London, March 15 (IANS) Adding a simple tetanus shot to another vaccine treatment for a lethal form of brain cancer dramatically extends patients' survival, finds a study.

Researchers from the Duke Cancer Institute found that three of six patients with glioblastoma - a brain tumour with a very poor prognosis - lived years longer than expected after receiving a tetanus shot.

The injection was given to enhance an immunotherapy targeting a virus in the tumour.

Earlier research had found that glioblastoma tumours harbour a strain of cytomegalovirus not present in surrounding brain tissue.

This creates a natural target for immunotherapy -- therapy that harnesses the power of a patient's own immune system to help destroy cancer cells.

"Because the average survival is 12 to 15 months in patients who receive a diagnosis of this tumour, we were quite surprised by the results of three patients who had much longer survival times," said Kristen Batich, a medical student at the Duke University and study author.

Batich and her colleagues split 12 glioblastoma patients into two groups: six received a tetanus booster and six received a placebo (dummy) shot.

Next day, all 12 patients underwent a treatment called dendritic cell immunotherapy.

This treatment uses dendritic cells, which "train" the immune system to respond to a specific infectious agent.

They extracted patients' white blood cells, coaxed the growth of dendritic cells and loaded them with an antigen (toxin) targeting the cytomegalovirus in glioblastoma tumours.

The dendritic cell vaccine was then injected back into the cancer patients.

The purpose was to signal lymph nodes to search and attack the cytomegalovirus-laden tumour.

One patient is still alive nearly nine years after the treatment, said the report that appeared online in the journal Nature.