Can Parasite Protein Assist in Fighting Ovarian Tumors in Mice?

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A new study published in PLOS Genetics reported that a specific protein secreted by the parasite Toxaplasma gondii causes the immune system to fight off ovarian tumors in mice.  Previously it had been discovered that using the bodies own immune system to fight tumor cells was hampered because of a phenomenon called immune tolerance in which the immune system has difficulty identifying which cells to attack.  In the current study, researchers build upon that previous work that a safe, non-reproducing vaccine strain of T. gonfii could cure mice of several types of solid tumors, and identified which parasite proteins and which immunological pathways are required to break immune tolerance. In the study they systematically deleted genes for secreted effective protein–molecules that the parasite injects into a host cell to modulate the immune system during infection–and injected the altered parasites into mice with aggressive ovarian cancer. Results showed that specific rhoptry and dense granule effector proteins that T gondii secretes before and after invading host cells, respectively, control the development of an effective host antitumor response. and increase the survival of mice with ovarian tumors.

This use of infectious organisms to break tumor immune tolerance may be an excellent treatment option for treating cancer in the future and is currently being used in clinical trials with pancreatic tumors where the bacterium Listeria monocytogenes is used to break the immune tolerance. More research is planned.

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