removed the innards of the virus and
substituted instead a gene for the carcinoembryonic antigen (CEA).
This immune system biomarker is overproduced in many different
types of cancer.
The vaccine was then administered multiple times over a period
of three months to 28 patients with advanced, recurrent forms of
lung, colon, breast, appendix or pancreatic cancer. The
participants had already failed several rounds of standard
Five patients displayed a response to the therapy: Two who had
already been in remission stayed in remission; two patients saw
their cancers stabilize; and a liver lesion in one patient with
pancreatic cancer was no longer evident.
The responses tended to occur in patients with smaller tumors
and in those receiving higher doses of the vaccine.
The alphavirus-based vaccine also managed to evade the immune
system's regulatory T cells, which could have shut down the body's
immune response, the researchers said.
Although T cell levels were elevated in some patients, the
vaccine was able to get around them.
Co-authors included employees from Alphavax, which develops new
vaccine technology. The study was partially supported by the U.S.
National Cancer Institute.
There's more on cancer vaccines at the
U.S. National Cancer Institute.
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