Study Links Microbiota to Human Immune System

Researchers from Memorial Sloan Kettering have shown that the gut microbiota directly shapes the makeup of the human immune system. Specifically, their research, which was published in Nature last week, demonstrated that the concentration of different types of immune cells in the blood changed in relation to the presence of different bacterial strains in the gut.

"The scientific community had already accepted the idea that the gut microbiota was important for the health of the human immune system, but the data they used to make that assumption came from animal studies," says Joao Xavier, co-senior author of the paper.

The data that were used in this study came from more than 2,000 blood cancer patients receiving allogeneic stem cell and bone marrow transplants (BMTs). After strong chemotherapy or radiation therapy is used to destroy cancerous blood cells, the patient's blood-forming system is replaced with stem cells from a donor. For the first few weeks until the donor's blood cells have established themselves, the patients are extremely vulnerable to infections. To protect them during this time, patients are given antibiotics.

But many of these antibiotics have the unwanted side effect of destroying healthy microbiota that live in the gut, allowing dangerous strains to take over. When the patient's immune system has reconstituted, the antibiotics are discontinued, and the gut microbiota slowly starts to grow back.

"The parallel recoveries of the immune system and the microbiota, both of which are damaged and then restored, gives us a unique opportunity to analyze the associations between these two systems," co-senior author Jonas Schluter explains.

The databank that the MSK team created contains details about the types of microbes that live in the patients' guts at various times. The team then used machine learning algorithms to mine electronic health records for meaningful data. The data from the health records included the types of immune cells present in the blood, information about the medications that patients were given, and the side effects patients experienced. "This research could eventually suggest ways to make BMTs safer by more closely regulating the microbiota," Marcel van den Brink, another author on the paper, adds.