Scientists have discovered that a parasite normally found in cat faeces could help them to formulate a cancer-fighting vaccine.

Though Toxoplasma gondii (T. gondii), a single-celled parasite, is happiest when hanging out in a cat’s intestines, it can live in any warm blooded animal and affects about one-third of the world’s population, including 60 million Americans. Most people have no symptoms, but some experience a flu-like illness, particularly those with suppressed immune systems who can develop a serious infection if they encounter T. gondii. Pregnant women are also advised to take extra care not to come into contact with the bacteria as it can threaten the health of unborn babies and cause miscarriage, still birth or birth defects.

Medical practitioners therefore usually advise taking strict precautions to avoid contracting the parasite, which is not just found in cat faeces. They suggest wearing gloves whilst handling soil, avoiding raw meat, washing fruit and vegetables prior to consumption, only drinking pasteurized milks as well as avoiding contact with cat faeces by wearing gloves and washing hands thoroughly after changing cat litter.

So how can this normally unwelcome visitor prove to be a useful ally in the fight against cancer?

It seems that a healthy immune system responds vigorously to T. Gondii in a manner that parallels how the immune system attacks a tumor, and scientists want to see if they utilise this same reaction to stimulate a similar response to cancer cells.

“We know biologically this parasite has figured out how to stimulate the exact immune responses you want to fight cancer,” said David J. Bzik, PhD, professor of Microbiology and Immunology, Geisel School of Medicine at Dartmouth.

In response to T. gondii, the body produces natural killer cells and cytotoxic T cells. These cell types wage war against cancer cells. Cancer can shut down the body’s defensive mechanisms, but introducing T. gondii into a tumor environment can jump start the immune system.

“The biology of this organism is inherently different from other microbe-based immunotherapeutic strategies that typically just tickle immune cells from the outside,” said Barbara Fox, senior research associate of Microbiology and Immunology. “By gaining preferential access to the inside of powerful innate immune cell types, our mutated strain of T. gondii reprograms the natural power of the immune system to clear tumor cells and cancer.”

So how will the vaccine be created?

Since it isn’t safe to inject a cancer patient with live replicating strains of T. gondii, Bzik and Fox created “cps,” an immunotherapeutic vaccine. Based on the parasite’s biochemical pathways, they deleted a Toxoplasma gene needed to make a building block of its genome and create a mutant parasite that can be grown in the laboratory but is unable to reproduce in animals or people. Cps is both nonreplicating and safe. Even when the host is immune deficient, cps still retains that unique biology that stimulates the ideal vaccine responses.

“Aggressive cancers too often seem like fast moving train wrecks. Cps is the microscopic, but super strong, hero that catches the wayward trains, halts their progression, and shrinks them until they disappear,” said Bzik.

The research to date shows promising results: published laboratory studies from the Geisel School of Medicine at Dartmouth labs have tested the cps vaccine in extremely aggressive lethal mouse models of melanoma or ovarian cancer and found unprecedented high rates of cancer survival.

“Cps stimulates amazingly effective immunotherapy against cancers, superior to anything seen before,” said Bzik. “The ability of cps to communicate in different and unique ways with the cancer and special cells of the immune system breaks the control that cancer has leveraged over the immune system.”

This new weapon against cancer could even be tailored to the individual patient:

“In translating cps therapy to the clinic, we imagine cps will be introduced into cells isolated from the patient. Then Trojan Horse cells harboring cps will be given back to the patient as an immunotherapeutic cancer vaccine to generate the ideal immune responses necessary to eradicate their cancer cells and to also provide life-long immunity against any future recurrence of that cancer,” said Bzik.

Fox and Bzik say a lot more study is needed before cps leaves the laboratory. They are trying to understand how and why it works so well by examining its molecular targets and mechanisms.

“Cancer immunotherapy using cps holds incredible promise for creating beneficial new cancer treatments and cancer vaccines,” said Bzik.