(HealthDay News) — Cellular immunotherapy and gene therapy alone or in combination are effective in reducing tumor size and improving survival in a mouse model of breast cancers that have metastasized to the brain, according to a study published in the Aug. 1 issue of Clinical Cancer Research.

Michelle J. Hickey, Ph.D., from the University of California Los Angeles, and colleagues tested two treatments for breast tumors in the brain, alone and in combination: a cellular immunotherapy consisting of alloreactive cytotoxic T lymphocytes (alloCTL) and gene therapy consisting of a retroviral replicating vector encoding the yeast cytosine deaminase, a suicide prodrug (5-fluorocytosine) activating gene.

Using a mouse model of breast cancer, the researchers found that alloCTLs were able to traffic from one tumor site to another in the brain and induce tumor apoptosis. Similarly, the retroviral vector was able to infect breast cancer cells and induce apoptosis in the presence of 5-fluorocytosine.

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Tumor volumes were also significantly reduced in both groups. When both therapies were used, median survival was 97.5 days compared with 50 to 83 days for either treatment alone and 31.5 or 40 days for sham treatment. Both treatments showed good safety and toxicity.

“The results indicate combining cellular and suicide gene therapies is a viable strategy for the treatment of established breast tumors in the brain,” Hickey and colleagues conclude.

The study was partially funded by Tocagen; one author disclosed a financial relationship with Tocagen.