NEW YORK, Sep 21 (Reuters Health) -- Gene therapy that boosts the body's immune system appears to be effective at preventing mesothelioma -- a lethal tumor of the lining of the chest -- from growing in mice, according to Australian researchers.

Mesothelioma can take from 15 to 40 years to develop, but despite the long lag time, once the cancer is diagnosed, the average survival time is just 9 months. Treatments such as chemotherapy, surgery, and radiation are not effective.

Dr. Bernadette Scott, of the University of Western Australia, and colleagues have been studying the effects of an immune system protein called interleukin-12 (IL-12). The hope is that treatment with IL-12 would encourage the immune system's natural killer T-cells to attack cancer cells. In an earlier experiment, Scott's team showed that the protein did fight mesothelioma tumors in mice, but the treatment also caused severe side effects.

In the current study, however, the researchers attempted to reduce the risk of side effects by encouraging the production of IL-12 only in the tumor, not throughout the body. They did this by modifying the tumor in the mice to include the genes for IL-12, Scott and her associates report in the September issue of the American Journal of Respiratory Cell and Molecular Biology.

Results of the experiment demonstrate that the approach prevented tumors from growing in the mice, according to the report. Furthermore, none of the mice who received the treatment developed any side effects.

Based on the findings, the investigators conclude ''production of IL-12 through gene therapy may be an appropriate means to treat malignant mesothelioma.'' However, they do note that the effectiveness of the therapy may depend on how much IL-12 can be produced within the tumor. And since treatment in one tumor may not have an effect on other tumors, combining gene therapy with another type of treatment may be necessary in some cases, Scott's team concludes.

SOURCE: American Journal of Respiratory Cell and Molecular Biology 1999;21:347-356. Tuesday September 21 1:38 PM ET

** POSTED SEPTEMBER 27, 1999 **