This parasite can kill, but it is a glimmer of hope for cancer patients.

Live parasites are injected into the body to stimulate the fighting spirit of the immune system, allowing them to kill a bigger enemy, cancer cells.

This anti-cancer idea, which sounds like a fantasy, has the opportunity to bring effective anti-cancer therapy.

Toxoplasma gondii (Toxoplasma gondii) is a parasite that we often come into contact with in our lives. It can infect almost all warm-blooded animals.

Toxoplasma gondii is usually found in soil or water contaminated with cat droppings, as well as in the meat of infected animals.

Although Toxoplasma gondii infection does not cause symptoms for most people, it can be fatal for people with low immune function, pregnant women and fetuses.

In the 1960s and 1970s, scientists observed that mice infected with Toxoplasma gondii were immune to some pathogen infections and cancers, so they came up with the idea of using the parasite to treat cancer.

In the decades that followed, there was growing evidence that Toxoplasma gondii infection helped to treat cancer.

Using a dangerous parasite to treat cancer sounds like playing with fire.

But in fact, a century ago, some clinicians had the idea of using pathogens to treat cancer.

Take poison as medicine.

At the end of the 19th century, William William Coley, a cancer surgeon in New York, made a startling discovery when he looked at the history of an old disease: a patient with advanced cancer was infected with bacteria seven years ago.

It didn't seem worth paying attention to, but when Corley looked through the old cases, the patient who was supposed to die of cancer soon was still alive and in good health.

Corley speculated that something related to a bacterial infection might have caused the tumor to shrink, so he began to try to inject live or dead bacteria into his cancer patients.

Although not every patient survived, the tumors of some patients who survived the infection usually shrunk.

Eventually, Colley standardized his treatment into a vaccine that contained a dead bacteria called Corydalis toxin.

After injection of this drug, patients can induce anti-cancer inflammatory response without being infected with live pathogens.

Many people tried to repeat Colley's research, but the results were not good.

With the advent of radiation therapy, colistin is no longer the first choice for the treatment of cancer.

However, the idea of strengthening the immune system to fight cancer remains.

In addition to colistin, scientists have tried other ways to stimulate the immune system to suppress tumors, also known as "in situ vaccination" (in situ vaccination).

In 2016, the team of Steven Fiering, a tumor immunologist at Dartmouth University's Geisel School of Medicine, confirmed that injecting nanoparticles containing the inactivated cowpea mosaic virus (cowpea mosaic virus) into tumors in mice could inhibit the growth of a variety of metastatic tumors, including ovarian, colon and breast cancer.

There is also a "T-Vec" therapy that injects oncolytic viruses into tumors, which has been used to treat patients with advanced melanoma.

Stop the immune "brake"

Our immune cells are equipped with receptor molecules called immune checkpoints (immune checkpoints), which act as the brakes of the immune system.

Nearby immune cells can pull the brakes to prevent the immune response from being triggered improperly or lasting too long.

However, many tumors also cunningly use the "brakes" to suppress the immune response that can resist the tumor.

The corresponding immune checkpoint inhibition therapy, the principle is to block the immune checkpoint molecules to transmit inhibitory signals, do not let the tumor tissue pull the immune "brake", so that the immune system can resume work and fight the tumor.

This treatment has been successful in some patients, but it doesn't work for everyone, and scientists don't fully understand why.

In November 2021, a study published in the journal Cancer Immunotherapy found that mice that received both immune checkpoint suppression therapy and Toxoplasma gondii in situ vaccination were compared with mice that received only immune checkpoint suppression therapy. the effect of tumor atrophy is better.

David Buzick (David Bzik), an immunologist at Dartmouth University, said: "this result is valuable and may help to treat patients who initially have no effect with immunosuppressive therapy."

"if we can figure out what this parasite and other immunotherapies do, we may be able to develop new anti-cancer treatments," said Christopher Hunter, an immune parasitologist at the University of Pennsylvania.

The stunt of Toxoplasma gondii.

We need different types of immune pathways to fight different types of diseases.

The immune system's immune response to Toxoplasma gondii infection is exactly the same as the response needed to fight cancer.

"when Toxoplasma gondii is introduced into a tumor, it does trigger an anti-cancer response and reverse immunosuppression."

Buzik said.

Why does Toxoplasma gondii trigger an immune response against cancer? this is because the parasite needs the host to survive long enough to reach the stage of life that can reproduce.

So Toxoplasma gondii triggers a strong immune response in the early stages of infection to control cell replication in its own body.

This immune response is exactly what we need.

In 2013, Buzik, Felin and colleagues found that infection with Toxoplasma gondii, a type of cell that does not replicate normally, significantly increased the number and activity of cancer-fighting T cells in mice with ovarian cancer.

Moreover, when the T cells of these mice were injected into other mice with cancer but not infected with Toxoplasma gondii, the tumor growth of the latter was significantly inhibited.

Other studies have shown that the parasite is also effective in mice with pancreatic cancer and melanoma.

And only the injection of live Toxoplasma gondii is effective, and the use of killed Toxoplasma gondii has no effect on tumor size.

The researchers also found that when mice had two tumors, when immunological checkpoint inhibitors were used but only one tumor was injected with Toxoplasma gondii, the other tumor still shrunk.

Buzick pointed out that an unfortunate situation is that many