Commonly found parasites can treat certain types of cancer, researchers say

Researchers have discovered that a deadly parasite, known to cause ill health in pregnant women and immunocompromised patients, could potentially be used to treat various types of tumors.

The research, published today in the Journal of ImmunoTherapy Cancer, was conducted by experts from the University of Nottingham, Ningbo University and Shanxi Agricultural University in China.

Improving the effectiveness of treatments for certain types of tumors is essential to beating certain cancers, stopping tumor progression and prolonging patients’ lives. In this new study, scientists revealed that a parasite that is common across the globe is capable of sensitizing cold tumors – tumors that are unlikely to trigger a strong immune response from the body – to immune checkpoint blockade therapy.

Schematic 3D model of Toxoplasma gondii inside a host cell

Researchers leading the study believe that this finding may have broader therapeutic implications for many types of cancer.

The team managed to ‘tame’ the parasite Toxoplasma gondii – a single-celled opportunistic protozoan that is capable of infecting a wide range of warm-blooded animals and has been reported in almost a third of the world’s human population.

Toxoplasma gondii must live inside the host cells and secrete many proteins to counteract the host’s immune system and to facilitate their own invasion and colonization of the host cells. The researchers first built a Toxoplasma gondii mutant strain with a limited ability to grow, in cultured cells or to cause disease in mice, but which is at the same time capable of manipulating the host’s immune system.

The researchers have shown that direct injection with this mutant parasite in solid tumors induces inflammatory reactions in the injected tumors and even in tumors located at a distant site in the mouse body. They have also shown that this treatment approach has made tumors more responsive to treatment with immune checkpoint inhibitor.

This dual treatment significantly prolonged mouse survival and reduced tumor growth in mouse models of melanoma, Lewis lung carcinoma, and colon adenocarcinoma.

Dr. Hany-Elsheikha

Dr. Hany Elsheikha, associate professor at the School of Veterinary Medicine and Science at the University of Nottingham, and one of the study’s lead authors, said: “The use of a mutant version of Toxoplasma gondii in the treatment of certain tumors in mouse models has previously been What makes this study different is the confirmation that intratumoral injection with mutant Toxoplasma gondii strain boosts antitumor immunity and the effectiveness of checkpoint inhibition therapy.

“These are significant findings and are relevant to future tumor therapy. The marked reduction in tumor size and the significant improvement in survival of mice receiving this new combination therapy are promising, but should be interpreted with caution as further research is needed.”

The entire study can be found here.

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