An enzyme that cancer cells use to keep themselves "immortal" might provide a target for a universal cancer vaccine, researchers said on Tuesday.

Experiments in mice suggest a vaccine based on the enzyme telomerase might work against a range of cancers, a team at Duke University in North Carolina and Geron Corp. reported.

"The question posed in the study was whether the telomerase-based vaccine can stimulate an immune response from cancer patients, and whether those cells can attack and kill the patient's tumour cells," Eli Gilboa, director of the Centre for Genetic and Cellular Therapies at Duke, said in a statement. "The results of this study are the first indication that a more broadly applicable cancer vaccine might be possible."

The findings, reported in the journal Nature Medicine, are a long way from being of any help to human cancer patients. Researchers say it is one thing to affect cancer in mice and quite another to treat it in people.

But the scientists said they were intrigued and had already started testing their "vaccine" in human cells.

Cancer is caused by defects in DNA, the basic genetic material. All chromosomes, which carry the DNA, also have little caps on each end called telomeres.

Each time a cell divides, these telomeres become a little more frayed. When they are too worn out, the cell dies.

But when cells become cancerous, they produce an enzyme known as telomerase. It can renew the telomeres and lets the cells reproduce out of control, eventually to form a tumour.

Gilboa's team found that the active part of telomerase can stimulate development of immune cells that can kill several different kinds of mouse and human cancers.

Many researchers are working on cancer vaccines. But there are many different kinds of cancers, and the cells often have their own specific surface proteins that the vaccines target.

These proteins are known as tumour-specific antigens.

"The thinking has been that because every cancer is different -- melanoma, breast, et cetera -- that each cancer has its own specific set of antigens that must be used for a vaccine," said Gilboa. "We're looking for a universal antigen -- one antigen to try to treat every cancer patient."

Telomerase might do the trick, he said.

"However, by itself, telomerase is not a strong antigen, so to make an effective, broadly applicable cancer vaccine we will need to optimize and possibly combine it with other universal antigens," he added.

His team's vaccine stimulated an immune response that slowed tumour growth of melanoma, breast and bladder cancers implanted into mice.

It also worked in human cells in laboratory dishes, they reported. The cells produced immune responses that killed a variety of patients' cancer cells in the lab.

(From China Daily)