- NEW YORK (Reuters) - An experimental vaccine can protect mice from developing
tumors that carry a virus-associated protein on their surface, known as
simian virus 40 T antigen (Tag).
-
- The finding suggests that the vaccine
may be useful in preventing or treating certain rare types of human cancers
which also express the monkey virus protein, according to a report in the
January 20th issue of the Journal of the National Cancer Institute.
-
- Such cancers include rare bone and brain
tumors, and mesothelioma " a rare lung cancer that is also associated
with exposure to asbestos.
-
- "The applicability of this particular
genetically engineered vaccine would be limited to a few types of cancer
in humans in which there has been evidence that the target of the vaccine,
which is this protein called SV40 large T antigen, is present in some form,''
said senior investigator Dr. Martin G. Sanda, an assistant professor at
the University of Michigan in Ann Arbor, in an interview with Reuters Health.
-
- The presence of the Tag protein indicates
that the cancer cells are infected with the monkey virus, simian virus
40 (SV40), although it is not clear if the viral infection is the reason
the cells became cancerous, or how individuals came into contact with the
virus in the first place.
-
- Although SV40 is known to have contaminated
some batches of polio vaccine administered in the late 1950s and early
1960s, researchers have not found an increase in cancer after the vaccination
or any link between rare, SV40-associated cancer and the polio vaccine,
Sanda emphasized.
-
- Sanda, Dr. Nicholas Restifo at the National
Cancer Institute and other colleagues created a genetically engineered
vaccine known as vac-mTag, which consists of a relatively harmless poxvirus
combined with SV40 Tag.
-
- The SV40 Tag had its cancer-promoting
regions removed, but still retained a portion that could stimulate the
immune system.
-
- The vaccine was given to mice, which
were then injected with SV40 Tag-expressing mouse cancer cells 3 weeks
later. The vaccinated mice did not develop tumors, although those not given
the vaccine did develop lethal tumors.
-
- Administration of the vaccine in combination
with the growth factor interleukin-2 appeared to help reduce tumor formation
in mice who had already been injected with tumor cells.
-
- The research team is currently exploring
the possibility of testing the vaccine in mesothelioma patients, according
to Sanda.
-
- "We've made a recombinant vaccine
that can prevent T antigen-expressing tumors in mice, and this has potential
use as a experimental preventative tumor vaccine against a few, very specific
tumors in humans, which are rare, but which have been found to have T antigen
protein and T antigen genes present in a significant number of cases,''
he said.
-
- SOURCE: Journal of the National Cancer
Institute 1999;91:169-175.
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