Vaccine Protects Mice
Against Certain Cancers
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.