The Cedars-Sinai Medical Center researchers in Los Angeles discovered that a protein known as high-mobility group box 1, or HMGB1, released from dying tumor cells activates key immune cells called dendritic cells and stimulates a strong and effective anti-tumor immune response.

But the number of dendritic cells in the brain is very small, reducing the brain's immune responses compared with those in other parts of the body, the researchers found.

So in laboratory tests and animal studies, they used a combined gene therapeutic approach to draw dendritic cells from bone marrow into the brain tumors, they said in a study published in the online journal PLoS Medicine late Monday.

The researchers also took a second protein -- herpes simplex type I thymidine kinase, or TK -- and combined it with the antiviral medicine gancyclovir, given to bone-marrow transplant recipients.

This triggered a strong immune response against the tumors, killing tumor cells and eliciting long-term survival, they said.

The researchers' next step is to test the therapeutic approach in a human clinical trial for recurrent brain tumors later this year, said Dr. Pedro Lowenstein, director of Cedars-Sinai's Board of Governors Gene Therapeutics Research Institute and one of the article's senior authors.

The institute seeks to harness the power of the Human Genome Project to develop gene therapy strategies that could cure if not prevent disease.