Cells melt mouse tumors.

Studies suggesting that the naturally occurring substance interleukin-2 boosts the immune system's response to cancer prompted a research team to engineer cells to fight tumors in mice.

Robert E. Sobol of the San Diego Regional Cancer Center and his colleagues hoped that by inserting the gene that codes for interleukin-2 into mouse cells, they could produce cells that would secrete interleukin-2. These cells would then spur the immune system to destroy malignant tumors in the animals.

To test this theory, the team engineered interleukin-2-producing mouse cells, put the altered cells and some tumor cells in a solution and injected the mixture into 10 mice. They gave another group of 10 mice injections of tumor cells and unaltered cells. The scientists knew that tumor cells by themselves would spur an immune response, but they wanted to compare it with the immune rally sparked by interleukin-2. Seven control mice got injections of saline solution.

Two weeks later, the San Diego team implanted a small tumor just under the skin of each mouse in the study. Twentyeight days after implanting the tumors, the scientists discovered that six of the 10 mice that had received the engineered cells showed no sign of cancer. The ten mice that received injections of unaltered and tumor cells showed a weak anti-tumor response - most had tumors that shrank in size. In contrast, all seven mice given only saline injections had tumors that got larger during the same period.

Sobol reported his team's data last week at the American Association for Cancer Research meeting held in San Diego. The team wants to try the same approach with human cancer patients.