A particular type of cell that surrounds tumors may what prevents the body's natural defenses, the immune system, from wiping the cancer out, according to a new study in mice.

Getting rid of these cells could improve the effectiveness of cancer vaccines , which rely on the immune system to work.

When the researchers killed these cells in mice that had tumors, the tumors started to die as they were pummeled by the immune system.

"It just shows that at least this stromal cell has a very dominant effect in causing immune suppression in the tumor," study researcher Douglas Fearon of the Department of Medicine at the University of Cambridge in the United Kingdom, told MyHealthNewsDaily.

However, Fearon noted that the tumors in these mice were not the same as tumors in people they were "artificial" in the sense that the mice were designed to grow tumors. In people, cancers arise spontaneously. The researchers are now conducting experiments on mice with tumors more similar to those in humans, but noted that any therapies are a long way off.

The study was published in the Nov. 5 issue of the journal Science.

Immune suppression

In theory, the immune system should be able to destroy tumors before they wreak havoc on the body, and the puzzle has been why it doesn't, Fearon said.

Researchers suspected that some cells around a tumor that are not cancerous themselves, but are thought to help the tumor grow may play a role in immune suppression, he said.

Fearon and his colleagues noticed some of these cells, called stromal cells, were found not only in tumors, but also in other sites in the body that might require immune suppression, such as the placenta. These tumor-protecting cells make a protein that other stromal cells in the body don't make.

The researchers designed mice so they could specifically kill off only stromal cells that make this protein. After 48 hours, 70 to 80 percent more tumor cells had died in these mice than in mice in which the researchers had not killed off these cells.

Future therapy

Fearon notes that any future therapy based on the findings could not be designed to destroy all stromal cells, since they have important functions in other parts of the body.

Instead, Fearon said he wants to find out how these cells cause immune system suppression, and then find a way to counteract that effect.

"We have to figure out what it is doing specially in the tumor, and block its effect, without eliminating the cells," Fearon said.

The study was funded by the Wellcome Trust and the Sheila Joan Smith Professorship endowment.