Introducing bacteria to a tumor microenvironment (TME) creates a state of acute inflammation that triggers the immune system's primary responder cells to attack the tumor, according to a study led by Australia's Garvan Institute of Medical Research.
The research team said on Monday that injecting inactivated Staphylococcus aureus microbes into a tumor could stimulate the first-responder cells, neutrophils, to destroy the tumor in a range of animal cancer models, including Lewis lung carcinoma, triple-negative breast cancer, melanoma and pancreatic cancer.
Published in the Cancer Research journal in February, the study indicated that most solid tumors generate a sub-acute inflammatory response which favors a TME that stimulates tumor growth and suppresses anti-tumor immunity, but certain microbial preparations can shift the TME towards an acute inflammatory response which inhibits cancer growth.
The researchers noted that neutrophils generally defend against diseases, but they can also promote tumor growth, partly because they produce molecules that protect the tumor and suppress other parts of the immune system.
"Since attacking bacteria is the reason for neutrophils' existence, we had a good inkling that introducing bacteria would bring neutrophils to the site and activate them," said Tatyana Chtanova, co-author of the study and head of the Innate and Tumor Immunology Lab at the Garvan institute.
"We discovered that it's very effective in getting them to kill the tumors, chewing up their matrix," Chtanova added.
The study found that neutrophils also change at the gene expression level, as they begin to secrete molecules which attract fighter T cells as reinforcements.
"We've shown that microbial therapy is an effective booster for checkpoint inhibitor therapy, another type of cancer immunotherapy. We hope this synergistic effect will ultimately lead to better treatments to improve outcomes for patients with advanced or previously untreatable cancers," said Andrew Yam, first author and Ph.D. student at the Garvan institute.
The team is planning to develop the therapy over the next three to five years to fight metastasis, and the spread of cancer to other areas of the body, with clinical trials to follow.