The mouse study, reported in the Sept. 21 issue of the journal Proceedings of the National Academy of Sciences by scientists at Cerus Corp. in Concord, Calif., employs a genetically engineered listeria bacteria based on a strain created by coauthor and University of California, Berkeley, microbiologist Daniel Portnoy. Buoyed by the success of the new cancer vaccine, Cerus scientists now are aiming for human trials.
Cerus ultimately hopes to use the genetically engineered listeria vaccine to target cancers such as pancreatic and ovarian cancer, and possibly leukemia and various solid tumors.
The listeria bacteria are uniquely effective vehicles for a cancer vaccine, Portnoy said, because the bacteria incite a strong "innate" response from the immune system and at the same time sneak cancer antigens into cells to optimally stimulate a potent "acquired" immune response. Together, these two independent arms of the human immune system can deliver a one-two punch to cancer cells. Antigens are like a red flag to a bull -- they draw an attack from cells of the immune system -- but the strength of the immune response depends on how the flag is waved.
"This immune therapy uses bacteria that induce both inflammation and an immune response to specific tumor antigens," which together hit the tumor with generalized antitumor chemicals, such as interferon and tumor necrosis factor, as well as activated T-cells that attack and kill the tumor, Portnoy said. "Listeria is the best bug so far to induce that response. With listeria, innate and acquired immunity work in concert."
Portnoy, a professor of molecular and cell biology and of public health and a member of UC Berkeley's Health Sciences Initiative, identified the genes in listeria that make
Contact: Robert Sanders
University of California - Berkeley